What a ridiculous, naive question that is. Does exercise help you lose weight? Common sense tells us it does, but the scientific literature seems to have difficulty confirming this. Gretchen Reynolds of the New York times’ well blog wrote an article about this exact question.
The first study she cites is one published in the British journal of sports medicine . For 12 weeks 58 sedentary overweight/obese subjects underwent supervised aerobic exercise at 70% of their max heart rate 5 days a week, for 12 weeks. They were instructed to not decrease their food intake.
Since a pound of fat contains about 3500 calories, these people should all lose about 8.5 pounds (12 weeks *5 days a week * 500 calories burnt per day = 30,000 / 3500 calories per pound). At the end of the study the mean loss in body weight was 3.3kg, or 7.2 pounds, which is almost what we predicted. But this value is misleading. After the results were compiled, the researchers divided the subjects into 2 groups: responders and nonresponders. The nonresponders (45% of all the subjects) only lost an average of 0.9kg or 1.98 pounds, including some who gained weight. Therefore, and I quote, “based on body weight alone, exercise could be regarded as ineffective and futile for the non-responders (and even counterproductive for the weight gainers).”
As you can see, for some of these people the exercise program worked beautifully. But for 46% of them, they lost less than 2 pounds, and 17% gained weight burning 500 calories a day.
Since each exercise session was monitored and measured, the results can not be blamed on poor adherence.
But they can be blamed on the diet. Throughout this entire paper, they only mention diet once, and all it says is “Subjects were instructed to not restrict their energy intake during the study.” No self reporting. Nothing. These results would be so much more intriguing if we knew they were eating similar amounts. Maybe the “non-responders” simply ate a lot more than the responders.
The New York times reported this study as support for the idea that exercise does not help you lose weight, which, according to a plethora of studies, may not be as ridiculous as it sounds. However in my opinion this study provides no evidence one way or the other.
Despite not losing weight, the non-responders did improve their blood pressure and reported a more positive mood throughout the study.