There’s a quite widely-held view that the solution to obesity is simple – we just need to eat less and exercise more. Despite the sense that seems to surround this notion, the reality is that such strategies generally fail to deliver significant weight loss benefits in the long term. I have written before about the now voluminous evidence that shows that regular aerobic exercise (such as brisk walking) generally fails to shed pounds.
This is not to decry exercise, by the way. I actually believe that activity is one of the key components to physical and emotional wellbeing. Is it absolutely essential to be active to healthy? I don’t know, to be honest – but I’m convinced it helps.
However, I was reminded of the relative ineffectiveness of exercise for weight loss this week by the publication of a study in the print edition of the International Journal of Obesity . I actually wrote about this study here when it was first published on-line back in September.
In this study, 320 post-menopausal women were randomised to one of two groups:
- an exercise group, instructed to engage in moderate-to-vigorous exercise for 45 minutes, 5 days a week.
- a control group, who were not to change their normal activity habits.
Both groups were asked not to change their diets. The study lasted a year.
At the end of the year, women in the exercise group were found to have exercised for an average of 178.5 minutes a week. This equates to 155 hours over the course of the year.
Compared to the control group, these women lost an average of 1.8 kg in weight. Loss of body fat was 2.0 kg (suggesting that the exercising women put on a little lean body mass compared to the control group). They also lost 2.3 cm (about an inch) off their waist circumferences.
Now, again, I believe there are benefits to exercise that go way beyond any loss of body fat. However, if we do the maths we see that women exercised for about 86 hours for each kg loss in weight.
Overall, dietary change appears to be significantly more effective for weight loss. And adding exercise to dietary change, appears not to add significantly to the weight loss benefit. Two major reviews have found that when exercise is taken alongside dietary change, the additional weight loss benefit is in the order of 1 kg (about 2 lbs) [2,3]. In other words, if someone loses 10 kg by changing their diet, adding regular exercise to this would make that loss 11 kg.
Why is it that aerobic exercise does not seem great for weight loss? Well, one thing we know is that exercise can make people hungrier. It doesn’t take much in the way of additional intake to undo any ‘calorie deficit’ induced by exercise. That’s partly because, to be frank, exercise doesn’t burn massive amounts of calories (unless heroic levels of exercise are being performed). Then there’s also some thought that individuals who take more formal exercise may end up, quite naturally, being more sedentary at times when they are not exercising. Also, endurance exercise can increase the levels of hormones, notably cortisol, that may work to stimulate fat storage.
The generally poor weight loss results people get with aerobic exercise can cause despondency in some, and may increase the risk of people just becoming sedentary again. I suggest that knowing that aerobic exercise is not particularly effective for weight loss helps aligns expectations with results, which can actually enhance the chances of someone staying active.
When people are about to embark on an exercise regime that involves, say, brisk walking or running, I generally discourage thoughts about ‘burning calories’ and fat magically melting away. I do, however, encourage individuals to enjoy whatever it is they are doing and to revel in the health benefits, enhanced fitness and self of achievement additional exercise is likely to bring. For me, aerobic exercises are not really about weight control, but about being healthy and having fun.
1. Friedenreich CM, et al. Adiposity changes after a 1-year aerobic exercise intervention among postmenopausal women: a randomized controlled trial. Int J Obes (Lond). 2011;35:427-435
2. Wu T, et al. Long-term effectiveness of diet-plus-exercise interventions vs diet-only interventions for weight loss: a meta-analysis. Obesity Reviews 2009;10:313-323
3. Shaw K, et al. Exercise for overweight or obesity. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003817.