Effect of dietary α-linolenic acid on thrombotic risk factors in vegetarian men
Li, D.L., Sinclair, A., Wilson, A., Nakkote, S., Kelly F., Abedin, L., Mann, N. Turner, A. 1999. Am J Clin Nutr. 69: 872-882.
Vegetarians may have potentially greater thrombotic risk than omnivores due to their lower n-3 platelet and plasma concentrations and lower n-3: n-6 ratio. The present study investigated seventeen male vegetarians who consumed their habitual diet (low alpha linolenic; ALA), a moderate- ALA diet, or a high-ALA diet for 42 days in order to examine the effect of dietary ALA on atherosclerotic and thrombotic risk factors. ALA was provided in the form of vegetable oils, such as canola and flax seed. Measurements of plasma lipids confirm that 20- and 22-carbon n-3 PUFAs can be endogenously synthesized form parent ALA, and the extent of synthesis varies with the amount of ALA consumed in the diet. The in vivo conversion of dietary ALA to EPA is not as effective in raising long chain PUFAs in platelet and plasma lipids as is direct consumption of EPA from fish or fish oil. No significant differences in platelet aggregation, and thromboxane B2 concentrations were noted. However, a larger trial population and a longer time period may be required. No significant differences with respect to plasma total cholesterol, triacylglycerol, LDL-cholesterol, or HDL-cholesterol concentrations were observed, which could be due to the habitually low saturated fatty acid and high PUFA content of the vegetarian diet. The authors conclude that the use of ALA from vegetable oils such as flax seed oil as a dietary fat for daily food preparation may have beneficial effects on increasing the n-3 PUFA content of platelet and plasma lipids. However, because such small amounts of EPA and other long-chain n-3 PUFAs are produced after ALA-rich diets, it is clear that vegetable and fish sources of n-3 PUFA do not have equivalent biological effects in humans.