On Monday, a friend sent me this link to an article about the role of exercise is weight loss. Basically, the article says it doesn’t work. I agree. I’m sure it may work for the odd individual, but overall, it’s a pretty hopeless. I mentioned this to a patient yesterday who was seeking to shed some unwanted pounds. His reply was that while he was surprised that such a common notion (exercises helps weight loss) is wrong, it utterly mirrors his experience in real life ” it doesn’t matter how much he exercises, his weight stays stubbornly the same.
Before we look at the evidence, let’s challenge the notion that exercise speeds weight loss from a theoretical perspective. While exercise burns more calories than sitting or sleeping, it doesn’t burn that many. A 30-minute jog will burn about 290 calories. However, just sitting watching television will burn about 40 calories in the same time, so the additional calorie burn for half and hour’s worth of jogging is 250 calories. Imagine doing this 5 times a week. The total calorie burn from exercise for the week comes out at 1250 calories (250 x 5). Now assuming that all of those calories will be lost in the form of fat, and that we don’t eat a bit more as a result of expending more energy (more on that in a moment), then the amount of fat lost over the week from our jogging endeavours is about 140 g (less than a third of a pound). Not exactly dramatic, is it?
The other problem with exercise is that people who exercise more tend to be hungrier and eat more too . To undo the calorie deficit induced by a 30-minute jog doesn’t take much, either (3 plain digestive biscuits will do it).
The fact that exercise does not burn that many calories and often causes increased food consumption could make getting into significant calorie deficit through exercise nigh impossible.
So, what does the science show regarding exercise and weight loss? The most comprehensive assessment of the impact of exercise on weight loss to date was conducted by members of an international group of independent researchers known as the Cochrane Collaboration. The review included 43 individual studies, and its point was to quantify the effect that exercise has on weight loss . The amount of exercise prescribed in these studies varied from study to study. Typically, exercise sessions lasted 45 minutes with a frequency of 3-5 times a week. Total length of the studies ranged between 3 and 12 months.
The individual studies in this review were designed to study different things. For instance, some of them compared the impact exercise or diet has on weight loss. Here, the results showed that the ‘dieters’ lost between 2.8 kg and 13.6 kg in weight. On the other hand, exercisers lost between just 0.5 and 4.0 kg in weight.
Some other studies in this review compared the effect of diet and exercise with diet alone. Here, it was found that weight loss for those dieting and exercising was between 3.4 and 17.7 kg, but for those just dieting was 2.3 ” 16.7 kg.
Overall, the additional weight loss from exercise averaged out at a shade over 1 kg.
For example, imagine sorting out your diet and in 6 months you find you’ve lost 10 kg in weight. If, on top of this, you had been exercising, say, for 45 mins, 4 times a week, you could expect to have lost about 11 kg. And the time you would have spent exercising to get this additional 1 kg weight loss benefit? – 69 hours (!)
There are plenty of good reasons for taking regular exercise. Weight loss isn’t one of them.
1. Finlayson G, et al. Acute compensatory eating following exercise is associated with implicit hedonic wanting for food. Physiol Behav. 2009 Apr 20;97(1):62-7
2. Shaw K, et al. Exercise for overweight or obesity. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003817. DOI:10.1002/14651858.CD003817.pub3