Energy and protein requirements*

The conventional method of analysing food energy requirements, according to T. B. Wood and J. W. Capstick, partitions the energy expenditure of an animal into three separate components: maintenance, growth, and activity. Two kinds of statement are commonly made about the amount of food which people need. Firstly, figures are quoted for quantities of nutrients which could safely be recommended for practically all individuals, even though they may be living under a wide variety of situations. Secondly, however, estimates are sometimes quoted for minimum physiological requirements, that is, levels of intake below which there is an increasing probability that some specified symptom of deficiency will appear. The concept of an adaptive, self-regulating system implies some type of negative feedback response by which the body is able in part to cancel out changes in inputs and outputs, and maintain the internal state near its original condition.