Dietary Strategies: Treatment Of Metabolic Syndrome
Dietary Strategies:
Abstract: Metabolic syndrome (MetS) is established as the combination of central obesity and different metabolic disturbances, such as insulin resistance, hypertension and dyslipidemia. This cluster of factors affects approximately 10%�50% of adults worldwide and the prevalence has been increasing in epidemic proportions over the last years. Thus, dietary strategies to treat this heterogenic disease are under continuous study. In this sense, diets based on negative-energy-balance, the Mediterranean dietary pattern, n-3 fatty acids, total antioxidant capacity and meal frequency have been suggested as effective approaches to treat MetS. Furthermore, the type and percentage of carbohydrates, the glycemic index or glycemic load, and dietary fiber content are some of the most relevant aspects related to insulin resistance and impaired glucose tolerance, which are important co-morbidities of MetS. Finally, new studies focused on the molecular action of specific nutritional bioactive compounds with positive effects on the MetS are currently an objective of scientific research worldwide. The present review summarizes some of the most relevant dietary approaches and bioactive compounds employed in the treatment of the MetS to date.
Keywords: metabolic syndrome; dietary strategies; bioactive compounds
1. Metabolic Syndrome
It was during the period between 1910 and 1920 when it was suggested for the first time that a cluster of associated metabolic disturbances tended to coexist together [1]. Since then, different health organisms have suggested diverse definitions for metabolic syndrome (MetS) but there has not yet been a well-established consensus. The most common definitions are summarized in Table 1. What is clear for all of these is that the MetS is a clinical entity of substantial heterogeneity, commonly represented by the combination of obesity (especially abdominal obesity), hyperglycemia, dyslipidemia and/or hypertension [2�6].
Obesity consists of an abnormal or excessive fat accumulation, for which the main cause is a chronic imbalance between energy intake and energy expenditure [7,8]. The excess of energy consumed is primarily deposited in the adipose tissue as triglycerides (TG) [9].
Dyslipidemia encompasses elevated serum TG levels, increased low density lipoprotein- cholesterol (LDL-c) particles, and reduced levels of high density lipoprotein-cholesterol (HDL-c) [10]. It is associated with hepatic steatosis [11], dysfunction of pancreatic ?-cells [12] and elevated risk of atherosclerosis [13], among others.
Another main modifiable MetS manifestation is hypertension, which is mainly defined as a resting systolic blood pressure (SBP) ? 140 mmHg or diastolic blood pressure (DBP) ? 90 mmHg or drug prescription to lower hypertension [14]. It usually involves narrowed arteries and is identified as a major cardiovascular and renal risk factor, related to heart and vascular disease, stroke and myocardial infarction [13,15�17].
Hyperglycemia, related insulin resistance and type 2 diabetes mellitus are characterized by an impaired uptake of glucose by the cells, that lead to elevated plasma glucose levels, glycosuria and ketoacidosis [18]. It is responsible for different tissue damage that shortens the life expectancy of diabetics, involving cardiovascular diseases (CVD), atherosclerosis, hypertension [19], ?-cell dysfunction [12], kidney disease [20] or blindness [21]. Currently, diabetes is considered the leading cause of death in developed countries [22].
Moreover, oxidative stress and low grade inflammation are two important mechanisms implicated in the etiology, pathogenesis, and development of MetS [23]. Oxidative stress is defined as an imbalance between the pro-oxidants and antioxidants in the body [24]. It plays a key role in the development of atherosclerosis by different mechanisms such as the oxidation of LDL-c particles [25] or impairment of HDL-c functions [26]. Inflammation is an immune system response to injury hypothesized to be a major mechanism in the pathogenesis and progression of obesity related disorders and the link between adiposity, insulin resistance, MetS and CVD [27].
Although the prevalence of the MetS varies broadly around the word and depends on the source used for its definition, it is clear that over the last 40�50 years the number of people presenting with this syndrome has risen in epidemic proportions [28]. Moreover, the frequency of this syndrome is increased in developed countries, sedentary people, smokers, low socioeconomic status population, as well as in individuals with unhealthy dietary habits [29,30].
For all of this, there is currently a wide concern to find effective strategies to detect, treat and control the comorbidities associated with MetS. This is a complex challenge as MetS is a clinical entity of substantial heterogeneity and therefore, the different cornerstones implicated in its development should be addressed. In this review we compiled and examined different dietary patterns and bioactive compounds that have pointed out to be effective in MetS treatment.
2. Dietary Patterns
Several dietary strategies and their potential positive effects on the prevention and treatment of the different metabolic complications associated to the MetS, are described below and summarized in Table 2.
2.1. Energy-Restricted Diet Strategies
Energy restricted diets are probably the most commonly used and studied dietary strategies for combating excess weight and related comorbidities. They consist in personalized regimes that supply less calories than the total energy expended by a specific individual [31].
A hypocaloric diet results in a negative energy balance and subsequently, in body weight reduction [31]. Weight loss is achieved via fat mobilization from different body compartments as a consequence of the lipolysis process necessary to provide energy substrate [32,33]. In people who are overweight or suffering from obesity, as is the case of most people with MetS, weight loss is important as it is associated with improvement of related disorders such as abdominal obesity (visceral adipose tissue), type 2 diabetes, CVD or inflammation [32�36].
Moreover, as described above, low grade inflammation is associated with MetS and obesity. Therefore, of particular importance is the fact that in obese individuals following a hypocaloric diet, a depletion of plasma inflammatory markers such as interleukin (IL)-6 has been observed [34]. Thus, caloric restriction in obese people suffering MetS may improve the whole-body pro-inflammatory state.
At the same time, body weight reduction is associated with improvements in cellular insulin signal transduction, increments in peripheral insulin sensitivity and higher robustness in insulin secretory responses [32,36]. People with excess body weight who are at risk of developing type 2 diabetes, may benefit from a hypocaloric regime by improving plasma glucose levels and insulin resistance.
In addition, different intervention trials have reported a relationship between energy restricted diets and lower risk of developing CVD. In this sense, in studies with obese people following a hypocaloric diet, improvements in lipid profile variables such as reductions of LDL-c and plasma�TG levels, as well as improvements in hypertension via depletion of SBP and DBP levels have been observed [35,37].
Among the different nutritional intervention trials, a reduction of 500�600 kcal a day of the energy requirements is a well-established hypocaloric dietary strategy, which has demonstrated to be effective in weight reduction [38,39]. However, the challenge lies in maintaining the weight loss over time, as many subjects can follow a prescribed diet for a few months, but most people have difficulty in maintaining the acquired habits over the long term [40,41].
2.2. Diets Rich in Omega-3 Fatty Acids
The very long-chain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential omega-3 polyunsaturated fatty acids (n-3 PUFAs) for human physiology. Their main dietary sources are fish and algal oils and fatty fish, but they can also be synthesized by humans from ?-linolenic acid [40].
There is a moderate body of evidence suggesting that n-3 PUFAs, mainly EPA and DHA, have a positive role in the prevention and treatment of the pathologies associated to MetS [42].
