Exercise-induced anorexia - does it exist?
Just back from a holiday backpacking in the Alps for about 8 days continuously (not everyone's idea of a holiday, I'll agree). During this time I noted that despite massive increases in my energy expenditure by comparison to sitting at a computer emailing or blogging, I experienced a much reduced motivation to eat. Having dabbled a little in appetite work over the last few years the one thing that I do now know is that appetite is very, very complex. All sorts of explanations occured to me - the heat affected appetite, the faff of campsite cooking and the prospect of yet another meal of pasta in vegetable stock might put one off, thirst quenching may itself have displaced appetite, the stressless environment and so on, but given how much expenditure was going on it did seem like a classic case of the phenomenon described by John Blundell's group of appetite-induced anorexia ( King, Burley & Blundell (1994) Eur J Clin Nutr. 48(10):715-24.). So why the question in the title?
As much as it was meant to be a holiday and not a thesis-generating exercise the notion started making less sense - why would exercise suppress appetite? If we're built to be homeostatic then it should elevate. Indeed Blundell's paper suggested it was more an effect against the onset of eating. However there seems to be no obvious evolutionary advantage to this mechanism given that we evolved, either as hunters or gatherers, to expend energy. What does make a little more sense to me is the exact opposite - indolence-induced-hyperphagy. This would have a clearer evolutionary basis as a circannual response to shortening days, motivation to feast before a period of low abundance. It would also dovetail with the increasingly sedentary lifestyle's impact upon consumption.
I'd be interested to learn from those in the know whether this notion is original or a well-trodden path and I'm also interested to know if it's possible to test between the two explanations.
Are there any better-read appetite biologists out there willing to comment?
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