At the University of Limburg at Maastricht in Holland, 16 men and 16 women were put through a five-month endurance training programme and their average daily metabolic rate – the amount of energy they each needed to keep their body functioning – was measured. All 32 of the subjects increased their physical activity by 60%, but the effects on the sexes were quite different. The men’s metabolic rate increased markedly: at the end of the 20 weeks they needed an extra 800 calories of food a day just to maintain their body weight, but no such change was detected in the women. The increased rate of exercise was burning the calories off men, but not off women, whose metabolic rate scarcely changed.8 Life is not fair. A man can jog away the pounds, but a woman cannot. She has to diet too.
It has long been known that men have less fat and more muscle than women. The average male body is one-seventh fat (15%), while fat makes up more than a quarter of the average woman’s body (27%). Weight for weight, she has 80% more body fat than he does. If she tries to get her body fat below 12%, by diet or extreme pysical excercise, normal body functions are impaired. For the male, that lower limit for fat is 3%.9
Equally striking is the sexual difference in musculature. In men 40% of body weight consists of muscle. Women have only about half this amount (23%). In the adolescent female the fat to muscle ratio increases as she adds fat to the pelvic area and breasts (her breasts contributing only four per cent of that total). In puberty the male growth spurt is accompanied by a hormonally stimulated jump in muscular development which typically doubles his physical strength.
Normal exercise increases the male’s metabolic rate. He then needs more energy from food to maintain a constant weight. The Lenox Hill Hospital study found that the female metabolic rate is little affected by exercise, so her exercise regime will not require more food. Nearly every man jack can lose weight by following the Jane Fonda Workout, but Jane can’t. A possible reason for the personal effectiveness of her own regime is found in Ms Fonda’s admission that her weight-reducing efforts had ‘been accompanied by bouts of bulimia’.10
A survey by Cosmopolitan magazine found that a quarter of its readers were perpetually on a diet, and that one-third of those dieters vomited to make themselves lose weight.11 That incidence of bulimia nervosa seems high; in the general population the figure is about one young woman in 33, while the occurrence of this disorder in males is a mere one-tenth of that in females.12
Women are fond of reminding us that food can spend ‘a moment on the lips and a lifetime on the hips’. For them that is true, but for men it is not. They are different.
Men use more energy than women, even to breathe
Scientists at the National Institutes for Health in Phoenix, Arizona, have discovered that, adjusting for differences in size, body composition and age, the resting male’s expenditure of energy is 5–10% greater than the resting female’s.13 Furthermore, since muscle is so much more metabolically active than fat, and men have more muscle, women more fat, the sex difference in body composition leads to even greater differences in resting expenditure of energy, favouring males. And not just while he is at rest; men generally expend more energy than women, even when they are engaged on identical tasks.14 His motor simply turns over at a higher speed than hers does, and the difference begins early in life. Researchers at the Dunn Nutrition Unit at Cambridge University found that even at 12 weeks old a sleeping male infant uses 12% more energy than a sleeping female infant.15
Typically, men are more active than women. In a study of some 2,000 adults in South Carolina (431 blacks and 1,574 whites) it was found that between the ages of 30 and 60 men were 43% more active than women.16 Higher levels of activity require more fuel, so his dietary needs are quantitatively greater than hers. If she eats too much the excess fuel will probably be stored as fat, while he has a greater chance of working it off.
Males need protein more than females
Canadian endurance athletes, both men and women, were put through a series of persistent and gruelling exercises.17 It was discovered that the women needed to increase their protein intake by about one-seventh, but the men needed to nearly double it. Regular exercise increases the need for protein much more sharply in a man than in a woman.18
Exercise produces muscle, and the manufacture of muscle demands protein. The reason a man needs more than a woman is not just because he typically has more muscle, but because of his androgen hormones – the most common of these being testosterone. Androgens are made by both sexes, though in far greater quantity by the male (over ten times the amount after puberty), and they are responsible for the development of such male characteristics as facial and chest hair, baldness, the deep voice, increased libido, and greater aggression. A higher androgen level means a higher rate of protein synthesis (requiring, of course, a higher intake of protein). Men make protein faster than women, they use it faster than women, they need more than women.
Protein
Proteins are an essential part of every cell in the body, and they consist of 20 or so amino acids, eight of which are crucial to our nutrition. Proteins are continually broken down and resynthesized – the average adult reprocesses about half a pound (250 grams) each day – but in that process some protein is lost and needs to be replenished from our diet. We need about 2.5 ounces (70 grams) to do this. Proteins should form 10–15 per cent – one part in seven – of our daily diet.
The body of the average adult man contains between 25 and 30 pounds of protein, of which only 12 ounces (340 grams) is held in reserve. This slender margin means his body (and hers) is reliant on new protein from food. Protein lost through prolonged fasting, or because of an inadequate diet, can result in the wasting of body protein, and when that protein is drawn from the heart muscles the loss is irreplaceable and life-threatening. Children on an inadequate protein diet are often stunted and show poor mental development.
Animal protein is the best available source for humans. Without it, care must be taken to balance the food one eats to compensate for the consequent deficiencies.
Meat is usually 17–20 per cent protein; egg, 12 per cent; cereals, 10 per cent; milk, 3 per cent; potatoes and French beans, 2 per cent; carrots and lettuce, 1 per cent.
Dutch scientists recently examined older adults to see how quickly they used up protein. Even when corrections were made for differences in body composition, it was found that ‘protein turnover rates were significantly higher for men when compared with women.’19 It was also found that protein requirements do not drop with age, but may even increase.20 Indeed, protein deficiency is the major nutritional problem of the elderly female.21
Another research paper reported that elderly people’s intake of high quality protein needs to be twice the current recommendation.22 However, the authors refer only to milk and eggs as ‘high quality protein’. There is no meat in their recommended diet. But ‘high quality protein’ has long had a specific meaning in nutrition circles: it refers to those animal products that have an amino acid balance that is closest to human needs. (Amino acids are the building-blocks of proteins, so to make protein you need the right amino acids in your food.) Some vegetables have a similar protein quantity to meats, but they do not have the quality amino acid balance. Vegetarians, who eat intermediate or low quality protein, may need twice the protein intake of non-vegetarians to provide themselves with the adequate amino acids.23
‘Didn’t I hear of a vegetarian body-builder who recently won a contest in south-east England?’ asks Anne.
‘A