In this context, it has been described that EPA and DHA have the ability to reduce the risk of developing CVD and cardiometabolic abnormalities as well as CVD-related mortality [42]. These beneficial effects are thought to be mainly due to the ability of these essential fatty acids to reduce plasma TG levels [43].
Moreover, different studies have shown that people following an increased n-3 PUFA diet have reduced plasma levels of the pro-inflammatory cytokines IL-6 and tumor necrosis factor-alpha (TNF?), as well as plasma C-reactive protein (CRP) [44]. These effects are probably mediated by resolvins, maresins and protectins, which are EPA and DHA metabolic products with anti-inflammatory properties [44].
There are some studies that have observed an association between n-3 ingestion and improvements or prevention of type 2 diabetes development. However, other studies found opposite results [44]. Thus, it cannot be made any specific affirmation in this respect.
The European Food Safety Authority recommends and intake of 250 mg EPA + DHA a day, in the general healthy population as a primary prevention of CVD [45]. These amounts can be achieved with an ingestion of 1�2 fatty fish meals per week [45].
2.3. Diets Based on Low Glycemic Index/Load
Over the last ten years, the concern about the quality of the carbohydrates (CHO) consumed has risen [46]. In this context, the glycemic index (GI) is used as a CHO quality measure. It consists in a ranking on a scale from 0 to 100 that classifies carbohydrate-containing foods according to the postprandial glucose response [47]. The higher the index, the more promptly the postprandial serum glucose rises and the more rapid the insulin response. A quick insulin response leads to rapid hypoglycemia, which is suggested to be associated with an increment of the feeling of hunger and to a subsequent higher caloric intake [47]. The glycemic load (GL) is equal to the GI multiplied by the number of grams of CHO in a serving [48].
There is a theory which states that MetS is a consequence of an elevated intake of high GI foods over time, among others unhealthy dietary habits [49]. In this sense, following a diet rich in high GI CHO has been associated with hyperglycemia, insulin resistance, type 2 diabetes, hypertriglyceridemia, CVD, and obesity [47,50,51], abnormalities directly related to MetS.
On the contrary, a low GI diet has been associated with slower absorption of the CHO and subsequently smaller blood glucose fluctuations, which indicate better glycemic control [46]. In patients with type 2 diabetes, diets based on low GI are associated with reductions in glycated hemoglobin (HbA1c) and fructosamine blood levels, two biomarkers used as key monitoring factors in diabetes management [52,53].
For all of this, it is common to find the limitation of CHO at high GI among the advice for MetS treatment [28], in particular with respect to �ready-to-eat processed foods� including sweetened beverages, soft drinks, cookies, cakes, candy, juice drinks, and other foods which contain high amounts of added sugars [54].
2.4. Diets with High Total Antioxidant Capacity
Dietary total antioxidant capacity (TAC) is an indicator of diet quality defined as the sum of antioxidant activities of the pool of antioxidants present in a food [55]. These antioxidants have the capacity to act as scavengers of free radicals and other reactive species produced in the organisms [56]. Taking into account that oxidative stress is one of the remarkable unfortunate physiological states of MetS, dietary antioxidants are of main interest in the prevention and treatment of this multifactorial disorder [57]. Accordingly, it is well-accepted that diets with a high content of spices, herbs, fruits, vegetables, nuts and chocolate, are associated with a decreased risk of oxidative stress-related diseases development [58�60]. Moreover, several studies have analyzed the effects of dietary TAC in individuals suffering from MetS or related diseases [61,62]. In the Tehran Lipid and Glucose Study it was demonstrated that a high TAC has beneficial effects on metabolic disorders and especially prevents weight and abdominal fat gain [61]. In the same line, research conducted in our institutions also evidenced that beneficial effects on body weight, oxidative stress biomarkers and other MetS features were positively related with higher TAC consumption in patients suffering from MetS [63�65].
In this sense, the World Health Organization (WHO) recommendation for fruit and vegetables consumption (high TAC foods) for the general population is a minimum of 400 g a day [66]. Moreover, cooking with spices is recommended in order to increase the TAC dietary intake and, at the same time, maintain flavor while reducing salt [67].
2.5. Moderate-High Protein Diets
The macronutrient distribution set in a weight loss dietary plan has commonly been 50%�55% total caloric value from CHO, 15% from proteins and 30% from lipids [57,68]. However, as most people have difficulty in maintaining weight loss achievements over time [69,70], research on increment of protein intake (>20%) at the expense of CHO was carried out [71�77].
Two mechanisms have been proposed to explain the potential beneficial effects of high-moderate protein diets: the increment of diet-induced thermogenesis [73] and the increase of satiety [78]. The increment of the thermogenesis is explained by the synthesis of peptide bonds, production of urea and gluconeogenesis, which are processes with a higher energy requirement than the metabolism of lipids or CHO [75]. An increment of different appetite-control hormones such as insulin, cholecystokinin or glucagon-like peptide 1, may clarify the satiety effect [79].
Other beneficial effects attributed to moderate-high protein diets in the literature are the improvement of glucose homeostasis [80], the possibility of lower blood lipids [81], the reduction of blood pressure [82], the preservation of lean body mass [83] or the lower of cardiometabolic disease risk [84,85]. However, there are other studies that have not found benefits associated to a moderate-high protein diet [76]. This fact may be explained by the different type of proteins and their amino acid composition [80], as well as by the different type of populations included in each study [85]. Therefore, more research in the field is needed in order to make these results consistent.
In any case, when a hypocaloric diet is implemented, it is necessary to slightly increase the amount of proteins. Otherwise it would be difficult to reach the protein energy requirements, established as 0.83 g/kg/day for isocaloric diets and which should probably be at least 1 g/kg/day for energy-restricted diets [86].
2.6. High Meal Frequency Pattern
The pattern of increasing meal frequency in weight loss and weight control interventions has currently become popular among professionals [87,88]. The idea is to distribute the total daily energy�intake into more frequently and smaller meals. However, there is no strong evidence about the efficacy of this habit yet [89]. While some investigations have found an inverse association between the increment of meals per day and body weight, body mass index (BMI), fat mass percentage or metabolic diseases such as coronary heart disease or type 2 diabetes [71,88,90�92], others have found no association [93�95].
Different mechanisms by which high meal frequency can have a positive effect on weight and metabolism management have been proposed. An increment of energy expenditure was hypothesized; however, the studies carried out in this line have concluded that total energy expenditure does not differ among different meal frequencies [96,97]. Another postulated hypothesis is that the greater the number of meals a day, the higher the fat oxidation, but again no consensus has been achieved [89,98]. An additional suggested mechanism is that increasing meal frequency leads to plasma glucose levels with lower oscillations and reduced insulin secretion which is thought to contribute to a better appetite control. However, these associations have been found in population with overweight or high glucose levels but in normal-weight or normoglycaemic individuals the results are still inconsistent [93,99�101].
2.7. The Mediterranean Diet
The concept of the Mediterranean Diet (MedDiet) was for the first time defined by the scientific Ancel Keys who observed that those countries around the Mediterranean Sea, which had a characteristic diet, had less risk of suffering coronary heart diseases [102,103].
