Influence of Fat Intake and Caloric Restriction on Bone in Aging Male Rats

Abstract
Caloric and fat intake may have important skeletal consequences. To evaluate this possibility, skeletal effects of adultonset caloric restriction (CR) at differing fat intakes were assessed in male Lobund–Wistar rats. At age 17 months, two groups of animals received an anti-obesity diet, restricted ≈ 35% from individual ad libitum baseline calorie consumption, and two groups received a diet ≈ 50% restricted. Dietary fat concentrations were 5, 15, 15, and 25% by weight, respectively. At ages 20,24,28,30, and 32 months, ex vivo femoral bone densitometry and serum biochemical analyses were performed. Body weight (BW) decreased with time on CR in each group (p < .005), declining faster at the more severe restriction (p = .001). Femoral bone mineral contents (BMC) were also reduced. After adjusting for bone area and BW differences among groups, the only significant difference was a reduction in distal femur BMC in the 25% fat group subjected to more severe CR (p = .02). No differences were observed in serum parathyroid hormone, calcium, phosphorus, or creatinine. Femoral bone loss occurred with CR. This was entirely accounted for by reduction in BW. Higher dietary fat content did not affect BW in CR animals, but did result in lower distal femur BMC.