How our beliefs about what controls our weight may actually affect our weight

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A couple of weeks ago I was talking to a lady who expressed the wish to lose weight. By her own account she was some 20 kgs heavier than she was many years ago when she was a competitive athlete. She worked full time, had a family and little time for exercise. Her view seemed to be that only if she had more time, she could exercise at a level more akin to her former existence, and would see her return to her original weight too.

It is not often the case that I attempt to disabuse someone of their view, but this was one instance. My experience in practice and also a fair amount of science demonstrates that rarely will someone lose appreciable quantities of weight through increasing their exercise alone. There are many reasons why this might be, but they include:

1. Exercise, unless it’s a lot of exercise, does not usually burn a whole lot of calories.

2. Many people get hungrier and eat more if they become more active.

3. Regular exercise can actually suppress the metabolism (see here for more about this).

4. Exercise can stimulate the secretion of the stress hormone cortisol, which may promote fat deposition (usually around the midriff).

So, imagine this lady were to liberate about an hour a day for exercise, about half of which might be spent actually exercising (after preparation, clothes changing, cool down, and showering). 30 minutes of running might burn, say, 250 calories. But there are about 7,700 calories in a kg of fat. So, theoretically, after exercising for 30 minutes every day for a month she might lose a kg of fat. That’s after 15 hours of exercise and maybe 30 hours of time commitment.

The fat loss here assumes that the additional exercise will not lead to her eating more, a suppression of her metabolism, or cause surges in cortisol that then leads to fat storage. I think exercise is a great thing generally speaking, but it’s difficult to make a strong case for exercise for the purposes of fat loss.

I put this these ideas to her, in the gentlest way possible, and recommended that she might look to her diet as the primary strategy for weight loss. I talked about how when individuals eat right, they very often eat less (often several hundred calories less a day), but without hunger. That, I would say, might be altogether a healthier, more effective, realistic and sustainable way of shedding unwanted fat. And it’s certainly an approach I see work often in practice.

This conversation came back to me this week while reading about a study about the attitudes people have to obesity [1]. This research found that, broadly speaking, people can be divided into one of two categories:

1. those who believe obesity is the result of inactivity

2. those who believe obesity is the result of an unhealthy diet

The interesting thing is that those in the former category tended to be heavier than those in the latter. To me, this is consistent with what I’ve found in practice. As I wrote above, my experience tells me that, by and large, dietary change is more powerful for reducing weight than exercise. Those that believe this are, perhaps, more likely to use diet as their primary weight loss strategy, and are more likely to be successful at weight control as a result. Those who believe that activity is the holy grail for weight loss may, unwittingly, find themselves flogging a dead horse.

Another finding of this recent research was that those who believed weight is primarily determined by activity generally ate more than those who believed diet is more important. I am wondering if this observation is, at least in part, a reflection of a belief some have that they can eat relatively freely as long as they ‘exercise it off’. For the reasons I’ve listed above, I’m not sure this strategy is likely to work out too well. And on top of this, sometimes the issue can be compounded by individuals ‘rewarding’ themselves after exercise with food or drink.

Again, I’m a fan of exercise, I advocate it strongly for those who can and want to take it, and even take it myself practically every day. However, my belief is that the amount of exercise I do is likely to have a negligible effect on my weight. Some may find this belief demotivating. However, for others (including me), it can be liberating and even lead to more consistent exercise habits. Here’s why…

Image I were sedentary and started exercising to lose weight. If I am expecting rapid results but get nowhere very fast, this may cause me to become demoralised and pack it in. However, if I my expectations are better aligned with the likely outcome, I am less likely to end up disappointed or frustrated.

Also, if I were using exercise to lose weight, I might be tempted to see the benefits of exercise mainly through the lens of ‘calories burned’. The truth is, though, that if this were the case there are lots of ‘exercise sessions’ I do which I might conclude were not worth the effort. For example, I regularly engage in brief resistance exercise ‘circuits’ that I think have done wonders for my strength and muscle tone and even built a bit of muscle. However, the calorie burn from these sessions is, I think, negligible. The same goes for my 15-minute swim sessions.

In my case, and perhaps in the case of others, the fact that I do not see exercise as a way to lose weight and burn calories means, in the end, that I am more active (not less).


1. McFerran B, et al. Lay Theories of Obesity Predict Actual Body Mass. Psychological Science 2013; DOI: 10.1177/0956797612473121 [hr]

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