Low-calorie and high-protein diet has diverse impacts on the muscle, bone, and bone marrow adipose tissues.

The present study was designed to evaluate the influence of a high-protein diet under conditions of calorie restriction (CR) in the muscle, adipose tissue, bone, and marrow adipose tissue (MAT). It included three groups of 20 female Wistar Hannover rats, fed with the following diets for 8 wk: control group (C) fed with an AIN93M diet, CR group (R) fed with an AIN-93M diet modified to 30% CR, and CR + high-protein group (H) fed with an AIN-93M diet modified to 30% CR with 40% protein. Body composition was determined by DXA. The femur was used for histomorphometry and the estimation of adipocytes. Microcomputed tomography (μCT) was employed to analyze the bone structure. Hematopoietic stem cells from the bone marrow were harvested for osteoclastogenesis. Body composition revealed that the gain in lean mass surpassed the increase in fat mass only in the H group. Bone histomorphometry and μCT showed that a high-protein diet did not mitigate CR-induced bone deterioration. In addition, the number of bone marrow adipocytes and the differentiation of hematopoietic stem cells into osteoclasts were higher in H than in the other groups. These results indicated that under CR, a high-protein diet was beneficial for muscle mass. However, as the μCT scanning detected significant bone deterioration, this combined diet might accentuate the detrimental effect on the skeleton caused by CR. Remarkably, the H group rats exhibited greater MAT expansion and elevated hematopoietic stem cell differentiation into osteoclasts than the CR and control counterparts. These data suggest that a high protein may not be an appropriate strategy to preserve bone health under CR conditions.