Omega-6 is Bad For You

For a long time, nutrition experts have told us to replace saturated fats (solid at room temperature) with polyunsaturated fats (liquid at room temperature). One polyunsaturated fat is omega-6. Omega-6 is found in large amounts in corn oil, soybean oil, and most other vegetable oils (flaxseed oil is the big exception). According to Eat Drink and Be Healthy (2001) by Walter Willett (and “co-developed with the Harvard School of Public Health”), “replacing saturated fats with unsaturated fats is a safe, proven, and delicious way to cut the rates of heart disease” (p. 71). “Plenty of proof for the benefits of unsaturated fats” says a paragraph heading (p. 71). Willett failed to distinguish between omega-3 and omega-6.

A recent study in the BMJ shows how wrong Willett (and thousands like him) were. This study began with the assumption that omega-3 and omega-6 might have different effects, so it was a good idea to try to measure the effect of omega-6 separately.

They reanalyzed data from a study done in Sydney Australia from 1966 to 1973.The study had two groups: (a) a group of men not told to change their diet and (b) a group of men told to eat more omega-6 by eating more safflower oil (and reducing saturated fat intake, keeping overall fat intake roughly constant). The hope was that the change would reduce heart disease, as everyone said.

As these studies go, it was relatively small, only about 500 subjects. The main results:

Compared with the control group, the intervention group had an increased risk of all cause mortality (17.6% v 11.8% [emphasis added]; hazard ratio 1.62 (95% confidence interval 1.00 to 2.64); P=0.051), cardiovascular mortality (17.2% v 11.0%; 1.70 (1.03 to 2.80); P=0.037), and mortality from coronary heart disease (16.3% v 10.1%; 1.74 (1.04 to 2.92); P=0.036).

A 50% increase in death rate! The safflower oil was so damaging that even this small study yielded significant differences.

The authors go on to show that this result (omega-6 is bad for you) is supported by other studies. Walter Willett and countless other experts were quite wrong on the biggest health issue of our time (how to reduce heart disease, the #1 cause of death).

14 Replies to “Omega-6 is Bad For You”

  1. The BMJ article is interesting, but that old Sydney study has drawbacks that make it almost meaningless today.

    First of all, 70% of the participants were smokers. That may have been representative of Australian men in the 60’s, but nowadays that level of smoking prevalence is unheard of in the West. Most of these guys had 2 strikes against them already, the omega 6 consumption may have had just a minor effect that pushed them over the edge.

    Second, trans fats. Nobody was talking trans fats in those unenlightened times, so nobody measured the trans fat of the Miracle margarine that was fed to the intervention group. The BMJ article’s response section has a good post from the authors arguing why they don’t think trans fat was the problem, but the bottom line is we just don’t know how much trans these men were eating. Today almost everyone (including Walter Willett) agrees that trans fats are far worse than saturated fats.

    Seth: The article I cite considers several other studies. Taken together, they support the main conclusion of the Sydney study.

  2. The striking lesson is that all that health propaganda was bruited about without there being any worthwhile data to support it. The propagandists were reckless bastards, eh?

  3. What do you think about the safety of olive oil?

    Seth: Safe in small amounts, shown by studies supporting the Mediterranean diet. Dangerous in large amounts because it is high in omega-6. I much prefer flaxseed oil to olive oil.

  4. @ Mike W, I don’t think we can rule out this study because some of the participants were smokers. There is no avoiding the fact that the intervention group, following the best medical advice of the day, had a 50% increase in death rate.

    A good discussion on this study, and the various doctors responses, is at George Henderson’s website. From there, is this quote from Professor Jean Gutierrez of Washington University;

    “In addition to increasing PUFA intake, participants in the intervention group reported reduced dietary saturated fat, cholesterol, and calorie intake from baseline. A negative energy balance was verified with a slight mean drop in BMI. As expected, circulating total cholesterol and triglycerides were reduced in the intervention group, but mortality outcomes were not improved consequent to these circulating lipid and anthropometric changes, which is unexpected and interesting. The more important question arising from this study may be why a dietary intervention that improved all of these commonly used surrogate end points did not reduce all-cause mortality? ”

    So these people did what we are told to do today – eat less sat fat, lose weight and lower cholesterol, and for doing all that, they died 50% faster!

    A modern version of this trial, the LOOK Ahead trial, was stopped last year after 11 years of diet and lifestyle intervention (following the advice of the ADA and the National Cholesterol Education program) failed to show any improvement in cardiovascular outcomes. Again, the intervention group showed “improvement” (lowering) in cholesterol, and a small BMI decrease, but did not show improvements in CV event or death rates. Good discussion of the trial at Hyperlipid.