The traditional MedDiet is characterized by a high intake of extra-virgin olive oil and plant foods (fruits, vegetables, cereals, whole grains, legumes, tree nuts, seeds and olives), low intakes of sweets and red meat and moderate consumption of dairy products, fish and red wine [104].
There is a lot of literature supporting the general health benefits of the MedDiet. In this sense, it has been reported that a high adherence to this dietary pattern protects against mortality and morbidity from several causes [105]. Thus, different studies suggested the MedDiet as a successful tool for the prevention and treatment of MetS and related comorbidities [106�108]. Moreover, recent meta-analysis concluded that the MedDiet is associated with less risk of developing type 2 diabetes and with a better glycemic control in people with this metabolic disorder [107,109,110]. Other studies have found a positive correlation between the adherence to a MedDiet pattern and reduced risk of developing CVD [111�114]. In fact, many studies have found a positive association between following a MedDiet and improvements in lipid profile by reduction of total cholesterol, LDL-c and TG, and an increase in HDL-c [111�115]. Finally, different studies also suggest that the MedDiet pattern may be a good strategy for obesity treatment as it has been associated with significant reductions in body weight and waist circumference [108,116,117].
The high amount of fiber which, among other beneficial effects, helps to weight control providing satiety; and the high antioxidants and anti-inflammatory nutrients such as n-3 fatty acids, oleic acid or phenolic compounds, are thought to be the main contributors to the positive effects attributed to the MedDiet [118].
For all these reasons, efforts to maintain the MedDiet pattern in Mediterranean countries and to implement this dietary habits in westernized countries with unhealthy nutritional patterns should be made.
3. Dietary: Single Nutrients and Bioactive Compounds
New studies focused on the molecular action of nutritional bioactive compounds with positive effects on MetS are currently an objective of scientific research worldwide with the aim of designing more personalized strategies in the framework of molecular nutrition. Among them, flavonoids and antioxidant vitamins are some of the most studied compounds with different potential benefits such as antioxidant, vasodilatory, anti-atherogenic, antithrombotic, and anti-inflammatory effects [119]. Table 3 summarizes different nutritional bioactive compounds with potential positive effects on MetS, including the possible molecular mechanism of action involved.
3.1. Ascorbate
Vitamin C, ascorbic acid or ascorbate is an essential nutrient as human beings cannot synthesize it. It is a water-soluble antioxidant mainly found in fruits, especially citrus (lemon, orange), and vegetables (pepper, kale) [120]. Several beneficial effects have been associated to this vitamin such as antioxidant and anti-inflammatory properties and prevention or treatment of CVD and type 2 diabetes [121�123].
This dietary component produces its antioxidant effect primarily by quenching damaging free radicals and other reactive oxygen and nitrogen species and therefore preventing molecules such as LDL-c from oxidation [122]. It can also regenerate other oxidized antioxidants like tocopherol [124].
Moreover, it has been described that ascorbic acid may reduce inflammation as it is associated with depletion of CRP levels [125]. This is an important outcome to take in consideration in the treatment of MetS sufferers, as they usually present low grade inflammation [27].
Supplementation with vitamin C have also been associated with prevention of CVD by improving the endothelial function [126] and probably by lowering blood pressure [121]. These effects are thought to be exerted by the ability of vitamin C to enhance the endothelial nitric oxide synthase enzyme (eNOS) activity and to reduce HDL-c glycation [127].
Additionally, several studies have attributed to ascorbate supplementation an antidiabetic effect by improving whole body insulin sensitivity and glucose control in people with type 2 diabetes [123]. These antidiabetic properties are thought to be mediated by optimization of the insulin secretory function of the pancreatic islet cells by increasing muscle sodium-dependent vitamin C transporters (SVCTs) [128].
Despite all of this, it should be taken into account that most people reach ascorbic acid requirements (established at 95�110 mg/day in the general population) from diet and do not need supplementation [122,129]. Besides, it should be considered that an excess of vitamin C ingestion leads to the opposite effect and oxidative particles are formed [130,131].
3.2. Hydroxytyrosol
Hydroxytyrosol (3,4-dihydroxyphenylethanol) is a phenolic compound mainly found in olives [132].
It is considered the strongest antioxidant of olive oil and one of the main antioxidants in nature [133]. It acts as a powerful scavenger of free radicals, as a radical chain breaker and as metal chelator [134]. It has the ability of inhibiting LDL-c oxidation by macrophages [132]. In this sense, it is the only phenol recognized by the European Food Safety Authority (EFSA) as a protector of blood lipids from oxidative damage [135].
Hydroxytyrosol has also been reported to have anti-inflammatory effects, probably by suppressing cyclooxygenase activity and inducing eNOS expression [136]. Thus, enhancement of olives/olive oil intakes or hydroxytyroxol supplementation in people suffering from MetS may be a good strategy in order to improve inflammatory status.
Another beneficial effect attributed to this phenolic compound is its cardiovascular protective effect. It presents anti-atherogenic properties by decreasing the expression of vascular cell adhesion protein 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) [132,137], which are probably the result of an inactivation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF?B), activator protein 1 (AP-1), GATA transcription factor and nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase [138,139]. Hydroxytyrosol also provides antidyslipidemic effects by lowering plasma levels of LDL-c, total cholesterol and TG, and by rising HDL-c [138].
Despite the beneficial effects attributed to hydfroxytyrosol as an antioxidant, for its antiinflamatory properties and as cardiovascular protector, it should be taken into account that most studies focused on this compound have been performed with mixtures of olive phenols, thus a synergic effect cannot be excluded [140].
3.3. Quercetin
Quercetin is a predominant flavanol naturally present in vegetables, fruits, green tea or red wine. It is commonly found as glycoside forms, where rutin is the most common and important structure found in nature [141].
Many beneficial effects that can contribute to MetS improvement have been attributed to quercetin. Among them, its antioxidant capacity should be highlighted, as it has been reported to inhibit lipid peroxidation and increase antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) or glutathione peroxidase (GPX) [142].
Moreover, an anti-inflammatory effect mediated via attenuation of tumor necrosis factor ? (TNF-?), NF?B and mitogen-activated protein kinases (MAPK), as well as depletion of IL-6, IL-1?, IL-8 or monocyte chemoattractant protein-1 (MCP-1) gene expression has also been attributed to this polyphenol [143].
As most people with MetS are overweight or obese, the role of quercetin in body weight reduction and obesity prevention has been of special interest. In this sense, it stands out the capacity of quercetin to inhibit adipogenesis through inducing the activation of AMP-activated protein kinase (AMPK) and decreasing the expression of CCAAT-enhancer-binding protein-? (C/EBP?), peroxisome�proliferator-activated receptor gamma (PPAR?), and sterol regulatory element-binding protein 1 (SREBP-1) [141,144].
According to the antidiabetic effects, it is proposed that quercetin may act as an agonist of peroxisome proliferator-activated receptor gamma (PPAR?), and thus improve insulin-stimulated glucose uptake in mature adipocytes [145]. Moreover, quercetin may ameliorate hyperglycemia by inhibiting glucose transporter 2 (GLUT2) and insulin dependent phosphatidylinositol-3-kinase (PI3K) and blocking tyrosine kinase (TK) [142].
