Thesis (Ph.D.)--Aberdeen University, 2008. / Includes bibliographical references.

The principal aim of this thesis was to investigate the effects of altering the energy density of the diet (kJ/g) on post-restriction weight regain in domestic cats and laboratory mice. Secondly, evidence for body weight regulation was examined in mice. In cats, consumption of the same number of calories of a low energy dense diet (with added water) induced significantly less weight rebound than a more energy dense diet (with no added water). This was accounted for by differences in physical activity, as cats on the low energy dense diet were significantly more active. It was assumed the less energy dense diet held cats in a perceived state of energy restriction and they were actively searching for more food. In mice, cellulose was used to alter the energy density of the diet. Post-restriction body weight rebound was also observed on an energy dense diet (no cellulose). However, body weight not did reach pre-restriction levels when consuming a low energy dense diet (with added cellulose) and digestibility was significantly reduced. It was likely that the fibre-rich induced a gut processing limit on the bulk of digestible food that could be consumed. Overall, the energy density of the diet was shown to modulate post-restriction body weight rebound, but results varied with species and the energy dilutant used. The implications for human weight management have yet to be elucidated. The second principle finding was that post-restriction hyperphagia was induced to replenish food deficiencies incurred during caloric restriction, rather than to replenish body mass loss in mice. This provided preliminary evidence for a ‘calorie-counting’ body weight regulatory system in mammals.