Why eating a lot of ‘polyunsaturates’ is not necessarily healthy

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Conventional nutritional wisdom dictates that we eat a diet rich in ‘polyunsaturated’ fats. At least part of the rationale for this relates to the fact that we are told that these fats help to reduce the risk of heart disease (you will, for instance, often see or hear ‘polyunsaturates’ being referred to in adverts for the highly-processed, chemicalised, non-food that we know as margarine). Having our fill of polyunsaturated fats may not be such a good idea, though. There are two main forms of polyunsaturated fats – omega-6 and omega-3 ” and these have generally different biochemical effects in the body. Omega-6 fats tend to encourage inflammation, for instance, while omega-3 fats do the reverse.

The opposing actions of omega-6 and omega-3 fats means that for optimal health, an ideal balance of these fats is required. In previous research, a relative excess of omega-6 over omega-3 (as is typical in the Western diet) has been liked with an enhanced risk of a variety of conditions including cardiovascular disease (e.g. heart disease and strokes), ‘auto-immune’ disease (such as rheumatoid arthritis), diabetes and depression. You can read more about these associations here and here.

In this context, I was interested to read a recent study which sought to assess the relationship between fat intake and ulcerative colitis – a condition characterised by inflammation in the lining of the large bowel (typical symptoms include episodes of pain, bloating and diarrhoea which can be bloody). This research followed more than 200,000 men and women aged 30-74 over a four-year period [1]. Dietary factors including intake of linoleic acid (the most abundant omega-6 fat in the diet) were assessed. Individuals with the highest intake of linoleic acid, compared to those with the lowest intakes, were about 2 and a half times more likely to develop ulcerative colitis. The authors estimated that about a third of all cases of ulcerative colitis might be due to a glut of linoleic acid in the diet.

This research adds to a significant body of evidence that suggests that blanket recommendations to eat plenty of ‘polyunsaturates’ may be doing some harm in the form of increased risk of certain chronic diseases. This research gives us another good reason to think about reducing our intake of omega-6 fats (e.g. refined vegetable oils and margarine).


1. The IBD in EPIC Study Investigators. Linoleic acid, a dietary n-6 polyunsaturated fatty acid, and the aetiology of ulcerative colitis: a nested case”control study within a European prospective cohort study. Gut 2009;58:1606-1611

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