Review challenges the health claims made for some vegetable oils

‘Vegetable oils’ derived from sunflower, soya, safflower and corn are generally promoted as healthy. They are rich in ‘polyunsaturated’ fats that come in two basic forms: omega-6 and omega-3. Omega-6 oils tend to be inflammatory in nature and also encourage clotting in the blood. Omega-3 fats tend to do the reverse. It’s generally well accepted, I think, that a balance of omega-6 and omega-3 fats in the diet is required for optimal health. The problem is, a typical Western diet tends to provide a glut of omega-6 (compared to omega-3), and some believe this is a potential driver of chronic (long-term) disease including cardiovascular disease.

In 2009, Health Canada (the government body which provides health advice to Canadian people) approved a health claim for polyunsaturated fats. The claim was that these fats could reduce the risk of heart disease through their ability to lower blood cholesterol levels. However, a paper published in the Canadian Medical Association Journal this week mounts a credible challenge to the appropriateness of this claim for some foodstuffs [1].

The authors of this study point out that the impact of fats modification on the diet does not always predict the health outcome of such a change. They draw our attention to the fact that omega-3 fats appear to reduce the risk of cardiovascular disease, although they generally have no effect on cholesterol levels or even increase them.

They also refer to a review published earlier this year in the British Medical Journal [2]. The authors of the review pooled together studies in which saturated fat in the diet was replaced with polyunsaturated fats. Overall, the review found no evidence of benefits when saturated fat was replaced with omega-6 fats. However, there was evidence of benefit when saturated fat was replaced with a mix of omega-6 and omega-3 fats. They raise the possibility that omega-6 fats might actually promote cardiovascular disease.

The authors quote a study that was featured in the BMJ review (The Sydney Diet Heart Study) [3]. In this study, about 220 men aged 30-59 were instructed to reduce saturated fat intake and increase polyunsaturated fat intake. The men were supplied with safflower oil and safflower oil-based margarine (rich in the omega-6 fat known as ‘linoleic acid’, but very low in the omega-3 fat found in plants known as ‘alpha-linolenic acid’). A similar number of men got no dietary instruction and acted as controls.

In the men eating the ‘heart-healthy’ diet, risk of death was elevated by 62 per cent. Risk of death from cardiovascular disease was increased by 70 per cent. The authors of the review concluded:

Advice to substitute polyunsaturated fats for saturated fats is a key component of worldwide dietary guidelines for coronary heart disease risk reduction. However, clinical benefits of the most abundant polyunsaturated fatty acid, omega 6 linoleic acid, have not been established. In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit. These findings could have important implications for worldwide dietary advice to substitute omega 6 linoleic acid, or polyunsaturated fats in general, for saturated fats.

The authors of the CMAJ analysis conclude:

In summary, much confusion has arisen from unclear nomenclature with regard to polyunsaturated fatty acids and the lack of reporting of food sources in prospective cohorts. Data from prospective cohort studies and randomized controlled trials generally support the replacement of saturated fats with mixed polyunsaturated fatty acids to reduce the risk of death from coronary artery disease. However, it is unclear whether oils rich in omega-6 linoleic acid but low in omega-3 alpha-linolenic acid also reduce this risk. We suggest that the health claim be modified such that foods rich in omega-6 linoleic acid but poor in omega-3 alpha-linolenic acid be excluded.

I feel these recommendations are supported by the science. I note that one of the authors of this review has received fees or financial support from Bunge (an agribusiness) and the food companies Unilever and Kraft. The summary of the paper closes:

Future research is needed to examine the dietary methodologies used to measure polyunsaturated fatty acid intakes in observational studies and the metabolism of polyunsaturated fatty acids, as well as their role in coronary artery disease and other diseases.

This last part is important, and in particular we need to know what the effect of fats on actual risk of death and disease is. Too often in the past have we been recommended to make changes to our diet based on the impact this has on our cholesterol levels.

As the authors of this study make clear, basing recommendations on this criterion can sometimes be misguided. And as the Sydney Diet Heart Study shows, judging a foodstuff by its impact on cholesterol levels rather than its impact on health can even be the death of us. Food companies please take note.

References:

1. Bazinet RP, et al. Omega-6 polyunsaturated fatty acids: Is a broad cholesterol-lowering health claim appropriate. CMAJ online before print 11 November 2013

2. Ramsden CE, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis BMJ 2013;346:e8707

22 Responses to Review challenges the health claims made for some vegetable oils

  1. Jon Buscall (@jonbuscall) 15 November 2013 at 11:56 am #

    I’d be very interested to know what you think about Coconut Oil. I seem to hear it referred to as a super oil right now.

  2. Xenia 15 November 2013 at 12:08 pm #

    Great commentary.

