Scientists from the University of California, Davis and the USDA’s Agricultural Research Service report that consuming at least 0.3 cups per day of dark-green vegetable in combination with omega-3 supplements could help African Americans obtain an Omega-3 Index of about 8%, said to be the ideal for optimal health.
Writing in the Journal of Nutrition the researchers added a note of caution with interpreting the results, however, stating that they identified the association between dark-green vegetable consumption and the efficacy of omega-3 supplementation after performing a secondary analysis of their data. In addition, they also used a food frequency questionnaire to track dietary intakes, which are known to have recall bias issues.
“Therefore, to assess the broader implications of these findings, it will be critical to determine how robust low dark-green vegetable intake is in predicting a low omega-3 FA supplementation response phenotype and to further determine if a person’s response phenotype can be altered by a change in dietary patterns,” they wrote.
“If supported, one could envisage a situation in which particular doses of omega-3 FAs could be recommended along with complementary guidelines (e.g., portions and types of vegetables to be consumed) on the basis of an individual’s basal red blood cell EPA concentrations and an assessment of habitual dietary patterns.
“Although further work will be required to confirm these findings and investigate their biologic mechanisms, this study has generated an intriguing and unexpected hypothesis for diet 3 diet interactions in the context of omega-3 fatty acid supplementation.”
The California-based scientists analysed data from a double-blind, placebo-controlled trial involving 83 people of African ancestry who were randomly assigned to receive either omega-3 supplements (2 g EPA + 1 g DHA) or corn/soybean oil (placebo) for six weeks.
Using data from food-frequency questionnaires and blood samples to monitor omega-3 levels in erythrocytes (red blood cells), the researchers noted that people could be divided into two groups, high and low omega-3 responders.
The high responders were found to have greater reductions in triglycerides and VLDL particle sizes.
A separate association between dark-green vegetables consumption the efficacy of omega-3 supplements was observed.
“Although elucidating the biologic mechanisms linking vegetable intake to omega-3 supplementation response is beyond the scope of this study, it is possible to hypothesize such mechanisms,” said the researchers. “The benefits of a diet rich in fruit and vegetables are well established. For instance, fruit and vegetable consumption can reduce oxidative stress, including in vivo lipid peroxidation. Thus, it is conceivable that lower vegetable intake induces a prooxidative state that may diminish omega-3 availability, thereby reducing their availability as substrates for developing red blood cell membranes in the [omega-3 low response group].”
The researchers also indicated a role for the gut microflora, noting that food rich in plant fiber and polyphenolics are known to influence the composition of the microbes in the gut, and some bacterial strains can influence how we metabolize lipids.
“Taken together, these findings suggest that diets rich in dark-green vegetable may modulate gut microbiota and in turn influence fatty acid availability and cellular composition in humans. Additional studies will be needed to determine whether an integrative network linking habitual dietary patterns, gut microbiota, and [omega-3] metabolism is a plausible biologic mechanism.”
Source: Journal of Nutrition
Published online ahead of print, doi: 10.3945/jn.113.181875
“Habitual Diets Rich in Dark-Green Vegetables Are Associated with an Increased Response to omega-3 Fatty Acid Supplementation in Americans of African Ancestry”
Authors: A. O’Sullivan, P. Armstrong, G.U. Schuster, T.L. Pedersen, H. Allayee, C.B. Stephensen, J.W. Newman