Fat | Losing Weight | Avoiding Obesity

There is still no established reliable formula for losing weight and avoiding obesity, other than limiting the intake of calories --- a painful proceeding. The old distinction between endogenous and exogenous obesity --- a genetic form that you cannot help, and the kind brought on by greed --- went out of fashion some decades ago, but it is recognized that there is quite wide variation, part-hereditary and part-acquired, between the response of individuals to diet.

The notion that fat people have a slower metabolic rate and therefore do not 'burn' off fat like lean people does not hold water, and the many dietary prescriptions based on this notion are specious. It is in fact now firmly established that obese people have a faster basal (fasting) metabolic rate than thin people and the more obese they become the more rapid their metabolism.

The resting metabolic rate (lowest during sleep), when the body is performing no external work, is a reflection of the biochemical processes that constitute life. These reactions produce heat that can be measured in a calorimeter. A part of the heat production is adaptive thermogenesis responsive, that is, to external temperature and especially to diet. With a high calorie intake the heat output goes up and during starvation it diminishes --- undoubtedly a survival characteristic.

The level of the adaptive response to calorie intake is controlled by complex biochemical processes in the brain that send out signals to the body's cells to speed up or slow down the heat-generating reactions. These responses are disturbed in obese people, but are also influenced by genetics. One strand of obesity research is aimed at finding agents that will modulate the level of adaptive thermogenesis. The health and obesity crisis continues to stimulate much nutritional research, and perhaps eventually there will be safe drugs to solve all problems. But the great molecular biologist Sydney Brenner has told how he reacted to the euphoria of a colleague who claimed to have discovered "the obesity gene." He, too, Brenner replied, had long ago discovered the obesity gene: it is the gene that opens the mouth.