    Not only is there a refusal by the medical community to consider that omega-6 might be unhealthy, there is equally a refusal to consider that lower cholesterol (achieved by “diet” or drugs) might not be healthy either.

  5. We can get a (US) population wide picture of Omega 6 consumption by looking at this paper, which charts trends in food, and n-3 and n-6 fat consumption over the last century.

    The most amazing change is the spike in soybean oil (mostly comprised of n-6) consumption since the late 60’s. there is also in increase in (soy based “shortening” while lard and butter decreased) Why did this increase?

    “The historical event immediately preceding the largest increase in apparent consumption of soy oil in the United States was the 1961 American Heart Association (AHA) Central Committee Advisory Statement (32) that advised Americans to replace their saturated fat intake with polyunsaturated fats. ”

    And what was the impact on heart disease from 1970 to now?

    From the American Heart foundation’s website, we can see from this graph that the incidence of heart disease, as measured by hospital admissions, has *doubled* from in that period.

    Now correlation is not causation, of course. But if something is anti- correlated – like the decrease in sat fat consumption with the increase in heart disease – chances are it is *not* the cause.

    The dramatic increase in consumption of soy-fed (and anti-biotic treated) chicken probably hasn’t helped, either.

    Seth: Your “this paper” link doesn’t work. I cannot find where you get the idea that the incidence of heart disease doubled from 1970 to now.

  6. “the idea that the incidence of heart disease doubled from 1970 to now”: once you allow for the age of the population, incidence has fallen, has it not? For reasons nobody understand (except for the effect of smoking); similarly, nobody knows why it raced upwards from about the 20s to the 60s (with the same exception). Or so I understand, but I’m no expert. The trouble is, the experts don’t seem to be expert either.

  7. I’ll try again.

    The paper in question is Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century.

    Which I found from a 2011 post from Stephan Guyenet on the topic of n-3 and n-6 consumption. It is an excellent summary of dietary changes over this time.

    As for the idea that incidence had doubled, that is from the graph on page 19 of the charts excerpt from the AHA 20123 statistical update.

    The number of “discharges” from hospitals for CV diseases went from 3.3m in 1970 to 6.2m in 2000 – an 88% increase. Discharges means a patient that was admitted, and left, alive or dead, with a CV diagnosis. Whereas the more commonly used “mortality” means dead only. Mortality rates have improved, but that is due to better acute care.

    I didn’t account for population. It was 200m in 1970, and 280m in 1980, so the CV incidence rate per capita increased by 35% over that time.

    So, not as dramatic, but certainly in the wrong direction.

    That paper shows that n-6 has increased and sat fats decreased over the last century, and most dramatically in the 60’s-80’s. If n-6 was good, and sat fat bad, this should cause a noticeable decrease in CV events, yet they have only increased.

    So I would say it is “not looking good for the myth”

  8. You say one group was told to eat “more sunflower oil,” then you say the “safflower oil was so damaging.”

    Which kind of oil was it, sunflower or safflower?

    Seth: Safflower. Thanks for pointing this out.

  9. Flaxseed oil is ~10% of calories from omega-6, about the same as olive oil. Obviously it may be healthful because of the omega-3 content, but consumption should probably be limited to a few tablespoons a day.

  10. So are we reasonably sure that omega-3 is good for us? Is that a conclusion unlikely to be challenged in the next decade?

    Otherwise, I think it’s back to the drawing board for this field.

    Seth: I’m sure omega-3 is good for me. The benefits are clear and repeatable.

  11. Is omega-3 good for us? Well all these things are contingent. Greenland Eskino with very high 3 and low 6 have such thin blood they suffer regular nosebleeds and stroke is more common than CVD. I think more to the point is that a balanced 3:6 ratio is better than a badly skewed one, and essential fatty acids are essential.
    The old “eat more PUFA,less SFA” advice was concocted before the role of omega 3s in diet was even discovered. It was a leap in the dark. “Eat a little more fish, fruit and greens and a lot less carbohydrate if your heart’s a bit dicky, and for God’s sake stop smoking and while you’re at it don’t drink so much and reduce your exposure to environmental toxins and dodgy drugs” would have been better advice.
    The form of PUFA is also important:
    n-3 PUFA added to high-fat diets affect differently adiposity and inflammation when carried by phospholipids or triacylglycerols in mice

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