Obesity - with its associated co-morbidities such as the metabolic syndrome and also its health costs - is one of the major biomedical problems of recent decades, and effective and satisfying preventive strategies and treatments are necessary. Compliance with conventional weight-management programs is notoriously poor, and there is room for innovation.
A plethora of over-the-counter dietary supplements to treat obesity are currently marketed worldwide. Many of them have not been tested in randomized controlled trials in humans.183 For those that have been tested in this way, evidence for effectiveness and safety is not compelling (reviewed in references 182 and 183). Products for which there actually is a scientific rationale have in general only minor weight-reducing effects, so that they must be considered to have at most an adjuvant role within the framework of more strict weight-loss regimens.222 Moreover, the risk/benefit balance is unfavorable for some supplements of proven effectiveness, because of adverse effects associated with their consumption, as is the case with supplements containing Ephedra or ephedrine.
Functional foods that affect energy metabolism and fat partitioning may also serve as adjuncts to a dietary approach to body weight control, when incorporated in a healthy and balanced diet. Some traditional foods - such as tea, milk and nuts - might be of value in this sense, as might be designed foods with saturated fat replaced by n-3 PUFA or CLA, with long-chain triacylglycerols replaced by medium-chain triacylglycerols or diacylglycer-ols, or enriched in thermogenic ingredients or certain amino acids, among other emerging possibilities.
Another important aspect to be considered is the macronutrient balance of the diet. Negative energy balance produces weight loss independently of the macronutrient composition of the diet (see references 99 and 223), but there is increasing evidence that the latter can affect weight loss/maintenance, by virtue of distinct effects of proteins, fats and carbohydrates on processes involved in body weight and body fat control. Elevated protein intake, for instance, might assist body weight management through increased satiety and reduced subsequent energy intake, increased diet-induced thermogenesis, its contribution to storage of fat-free mass and its low energy efficiency during overfeeding (due to the increased diet-induced thermogenesis and to the composition of the body mass gained, with more fat-free mass) (see reference 129). The results of human studies using high-protein diets that have been conducted so far - together with the evidence pointing to undesirable effects associated with high levels of consumption of refined carbohydrates, such as decreased satiety and increased carbohydrate-induced hypertriglyceridemia - suggest that, in dietary practice, it may be beneficial to partially replace refined carbohydrate with protein sources that are low in saturated fat for weight-management purposes.46 However, longer-term studies are needed to establish the safety and efficacy of highprotein diets in the long-term.
The system of body weight control is highly complex and redundant, and very often intended changes in one pathway are compensated for by non-intended changes in another one. Because of this, strategies/developments that affect different targets are of special interest. The combination of different bioactive ingredients in a unique dietary supplement or nutraceutical is already a common practice, and, likewise, multi-factorial functional foods for weight management may become commonplace in the near future. For instance, a functional food product containing low-glycemic index carbohydrates, 5-hydroxytryptophan, green tea extract and chromium has already been developed and is undergoing clinical testing;224 the first two nutrients are purported to decrease appetite, while green tea is purported to increase energy expenditure and chromium to promote the composition of the weight loss to be fat rather than lean tissue.
With the advancing sciences of nutrition and nutrigenomics (which studies nutrient-gene interactions globally using post-genomic approaches) new developments in the functional foods and nutraceutical arenas are envisaged for obesity control based on an increasing knowledge of how specific nutrients and other food components affect hunger and satiety, thermogenesis, fat oxidation, lipogenesis or body composition. Hand in hand with this, increasing knowledge of how the individual's genetic background influences his/her response to nutrients/diets and drugs will lead to more individualized approaches for weight management.
Nutritional strategies and dietary patterns for obesity management become increasingly important as we recognize from previous experience the value of promoting positive behaviors rather than using a prohibitive approach to accomplish a given health outcome. Most probably, however, these measures will still have to be combined with energy restriction and increased physical activity to achieve significant weight loss. In any case, knowledge of the molecular mechanisms and mechanistic aspects explaining the biological activity/effects, assessment of long-term efficacy and safety in well-designed human trials, proper risk/benefit evaluation and, where appropriate, product quality (e.g. absence of contamination, accuracy of labeling), are aspects that will become progressively more important if weight-loss claims are to be made for a given food/product, or if dietary patterns are to be recommended for weight-management purposes.
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