Hurdles and hopes in the management of human obesity.
A population shift towards obesity is a major side-effect of changes in lifestyle that accompany economic prosperity, and a high risk factor for many chronic degenerative diseases including non-insulin-dependent diabetes mellitus (NIDDM), coronary heart disease and hypertension. According to current WHO population statistics, 40% of obese patients eventually develop NIDDM, 80% of individuals with NIDDM are obese and the incidence of hypertension in obesity and NIDDM could be as high as 50%. Of particular concern for developing countries is the strong epidemiological evidence indicating that the prevalence of obesity and diabetes often increase in epidemic proportions in communities emerging from lifestyles of subsistence into affluence. Even modest increase in prosperity seem to be associated with the most marked increases in the proportion of these chronic diseases. Indeed, obesity and its pathophysiological complications have become health priorities among American Indians, Australian Aborigines, Pacific Islanders, and are rapidly becoming major concerns among many other developing countries. For example, the prevalence of obesity (BMI >30) for the middle-age group is 32% in women living in Urban Trinidad, 16.4% in Nicaragua, 14% in Costa Rica, values which are higher than for the USA (12-15%) or in the UK (8-9%). Even more spectacular are the health statistics about the middle-aged Pima Indians in Arizona and inhabitants of the South Pacific Island of Nauru, showing that more than 80% are obese, and 50-70% have NIDDM. These grim figures must be weighed against the hard fact that there is at present no effective cure for obesity, and judging from the outcome of health policies in countries with a long experience in dealing with this problem, the management of obesity has a long and disappointing history. In fact, for the past decades, a wide array of treatment has been available to their public (low-calorie regimes, low-fat or high fibre foods, anorectic drugs, exercise and behavioural therapy, etc), but in the vast majority of cases, the result is a transient phase of weight loss, followed by a return to the obese condition within a few years. Despite the poor prognosis of treating obesity by reducing food intake (by dieting alone or with the help of anorectic drugs), thi approach will continue to be the most common form of treatment in the foreseeable future. However, there is growing realisation that in response to reduced food intake, the accompanying fall in energy expenditure is a major factor that limits weight loss and contributes to obesity relapse. After an analysis of the various approaches to reduce energy intake, this paper will examine the extent to which re-adjustments in the various compartments of energy expenditure contribute to this apparent adaptation to reduced food intake. It will then analyze the rationale, applicability and effectiveness of various approaches (behavioural, dietary, and pharmacological) that could conceivably stimulate the metabolic rate and thus counteract such adaptive changes in energy expenditure in order to improve the efficacy of obesity management.
Department of Physiology, Faculty of Medicine, University of Geneva, 1, Rue Michel Servet, 1211 Geneva 4, Switzerland.
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Dulloo