    One of the main misunderstandings (and misrepresentations which vegetable oil and margarine industry is plentifully using for touting their unhealthy products) is the fact that the omega 3s found in such oils are actually not the right ones. Possibly that was the reason why they are sometimes found to elevate the risks. The right omega 3 is not ALA, The right omega 3s that our body can truly utilize are EPA and DHA and they only come from animal sources

    They are one of the reasons wha vegetarians, and especially vegans – given that our bodies cannot convert enought ALA into EPA and DHA, actually far from it! – have increased CV disease risks and are more frequently subject to brain disorders, including Alzheimer’s. It is indeed about the balance of omega 3 versus omega 6, but they have to be the right type of omega 3.

  3. David 15 November 2013 at 12:24 pm #

    It’s worth noting that when the revised Sydney Diet Heart Study was published it was dismissed on the NHS behind the headlines web site because, they claimed, the sunflower oil used in the UK is not the same as the safflower oil used in Australia. This is an untruth, the oil in both cases is linoleic acid. Why would they do this?

    It should also be noted that the study, originally favouring the establishment line, was revised when missing data was found on a computer tape in someone’s garage. It is unlikely that the tape was the cassette type used on early computers, more the type seen on 60s and 70s movies involving computers, not something you could put in a pocket and forget about.

    Sorry if this comes across as a bit of a conspiracy theory.

  4. David 15 November 2013 at 1:06 pm #

    Found the NHS reference http://www.nhs.uk/news/2013/02February/Pages/omega-6-fat-diet-heart-disease-death-risk.aspx

    It includes:

    But British consumers should not panic – the safflower oil used as a source of omega-6 in this study is rarely used in this country.

    and

    When these results were added to a meta-analysis of other trials that have assessed the effects of linoleic acid, it was found that linoleic acid increased the risk of death from coronary heart disease and cardiovascular disease, although these results were not significant.

    Same oil – and this from the NHS.

  5. Robert Park 15 November 2013 at 3:14 pm #

    At last the scientists are beginning to take note of what many of the public have been saying for years. There is research which today is probably hidden in the archives and judiciously forgotten which showed that when plaque from cadavers was analysed that a massive 70% arose from polyunsaturated fats, 23% from saturated fat, and 7% from other sources. When it is considered that saturated fat in its composition consists also of poly and mono unsaturated fats then it might be appreciated that saturation is not the problem.

    Attention is often given to the traditional Inuits whose diet was mainly that of marine oils but principally of polyunsaturated fat. It was found that the Inuits had almost no heart disease yet they failed to live longer than those on a western diet. The problem with this diet was that when injured bleeding to death was common as the Inuit’s blood was exceedingly thin. Apparently, this diet, rich in polyunsaturated fat, also thinned the walls of the arteries causing anuerisms.

    When surgeons introduced organ transplants it was found that the body’s immune system attacked the organs recognising them as foreign agents. Research was undertaken to find a product that could effectively suppress the immune system when it was discovered that the most potent suppressor was polyunsaturated fats which, amazingly, has been touted since as being dietary healthy!

    Arctic explorers recognised the necessity to have saturated fat in the pemmican which Captain Scott of the Antarctic ignored (taking as he did the best advice of the medical profession) and probably why his team failed in their efforts.

    To my current knowledge there is a lack of research on the impact which carbohydrates in the diet have other than that of glycosylation yet it might be found that fats furr the arteries only in the presence of carbohydrates.

    It will probably have been noted that olive oil (a monounsaturated fat) is most frequently sold to the public in dark glass bottles which is to slow its deterioration. The problem with olive oil is that it apparently creates masses of those nasty wee free radicals which is harmful at the cellular level of the body.

    Prior to the discovery and many uses of crude oil paint manufacturers used vegetable oils to make their products and were nearly put out of business when crude oil came on to the scene. To survive it was discovered that vegetable oils possessed nutrients so those vegetables oils were touted and sold in the food market and this was probably the genesis of the war against traditional saturated fats which continues to be waged today. As is generally known, when paint is subjected to both heat and oxygen it hardens and guess what vegetable oil does in the body when subjected to the heat and oxygen of the body? Need more be said?

    Meantime, I am sticking to my lashings of saturated fat which I love and adore and which provides a cushion against ill-health. This information has been culled from my general but extensive reading, from experimentation, and from observation.

  6. Jennifer 15 November 2013 at 4:07 pm #

    Xenia……I am now at a loss!
    I avoid all processed vegetable and seed oils, except for coconut oil. I also use saturated fat from all dairy sources.
    However, I consume whole, fresh nuts and seeds on a daily basis with Greek yogurt, to ensure I have a reasonable supply of healthy Omega 3. I choose food where the ratio of O3:O6 is deemed as healthy as we can hope for, so are you saying I will have little benefit from this approach?So, should I abandon this practice in favour of getting O3 from fish alone?

  7. Betsy Branstetter 15 November 2013 at 4:28 pm #

    What oil should I use then?

  8. Jo Piercey 15 November 2013 at 5:28 pm #

    What oil is best to use and does cooking with an oil change the way it is utilised by the body? In particular, the Omega 3′s..

