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 one in 10,000 exception among muscle-men,’ says Bill. ‘Were it one in 20 we might take note.’
High quality proteins are, in order of merit: meat, fish, eggs and milk. Meat is by far the most efficient provider of protein, containing five times more than milk. Egg protein used to be the reference point for human needs; its amino acid balance is now found to be perfect for a chicken but not for a human, for whom lean meat or fresh fish is closer to the ideal.24 We need protein, men need it more than women, and meat is the ideal source.
Brain neurotransmitters are affected by diet
Neurotransmitters are chemicals released from nerve endings. They transmit impulses – pass messages – from one nerve cell (neuron) to another. Mostly they work within the brain, but some are manufactured elsewhere in the body. In later chapters we shall see that there are differences in the levels of neurotransmitters used by men and women, but for now it is enough to note a few salient facts that are related to men’s and women’s dietary needs.
Serotonin is a brain chemical that is much involved with mood control. It promotes sleep and helps govern impulsive behaviour. Low levels, much more common in males, are related to aggressive behaviour. Serotonin, like the female hormone oestrogen, also acts as an appetite suppressant, which is why weight-reducing drugs are designed to raise serotonin levels in the brain. Women, on average, have slightly more serotonin than men, and many more men than women have the lower levels. (See Chapter six for more details about serotonin.)
Neurotransmitters affect far more than appetite. A high carbohydrate meal (starch or sugars, say) will raise the level of tryptophan.25 Tryptophan is a chemical forerunner of serotonin, and an increase in its level acts as a sedative.26 A high protein meal like red meat, on the other hand, lowers tryptophan and serotonin levels, thus increasing mental alertness. Men facing a challenging task can sharpen their edge by eating steak for breakfast and by drinking coffee. Caffeine increases our ability to concentrate.27 What you eat changes how you think.28
Why men need iron
The body needs a host of micronutrients to function properly. Iron, for instance, is intimately related to the manufacture of blood: deny your body its fix of iron and haemoglobin levels drop, leading to lethargy. It was briefly thought that too much iron in the diet could lead to coronary heart disease,29 but a study of more than 12,000 men and women found no relationship between iron stores in the body and death by heart disease in men. The results for women were more ambiguous.30
Research
