Seismic shift in dietary fats?

vegetable oils are our main source of omega-6 fats

The paradigm underlying our notions about dietary fats and disease may be shifting.  A recent review in the British Journal of Nutrition registers about a 4 on my nutritional Richter scale.  Conventional thinking goes this way: unsaturated fats = good; saturated fats = bad; trans fats = evil.  This thinking is based on the fact that saturated fat intake is related to higher LDL (bad) cholesterol, while higher unsaturated fat intake is related to lower levels.  Since higher LDL cholesterol is associated with higher risk for heart disease, it made sense to tell people to swap saturated fats (animal fats, hydrogenated fats) for unsaturated fats (vegetable oil products, like margarine).   The catch is that unsaturated fats come in several different shapes and sizes.  Omega-6 fats are the most common in vegetable oils, while omega-3 fats are less common, and not present in many common vegetable oils.  Over the past decades, our diets have become increasingly heavy in omega-6 fats, because lots of foods are prepared with vegetable oils or margarine.  Why?  They’re cheap and they keep well.

A group of researchers reviewed past studies on fat intake and heart disease, comparing studies that increased just omega-6 fats to studies that increased both omega-6 and omega-3 fats.  Conventional wisdom would say that either diet would result in reduced risk for heart disease.  That turns out to be wrong.  The diets that increased both omega-6 and omega-3 fats reduced risk, while the omega-6 only diet increased risk.  Heart attacks and death from coronary heart disease (CHD) were higher in the groups that just increased omega-6 fat intake.  The authors concluded that:

Advice to specifically increase (omega-6 fat) intake … is unlikely to provide the intended benefits, and may actually increase the risks of CHD and death.

Not only does this study reinforce the importance of omega-3 fats, but it questions the idea that any old unsaturated fat is healthy.   Omega-6 fats are linked to increased oxidation of LDL (bad) and increased inflammatory metabolites (bad for everything, including heart disease).  Omega-6 intake is also related to increased risk for cancer in animal models.

Meanwhile the American Heart Association published an advisory in 2009 stating flatly that omega-6 fats were healthy and everyone should be eating more of them, substituting vegetable-oil based products for higher saturated fat animal products, such as margarine for butter.  The British Journal of Nutrition review criticized this advisory statement for dismissing the issue of inflammation, and for basing their conclusions on studies that had design flaws.  The title of the BJN review questioned whether the AHA was using “biased evidence” to promote the consumption of high omega-6 vegetable oil products.

What these reviews do not say is that saturated fat is OK after all.  This argument is about official promotion of certain types of food products, allegedly for the health benefits.  So what should you do?   Dr. William Harris, a well known omega-3 expert, who contributed to AHA policy, believes the key to unsaturated fat benefits is to have an adequate intake of omega-3 fats, along with higher general intake of unsaturated fats vs. saturated fats.  The BJN results would seem to agree with that advice.  One thing that’s certain: this controversy is not over.  Hopefully more good research on dietary fats and health will provide answers.  The nutritional Richter scale may yet register a 6 or 7, if thinking about dietary fats shifts dramatically.

For another opinion: Evelyn Tribole MS RD, expresses her thoughts about the BJN vs. AHA fat recommendations.

The highest omega-3 vegetable oils are:

  • Flax (57%)
  • Canola oil (11%)
  • Soy (8%)

Other vegetable fats are 1% or less omega-3.

Olive oil is the lowest in omega-6 fats (linoleic acid) at 9%.  Only lard, coconut oil and butter are lower, but they’re high saturated fat.

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