Influence of high-fat diet from differential dietary sources on bone mineral density bone strength and bone fatty acid composition in rats.

Previous studies have suggested that high-fat diets adversely affect bone development. However, these studies included other dietary manipulations, including low calcium, folic acid, and fiber, and (or) high sucrose or cholesterol, and did not directly compare several common sources of dietary fat. Thus, the overall objective of this study was to investigate the effect of high-fat diets that differ in fat quality, representing diets high in saturated fatty acids (SFA), n-3 polyunsaturated fatty acids (PUFA), or n-6 PUFA, on femur bone mineral density (BMD), strength, and fatty acid composition. Forty-day-old male Sprague Dawley rats were maintained for 65 days on high-fat diets (20% by weight), containing coconut oil (SFA; n = 10), flaxseed oil (n-3 PUFA; n = 10), or safflower oil (n-6 PUFA; n = 11). Chow-fed rats (n = 10), at 105 days of age, were included to represent animals on a control diet. Rats fed high-fat diets had higher body weights than the chow-fed rats (p < 0.001). Among all high-fat groups, there were no differences in femur BMD (p > 0.05) or biomechanical strength properties (p > 0.05). Femurs of groups fed either the high n-3 or high n-6 PUFA diets were stronger (as measured by peak load) than those of the chow-fed group, after adjustment for significant differences in body weight (p = 0.001). As expected, the femur fatty acid profile reflected the fatty acid composition of the diet consumed. These results suggest that high-fat diets, containing high levels of PUFA in the form of flaxseed or safflower oil, have a positive effect on bone strength when fed to male rats 6 to 15 weeks of age. (Author's Abstract)Research has demonstrated that high-fat diets over short- and long-term feeding regimes,
significantly affect (for the most part in a negative way) both bone quantity and quality.
Previous studies though have been confounded as other dietary constituents were also manipulated – not just fat, including lower levels of calcium, folic acid, fiber, sucrose and cholesterol. The type of dietary fat, such as saturated fatty acids (SFA),n-3 polyunsaturated
fatty acids (PUFA), andn-6 PUFA, may also have important roles in bone health. Previous research has suggested that dietary supplementation of flaxseed oil, rich in alpha-linolenic acid (ALA), appears to improve bone mineral composition (BMC) and bone mineral density (BMD). Thus the  hypothesis of this research is that a high-fat diet containing n-3 PUFA will have a favorable effect on bone outcomes. The findings demonstrate that rats fed high-fat diets, regardless of their dietary fat source, had greater femoral size, strength, BMD, and BMC than the chow-fed rats. As bone turnover and density are influenced by body weight,  the markedly higher body weight among rats fed high-fat diets may have led to these results. However, after adjustment for differences in final body weight, differences in femur weight and depth persisted, and the n-3 PUFA and n-6 PUFA groups had higher peak load and stiffness than the chow group. The study also demonstrated thatn-3 and n-6 PUFA-enriched diets had similar effects on the biomechanical strength and BMD of femurs, despite the fatty acid compositions of bone
marrow and 3 femur regions being very different. The results suggest positive effects of
PUFA in bone metabolism. Further studies will pursue the mechanisms of how these
fatty acids mediate the effects on bone strength in the context of a high-fat diet. (Editor's Comments)