Finally, different studies observed that quercetin has the ability to reduce blood pressure [146�148]. However, the mechanisms of action are not clear, since some authors have suggested that quercetin increases eNOS, contributing to inhibition of platelet aggregation and improvement of the endothelial function [146,147], but there are other studies that have not come across these results [148].
3.4. Resveratrol
Resveratrol (3,5,4?-trihidroxiestilben) is a phenolic compound mainly found in red grapes and derived products (red wine, grape juice) [149]. It has shown antioxidant and anti-inflammatory activities, and cardioprotective, anti-obesity and antidiabetic capacities [150�156].
The antioxidant effects of resveratrol have been reported to be carried out by scavenging of hydroxyl, superoxide, and metal-induced radicals as well as by antioxidant effects in cells producing reactive oxygen species (ROS) [150].
Moreover, it has been reported that the anti-inflammatory effects of resveratrol are mediated by inhibiting NF?B signaling [151]. Furthermore, this polyphenol reduces the expression of proinflammatory cytokines such as interleukin 6 (IL-6), interleukin 8 (IL-8), TNF-?, monocyte chemoattractant protein-1 (MCP-1) and eNOS [152]. In addition, resveratrol inhibits the cyclooxygenase (COX) expression and activity, a pathway involved in the synthesis of proinflammatory lipid mediators [152].
Concerning the effects of resveratrol against development of type 2 diabetes, it has been reported that treatment of diabetes patients with this polyphenol provides significant improvements in the status of multiple clinically relevant biomarkers such as fasting glucose levels, insulin concentrations or glycated hemoglobin and Homeostasis Model Assessment Insulin Resistance (HOMA-IR) [153,154].
Additionally, cardioprotective effects have been attributed to resveratrol. In this sense, it is suggested that resveratrol improves the endothelial function by producing nitric oxide (NO) through increasing the activity and expression of eNOS. This effect is thought to be conducted through activation of nicotinamide adenine dinucleotide-dependent deacetylase sirtuin-1 (Sirt 1) and 5? AMP-activated protein kinase (AMPK) [155]. Besides, resveratrol exerts endothelial protection by stimulation of NF-E2-related factor 2 (Nrf2) [156] and decreasing the expression of adhesion proteins such as ICAM-1 and VCAM-1 [152].
Finally, it has been described that resveratrol may have a role in preventing obesity as it has been related with energy metabolism improvement, increasing lipolysis and reducing lipogenesis [157]. However, more studies are needed in order to corroborate these findings.
3.5. Tocopherol
Tocopherols, also known as vitamin E, are a family of eight fat-soluble phenolic compounds whose main dietary sources are vegetable oils, nuts and seeds [130,158].
For a long time, it has been suggested that vitamin E could prevent different metabolic diseases as a potent antioxidant, acting as scavenger of lipid peroxyl radicals by hydrogen donating [159]. In this sense, it was described that tocopherols inhibit peroxidation of membrane phospholipids and prevent generation of free radicals in cell membranes [160].
Moreover, it has been shown that supplementation with ?-tocopherol or ?-tocopherol, two of the different isoforms of vitamin E, could have an effect on inflammation status by reducing CRP levels [161]. Additionally, inhibition of COX and protein kinase C (PKC) and reduction of cytokines�such as IL-8 or plasminogen activator inhibitor-1 (PAI-1) are other mechanisms that may contribute to these anti-inflammatory effects [162,163].
However, the beneficial effects attributed to this vitamin previously have lately became controversial as different clinical trials have not come across such benefits, but ineffective or even harmful effects have been observed [164]. It has been recently suggested that this may be explained by the fact that vitamin E may lose most of the antioxidant capacity when ingested by human beings through different mechanisms [162].
3.6. Anthocyanins
Anthocyanins are water-soluble polyphenolic compounds responsible for the red, blue and purple colors of berries, black currants, black grapes, peaches, cherries, plums, pomegranate, eggplant, black beans, red radishes, red onions, red cabbage, purple corn or purple sweet potatoes [165�167]. Actually, they are the most abundant polyphenols in fruits and vegetables [167]. Moreover, they can also be found in teas, honey, nuts, olive oil, cocoa, and cereals [168].
These compounds have high antioxidant capacity inhibiting or decreasing free radicals by donating or transferring electrons from hydrogen atoms [167].
Regarding clinical studies, it has been shown that these bioactive compounds may prevent type 2 diabetes development by improving insulin sensitivity [169]. The exact mechanisms by which anthocyanins exert their antidiabetic effect are not yet clear, but an enhancement of the glucose uptake by muscle and adipocyte cells in an insulin-independent manner has been suggested [169].
Moreover, it has been shown that anthocyanins may have the capacity to prevent CVD development by improving endothelial function via increasing brachial artery flow-mediated dilation and HDL-c, and decreasing serum VCAM-1 and LDL-c concentrations [170�173].
Finally, these polyphenolic compounds may exert anti-inflamatory effects via reducing proinflamatory molecules such as IL-8, IL-1? or CRP [172,174].
However, most studies have used anthocyanin-rich extracts instead of purified anthocyanins; thus, a synergic effect with other polyphenols cannot be discarded.
3.7. Catechins
Catechins are polyphenols that can be found in a variety of foods including fruits, vegetables, chocolate, wine, and tea [175]. The epigallocatechin 3-gallate present in tea leaves is the catechin class most studied [176].
Anti-obesity effects have been attributed to these polyphenols in different studies [176]. The mechanisms of action suggested to explain these beneficial effects on body weight are: increasing energy expenditure and fat oxidation, and reducing fat absorption [177]. It is thought that energy expenditure is enhanced by catechol-O-methyltransferase and phosphodiesterase inhibition, which stimulates the sympathetic nervous system causing an activation of the brown adipose tissue [178]. Fat oxidation is mediated by upregulation of acyl-CoA dehydrogenase and peroxisomal b-oxidation enzymes [178,179].
Moreover, catechin intake has also been associated with lower risk of CVD development by improving lipid biomarkers. Thus, it has been reported that consumption of this kind of polyphenols may increase HDL-c and decrease LDL-c and total cholesterol [180].
Finally, and antidiabetic effect has also been related to catechin comsumption, lowering fasting glucose levels [175] and improving insulin sensitivity [178].
4. Conclusions
As the prevalence of MetS reaches epidemic rates, the finding of an effective and easy-to-follow dietary strategy to combat this heterogenic disease is still a pending subject. This work recompiled different dietary nutrients and nutritional patterns with potential benefits in the prevention and�treatment of MetS and related comorbidities (Figure 1) with the aim of facilitating future clinical�studies in this area. The challenge now is to introduce precision bioactive compounds in personalized�nutritional patterns in order to gain the most benefits for prevention and treatment of this disease�through nutrition.
Conflicts of Interest: The authors declare no conflict of interest.
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PubMed was searched from the earliest possible date to May 2014 to identify review articles that outlined the pathophysiology of MetS and T2DM. This led to further search refinements to identify inflammatory mechanisms that occur in the pancreas, adipose tissue, skeletal muscle, and hypothalamus. Searches were also refined to identify relationships among diet, supplements, and glycemic regulation. Both animal and human studies were reviewed. The selection of specific supplements was based on those that were most commonly used in the clinical setting, namely, gymnema sylvestre, vanadium, chromium and ?-lipoic acid.
