Long-chain n-3 polyunsaturated fatty acids (PUFAs), found in oily fish and fish oils, may protect against cardiovascular disease by improving the stability of atherosclerotic plaques, say researchers from the University of Southampton in the UK.

They found that the plaques readily incorporated the n-3 PUFAs into the lipids of atherosclerotic plaques, even if the fatty acid was only consumed at modest doses. In contrast, n6-PUFAs, such as the linoleic acid found in sunflower oil, did not affect the composition or stability of the carotid plaques.

"This finding suggests that atherosclerotic plaques are fairly dynamic, with some degree of lipid turnover, even at an advanced stage of atherosclerosis," Frank Thies and colleagues report in The Lancet.

Thies and colleagues conducted a randomized double-blind trial into fatty acid supplementation in 188 patients awaiting carotid endarterectomy. Participants were randomly allocated to receive one of three types of oil in capsules.

Control oil closely matched the fatty acid composition of the average adult UK diet, while sunflower oil provided 3.6 g/day linoleic acid, representing a 40 per cent increased intake of this fatty acid, and fish oil provided 1.4 g/day long-chain n-3 PUFAs, similar to the amount used in secondary prevention trials.

In all, 18 patients withdrew from the trial, and eight were excluded, with the remainder treated for a mean of 42 days.

The team found that the proportions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were higher in carotid plaque fractions of patients receiving the fish oil compared with those receiving control oil, and that sunflower oil had little effect on fatty acid composition of lipid fractions.

Patients given fish oil had fewer plaques with thin fibrous caps and signs of inflammation than those given control oil (odds ratio [OR]=0.52) or sunflower oil (OR=0.49). The fish oil patients also had more plaques with thick fibrous caps and no signs of inflammation compared with the control (OR=1.19) and sunflower (OR=1.16) groups.

Plaques from the patients given fish oil also had lower numbers of macrophages than those in the other two groups, although carotid plaque morphology and infiltration by macrophages were similar in all three.

Thies et al say that their study indicates that "plaques are dynamic and responsive to dietary modification, which can affect plaque stability."

They suggest that the sunflower oil had little effect on plaque because the patients were already consuming a substantial quantity of linoleic acid in their diet.