McGrath C, Sankaran JS, Misaghian-Xanthos N, et al. - Since marrow adipose tissue (MAT) and its relevance to skeletal health during caloric restriction (CR) is unclear, researchers ascertained if exercise, which is anabolic to the bone in a calorie-replete state, affects bone or MAT in CR. They hypothesized that bone and MAT response to CR exercise differs from the state of calorie-replete. Sedentary (regular diet [RD], CR, n = 10/group) and running exercise (RD-E, CR-E, n = 7/group) was allocated to ten-week-old B6 mice given an RD or 30% CR diet. According to findings, exercise induces skeletal anabolism and alters skeletal architecture through effects on a multiplicity of cells during the calorie-replete state. Data support in the calorie-replete state is that energy stored in marrow adipocytes is used during exercise for energy. In striking contrast, exercise, in accordance with clinical data, seems to be harmful to the bone during calorie restriction. Thus, despite the expansion of MAT in CR, this fat depot may not be harnessed to support the energy needed to sustain bone anabolism and to prevent bone resorption in the energy-restricted sedentary and exercised states.