Under normal conditions, skeletal muscle, hepatic, and adipose tissues require the action of insulin for cellular glucose entry. Insulin resistance represents an inability of insulin to signal glucose passage into insulin-dependent cells. Although a genetic predisposition can exist, the�etiology of insulin resistance has been linked to chronic low-grade inflammation.1 Combined with insulin resistance-induced hyperglycemia, chronic low-grade inflammation also sustains MetS pathophysiology.1
Caloric excess and a sedentary lifestyle contribute to the accumulation of subcutaneous and visceral adipose tissue. Adipose tissue was once thought of as a metabolically inert passive energy depot. A large body of evidence now demonstrates that excess visceral adipose tissue acts as a driver of chronic low-grade inflammation and insulin resistance.27,34
Eating behavior in the obese and overweight has been popularly attributed to a lack of will power or genetics. However, recent research has demonstrated a link between hypothalamic inflammation and increased body weight.41,41
Feeding generally leads to a short-term increase in both oxidative stress and inflammation. 41 Total�calories consumed, glycemic index, and fatty acid profile of a meal all influence the degree of postprandial inflammation. It is estimated that the average American consumes approximately 20% of calories from refined sugar, 20% from refined grains and flour, 15% to 20% from excessively fatty meat products, and 20% from refined seed/legume oils.45 This pattern of eating contains a macronutrient composition and glycemic index that promote hyperglycemia, hyperlipemia, and an acute postprandial inflammatory response. 46 Collectively referred to as postprandial dysmetabolism, this pro-inflammatory response can sustain levels of chronic low-grade inflammation that leads to excess body fat, coronary heart disease (CHD), insulin resistance, and T2DM.28,29,47
Diagnosis of MetS has been linked to an increased risk of developing T2DM and cardiovascular disease over the following 5 to 10 years. 1 It further increases a patient’s risk of stroke, myocardial infarction, and death from any of the aforementioned conditions.1
Research has identified nutrients that play key roles in promoting proper insulin sensitivity, including vitamin D, magnesium, omega-3 (n-3) fatty acids, curcumin, gymnema, vanadium, chromium, and ?-lipoic acid. It is possible to get adequate vitamin D from sun exposure and adequate amounts of magnesium and omega-3 fatty acids from food. Contrastingly, the therapeutic levels of chromium and ?-lipoic acid that affect insulin sensitivity and reduce�insulin resistance cannot be obtained in food and must be supplemented.
Vitamin D, magnesium, and n-3 fatty acids have multiple functions, and generalized inflammation reduction is a common mechanism of action.74�80 Their supplemental use should be considered in the context of low-grade inflammation reduction and health promotion, rather than as a specific treatment for MetS or T2DM.
Gymnemic acids are the active component of the G sylvestre plant leaves. Gymnemic acids are the active component of the G sylvestre plant leaves. Studies evaluating G sylvestre’s effects on diabetes in humans have generally been of poor methodological quality. Experimental animal studies have found that gymnemic acids may decrease glucose uptake in the small intestine, inhibit gluconeogenesis, and reduce hepatic and skeletal muscle insulin resistance.99 Other animal studies suggest that gymnemic acids may have comparable efficacy in reducing blood sugar levels to the first-generation sulfonylurea, tolbutamide.100
Vanadyl sulfate has been reported to prolong the events of insulin signaling and may actually improve insulin sensitivity.101 Limited data suggest that it inhibits gluconeogenesis, possibly ameliorating hepatic insulin resistance. 100,101 Uncontrolled clinical trials have reported improvements in insulin sensitivity using 50 to 300 mg daily for periods ranging from 3 to 6 weeks. 101�103 Contrastingly, a recent randomized, double-blind, placebo-controlled trial found that 50 mg of vanadyl sulfate twice daily for 4 weeks had no effect in individuals with impaired glucose tolerance. 104 Limited clinical and experimental data exist supporting the use of vanadyl sulfate to improve insulin resistance,�and further research is warranted regarding its safety and efficacy.
Diets high in refined sugar and flour are deficient in chromium (Cr) and lead to an increased urinary excretion of chromium. 105,106 The progression of MetS is not likely caused by a chromium deficiency, 107 and dosages that benefit glycemic regulation are not achievable through food. 106,108,109
Humans derive ?-lipoic acid through dietary means and from endogenous synthesis. 111 The foods richest in ?-lipoic acid are animal tissues with extensive metabolic activity such as animal heart, liver, and kidney, which are not consumed in large amounts in the typical American diet. 111 Supplemental amounts of ?-lipoic acid used in the treatment of T2DM (300-600 mg) are likely to be as much as 1000 times greater than the amounts that could be obtained from the diet.112
This is a narrative overview of the topic of MetS. A systematic review was not performed; therefore, there may be relevant information missing from this review. The contents of this overview focuses on the opinions of the authors, and therefore, others may disagree with our opinions or approaches to management. This overview is limited by the studies that have been published. To date, no studies have been published that identify the effectiveness of a combination of a dietary intervention, such as the Spanish 
Obesity is a complex, multifactorial disease, and better understanding of the mechanisms underlying the interactions between lifestyle, environment, and genetics is critical for developing effective strategies for prevention and treatment [1].
Animal models provide unique opportunities for highly controlled studies that provide mechanistic insight into�the role of specific epigenetic marks, both as indicators of current metabolic status and as predictors of the future risk of obesity and metabolic disease. A particularly important aspect of animal studies is that they allow for the assessment of epigenetic changes within target tissues, including the liver and hypothalamus, which is much more difficult in humans. Moreover, the ability to harvest large quantities of fresh tissue makes it possible to assess multiple chromatin marks as well as DNA methylation. Some of these epigenetic modifications either alone or in combination may be responsive to environmental programming. In animal models, it is also possible to study multiple generations of offspring and thus enable differentiation between trans-generational and intergenerational transmission of obesity risk mediated by epigenetic memory of parental nutritional status, which cannot be easily distinguished in human studies. We use the former term for meiotic transmission of risk in the absence of continued exposure while the latter primarily entails direct transmission of risk through metabolic reprogramming of the fetus or gametes.
(i) Epigenetic Changes In Offspring Associated With Maternal Nutrition During Gestation
Maternal nutritional supplementation, undernutrition, and over nutrition during pregnancy can alter fat deposition and energy homeostasis in offspring [11, 13�15, 19]. Associated with these effects in the offspring are changes in DNA methylation, histone post-translational modifications, and gene expression for several target genes,�especially genes regulating fatty acid metabolism and insulin signaling [16, 17, 20�30]. The diversity of animal models used in these studies and the common metabolic pathways impacted suggest an evolutionarily conserved adaptive response mediated by epigenetic modification. However, few of the specific identified genes and epigenetic changes have been cross-validated in related studies, and large-scale genome-wide investigations have typically not been applied. A major hindrance to comparison of these studies is the different develop mental windows subjected to nutritional challenge, which may cause considerably different outcomes. Proof that the epigenetic changes are causal rather than being associated with offspring phenotypic changes is also required. This will necessitate the identification of a parental nutritionally induced epigenetic �memory� response that precedes development of the altered phenotype in offspring.
