In this case, however, the calorie-restricted animals did not stop producing leptin in their adipose tissue.

ECONOMIST: Obesity

At the end of their binges, all the rats were injected with leptin, in order to test the adipose tissue's response.

ECONOMIST: Obesity

The rats who dined carte blanche, on the other hand, did reduce the amount of leptin that their adipose tissue produced.

ECONOMIST: Obesity

The problem of lipid damage, they believe, is linked to hormones produced not by the pancreas, but by adipose tissue itself.

ECONOMIST: Metabolic syndrome

Leptin production, meanwhile, grows along with the mass of the adipose tissue.

ECONOMIST: Metabolic syndrome

How this happens has been the subject of a lot of hand waving, though the tendency of adipose tissue to produce chemicals that encourage inflammation is often mentioned.

ECONOMIST: Metabolic syndrome

Adiponectin, meanwhile, encourages the body's adipose tissue to absorb lipids.

ECONOMIST: Metabolic syndrome

As adipose tissue grows, however, its production of adiponectin falls.

ECONOMIST: Metabolic syndrome

In a healthy mouse (one with working leptin receptors) even a diet that is 60% fat does not cause a build-up of lipids anywhere except in the adipose tissue.

ECONOMIST: Metabolic syndrome

Dr Unger and Dr Scherer suggest that this failure of the leptin mechanism, particularly its role in oxidising lipids, is crucial to the development of metabolic syndrome, and that it is a pathology of adipose tissue that has become overloaded.

ECONOMIST: Metabolic syndrome