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

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

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

  1. SamMackrill 15 December 2009 at 4:05 pm #

    Thanks Dr B – small typo

    There are two main forms of polyunsaturated fats – omega-6 and omega-6

  2. Methuselah - Pay Now Live Later 15 December 2009 at 4:08 pm #

    John – think you have a typo in the first para – you say omega 6 twice when I think you mean omega 6 and omega 3….

  3. Chris 15 December 2009 at 5:44 pm #

    Dr B – I think you have made a typo, repeating “omega-6” twice on the following line:

    “There are two main forms of polyunsaturated fats – omega-6 and omega-6 ” and these have generally different biochemical effects in the body.”


  4. Dennis Mullins 15 December 2009 at 10:25 pm #

    To me this is just another example (one of very many) of the need to eat a NATURAL UNREFINED UNPROCESSED WHOLE food diet. In such a diet, significant amounts of unsaturated fats would only come from whole unprocessed nuts and seeds as well as fish and some animal foods which would constitute a small part of the diet. Oils extracted from nuts , seeds and corn etc could perhaps be described as ‘foodlike substances’ – a modern day development – they certainly do not count as ‘foods’ in my book. If one has to use a ‘processed’ food as a spread, use a small amount of butter mixed with a small amount of extra virgin olive oil.

  5. Dr John Briffa 16 December 2009 at 12:45 am #

    Thanks you three – corrected now.

  6. Jamie 16 December 2009 at 3:16 am #

    Roll out the standard Heart Foundation lines where they attempt to show evidence of omega 6 being ‘heart healthy’. The likes of the heart foundation seem to forget that the body requires all of its other systems to be running well for optimal health – not just the heart. Seemingly, it is OK to consume margarine plastics & increase the chances of the likes of ulcerative colitis, as long as your heart is in good nick.

  7. Chris 16 December 2009 at 1:09 pm #

    At least you know you have an attentive readership!


  8. Angie 16 December 2009 at 2:55 pm #

    There has long been an association described between the growing consumption of polyunsaturates via margarines and increasing cancer rates, and Gary Taubes describes the balancing act performed by public health policy makers in the USA between this and their (erroneous) belief that these were good for the heart. Malcolm Kendrick concedes that this may be true of Omega 3 (and here, I think fish oils are different from those of vegetable origin, although I don’t think he mentions this), but that is all.

  9. Chris 17 December 2009 at 9:44 am #

    Hi Jamie,
    Speaking generally about the generic type of ‘charitable’ institutions that mention of the Heart Foundation suggests within me then I would caution against taking any message or statement of ‘fact’ for granted. Such institutions must be supported with funding and it doesn’t hurt to ask yourself who the principal sponsors might be. Next line of healthy scepticism is to wonder if any message is intended to virtuously serve the needs of an intended audience or to satisfy an agenda for a principal sponsor; often to sell more of something.
    Along the same lines don’t accept everything in Wikepedia without question. You do not know who has contributed and there is no guarantee that bias has not crept in.

    Wikepedia has an entry for Omega-6 fatty acid which looks largely free from bias. It emphasises the important role of omega-6 EFAs as precursors for some important biochemical messengers. It also cautions that an excess of omega-6 relative to omega-3 may be highly disruptive long term. Dietary omega EFA imbalance leads to eicosanoid imbalance, and eicosanoid imbalance is associated with “heart attacks, thrombotic stroke, arrhythmia, arthritis, osteoporosis, inflammation, mood disorders, obesity, and cancer”, according to the Wikipedia entry. Probably, Type 2 diabetes, Alzheimers, Hypertension and Depression belong on the list, too. It’s a complicated subject and one I hope to get to grips with. Much as the subject fascinates me I resent having to delve so deep into something that my education has not really prepared me for. For if the state machinery for ‘Nannying’ us was doing it’s job right it would not be necessary for a layman to have to contemplate such matters. As things stand there is scope to argue that aspects of health promotional policy may actually make matters worse.

    The ‘boffins’ dance carefully; none want to incur the wrath of the giants such as Kraft or Unilever. So far as I know this is closest any have come to saying vegetable oils and derivatives, consumed to excess as is typical to western diets, are toxic to humans. Dr Briffas book makes a good introductory text to the significance of oils and eicosanoids. Sears and Erasmus are good authors on the topic, too.

