Body-weight regulation: causes of obesity

Abstract

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 selfcontrolled 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. Obesity: Body-weight regulation: Lifestyle: GeneticsWeight and body energy content remain quite stable in most adult individuals for long periods of time (Jequier & Tappy, 1999), despite daily fluctuations in energy balance (energy intake v. energy expenditure). It is assumed, therefore, that regulatory processes match the dietary fuel supply with energy requirements in order to maintain a stable body mass and adiposity (Weigle, 1994;Flatt, 1998;Schwartz et al. 1999). Thus, this lasting steady-state appears to involve a number of integrated mechanisms which contribute to the regulation of body weight and fuel stores

Genes, lifestyles and obesity

“…3 The control of the maintenance of body composition has been the subject of a number of theories or pathways ( Figure 1) such as the occurrence of a physiological set point for body weight, glucostatic or glycogen drives for feeding, metabolic/nutrient partitioning approaches, the participation of the nervous system, an adipostat mediated by signals from the adipose tissue, all of which might be under genetic control and explain individual variability. 4 In this context, it has been hypothesised that the stability of body weight and composition depends upon an axis with three inter-related and self-controlled components: (1) food intake; (2) nutrient turnover and thermogenesis, and (3) body fat stores. 5 All three elements underlie complex interrelated feedback mechanisms, which are affected by the individual's genetic background.…”

“…5 All three elements underlie complex interrelated feedback mechanisms, which are affected by the individual's genetic background. 3,4 It should be emphasised that body weight is ultimately determined by the interaction of genetic, environmental, physiological and psychosocial factors [6][7][8] Furthermore, the specific distribution of energy expenditure requirements and individual substrate partitioning 3,7 are known to influence the energy balance equation depending on the genetic make-up.…”

Efeito de um programa de exercício físico moderado em ratos de diferentes modelos de obesidade

“…A esta patologia estão associados distúrbios metabólicos/endócrinos e cardiovasculares, entre os quais se destacam o diabetes mellitus tipo 2, dislipidemias e hipertensão arterial, caracterizando a síndrome metabólica (MARTINEZ, 2000;BRAY et al, 2005).…”

Genetics of Obesity: Gene × Nutrient Interactions

“…There are several well-documented environmental variables that influenced body weight gain and increased obesity risk [9][10][11][12][13][14][15][16]. These variables include excessive calorie intake and sedentary lifestyles.…”

“…A controversial question is whether or not high-fat diets versus low-fat diets with the same equivalent total energy contributed to weight gain [10,11]. In several weight-loss studies prescribing low carbohydrate diets (moderate to high fat content) as compared to low fat diets, there was no major difference in the average weight reduction [17].…”