How much food does man require? An evaluation of human energy needs.

Nutritional individuality is a characteristic of mankind and this is as true of energy intakes and needs as of other attributes. Studies over the years have shown that individuals vary by a factor of two or more in their intakes of energy from the first year after birth to 75 years and over. The metabolic differences that must lie behind this are still not fully understood. Recent ideas about the importance of dietary thermogenesis in energy expenditure seemed as though they might provide an explanation, but not all investigators agree, and the problem has still not been satisfactorily solved. In spite of these individual variations, average intakes and expenditures show predictable changes with age, and males always seem to take more energy than females throughout their lives. This is still true when the intakes are expressed per kg body weight, per square metre surface area and per kg lean body mass. The explanation of this is not certain, but various suggestions have been made. There is evidence that energy intakes, at any rate in the United Kingdom, were falling between the 1950's and 1970's, and this has been attributed to a decrease in physical activity. However, some of the apparent difference is due to the fact that higher factors were used to calculate the energy derived from protein, fat and carbohydrate in the 1930's and 1940's than were used later; if the later factors are applied to the results of the earlier surveys the values for energy are reduced by about 10%. This correction brings the results of the earlier surveys into line with those of the later ones for boys up to 14 years and girls up to 10 years. Older children of both sexes and adults, however, do seem to be eating less than they used to do. The question as to whether women should and do increase their intake of food during pregnancy has been discussed at two previous meetings sponsored by Nestlé. The evidence seems to be that they do not, and it is postulated that metabolic economies enable the women to produce 4 kg of body fat and a foetus weighing 3.5 kg without any increase in energy intake at all.(ABSTRACT TRUNCATED AT 400 WORDS)