The effects of a high fat diet on musculoskeletal health in aged male C57BL/6J mice
Aging and obesity are two major aspects that can negatively impact musculoskeletal structure and function. It is important to study these aspects because of current high rates of obesity and the increasing proportion of seniors in North America. This study investigated the effects of a long-term high fat and sucrose diet (HFS) superimposed with aging on bone and muscle structure and function. Male C57BL/6J mice were randomized 1 of 2 diets: control (AGE, AIN93M, 10.3% kcal fat, 100 g/kg sucrose) or HFS (HFS-AGE, 45.3% kcal fat 200 g/kg sucrose) for 13 weeks starting at 20 weeks of age to represent middle age. Trabecular bone structure and volumetric bone mineral density (vBMD), body composition, and grip strength were measured longitudinally at 20, 24, 28, and 32 weeks of age. In vitro contractile measures were performed on isolated soleus and extensor digitorum longus (EDL) muscles at baseline (BSL, 20 weeks of age, n=11) and at the end of the 13-week intervention when AGE (n=12) and HFS-AGE (n=12) mice were 33 weeks of age. Both the AGE and HFS-AGE groups had similar declines in trabecular bone (bone structure and vBMD). For muscle contractile function, HFS+AGE resulted in increased soleus cross-sectional area (CSA) compared AGE (p=0.0008), but this did not translate to greater twitch or tetanus peak force. The ratio of outcomes of bone to muscle declined in both the AGE and HFS-AGE groups as a result of a greater decline in key measures of bone structure (BV/TV) than muscle function (soleus and EDL peak tetanus and CSA) and was not altered by feeding HFS. In conclusion, beginning a HFS diet during middle age did not exacerbate age-related declines in bone or muscle, but these tissues do not decline in a coordinate manner with aging as bone structure declined at a greater rate than muscle function.