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There’s plenty of evidence that lack of sleep puts you at higher risk of gaining weight. A new Swedish study in the Journal of Clinicla Endocrinology and Metabolism (press release here, abstract here) offers some new insights with fMRI brain scans:
We already know that obese people tend to find food more rewarding, as indicated by brain scans of activity in the anterior cingulate cortex:
Higher activation of this brain region has been found in obese compared with normal-weight subjects when anticipating food, suggesting that the rewarding quality of food is enhanced in obesity.
The study took a dozen volunteers and kept them up all night, then looked at their brain’s response to images of food. Compared to after a normal night of sleep, they observed the same changes that you see in obesity: stronger activation of the ACC, indicating higher dopamine signalling. You want more food than normal, because food makes you feel better than it normally would. As the graph on the right shows, those with the biggest changes in brain activity also reported the biggest appetite.
A study like this, where the subjects stayed up all night, isn’t a great way of figuring out what happens in the much more common situation of, say, getting half an hour less sleep than you need, night after night for weeks or months on end. But other studies looking at appetite hormones like ghrelin and leptin suggest that the effects are similar: too little sleep = greater appetite relative to energy needs.
Of course, this leaves us with a riddle: if you have to get up an hour early to fit your workout in, do the benefits outweigh the downsides? That depends on a lot of things, but my general sense is that exercise has so many benefits that it’s still worthwhile. The real answer, of course, is to organize your life so that you can sleep enough and get some exercise.