The Hindu Business Line : Weighing the causes

Obesity and overweight have recently been recognised by the World Health Organisation as one of the top 10 global health problems. According to the latest estimates, one billion adults and more than 22 million children under five years around the world are overweight. Of these, 300 million adults are obese.

Obesity is a problem not only in developed countries but is also increasingly extending to the developing countries, where an estimated 115 million people are affected.

According to WHO projections, by 2015, approximately 2.3 billion people will be overweight and 700 million will be obese.

Reaching epidemic proportions globally, it poses a major risk for diet-related chronic diseases, including type-2 diabetes, cardiovascular diseases, hypertension and stroke, and certain forms of cancer. It is a very complex issue, closely linked with lifestyle and biological factors as well as social and psychological dimensions and affects virtually all age and socioeconomic groups.

Most people in western societies, and even in emerging countries, today have access to an abundance of food, and they lead a more sedentary lifestyle than did their hunter-gatherer ancestors. The environment has indeed contributed to the increase in the average weight of the population over time, but it can’t be the cause of the huge differences in weight among the population at the present time. While the problem of obesity has proven difficult to solve, great strides toward a thorough understanding of the biology of obesity have been made.

Twenty years ago, little was known about the biological mechanisms that control body weight. While it was known that the hypothalamus, a region of the brain, regulates food intake and metabolism, the molecular elements of this system were not known.

Weight control is often considered just a question of healthy eating and lifestyle, an assumption which, in the end, stigmatises obese people, who are often perceived as lacking the willpower and discipline to lose weight. This assumption is invalidated by a growing body of scientific evidence demonstrating that a precise and powerful biological system maintains body weight at a constant level. Voluntary efforts to reduce weight are thus resisted by potent compensatory biological responses.

A revolution in the understanding of obesity was started in 1994 when I identified a gene in mice and humans called obese and its product, the hormone leptin, as two of the molecular components of that system regulating appetite and adiposity. Subsequent research on leptin and the identification of its receptors led scientists to understand that appetite and adiposity are regulated by a physiological system balancing food intake and energy expenditure. Today, scientists have identified other genes that play a role in obesity, demonstrating even more strongly the implication of genetics in obesity and the complexity of this system.

By discovering leptin and by proposing a hormonal relationship of the adipose tissue with the centres in the brain responsible for satiety and hunger, I was then able to demonstrate that appetite and body weight depend on a complex physiological system. This also opened research on the biology of obesity and brought new angles to research on nutrition and food intake.

It is a propitious time to discuss the need for understanding the biological basis of obesity. A different kind of understanding is called for. Obesity is not a personal failing. In trying to lose weight, the obese are fighting a difficult battle. It is a battle against biology. It is my hope that a better understanding of the genes and genetic variants will provide help to obese people. Still, scientific advances take time, and the translation of those in new treatments often takes even longer.

Today, scientists are still at the forefront of research, studying regulation of appetite and adipogenesis by leptin and other relevant new compounds. So it is understandable why, if public health recommendations on healthy diet and lifestyle can have a positive effect on moderately overweight people, such measures have generally little results on obese people’s health. For them, new scientific findings are providing new perspectives in the struggle against obesity.

The author is the winner of the 2007 Danone International Prize for Nutrition.