  10. rachel 18 December 2009 at 12:13 pm #

    What about those “fry light” oils that seem to be polyunsaturates – or monounsaturates in emulsion? Can’t find much out about them.

  11. Kevin eakins 18 December 2009 at 5:14 pm #

    This is an interesting topic and one which fascinates me. There are two points that are worthy of consideration here. Firstly to descirbe Omega-6 as pro-inflammatory and Omega-3 as anti-inflammatory is an over-simplification. Sometimes its OK to simplify especially when you are refering to a factor whose influence predominates (ie: vit D deficiency). However in this case I am not convinced. I think that the boundary conditions of the micro-environment where fatty acids are being used within the body are more important. In other in the prescence of disease the action fatty acids may be distorted into a pro-inflammatory action. The problem is not the fatty acid but the imbalance that causes it to be misused or to be utilised in a sub-optimal way. In the study referred to above the subjects were suffereing from ulcerative colitis and in that pro-inflammatory environment maybe the patients have to be more careful to reduce their intake of fatty acids but this does not mean that they are the cause of the problem. One man’s meat in this case would be another’s poison. Secondly the reductionist approach of studying a nutrient outside of its natural food setting can lead to all sorts of wrong conclusions. In this study, what percentage of the intake of fatty acids came from processed food sources which caused them to be oxidized or subverted into trans-fats or contaminated in some other way? I think you would agree that fatty acids from margarine are not the same as fatty acids that occur naturally in vegetables or virgin, cold pressed vegetable oils. The problem is not the fatty acids per se ; its the processing that destroys them.

  12. DrDobbin 18 December 2009 at 10:23 pm #


    I’ve always wondered when seeing evidence of omega 3 vs omega 6 ratios and their effects on health, whether the results are skewed by the presence of trans fats in the omega 6 foods present in studies.

    The only reliable way of making this comparison would be if trans fats were negligible in both the omega 3 and omega 6 foods. Are you aware of any studies which have used this approach?

  13. Dominic Gill 18 December 2009 at 10:51 pm #

    It would be useful also to mention at some point the essential difference between long-chain and short-chain Omega-3. The plant-based short-chain Omega-3 (flax seeds & oil, etc etc) is virtually useless, since our bodies can’t process it adequately. The only useful Omega-3 is the long-chain (DHA/EPA), which *is* vitally important, and only derived from fish or algae.
    Discussion of the relative merits of “cold-pressed vegetable oils” etc simply ignores this central fact. The products (like Flora margarine & various healthfood preparations) which claim to contain “Omega-3” almost always contain short-chain Omega-3, and are thus essentially useless.
    There is an excellent discussion of this on a recent R4 Food Programme which you can hear at http://www.bbc.co.uk/iplayer/console/b00ncwwm

  14. Jill H 19 December 2009 at 1:13 am #

    I think the very first margarines made possible by the use of hydrogenation techniques utilized polyunsaturated oils from fish and whales. After a bit of deodorizing the claim was that you could not tell the difference between the margarine and butter and then the use of seed oils came later. What was not understood was that the process of hydrogenation changes the ‘cis’ form of the essential fatty acid into a ‘trans’ form that more and more evidence seems to suggest that the body does just not recognize and is possibly more harmful than excessive use of saturated fats. When some of the margarine manufactures finally took on board this information they quietly went away and changed their process from hydrogenation to ‘interesterification’ and are able now to put ‘contains no or few trans fats’ on the tub. I still cannot trust that this will be any better for our health. This along with the highly processed, deodorized and damaged seed oils used for cooking has meant that our intake of damaged omega 6 essential fatty acids has completely changed the balance of fats in the diet. Graham Harvey who writes for the Guardian – guardian.co.uk Let’s get our fats right – looks at the significant change in composition of modern animal fats when animals are no longer pastured but fed large quantities of corn in ‘modern’ feedlots. Not eating a diet mainly composed of processed foods and keeping and feeding animals in a way that is healthful and natural for them would go a long way to address this imbalance in the essential fatty acids in our diets and the ill health it seems to be causing.

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