Three major studies involving hundreds of thousands of subjects—the Harvard Nurses’ Health Study and Health Professionals Follow-Up Study, and the largest study in history on diet and health, co-sponsored by the National Institutes of Health and AARP—found similar results: Meat consumption was associated with increased risk of dying from cancer, dying from heart disease, and dying prematurely in general. This conclusion was reached after controlling for diet and other lifestyle factors such as smoking, exercising, or failing to eat enough fruits and veggies, suggesting there may be something harmful in meat itself.
What does meat contain that may raise risk of premature death? One possibility is heme iron, the form of iron found predominantly in blood and muscle. Because iron can generate cancer-causing free radicals by acting as a pro-oxidant, iron is like a double-edged sword—too little of it and you risk anemia, too much and you may increase cancer and heart disease risk.
Our body has no specific mechanism to rid itself of excess iron. If we don’t have enough, our intestines begin boosting iron absorption; if we have too much, absorption is decreased. But this system only works effectively with the non-heme iron found predominantly in plant foods. Once a sufficient amount of iron is in our blood, our body is about five times more effective at blocking absorption of excess iron from plant foods than from animal foods. This may be why heme iron is associated with cancer and heart disease risk, and higher risk of diabetes, but non-heme iron is not.
Compared with people who eat meat, vegetarians tend to consume more iron (and more of most nutrients), but since the iron in plants is not absorbed as efficiently as the heme iron in meat, about 1 in 30 U.S. menstruating women may lose more iron than they take in, which can lead to anemia. Women who eat plant-based diets don’t appear to have higher iron deficiency anemia rates than women eating a lot of meat, but all women of childbearing age should ensure adequate iron intake.
Those diagnosed with iron deficiency should talk with their doctors about first trying to treat it with diet, as iron supplements have been shown to increase oxidative stress. The healthiest iron sources are whole grains, legumes, nuts, seeds, dried fruits, and green, leafy vegetables, which can be paired at the same meal with vitamin C-rich foods such as citrus, bell peppers, broccoli, and tropical fruits to boost iron absorption.
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