Emerging studies have demonstrated that paternal plane of nutrition can impact offspring fat deposition and epigenetic marks [31�34]. One recent investigation using mice has demonstrated that paternal pre-diabetes leads to increased susceptibility to diabetes in F1 offspring with associated changes in pancreatic gene expression and DNA methylation linked to insulin signaling [35]. Importantly, there was an overlap of these epigenetic changes in pancreatic islets and sperm suggesting germ line inheritance. However, most of these studies, although intriguing in their implications, are limited in the genomic scale of investigation and frequently show weak and somewhat transient epigenetic alterations associated with mild metabolic phenotypes in offspring.
Stable transmission of epigenetic information across multiple generations is well described in plant systems and C. elegans, but its significance in mammals is still much debated [36, 37]. An epigenetic basis for grand- parental transmission of phenotypes in response to dietary exposures has been well established, including in livestock species [31]. The most influential studies demonstrating effects of epigenetic transmission impacting offspring phenotype have used the example of the viable yellow agouti (Avy) mouse [38]. In this mouse, an insertion of a retrotransposon upstream of the agouti gene causes its constitutive expression and consequent yellow coat color and adult onset obesity. Maternal transmission through the germ line results in DNA methylation�mediated silencing of agouti expression resulting in wild-type coat color and lean phenotype of the offspring [39, 40]. Importantly, subsequent studies in these mice demonstrated that maternal exposure to methyl donors causes a shift in coat color [41]. One study has reported transmission of a phenotype to the F3 generation and alterations in expression of large number of genes in response to protein restriction in F0 [42]; however, alterations in expression were highly variable and a direct link to epigenetic changes was not identified in this system.
While many studies have identified diet-associated epigenetic changes in animal models using candidate site-specific regions, there have been few genome-wide analyses undertaken. A recent study focussed on determining the direct epigenetic impact of high-fat diets/ diet-induced obesity in adult mice using genome-wide gene expression and DNA methylation analyses [43]. This study identified 232 differentially methylated regions (DMRs) in adipocytes from control and high-fat fed mice. Importantly, the corresponding human regions for the murine DMRs were also differentially methylated in adipose tissue from a population of obese and lean humans, thereby highlighting the remarkable evolutionary conservation of these regions. This result emphasizes the likely importance of the identified DMRs in regulating energy homeostasis in mammals.
(i) Genetic association studies. Genetic polymorphisms that are associated with an increased risk of developing particular conditions are a priori linked to the causative genes. The presence of differential�methylation in such regions infers functional relevance of these epigenetic changes in controlling expression of the proximal gene(s). There are strong cis-acting genetic effects underpinning much epigenetic variation [7, 45], and in population-based studies, methods that use genetic surrogates to infer a causal or mediating role of epigenome differences have been applied [7, 46�48]. The use of familial genetic information can also lead to the identification of potentially causative candidate regions showing phenotype-related differential methylation [49].
From these studies, altered methylation of PGC1A, HIF3A, ABCG1, and CPT1A and the previously described RXRA [18] have emerged as biomarkers associated with, or perhaps predictive of, metabolic health that are also plausible candidates for a role in development of metabolic disease.
Epigenetic variation is highly influenced by the underlying genetic variation, with genotype estimated to explain ~20�40 % of the variation [6, 8]. Recently, a number of studies have begun to integrate methylome and genotype data to identify methylation quantitative trait loci (meQTL) associated with disease phenotypes. For instance, in adipose tissue, an meQTL overlapping�with a BMI genetic risk locus has been identified in an enhancer element upstream of ADCY3 [8]. Other studies have also identified overlaps between known obesity and T2DM risk loci and DMRs associated with obesity and T2DM [43, 48, 62]. Methylation of a number of such DMRs was also modulated by high-fat feeding in mice [43] and weight loss in humans [64]. These results identify an intriguing link between genetic variations linked with disease susceptibility and their association with regions of the genome that undergo epigenetic modifications in response to nutritional challenges, implying a causal relationship. The close connection between genetic and epigenetic variation may signify their essential roles in generating individual variation [65, 66]. However, while these findings suggest that DNA methylation may be a mediator of genetic effects, it is also important to consider that both genetic and epigenetic processes could act independently on the same genes. Twin studies [8, 63, 67] can provide important insights and indicate that inter-individual differences in levels of DNA methylation arise predominantly from non-shared environment and stochastic influences, minimally from shared environmental effects, but also with a significant impact of genetic variation.
Prenatal environment: Two recently published studies made use of human populations that experienced �natural� variations in nutrient supply to study the impact of maternal nutrition before or during pregnancy on DNA methylation in the offspring [68, 69]. The first study used a Gambian mother-child cohort to show that both seasonal variations in maternal methyl donor intake during pregnancy and maternal pre-pregnancy BMI were associated with altered methylation in the infants [69]. The second study utilized adult offspring from the Dutch Hunger Winter cohort to investigate the effect of prenatal exposure to an acute period of severe maternal undernutrition on DNA methylation of genes involved in growth and metabolism in adulthood [68]. The results highlighted the importance of the timing of the exposure in its impact on the epigenome, since significant epigenetic effects were only identified in individuals exposed to famine during early gestation. Importantly, the epigenetic changes occurred in conjunction with increased BMI; however, it was not possible to establish in this study whether these changes were present earlier in life or a consequence of the higher BMI.
Postnatal environment: The epigenome is established de novo during embryonic development, and therefore, the prenatal environment most likely has the most significant impact on the epigenome. However, it is now clear that changes do occur in the �mature� epigenome under the influence of a range of conditions, including aging, exposure to toxins, and dietary alterations. For example, changes in DNA methylation in numerous genes in skeletal muscle and PGC1A in adipose tissue have been demonstrated in response to a high-fat diet [75, 76]. Interventions to lose body fat mass have also been associated with changes in DNA methylation. Studies have reported that the DNA methylation profiles of adipose tissue [43, 64], peripheral blood mononuclear cells [77], and muscle tissue [78] in formerly obese patients become more similar to the profiles of lean subjects following weight loss. Weight loss surgery also partially reversed non-alcoholic fatty liver disease-associated methylation changes in liver [79] and in another study led to hypomethylation of multiple obesity candidate genes, with more pronounced effects in subcutaneous compared to omental (visceral) fat [64]. Accumulating evidence suggests that exercise interventions can also influence DNA methylation. Most of these studies have been conducted in lean individuals [80�82], but one exercise study in obese T2DM subjects also demonstrated changes in DNA methylation, including in genes involved in fatty acid and glucose transport [83]. Epigenetic changes also occur with aging, and recent data suggest a role of obesity in augmenting them [9, 84, 85]. Obesity accelerated the epigenetic age of liver tissue, but in contrast to the findings described above, this effect was not reversible after weight loss [84].
DNA methylation changes associated with obesity or induced by diet or lifestyle interventions and weight loss are generally modest (<15 %), although this varies depending on the phenotype and tissue studied. For instance, changes greater than 20 % have been reported in adipose tissue after weight loss [64] and associations between HIF3A methylation and BMI in adipose tissue were more pronounced than in blood [52].
