Glucostatic control of intake and obesity

Body-weight regulation: causes of obesity

The aetiology and treatment of obesity have been fraught with disappointment for researchers, because the mechanisms that control fuel homeostasis and adiposity are incompletely understood. It is assumed that regulatory processes match the dietary fuel supply with energy requirements in order to maintain a stable body mass and adiposity. In this context several theories have been proposed to explain the laws of thermodynamics describing the conservation and transformation of energy in living organisms. In the light of new evidence it can now be hypothesized that the control of body weight and composition depends on an axis with three interrelated and self-controlled components: (1) food intake; (2) nutrient turnover and thermogenesis; (3) body fat stores. Complex feedback mechanisms underlie all these components. The major factors involved in obesity seem to be dietary and physical activity habits. These factors are affected by susceptibility genes that in turn may influence energy expenditure, fuel metabolism, muscle fibre function and appetite or food preferences. However, the increasing rates of obesity cannot be explained exclusively by changes in the gene pool, although genetic variants that were previously 'silent' are now being triggered by the high availability of energy- and fat-dense foods, and by the increasingly sedentary lifestyle of modern societies. The study of factors such as genetics and lifestyle implicated in weight gain and obesity is crucial for predictions about the future impact of the global epidemic of obesity, and provides a unique opportunity for the implementation of preventive action.

The role of reduced fat diets and fat substitutes in the regulation of energy and fat intake and body weight

The suggested link between a high intake of dietary fat and obesity has led to a proliferation on the market of reduced fat foods. The preceding year has seen the publication of more long-term studies investigating the effects of reduced fat and fat substituted foods on energy intake, fat intake and body weight. Effects on the proportion of the diet consumed as fat are encouraging (with most studies showing a decrease towards dietary recommendations), whilst effects on energy intake and body weight remain equivocal.

The role of low-fat diets and fat substitutes in body weight management: what have we learned from clinical studies?

The introduction of low-fat, high-complex carbohydrate diets far the prevention and treatment of obesity was based on the causal link established between dietary fat and body fatness. Observational and mechanistic studies show that because fat possesses a lower satiating power than carbohydrate and protein, a diet rich in fat can increase energy intake. The propensity to gain weight is enhanced in susceptible persons, particularly sedentary people who have a genetic predisposition to obesity. Low-fat diets cause weight loss proportional to pretreatment body weight in a dose dependent manner; that is, weight loss is correlated positively to the reduction in dietary fat content. A reduction of 10% fat energy produces an average 5-kg weight loss in obese persons. As with traditional caloric counting diets, obese persons lose weight only if they adhere to the prescribed low-fat diet. Failure to achieve a weight loss and to maintain it may be attributed in part to lack of adherence to the diet. After a major weight loss, an ad libitum low-fat diet program appears to be superior to caloric counting in maintaining the weight loss 2 years later. Replacing some fat with protein instead of carbohydrate may increase the weight loss further. Moreover, fat substitutes may make it easier to prevent and treat obesity by making the diet palatable. More randomized, controlled, long-term dietary intervention studies are warranted to identify the optimal diet composition for the treatment of obesity.