  9. André 15 November 2013 at 6:31 pm #

    It’s not just that too much omega 6 increases inflamation (we do need some omega 6), it also weakens your immune system. In the early days of organ transplants, the patient were given sunfloweroil to avoid the rejection of the organ. And it worked beautifully. Reason is of course that the immune system was shut down. And that could be the reason that those patients had a high risk of dying from cancer.

    Sugar, grains and vegetable oil; that’s all you have to take out of your diet if you want to stay healthy.

  10. Geraldine 15 November 2013 at 9:20 pm #

    Would be interested to know your opinion on the work of Dr Udo Erasmus and his product “Udo’s Choice “, a blend of omega 3, 6 and 9 oils.

  11. Dolan 15 November 2013 at 9:40 pm #

    Is linseed good for one (omega 3) or does it count as a grain?

  12. Frederica Huxley 15 November 2013 at 10:48 pm #

    Modern vegetable oils are not food! Do some research into the production processes, and you will find that the seeds are ‘washed’ through a petroleum solvent, usually hexane, before being heated, degummed and deodorised. Any omega 3 in the seed is severely degraded, and any vitamins are destroyed. With the best will in the world, there are always traces of trans fats from the heating of the oil.

  13. Delia 16 November 2013 at 1:15 am #

    Is there a specific reason that no one has addressed the elephant in the room – the damage done to both omega 3 and 6 PUFAs when they are processed using conventional methods, which include solvent extraction, deoderization, bleaching, de-gumming, all of which leave the oil containing trans fats, polymerized fats, cyclised fats etc? Surely this has to impact the results of the research?

  14. paulc 16 November 2013 at 11:15 am #

    If you want an oil for cooking go back to lard, butter, ghee and beef tallow, save the grease that drips from your bacon while grilling it and use that for frying with. Basically stick to using what your old relatives would have been using way back in the 1800′s. Olive oil is for salads and making mayonaisse with…

  15. Stephen Blackbourn 16 November 2013 at 12:30 pm #

    I rarely use any veg or nut oil these days. The last bottle of olive oil I used wasn’t that great and I got sick of it towards the end. (Perhaps olive oils have good years and bad ones just like wine)?

    I now use coconut oil, ghee or beef dripping depending on the dish I’m cooking.

  16. Fiona 16 November 2013 at 12:30 pm #

    From what I have read elsewhere, my understanding is that Extra Virgin Olive Oil is best except when it needs to be heated; I sprinkle it on toast, for instance, as I’m cow’s milk intolerant and avoid butter. Coconut oil is best, I’m told, for cooking because, being a saturated fat, it changes less in the process. Will my commentator friends please let me know whether I have got this right?

  17. André 16 November 2013 at 1:22 pm #

    Fiona,

    I think olive oil is not too bad. And for a salad saturated fat is not practical. Only saturated fat is heat resistant. So either butter (when your lactose tolerant) or coconut oil.

    Not all saturated fats are the same and within this group there are fats that are even better. Coconut oil has a lot of the best saturated fat you can find. But I use the combination of butter and coconut to get the most complete package.

    Nature gave you mostly saturated fat in your body. Simply because it is stable.

    The only PUFA I take is cod liver oil. Omega 3 has become a marketing slogan. We need FISH oils. But most people don’t like the taste of that. Too bad; your brain needs fish oil, not the omega 3 from flax.

    Hope this helps a bit.

  18. William L. Wilson, M.D. 18 November 2013 at 3:11 pm #

    It really isn’t really that difficult. Eat natural healthy fats and avoid fake fats produced by the Food-Industrial Complex. Duh.

  19. Ted 19 November 2013 at 2:42 pm #

    This article got me thinking about what I eat whilst at work. In order to avoid the usual canteen sandwiches I have taken to bringing in a couple of pots of mixed nuts (brazil, hazlenuts, pecans, walnuts, almonds) that see me through the day. I’ll eat the contents of a 200ml pot for lunch plus the contents of further 100ml pot as a late afternoon snack. Given that I’ve read nuts are high in Omega 6 fats, is eating such quantities of nuts every day a healthy alternative to the usual office sandwich?

  20. Chris 20 November 2013 at 1:52 am #

    Stability of fats declines with the degree of unsaturation – those double bonds are weaker not stronger. All polys (PUFAs) can be prone to oxidation. Hence the sources should fresh and native to good food.
    Under consumption of PUFAs is not good but supply can be overdone.
    Sat fats are stable and good. They have purpose when they shroud organs, and are a structural component of cell membranes along with cholesterol.
    Eating insufficient fat (sat & mono) greatly enhances prospects of weight gain – now isn’t that odd?
    Good thread.

Trackbacks/Pingbacks

  1. Ifrågasätt hälsopåståendena för fleromättat fett - 17 November 2013

    […] Dr Briffa skrev om The Sidney Diet Heart Study. Personer som åt vegetabiliska omega-6-oljor dog mera i hjärtinfarkt än de som inte fisk kostråd om att äta sådana. […]

  2. Is Passion Overrated? - Weekly Roundup #78 - 18 November 2013

    […] Are vegetable oils healthy? John Briffa answers. […]

Leave a Reply