Conclusions
Chronic undernutrition is characterized by a progressive reduction of the�fat-free mass (FFM) and fat mass (FM)�and �which has deleterious consequences on health. Undernutrition is insufficiently screened and treated in hospitalized or at-risk patients despite its high prevalence and negative impact on mortality, morbidity, length of stay (LOS), quality of life, and costs [1�4]. The risk of underestimating hospital undernutrition is likely to worsen in the next decades because of the increasing prevalence of overweight, obesity, and chronic diseases and the increased number of elderly subjects. These clinical conditions are associated with FFM loss (sarcopenia). Therefore, an increased number of patients with FFM loss and sarcopenic obesity will be seen in the future.
Academic societies encourage systematic screening of undernutrition at hospital admission and during the hospital stay [14]. The detection of undernutrition is generally based on measurements of weight and height, calculations of BMI, and the percentage of weight loss. Nevertheless, screening of undernutrition is infrequent in hospitalized or nutritionally at-risk ambulatory patients. For example, in France, surveys performed by the French Health Authority [15] indicate that: (i) weight alone, (ii) weight with BMI or percentage of weight loss, and (iii) weight, BMI,�and percentage of weight loss are reported in only 55, 30, and 8% of the hospitalized patients� records, respectively. Several issues, which could be improved by specific educational programs, explain the lack of implementation of nutritional screening in hospitals (table 1). In addition, the accuracy of the clinical screening of undernutrition could be limited at hospital admission. Indeed, patients with undernutrition may have the same BMI as sex- and age- matched healthy controls but a significantly decreased FFM hidden by an expansion of the FM and the total body water which can be measured by bioelectrical impedance analysis (BIA) [13]. This example illustrates that body composition evaluation allows a more accurate identification of FFM loss than body weight loss or BMI decrease. The lack of sensitivity and specificity of weight, BMI, and percentage of weight loss argue for the need for other methods to evaluate the nutritional status.
In 2008, twelve and thirty percent of the worldwide adult population was obese or overweight; this is two times higher than in 1980 [16]. The prevalence of overweight and obesity is also increasing in hospitalized patients. A 10-year comparative survey performed in a European hospital showed an increase in patients� BMI, together with a shorter LOS [17]. The BMI increase masks undernutrition and FFM loss at hospital admission. The increased prevalence of obesity in an aging population has led to the recognition of a new nutritional entity: �sarcopenic obesity� [18]. Sarcopenic obesity is characterized by increased FM and reduced FFM with a normal or high body weight. The emergence of the concept of sarcopenic obesity will increase the number of situations associated with a lack of sensitivity of the calculations of BMI and�body weight change for the early detection of FFM loss. This supports a larger use of body composition evaluation for the assessment and follow-up of nutritional status in clinical practice (fig. 1).
Fig. 2. Current and potential applications of body composition evaluation in clinical practice. The applications are indicated in the boxes, and the body composition methods that could be used for each application are indicated inside the circles. The most used application of body composition evaluation is the measurement of bone mineral density by DEXA for the diagnosis and management of osteoporosis. Although a low FFM is associated with worse clinical outcomes, FFM evaluation is not yet implemented enough in clinical practice. However, by allowing early detection of undernutrition, body composition evaluation could improve the clinical outcome. Body composition evaluation could also be used to follow up nutritional status, calculate energy needs, tailor nutritional support, and assess fluid changes during perioperative period and renal insufficiency. Recent evidence indicates that�a low FFM is associated with a higher toxicity of some chemo- therapy drugs in cancer patients. Thus, by allowing tailoring of the chemotherapy doses to the FFM in cancer patients, body com- position evaluation should improve the tolerance and the efficacy of chemotherapy. BIA, L3-targeted CT, and DEXA could be used for the assessment of nutritional status, the calculation of energy needs, and the tailoring of nutritional support and therapy. Further studies are warranted to validate BIA as an accurate method for fluid balance measurement. By integrating body composition evaluation into the management of different clinical conditions, all of these potential applications would lead to a better recognition of nutritional care by the medical community, the health care facilities, and the health authorities, as well as to an increase in the medico-economic benefits of the nutritional evaluation.
Body Composition Techniques For FFM Measurement
Body composition evaluation allows measurement of the major body compartments: FFM (including bone mineral tissue), FM, and total body water. Table 2 shows indicative values of the body composition of a healthy subject weighing 70 kg. In several clinical situations, i.e. hospital admission, chronic obstructive pulmonary dis- ease (COPD) [21�23], dialysis [24�26], chronic heart failure [27], amyotrophic lateral sclerosis [28], cancer [5, 29], liver transplantation [30], nursing home residence [31], and Alzheimer�s disease [32], changes in body compartments are detected with the techniques of body composition evaluation. At hospital admission, body composition evaluation could be used for the detection of FFM loss and undernutrition. Indeed, FFM and the FFM index (FFMI) [FFM (kg)/height (m2)] measured by BIA are significantly lower in hospitalized patients (n = 995) than in age-, height-, and sex-matched controls (n = 995) [3]. Conversely, clinical tools of nutritional status assessment, such as BMI, subjective global assessment, or mini-nutritional assessment, are not accurate enough to estimate FFM loss and nutritional status [30, 32�34]. In 441 patients with non-small cell lung cancer, FFM loss deter- mined by computerized tomography (CT) was observed in each BMI category [7], and in young adults with all�types of cancer, an increase in FM together with a de- crease in FFM were reported [29]. These findings reveal the lack of sensitivity of BMI to detect FFM loss. More- over, the FFMI is a more sensitive determinant of LOS than a weight loss over 10% or a BMI below 20 [3]. In COPD, the assessment of FFM by BIA is a more sensitive method to detect undernutrition than anthropometry [33, 35]. BIA is also more accurate at assessing nutrition- al status in children with severe neurologic impairment than the measurement of skin fold thickness [36].
FFM loss is correlated with survival in different clinical settings [5, 21�28, 37]. In patients with amyotrophic lateral sclerosis, an FM increase, but not an FFM in- crease, measured by BIA, was correlated with survival during the course of the disease [28]. The relation between body composition and mortality has not yet been demonstrated in the intensive care unit. The relation between body composition and mortality has been demonstrated with anthropometric methods, BIA, and CT. Measurement of the mid-arm muscle circumference is an easy tool to diagnose sarcopenia [38]. The mid-arm muscle circumference has been shown to be correlated with survival in patients with cirrhosis [39, 40], HIV infection [41], and COPD in a stronger way than BMI [42]. The relation between FFM loss and mortality has been extensively shown with BIA [21�28, 31, 37], which is the most used method. Recently, very interesting data suggest that CT could evaluate the disease prognosis in relation to muscle wasting. In obese cancer patients, sarcopenia as assessed by CT measurement of the total skeletal muscle cross-sectional area is an independent predictor of the survival of patients with bronchopulmonary [5, 7], gastrointestinal [5], and pancreatic cancers [6]. FFM assessed by measurement of the mid-thigh muscle cross- sectional area by CT is also predictive of mortality in COPD patients with severe chronic respiratory insufficiency [43]. In addition to mortality, a low FFMI at hospital admission is significantly associated with an in- creased LOS [3, 44]. A bicentric controlled population study performed in 1,717 hospitalized patients indicates that both loss of FFM and excess of FM negatively affect the LOS [44]. Patients with sarcopenic obesity are most at risk of increased LOS. This study also found that ex- cess FM reduces the sensitivity of BMI to detect nutritional depletion [44]. Together with the observation that the BMI of hospitalized patients has increased during the last decade [17], these findings suggest that FFM and�FFMI measurement should be used to evaluate nutritional status in hospitalized patients.
