Sexual intercourse is an energetic occupation, whether it's a vivid romp in the hay or a refined coupling in the missionary position. Metabolic studies show that on average it uses up about 200 calories, which makes it as physically demanding as a thirty minute stint of jogging. This makes it an excellent way to keeping in shape. Some years ago a reporter asked the film star Ursula Andress how she managed to maintain her sylph-like figure, to which the Swiss sex symbol replied: 'Loving keeps me slim.' That's one of the unfortunate side effects of carrying excess weight, that it often acts as a barrier to sexual intercourse. For corpulent people, the spirit is often willing while the flesh is weak. This same problem is suffered by other animal species, according to the managers of a zoo in eastern China, who had to put their caged tigers, leopards and lions on a strict get-fit routine when they found they were showing a 'lowering ability to breed as a result of obesity. '

Researchers at the John Hopkins Hospital in Baltimore have found the same tension in humans. They carried out interviews, and pre-medical examinations, on a small group of obese men and women who were about to undergo an intestinal bypass. The patients – thirteen men and ten women – were questioned about their sex lives, body image, libidinal drives and sexual functioning. The results revealed that there was little or no decline in their sexual appetite. The women had no trouble getting orgasm, and the men's sexual drive and performance remained unchanged, apart from two who declared that they had occasional potency problems. But what plagued the entire group was the sheer mechanical difficulties they faced. Because of their bulk, they found it difficult to find a position in which they could enjoy easy sexual union. As several explained, their paunches 'got in the way'. Lack of stamina and shortness of breath were other frequent problem. The major finding, however, was that although amorous they felt they were all related to take their clothes and reveal their unsightly bodies All 23 were recorded as having 'markedly negative feelings' about their body and admitted that they were tagged of their appearance.

The remedy is clear. Everyone bought to be able to enjoy an active sex life. If obesity makes this difficult, enough surplus fat should be shed to permit comfortable coupling. This should be done by making gradual life style changes, rather than by crash dieting. The body's fat tissues provide a store for sex hormones, which is why a general reduction in adipose tissue frequently leads to a decline in sexual function. This explains why anorexic girls, and sometimes excessively skinny ballerinas, tend to suffer a fall in estrogen levels, missed periods and reduced fertility. With regard to sexual performance, it's unduly better for a woman to be overweight than underweight. This was shown by researchers at the Michael Reese Hospital, Chicago, who tested a group of women using scales that measured their sexual readiness and erotic excitability. Using these yardsticks they found that mildly overweight women outscored their skinny counterparts by a factor of nearly two to one. So do not try to soup up your sex life by crash dieting, one trial having shown that women often stop masturbating and having sexual fantasies when they reduce their energy intake to 1,700 calories a day – which is 500 more than that provided by the Beverly Hills Diet.