Proponents of the ‘eat-too-much, do-too-little’ theory of obesity claim that exercise is effective at causing weight loss. The failure of obese individuals to experience weight loss from exercise is largely dismissed as the individual not adhering to the exercise regimen. Little thought is given to the subject as it is assumed by many that exercise causes weight loss. In metabolically normal individuals this is partly true, however it is known that increasing physical activity levels causes a compensatory increase in energy intake in most people. In obesity this compensatory eating can prevent weight loss, and can actually cause weight gain in many cases. Researchers have investigated the use of exercise in obese individuals and generally the results have been disappointing. This is because most exercise regimens involve endurance exercise, which is catabolic in nature, can decrease muscle mass and thus lower resting metabolic rate (RMR), and also stimulate appetite.
For example, one group of researchers1 investigated the changes in body composition and energy intake in a group of 35 subjects during a 12 week intervention of endurance exercise. The subjects trained for 5 days per week on a variety of endurance machines such as rower, bicycle and stepper. The study authors claimed that the exercise was designed to expend 500 kcal per session at 70 % of maximum heart rate. When the mean weight loss was calculated after 12 weeks, it was found that the subjects had lost an average of 3.7 kg of body weight, of which 3.7 kg was fat. However, examination of the individual data revealed large differences in the response to exercise between subjects. Some individuals lost as much as 14.7 kg body weight, whereas others gained up to 1.7 kg. Likewise, some individuals lost up to 9.5 kg fat mass, while others gained up to 2.6 kg.
Therefore, the effects of exercise are variable and depend largely on the individual. No trends were found between genders in the groups that improved or did not improve body composition. In addition, there was no difference in the exercise induced energy expenditure between the groups or the number of sessions attended by the subjects. The failure of some subjects to lose weight cannot be claimed to be due to non-adherence to the exercise regimen, as all exercise was chaperoned. However, when the researchers investigated the lean mass of the subjects, they found that those individuals that had improved their body composition, were the ones who had gained lean mass. Those who had not improved their body composition had actually lost lean mass. In addition, the exercise responders had a decrease in energy intake of 130 kcal per day, whereas the non-responders increased energy intake by 268 kcal per day.
Although the change in RMR was not significant between the exercise responders and the non-responders, there was a trend for the responders to increase RMR (14.2 kcal per day), and a trend for the non-responders to decrease RMR (-60 kcal per day). These results therefore support the contention that exercise is not effective at causing weight loss unless it results in an increase in lean body tissue, particularly skeletal muscle. The RMR of an individuals in proportional to the amount of skeletal muscle they possess. This is important because the RMR is the largest contributor to the total energy expended in one day. Exercise itself constitutes a smaller percentage of the total calories and it also causes compensatory eating behaviour in some individuals which can be counter productive in weight loss. Exercise regimens that aim to treat overweight individuals should therefore centre on resistance training.
RdB
