Genes, not greed, make you fat

Genes and hormones, and not how much you eat, make you fat.

Scientists at New York's Rockefeller University have made a discovery worth billions of dollars: a gene responsible for obesity in mice and humans. The university has filed for patents to cover the researchers' work, published in today's issue of Nature.

The discovery, by Jeffrey Friedman and five colleagues at the university, will make the diets beloved of magazines and health books redundant. The gene holds the key to the first rationally designed weight-loss pill, one virtually guaranteed to be effective.

Nearly a third of adults in the US are 20 per cent or more overweight. Obesity is a public health problem in all western countries, associated with conditions such as adult-onset diabetes and some cancers.

The gene represents the biochemical ''recipe'' for a hormone secreted by the body's fat cells. This hormone is central to how body weight is regulated: more fatty cells produce more hormone, which cuts appetite or raises energy consumption, thus cutting weight.

By reading the gene sequence, pharmaceutical companies will be able to manufacture the hormone artificially or devise ways of blocking its action. People will be able to alter their natural feedback mechanism and thus control their weight as they like.

Dr Timothy Rink, president of the Californian biotechnology company Amylin Pharmaceuticals, said earlier attempts to control appetite and weight were like ''controlling diabetes before insulin''. The discovery ''translates directly into medical and commercial programmes. A lot of companies that have an interest in metabolism will be very interested.''

Obesity in humans is not dictated by the genes, but by imbalance in the hormonal regulatory system. It is a medical rather than a behavioural problem, says Dr Rink. ''People who are obese - other than food addicts - come to a body weight determined by hormones. Trying to reduce weight by dieting is liable to fail because the basic controlling factor is working against them. Fat people regulate their weight, but at a point they do not feel comfortable with.''

But Dr Rink stressed that although the obesity gene was a key component of weight regulation, it was not the only one. By eating too much sugar ''you can move the balance point''. The gene discovery is not a universal answer, he warned, adding that it would take more than 10 years to produce a rational therapeutic.