According to Dr Matthew Walker when your sleep becomes short, you will gain weight.

The first concerns are 2 hormones that control appetite: Leptin and Ghrelin.

Leptin signals sense of feeling full, when leptin levels are high, appetite will be be blunted and we don't feel like eating.

Ghrelin in contrast, triggers a strong sensation of hunger. When Ghrelin levels increase so does hunger.

An imbalance of either one of these hormones can trigger increased eating and thus body weight.

Perturb both in the wrong direction, and weight gain is more than probable.

Over the past 30 years Dr. Eve Van Cauter at the university of Chicago has been conducting research that link sleep and appetite.

Participants that took part in the studies got given a room with a bed, clean sheets, TV and internet access but not tea or coffee as caffeine was not allowed.

In one arm of the experiment, subjects were given an 8 and half hour sleep opportunity each night for 5 nights. recorded with electrodes placed on their head.

In the other arm of the study, the subjects were only allowed 4 to 5 hours sleep for 5 nights, measured the same way.

In both studies they received the same amount and type of food, and their physical activity was kept constant.

Each day the sense of hunger and food intake were monitored, as were circulating levels of leptin and ghrelin.

Van Cauter discovered that individuals were far more ravenous when only sleep 4 to 5 hours per night. This despite being given the same amount of food and being similarly active.