Sir: Whilst one might understand the need for Jerome Burne to offer some Christmas cheer to the "circumferentially challenged", the assertion that being fat is healthy is a good example of how a superficial acquaintance with complex biological data can lead to wholly incorrect conclusions ("Something Big", 16 December).

Scientific evidence strongly supports the view that being overweight is associated with an increased risk of various diseases, including coronary heart disease (CHD), the second leading cause of mortality in this country.

This is primarily because obesity is associated with various adverse metabolic factors such as high blood pressure (hypertension), high blood cholesterol, physical inactivity and diabetes - all powerful, independent risk factors for CHD. In other words, being overweight is of importance because of its association with other risk factors; if these factors are absent, being overweight is very much less important.

The problem is that a simple measurement of body weight provides only very crude information. Recent evidence suggests that the way in which fat is distributed may be the more important factor. There is an important distinction between android (central) obesity and gynaecoid (peripheral) obesity.

Gynaecoid obesity is associated with an exaggeration of the normal feminine fat distribution, ie fat deposited on the hips, thighs and buttocks. Although women spend a huge amount of time, money and effort in trying to rid themselves of this fat, it is actually metabolically inert and not associated with a significantly increased risk.

In contrast, android or central obesity, the most common manifestation of which is the protuberant belly in men, is strongly associated with a variety of coronary risk factors, including high blood cholesterol, diabetes and hypertension. So the key issue is not simply whether one is carrying too much fat, but where the fat is distributed. Both Marilyn Monroe and Jane Russell were good examples of "voluptuous" women, with low-risk peripheral fat distribution.

Being fat is never healthy. The only comfort is that people can be fat in different ways, some of which are harmful and others of which are not.

Dr DAVID ASHTON

Cardiac Medicine,

National Heart & Lung Institute,

Imperial College School of Medicine

University of London