Numerous methods of body composition evaluation have been developed: anthropometry, including the 4-skinfold method [58], hydrodensitometry [58], in vivo neutron activation analysis [59], anthropogammametry from total body potassium-40 [60], nuclear magnetic resonance [61], dual-energy X-ray absorptiometry (DEXA) [62, 63], BIA [45, 64�66], and more recently CT [7, 43, 67]. DEXA, BIA, and CT appear to be the most convenient methods for clinical practice (fig. 2), while the other methods are reserved for scientific use.
The evaluation of FFM could be used for the calculation of energy needs, thus allowing the optimization of nutritional intakes according to nutritional needs. This could be of great interest in specific situations, such as severe neurologic disability, overweight, and obesity. In 61 children with severe neurologic impairment and intellectual disability, an equation integrating body composition had good agreement with the doubly labeled water method. It gave a better estimation of energy expenditure than did the Schofield predictive equation [36]. However, in 9 anorexia nervosa patients with a mean BMI of 13.7, pre- diction formulas of resting energy expenditure including FFM did not allow accurate prediction of the resting energy expenditure measured by indirect calorimetry [76]. In overweight or obese patients, the muscle catabolism in response to inflammation was the same as that observed�in patients with normal BMI. Indeed, despite a higher BMI, the FFM of overweight or obese individuals is similar (or slightly increased) to that of patients with normal BMI. Thus, the use of actual weight for the assessment of the energy needs of obese patients would result in over- feeding and its related complications. Therefore, the ex- perts recommend the use of indirect calorimetry or calculation of the energy needs of overweight or obese patients as follows: 15 kcal/kg actual weight/day or 20�25 kcal/kg ideal weight/day [77, 78], although these predictive formulas could be inaccurate in some clinical conditions [79]. In a US prospective study conducted in 33 ICU medical and surgical ventilated ICU patients, daily measurement of the active cell mass (table 2) by BIA was used to assess the adequacy between energy/protein intakes and needs. In that study, nutritional support with 30 kcal/ kg actual body weight/day energy and 1.5 g/kg/day protein allowed stabilization of the active cell mass [75]. Thus, follow-up of FFM by BIA could help optimize nutritional intakes when indirect calorimetry cannot be performed.
Body composition evaluation allows a qualitative assessment of body weight variations. The evaluation of body composition may help to document the efficiency of nutritional support during a patient�s follow-up of numerous clinical conditions, such as surgery [59], anorexia nervosa [76, 80], hematopoietic stem cell transplantation [81], COPD [82], ICU [83], lung transplantation [84], ulcerative colitis [59], Crohn�s disease [85], cancer [86, 87], HIV/AIDS [88], and acute stroke in elderly patients [89]. Body composition evaluation could be used for the follow-up of healthy elderly subjects [90]. Body composition evaluation allows characterization of the increase in body mass in terms of FFM and FM [81, 91]. After hematopoietic stem cell transplantation, the increase in BMI is the result of the increase in FM, but not of the increase in FFM [81]. Also, during recovery after an acute illness, weight gain 6 months after ICU discharge could be mostly related to an increase in FM (+7 kg) while FFM only increased by 2 kg; DEXA and air displacement plethysmography were used to measure the FM and FFM [91]. These two examples suggest that body composition evaluation could be helpful to decide the modification and/or the renewal of nutritional support. By identifying the patients gaining weight but reporting no or insufficient FFM, body composition evaluation could contribute to influencing the medical decision of continuing nutrition- al support that would have been stopped in the absence of body composition evaluation.
In clinical situations when weight and BMI do not reflect the FFM, the evaluation of body composition should be used to adapt drug doses to the FFM and/or FM absolute values in every patient. This point has been recently illustrated in oncology patients with sarcopenic obesity. FFM loss was determined by CT as described above. In cancer patients, some therapies could affect body com- position by inducing muscle wasting [92]. In patients with advanced renal cell carcinoma [92], sorafenib induces a significant 8% loss of skeletal muscular mass at 12 months. In turn, muscle wasting in patients with BMI less than 25 was significantly associated with sorafenib toxicity in patients with metastatic renal cancer [8]. In metastatic breast cancer patients receiving capecitabine treatment, and in patients with colorectal cancer receiving 5-fluorouracile, using the convention of dosing per unit of body surface area, FFM loss was the determinant of chemotherapy toxicity [9, 10] and time to tumor progression [10]. In colorectal cancer patients administered 5-fluoruracil, low FFM is a significant predictor of toxicity only in female patients [9]. The variation in toxicity between women and men may be partially explained by the fact that FFM was lower in females. Indeed, FFM rep- resents the distribution volume of most cytotoxic chemo- therapy drugs. In 2,115 cancer patients, the individual variations in FFM could change by up to three times the distribution volume of the chemotherapy drug per body area unit [5]. Thus, administering the same doses of chemotherapy drugs to a patient with a low FFM compared to a patient with a normal FFM would increase the risk of chemotherapy toxicity [5]. These data suggest that FFM loss could have a direct impact on the clinical outcome of cancer patients. Decreasing chemotherapy doses in case of FFM loss could contribute to improving cancer patients� prognosis through the improvement of the tolerance of chemotherapy. These findings justify the systematic evaluation of body composition in all cancer patients in order to detect FFM loss, tailor chemotherapy doses according to FFM values, and then improve the efficacy- tolerance and cost-efficiency ratios of the therapeutic strategies [93]. Body composition evaluation should also be used to tailor the doses of drugs which are calculated based on patients� weight, e.g. corticosteroids, immuno-suppressors (infliximab, azathioprine or methotrexate), or sedatives (propofol).
The implementation of body composition evaluation in routine care presents a challenge for the next decades. Indeed the concomitant increases in elderly subjects and patients with chronic diseases and cancer, and in the prevalence of overweight and obesity in the population, will increase the number of patients nutritionally at risk or undernourished, particularly those with sarcopenic obesity. Body composition evaluation should be used to improve the screening of undernutrition in hospitalized patients. The results of body composition should be based on the same principle as BMI calculation, towards the systematic normalization for body height of FFM (FFMI) and FM [FM (kg)/height (m)2 = FM index] [94]. The results could be expressed according to previously de- scribed percentiles of healthy subjects [95, 96]. Body com- position evaluation should be performed at the different stages of the disease, during the course of treatments and the rehabilitation phase. Such repeated evaluations of body composition could allow assessment of the nutritional status, adjusting the calculation of energy needs as kilocalories/kilogram FFM, following the efficacy of 
