Why does exercise blunt your appetite?

THAT'S THE WHY:It's one of those "How did that happen?" moments: why is it that you felt peckish before you went to the gym, jogged home from work or got dragged around the neighbourhood by your enthusiastic dog, then after the exercise your appetite wasn't quite so beastly any more?

Simple arithmetic suggests that after burning off all those calories your body should surely be in the market for more, but the regulation of appetite is anything but simple.

A small but powerful region of the brain called the hypothalamus helps to control food intake and energy expenditure by keeping track of our nutritional status and responding to signalling molecules such as leptin and insulin.

Now new research has teased out at a molecular level how exercise can more generally help to sharpen the brain’s response to such important regulatory signals – in obese rats at least.

The study, published in the journal PLoS, compared lean and obese rats after they exercised by swimming or running on a treadmill. In the obese animals, the brain chemistry changed – the researchers found that the workouts were associated with a boost in anti-inflammatory molecules in the hypothalamus – and in the short term their appetites reduced to that of their lean counterparts.

There’s plenty of research left to be done on this, but in the meantime maybe next time your hypothalamus starts idly nudging you for that tub of ice cream in the freezer, try taking it for a run instead.