Exercise fights weight regain after dieting

US researchers say the key to keeping the weight off is regular exercise

  How often have you battled through weeks or months of dieting, only to put it all back on again, and then some?

  However, there are always a few fortunate souls who do manage to keep their weight under control, and according to research carried out by the US National Weight Control Registry, those dieters share a number of common characteristics, including a programme of regular exercise.

   Researchers from the University of Colorado Denver therefore set out to discover how exercise affects the body’s physiology to minimise weight regain by studying obesity-prone laboratory rats.

   For the first 16 weeks, the rats ate a high-fat diet, as much as they wanted, and remained sedentary. They were then placed on a diet. For the following two weeks, the animals ate a low-fat and low-calorie diet, losing about 14 percent of their body weight. The rats maintained the weight loss by dieting for eight more weeks. Half the rats exercised regularly on a treadmill during this period while the other half remained sedentary.

   In the final eight weeks, the relapse phase of the study, the rats stopped dieting and ate as much low-fat food as they wanted. The rats in the exercise group continued to exercise and the sedentary rats remained sedentary.

   The study's findings showed that exercise helps prevent weight regain after dieting by reducing appetite and by burning fat before burning carbohydrates. Burning fat first and storing carbohydrates for use later in the day slows weight regain and may reduce overeating by signalling a feeling of fullness to the brain.

   Moreover, their results also revealed that, contrary to popular wisdom, the number of fat cells is not pre-ordained by your genetic make-up, but that during the relapse period, when dieters start to regain the lost weight, sedentary types start to produce small, new fat cells. Those who exercise regularly, however, do not create these new fat cells.

  Writing in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, the team says that taken together, these physiological changes in the brain and body lower the 'defended' weight - the weight that our physiology drives us to achieve.

   Conventional wisdom holds that the number of fat cells is determined by genetics, rather than being regulated by diet or lifestyle. Because this effect of exercise is a novel finding, the team will do further research to demonstrate that exercise is preventing the formation of new fat cells early in relapse and not simply altering the size of pre-existing fat cells.