The hypothesis that long-term energy intake is matched to energy expenditure arose during the 1950s, and this formed the basis of the lipostatic model for the control of food intake in mammals. This gave rise to an additional hypothesis that body weight varies little over adult life because body fat, a variable related to body mass, is regulated. There is now a large body of evidence that adipose tissue plays a role in the regulation of feeding and body weight in mammals, and the study of the mechanisms by which the brain monitors the signals arising from the adipose tissue is currently a major area of research. After a period of nutritional restriction, a number of compensatory responses are invoked, and these result in hyperphagia, rapid weight increase and the repletion of energy reserves. However, the extent to which animals recover lost body weight has been reported to vary between studies. It is hypothesized that the rate at which animals replete their lipid reserves during catch-up growth may influence the hyperphagic response and, hence, whether or not there is complete recovery of body weight. Preliminary tests carried out using some data collected in studies of catch-up growth in salmonids appear to provide support for the model, but more experimental studies are needed to provide rigorous testing.