Background: Docosahexaenoic acid (DHA) is an -3 (n–3) polyunsaturated fatty acid (PUFA) thought to be important for brain function. Although the main dietary source of DHA is fish, DHA can also be synthesized from α-linolenic acid (ALA), which is derived from plants. Enzymes involved in DHA synthesis are also active toward -6 (n–6) PUFAs to synthesize docosapentaenoic acid n–6 (DPAn–6). It is unclear whether DHA synthesis from ALA is sufficient to maintain brain DHA.
Objective: The objective of this study was to determine how different amounts of dietary ALA would affect whole-body DHA and DPAn–6 synthesis rates.
Methods: Male Long-Evans rats were fed an ALA-deficient diet (ALA-D), an ALA-adequate (ALA-A) diet, or a high-ALA (ALA-H) diet for 8 wk from weaning. Dietary ALA concentrations were 0.07%, 3%, and 10% of the fatty acids, and ALA was the only dietary PUFA that differed between the diets. After 8 wk, steady-state stable isotope infusion of labeled ALA and linoleic acid (LA) was performed to determine the in vivo synthesis-secretion rates of DHA and DPAn–6.
Results: Rats fed the ALA-A diet had an ~2-fold greater capacity to synthesize DHA than did rats fed the ALA-H and ALA-D diets, and a DHA synthesis rate that was similar to that of rats fed the ALA-H diet. However, rats fed the ALA-D diet had a 750% lower DHA synthesis rate than rats fed the ALA-A and ALA-H diets. Despite enrichment into arachidonic acid, we did not detect any labeled LA appearing as DPAn–6.
Conclusions: Increasing dietary ALA from 3% to 10% of fatty acids did not increase DHA synthesis rates, because of a decreased capacity to synthesize DHA in rats fed the ALA-H diet. Tissue concentrations of DPAn–6 may be explained at least in part by longer plasma half-lives.
From: Domenichiello, A. F., Kitson, A. P., Metherel, A. H., Chen, C. T., Hopperton, K. E., Stavro, P. M., Bazinet, R. P. http://jn.nutrition.org/cgi/content/short/147/1/37?rss=1
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