If food is plentiful the requirement for energy is met by an accurate system of control so that intake balances expenditure. Energy requirements are therefore often assessed by measuring energy intakes. Intakes of protein, however, are no measure of protein requirements and the amounts customarily taken in Western diets are considerably more than man needs. The requirements for calcium are difficult to assess, for they are affected not only by age, but by other constituents of the diet, by the time of year, by individual peculiarities and by the previous intake. There is a physiological loss of calcium from the body starting in middle age which is not prevented by a high calcium intake.