Alpha-linolenic acid in rapeseed oil partly compensates for the effect of fish restriction on plasma long chain n-3 fatty acids

Abstract

Objective: To examine the ability of alpha-linolenic acid (ALA) in low erucic acid rapeseed oil (RO) to compensate for the effects of a restriction in fish intake on plasma fatty acid composition.

Design and subjects: Two times 6 weeks' randomized dietary intervention was used with blind crossover design in 40 healthy unconfined women and men (age 20-46y).

Interventions: Subjects were assigned to two fish restricted diets, namely RO diet and Trisun-sunflower oil (TSO) diet, with similar proportions of saturated : monounsaturated : polyunsaturated fatty acids (11.5:17.5:8.5% of total energy, En%), but differing in their ALA content (2.2 and 0.3 En%) and n-6 : n-3-ratio (3 : 1 and 23 : 1, respectively). The fatty acid compositions of plasma triglycerides (TG), cholesterol esters (CE), and phospholipids (PL) were analyzed by gas chromatography. Dietary intake was evaluated based on 3- to 7-day food records.

Results: The proportion of TG and CE ALA decreased on the TSO diet (from 1.6% to 0.9% and from 0.9% to 0.4%, respectively, P < 0.001) and increased on the RO diet (from 1.7% to 3.4% and from 0.9% to 1.3%, respectively, P < 0.001) compared to the baseline level. The proportion of eicosapentaenoic acid (EPA) in all three plasma fractions decreased on the TSO diet but not on the RO diet. The proportions of docosa-hexaenoic acid (DHA) decreased on both experimental diets and there was no difference in CE DHA between the diets. PL docosa-pentaenoic acid (DPA) and PL DHA remained at a higher level on the RO diet compared to the TSO diet (P < 0.001 and P < 0.05, respectively).

Conclusions: ALA is metabolized to EPA in humans to a significant extent. The degree to which rapeseed oil (ca 50g/day) affects the proportion of EPA resembled the effect of a weekly portion (50-100g) of fatty fish depending on the fat content of the fish.