Let's cut to the data. The investigators examined the fat composition of red blood cells in people who had suffered a heart attack, versus an equal number who had not. Participants who had heart attacks had less omega-3, more long-chain omega-6, and particularly higher trans fat in their red blood cells. In fact, 96% of the heart attack patients had elevated trans fat levels, compared to 34% of those without heart attacks. This is consistent with a number of other studies showing a strong association between blood levels of trans fat and heart attack risk (ref).
92% of heart attack patients were in the lowest category of EPA in their red blood cells, as opposed to 32% of those without heart attacks. EPA is an omega-3 fat that comes from fish, and is also made by the body if there's enough omega-3 alpha-linolenic acid (think flax and greens) around and not too much linoleic acid (industrial vegetable oil) to inhibit its production. 96% of heart attack patients were in the lowest category for alpha-linolenic acid, compared to 34% of the comparison group. 0% of the heart attack patients were in the highest category for alpha-linolenic acid.
62% of heart attack patients were in the highest category of arachidonic acid (AA), compared to 34% of the comparison group. AA is made from linoleic acid, and is also found in animal foods such as eggs and liver. Animal foods from pasture-raised animals are lower in AA than their conventionally-raised counterparts, and also contain more omega-3 fats to balance it.
The investigators found that low omega-3, high AA and high trans fats in red blood cells associate with heart attack risk far better than the Framingham risk score, a traditional and widely-used measure that incorporates age, sex, smoking status, total cholesterol, HDL, hypertension and diabetes.
If the associations in this study represent cause-and-effect, which I believe they do based on their consistency with other observational studies and controlled trials, they imply that we can have a very powerful effect on heart attack risk by taking a few simple steps:
- Avoid trans fat. It's found in margarine, shortening, refined soy and canola oils, many deep fried foods and processed foods in general.
- Avoid industrial vegetable oils and other sources of excess omega-6. Eating pastured or omega-3 eggs, rather than conventional eggs, can help reduce dietary AA as well.
- Ensure a regular intake of omega-3 fats from seafood, or small doses of high-vitamin cod liver oil or fish oil. Flax oil is also helpful, but it's an inferior substitute for fish oil.
In the future, I hope that most doctors will measure blood fatty acids to predict heart attack risk, with more success than current approaches. Instead of measuring cholesterol and prescribing a statin drug, doctors will prescribe fish oil and easy-to-follow diet advice**. Fortunately, some doctors are beginning to measure red blood cell fatty acid levels in their patients. The forward-thinking cardiologist Dr. William Davis has discussed this on his blog here. Take a good look at the graphs he posted if you get the chance.
*The title of the study is misleading because it implies a prospective design, in which blood fatty acids would be measured and volunteers followed to see who develops heart disease at a later time point. This study was cross-sectional (also called case-control), meaning they found people who had just had a heart attack and measured their blood fatty acids retrospectively. The other study I referenced above was prospective, which is a nice confirmation of the principle.
**"Eat butter on your toast. Ditch the margarine."