One of the world's most revered scientists has developed a theory that fat people are happier than thin ones.
James Watson, the Nobel prize-winning geneticist who was jointly responsible for discovering the structure of DNA, believes that plumper women are also likely to enjoy a better sex life than their thin counterparts.
Watson, who directed the successful human genome project, has moved into the controversial science of body image. He recently told an audience at University College London that his research suggested extra pounds had the biological effect of making a woman well-rounded in character and better in bed.
''Thinness is never associated with sexuality,'' said Watson, 72. Posh Spice and Calista Flockhart might smile for the photographers, he claimed, but beneath their sleek exteriors lurk miserable thin souls.
His study of chemicals in the body has led him to conclude that extra fat has the effect of boosting endorphins - the natural mood-enhancing chemical - and a hormone linked to sexual desire.
In thin people, he said, the opposite effect was observed: less fat led to the brain receiving fewer endorphins.
Watson's theory, which applies equally to men, is that in the past man would have spent his life constantly looking for food. The reward for the hard work would be eating and gaining weight. Hence, if you are thin you may be constantly looking for the next meal.
Watson concludes that in evolutionary terms, ''thin equals discontent. Content people have weight on them. That is why we hire thin people because they are discontent and will work harder. Heavier people are more mellow and less successful.''
Thin people, on the other hand, are so driven by the need to find that elusive happiness that they become overachievers. So worldly success may well come more easily to the slender.
''Kate Moss is probably the most famous thin person in the world and she's looking particularly sad. Who has ever heard of a happy supermodel?'' asked Watson. ''Why is the association with these people and drugs so strong? It may not be a moral weakness but in fact a thin person trying to find happiness in artificial opiates.''
Watson's interest is purely scientific. He stumbled on what he calls his latest ''obsession'' while chatting to a taxi driver in New York who told him of an Arizona scientist who, trying to create a self-tanning drug, had injected himself with a hormone which gave him an 8-1/2-hour erection.
The hormone was MSH, linked to sexual desire and also to sunlight. ''It was one hormone which had always bored me before,'' said Watson. His interest excited, he began to look at MSH and discovered it was closely linked to two other chemicals in the body - endorphins, the feel-good chemical, and leptin. Leptin is made in fat tissue; the more fat, the more leptin. MSH is affected by leptin and is connected to sexual desire.
''The heavier you are, the more leptin and possibly the more MSH,'' said Watson. ''My guess is that your mood is controlled by endorphins and you make more of these when you are fat. Hence nobody has ever drawn Santa Claus thin - thin people are discontented.''
Since MSH can also be affected by sun, happiness could depend on either being in the sun or being fat.
''The people who are the hottest sexually are fat white people who are burning in the sun,'' he said.
''I now really look at fat couples in a totally different way,'' he said. ''When you see two thin people together, you know they've got problems.''
So Watson recommends that curvy women match with larger-proportioned partners for the best sex life.
He also credits the drop in U.S. crime rates to the rise in obesity there. Watson hopes to publish a paper on the subject by the end of the year.
(Distributed by Scripps Howard News Service. For more Observer news go to http://www.guardian.co.uk/.)
