New data challenge popular set point theory of obesity.(Physical Activity Seems Key)

DENVER -- It's high time to toss out the long-popular set point theory of obesity, according to speakers at an international conference of the Academy for Eating Disorders.

The set point theory holds that obesity entails a metabolic defect that functions as a homeostatic mechanism. This defect is supposed to result in a slowdown of resting metabolic rate in an overweight or obese individual who has lost weight. The resultant reduction in energy expenditure is said to be responsible for the often-observed scenario in which the individual regains the weight that was lost and thereby returns to his or her set point.

The set point theory enjoys widespread popularity among the overweight public, in whom it fosters a fatalism regarding the condition of obesity. The theory also holds sway among many physicians who work with obese patients and/or those with eating disorders.

But scientific support for the set point theory is limited to old data derived from outdated methods of physiologic measurement.

Recent studies using far more sophisticated and accurate methods of metabolic assessment consistently challenge the theory, said Cheryl L. Rock, Ph.D., professor of family and preventive medicine at the University of California, San Diego.

One new method is the doubly labeled water technique, a form of indirect calorimetry based on the elimination of deuterium and oxygen-18 from urine. It allows researchers to measure total energy expenditure over a period of days, using only periodic sampling of urine to measure turnover of hydrogen and oxygen into water and carbon dioxide.

Such modern methods have shown that although a metabolic slowdown can occur during active weight loss because the patient has a marked caloric deficit, the slowdown ends once the patient reaches the target weight and shifts into ...