Effects of the amount and source of dietary protein on bone status in rats

Effects of a moderately high-protein diet and interval aerobic training combined with strength-endurance exercise on markers of bone metabolism, microarchitecture and turnover in obese Zucker rats

BACKGROUND

Weight loss is a public health concern in obesity-related diseases such as metabolic syndrome, and the protein level of the diets seem to be crucial for the development and maintenance of bone. The nature of exercise and whether exercise in combination with moderately high-protein dietary interventions could protect against potential bone mass deficits remains unclear.

OBJECTIVES

To investigate the effects of a moderately high-protein diet and interval aerobic training combined with strength-endurance exercise (IASE) protocol on bone status, and to assess potential interaction effects (i.e. diet*IASE).

METHODS

Male Zucker fatty rats were randomized distributed into 4 groups (n=8): normoprotein+sedentary; normoprotein+exercise; moderately high-protein+sedentary, and moderately high-protein+exercise. Training groups conducted an IASE program, 5days/week for 2months. Markers of bone metabolism were measured in plasma. Parameters of bone mass and 3D outcomes for trabecular and cortical bone microarchitecture were assessed by micro-computed tomography.

RESULTS

Femur length, plasma osteocalcin, sclerostin, osteoprotegerin, receptor activator of nuclear factor kappa-B ligand, insulin, leptin, PTH, uric acid and urinary phosphorus levels were lower in the moderately high-protein compared to the normoprotein groups (all, p<0.05), whereas plasma alkaline phosphatase, aspartate aminotransferase, alanine transaminase, and urinary uric acid concentrations, and cortical total volume (TV) and bone volume (BV) were higher in the moderately high-protein (all, p<0.01). Final body weight and alkaline phosphatase levels were lower in the exercise compared to the sedentary (both, p<0.05), whereas femur length and weight, aminoterminal propeptides of type I procollagen and C-terminal telopeptides of type I collagen concentrations, and cortical TV and BV were higher in the exercise compared to the sedentary groups (all, p<0.05).

CONCLUSION

The combination of interventions may be effective to enhance trabecular bone microarchitecture and BMD, and has a partial impact on cortical bone in obese rats. Nevertheless, they do not induce any alteration on the bone turnover markers.

High fat diet enriched with saturated, but not monounsaturated fatty acids adversely affects femur, and both diets increase calcium absorption in older female mice

Diet induced obesity has been shown to reduce bone mineral density (BMD) and Ca absorption. However, previous experiments have not examined the effect of high fat diet (HFD) in the absence of obesity or addressed the type of dietary fatty acids. The primary objective of this study was to determine the effects of different types of high fat feeding, without obesity, on fractional calcium absorption (FCA) and bone health. It was hypothesized that dietary fat would increase FCA and reduce BMD. Mature 8-month-old female C57BL/6J mice were fed one of three diets: a HFD (45% fat) enriched either with monounsaturated fatty acids (MUFAs) or with saturated fatty acids (SFAs), and a normal fat diet (NFD; 10% fat). Food consumption was controlled to achieve a similar body weight gain in all groups. After 8wk, total body bone mineral content and BMD as well as femur total and cortical volumetric BMD were lower in SFA compared with NFD groups (P<.05). In contrast, femoral trabecular bone was not affected by the SFAs, whereas MUFAs increased trabecular volume fraction and thickness. The rise over time in FCA was greater in mice fed HFD than NFD and final FCA was higher with HFD (P<.05). Intestinal calbindin-D9k gene and hepatic cytochrome P450 2r1 protein levels were higher with the MUFA than the NFD diet (P<.05). In conclusion, HFDs elevated FCA overtime; however, an adverse effect of HFD on bone was only observed in the SFA group, while MUFAs show neutral or beneficial effects.