Reduced arachidonate in serum phospholipids and cholesteryl esters associated with vegetarian diets in humans

Lipid fractions such as phospholipids (PLs), cholesteryl esters (CEs), and free fatty acids (FFAs) represent source pools for eicosanoid synthesis. To determine whether dietary habits affect the enrichment of 20:4n-6 in these precursor pools, we studied humans with partial or complete arachidonate restriction resulting from chronic avoidance of animal fat and tissue. Fasting serum was obtained from omnivorous control subjects (Omni, n = 100), semivegetarians (Semiveg, n = 16), and vegetarians (Veg, n = 25). PLs, CEs, FFAs, and triglyceride (TG) fatty acids were quantitated by thin-layer and gas chromatography. Serum 20:4n-6 was lower in the PL fraction in both Veg (p less than 0.01) and Semiveg groups (p less than 0.05) than in the Omni group and lower in the CE fraction in the Veg group (p less than 0.05). Serum 18:2n-6 did not differ between groups for any serum lipid fraction. 18:3n-3 was elevated in PLs and CEs of both Veg (p less than 0.05 and 0.01) and Semiveg groups (p less than 0.05 and 0.01) compared with the Omni group but did not result in differences in 20:5n-3 in PLs or CEs between diet groups. The lower concentration of 20:4n-6 in serum PLs and CEs of the Veg group indicates that dietary arachidonic acid enriches its circulating pool in humans; however, 20:5n-3 is not similarly responsive to dietary restriction.