Increasing energetic cost of biosynthesis during growth makes refeeding deleterious.

Diet restriction (DR) enhances animals' health maintenance, but refeeding reverses its beneficial effects. However, to what degree refeeding reverses the beneficial effects of DR remains controversial. Here, I develop a theoretical model for reconciling the results of refeeding studies and understanding the dynamic and reversible mechanism underlying the effects of diet on health from the energetic viewpoint. By illustrating the negative correlation between health maintenance and the energetic cost of growth in animals under different diet regimes, the model explains why, in some cases, refed animals have better health and live longer than freely fed controls. More importantly, the model reveals that, in some species, the energetic cost of synthesizing biomass increases during growth, so the expensive compensatory growth induced by refeeding later in life offsets the benefits of the inexpensive retarded growth induced by diet restriction early in life. Thus, in these species, refeeding drives animals to allocate more energy to growth and less to maintenance and therefore leads to poor health status and shorter life span compared to freely fed controls.