Sex differences in energy intake and expenditure.

Men are different from women. We might even say ‘males are different from females’, which is not such an obviously basic statement, since a male child of only 3 months, might, apart from some superficial and relatively unimportant areas of distinction, appear to have few real differences from a 3-month-old female. However, it is an opinion which I shall attempt to argue, in relation to energy, that males are indeed basically different from females. An interesting subject for conjecture is whether, energetically speaking, there are sexual differences between the sexes. I suppose there is a large cultural factor here, confused by social, psychological and individual variability. I have frequently thought what a great pity it is that, even in this pseudo-liberal, quasi-enlightened era, where the emphasis on sex is so exaggerated, the subject of sex receives so little scientific attention. I wish I knew-I was going to say ’more’ but I really mean ‘something’-about the effect of sexual activity on energy balance and whether this differs between the sexes. Apart from mildly Rabelaisian comments made in a non-scientific atmosphere, one rarely discusses the possible significance of the variation in energy expenditure related to sexual activity. It must be the only common and frequent source of physical activity which has received virtually no attention from nutritionists. I don’t recall that it even appears in any of the tables in the comprehensive review of energy expenditure by Durnin & Passmore ( I 967). I don’t think Garrow (1974) mentions it in his excellent book on energy balance. Yet, the difference between physically inactive evenings of excessive energy intake, drinking with the boys, followed by a long night’s sleep in a state of torpor, when contrasted with frenetic evenings at a disco as a preliminary to a short night’s sleep preceded and perhaps interrupted by periods of strenuous muscular activity, may have some bearing on the contrasting physiques of the lean and the obese. I realize this is not being expressed in the most seriously convincing way but the problem surely is of scientific interest. It is regarded as of sufficient medical importance to receive at least an honourable mention in a new publication on