An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans.

Human, animal, and in vitro studies have reported a favorable effect of omega 3 fatty acids on bone health, specifically inhibiting osteoclast activity (bone resorption), while enhancing the activity of osteoblasts (bone formation).  Reducing the n6:n3 fatty acid ratio and saturated fatty acid intake may also exert a beneficial effect on bone health.  The objective of the present study was to investigate the effect of an increased dietary intake of alpha-linolenic (ALA) and a decreased n6:n3 ratio, on bone health in men and women. 

Twenty-three men (n=20) and women (n=3) participated in this randomized, 3-period crossover study.  Each participant consumed three diets for a 6-week period, separated by a 3-week compliance break.  Diets consisted of the following:  1) Average American Diet (AAD): 34% Total fat, 13% saturated fatty acids (SFA), 13% monounsaturated fatty acids (MUFA), 9% PUFA (7.7% LA, 0.8% ALA); 2) Linoleic Acid Diet (LA):  37% Total fat, 9% SFA, 12% MUFA, 16% PUFA (12.6% LA, 3.6% ALA); and 3) Alpha-linolenic diet (ALA): 38% Total fat, 8% SFA, 12% MUFA, 17% PUFA (10.5% LA, 6.5% ALA).  Walnuts and flaxseed were the predominant sources of ALA in the diet. The ratio of n6:n3 fatty acid were 3.5:1 and 1.6:1 for the LA and ALA diets, respectively.  N6:n3 ratio for the AAD diet was 9:1.  Subjects consumed either breakfast or dinner at the diet center during the week (Monday-Friday), while all other meals were prepared and packed for offsite consumption.  Fasting serum blood samples were obtained at baseline, and following each dietary intervention period for subsequent analysis of lipid profiles, N-telopeptides of type 1 collagen (NTx), and bone-specific alkaline phosphatase (BSAP) levels.  NTx is regarded as a reliable indicator of bone resorption, while BSAP is a general index of bone formation and a specific index of total osteoblast activity. 

The results demonstrated that NTx levels were significantly lower after consumption of the ALA diet (13.20 +/- 1.21 nM BCE), compared to the AAD diet (15.59 +/- 1.21 nM BCE).  A similar trend was also observed for the LA diet (13.80 +/- 1.21 nM BCE) when compared to the AAD diet.  An overall 15.3% and 11.3% reduction in NTx value was observed following the ALA and LA diets, respectively, when compared to the AAD dietary pattern.  There was no observed difference in BSAP values between any of the intervention diets.  Serum total n6 PUFAs were highest following the LA diet, while serum total n3 PUFA, ALA, and EPA values increased progressively across the LA and ALA diets.  Highest levels were observed following consumption of the ALA diet.  Ratios of serum SFA: UNSAT, LA:ALA, and n6:n3 decreased significantly following the consumption of the LA and ALA diets when compared to the AAD, as well as following consumption of the ALA diet when compared to the LA diet. 

In conclusion, these data indicate that incorporating ALA rich walnuts and flaxseed into the diet results in a reduction in both the n6:n3 ratio and serum NTx values (bone resorption), while maintaining serum BSAP levels (bone formation).  Consuming ALA may exert favorable effects on the skeletal system.