Sedentary behaviour does not lead to weight gain (it’s the other way round)

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I think it’s true that our preconceived ideas about something can make us somewhat rigid in our thinking and generally unable to consider other possibilities. By way of example, I’d like to recount an experience I had shortly after delivering a presentation in Edam in the Netherlands.

During the presentation, I had been detailing some of the apparent benefits of aerobic exercise for body and mind, but also remarked that one thing that this sort of activity does not appear to be particularly good for is weight loss. See here, here, here and here for more about this.

Over lunch, after my presentation, I was talking to the one of delegates who expressed doubt about my ‘opinion’ that aerobic exercise does not generally promote weight loss. On what basis? He told me that there are no overweight elite marathon runners. So, marathon running must lead to weight loss.

So commonly and strenuously have we had the idea that aerobic exercise drummed into our psyches, that perhaps it’s no surprise that this man held this opinion. However, the thinking here is obviously limited, and in more than one way.

To start with, there are plenty of people who do oodles of aerobic exercise and are still by standards measures carrying excess fat. But getting back to those ‘elite’ marathon runners for a moment, I asked if people who tend to be on the heavy side get to be elite marathon runners? Unlikely. Could it be, though, that those who are naturally rakishly thin and with the metabolisms of greyhounds that have the basic physiologies that lend towards marathon running?

In other words, I was asking him to consider that people don’t get thin because they are marathon runners, but are marathon runners because, at least in part, they are thin.

(Also, I did point out that my view on exercise and body weight is not really an ‘opinion’ – it’s actually based on quite overwhelming evidence in the scientific literature.)

Anyway, I remembered this conversation yesterday while reading about a recently-published study which assessed the relationship between physical activity and body fatness in children over a 3-year period. Basically, the most sedentary children were most likely, also, to be carrying excess body fat. At first glance, the reason for this relationship may seem obvious: the sedentary children ‘burned’ less calories and got fatter as a result.

However, not all was as it seems. Following children over time allowed the researchers to ascertain that lower levels of activity did not lead to increased body fatness. In fact, it was the other way round: children appeared to accumulate fat first, and then this was followed by them becoming more sedentary.

The authors note that this finding “may explain why attempts to tackle childhood obesity by promoting PA (physical activity) have been largely unsuccessful.”

I think this study should serve to remind us of the importance of considering all possibilities when looking for explanations for observations. And it also adds to the body of evidence which shows that aerobic exercise tends not to be particularly effective for the purposes of weight loss.

Please do not interpret this as me being ‘anti-exercise’ or ‘discouraging’ exercise in some way. I am a massive fan of activity of exercise, partake in quite a lot of it myself, and strongly encourage it for a variety of reasons. However, I’ve seen a lot of people who have found that aerobic exercise is not the weight loss holy grail it’s often claimed to be. These individuals generally do well to know that when they fail to get the results they’re seeking, they are not the problem – the approach is. And it also means that individuals can exercise for fun and fitness or whatever, and liberate themselves from thoughts about how many calories they’re burning or how much weight they ‘should’ be losing.


1. Metcalf BS, et al. Fatness leads to inactivity, but inactivity does not lead to fatness: a longitudinal study in children (EarlyBird 45). Arch Dis Chil 23 June 2010 [epub before print publication]

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