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Selasa, 27 Oktober 2009
Heart Attack Risk Reduction: The Low-Hanging Fruit
19.00 | 
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Dr. Yongsoon Park and colleagues recently published a great article in the British Journal of Nutrition titled "Erythrocyte fatty acid profiles can predict acute non-fatal myocardial infarction". Stated simply, the title says that the fat in your red blood cell membranes, which reflects dietary fat composition, can predict your likelihood of having a heart attack*. More accurately than standard measures of heart attack risk such as blood cholesterol.
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:
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."
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."
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