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“This is the first controlled feeding study in humans to evaluate the effect of dietary plant-derived omega-3 PUFA on bone turnover, assessed by serum concentrations of [the markers of bone resorption and formation] N-telopeptides (NTx) and bone-specific alkaline phosphatase (BSAP),” wrote lead author Amy Griel from the Penn State Univerisity.
Previous studies have reported that diets with a low ratio of omega-6 fatty acids to omega-3 fatty acids may minimise bone loss, but the studies have mostly focused on improving omega-3 using the longer-chain omega-3 fatty acids from fish, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
How the research was done
Writing in the Nutrition Journal, Griel and her co-workers report the results of their randomised, double-blind, balanced order, three-period crossover study with 23 overweight, people (20 men, average age 49.9, average BMI 28.1kg per sq. m) with moderately high cholesterol levels (5.85millimoles per litre of serum).
The subjects were randomly assigned to one of three diet groups for six weeks, with three-week washout periods between diet interventions.
The first diet intervention saw the subjects consumed an average American diet (AAD) consisting of 34 percent total fat, 13 percent saturated fatty acids (SFA), 13 percent monounsaturated fatty acids (MUFA), and 9 percent polyunsaturated fatty acids (PUFA, of which 7.7 percent was the omega-6 linoleic acid (LA) and 0.8 percent was the plant omega-3 ALA).
The second diet intervention was the omega-6 rich linoleic acid diet, consisting of 37 percent total fat, 9 percent SFA, 12 percent MUFA, 16 percent PUFA, of which 12.6 percent was LA, and 3.6 percent was ALA).
The third diet intervention was the omega-3 ALA-rich diet, providing 38 percent of energy from total fat, 8 percent from SFA, 12 percent from MUFA, and 17 percent PUFA, of which 10.5 percent was from LA, and 6.5 percent from ALA. Flaxseed oil and walnuts were the main sources of ALA.
At the end of all three intervention diets, the researchers report that mean concentrations of the bone resorption marker NTx were significantly decreased following the ALA diet (13.2 versus 13.8 and 15.59 nanomoles bone collagen equivalents (BCE), respectively).
No changes in the marker for bone formation, BSAP, were observed.
Levels of tumour necrosis factor alpha (TNF-alpha), a marker for inflammation, was also found to decrease more after consuming the ALA-rich diet than the other two diets: 10.3 nanograms per litre for ALA, compared to 13.3 and 18.2 for the LA and AAD diets, respectively.
Effect on bone metabolism
“The results indicate that plant sources of dietary n-3 PUFA may have a protective effect on bone metabolism via a decrease in bone resorption in the presence of consistent levels of bone formation,” said the researchers.
The mechanism behind the benefits appears to be the ratio between omega-6 to omega-3 fatty acids, they said. Previous research has reported that omega-6 fatty acids are converted into pro-inflammatory prostaglandins, while omega-3 fatty acids are metabolised into anti-inflammatory prostaglandins.
Further studies are necessary to further clarify these relationships, they said.
“The present results suggest that incorporating plant sources of n-3 PUFA into the diet may provide health benefits not only to the cardiovascular system, but also to the skeletal system,” concluded the researchers. - (Decision News Media, January 2007)
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