Diietary Fat Retention In Cortical Bone In Rats Fed High Fat Diet

Abstract

Excess adiposity during childhood and adolescence are associated with poorer bone quality and increased risk of fracture. A high fat diet (HFD) may promote marrow adipogenesis at the expense of osteogenesis and may also promote excess lipid accumulation in osteoblasts and osteocytes. Exercise is prescribed for bone health primarily because of its mechanical loading attributes, but little is known about how obesity or exercise training status affects nutrient trafficking and retention in bone. PURPOSE: To determine the effects of obesity and exercise on fat retention in bone. METHODS: Female Wistar rats, 5 weeks in age (n=18), were fed a high fat diet (HFD) for 20 weeks and designated as obese (OB) or lean (LN) based on weight gain. OB and LN rats performed treadmill running (EX) (5 d/w, 1h/d, 15 m/min) or sedentary control (SED) for 10 weeks. In a 24-hour tracer study, rats were given ad libitum access to 14C oleate and 14C palmitate blended in food. Marrow was removed from hind limb bones and lipid was extracted from the remaining cortical bone. Data are mean ± SEM. RESULTS: Fat intake was not different between groups. Obesity status had no significant effect on fat retention in cortical bone. Lipid in hindlimb cortical bone was higher in EX compared to SED (EX: 6.66 ± 1.64 vs SED: 1.50 ± 1.47 mg, p<0.05). LNEX had the highest dietary fat retention in cortical bone lipid compared to other groups (LNEX: 0.69 ± 0.14, OBEX: 0.24 ± 0.14, LNSED: 0.27 ± 0.13, OBSED: 0.41 ± 0.13 mg, interaction p<0.05). The proportion of the meal retained, and the magnitude of lipid turnover did not differ between groups. Dietary fat retention in bone was positively (p<0.05) associated with fat intake, bone mineral density and bone mineral content (BMC; r=0.51-0.64). BMC in bone was associated (r=0.54, p<0.05) with total energy expenditure. CONCLUSION: Although cortical bone constitutes a minor fraction of overall dietary fat retention, we demonstrate that fat is trafficked to and retained in cortical bone in proportion to meal size and bone size. Future work is needed to test whether fat accumulation influences the ability to adapt to mechanical loading.