Transcript: The Safety of Heme vs. Non-heme Iron
It is commonly thought that those who eat plant-based diets may be more prone to iron deficiency, but it turns out that they’re no more likely to suffer from iron deficiency anemia than anybody else. This may be because not only do those eating meat-free diets tend to get more fiber, and magnesium, and vitamins like A, C, and E; they also get more iron. But the iron found in plants is non-heme iron. Those eating meat-free diets don’t get any of the heme iron found in blood and muscle, which may be a good thing. The avoidance of heme iron may be one of the key elements of plant-based protection against metabolic syndrome, and may also be beneficial in lowering heart disease risk.
The link between iron intake and coronary heart disease has been contentiously debated, but the inconsistency of the evidence may be because the majority of total dietary iron comes mostly from plants and so total iron intake is associated with lower heart disease risk. But if you just look at iron intake from meat, it’s associated with significantly higher risk for heart disease. This is thought to be because iron can act as a pro-oxidant contributing to the development of atherosclerosis by oxidizing cholesterol with free radicals. The risk has been quantified as a 27% increase in coronary heart disease risk for every one milligram of heme iron consumed daily.
The same has been found for stroke risk. The studies on iron intake and stroke have had conflicting results, but that may be because they had never separated out heme from non-heme iron, until this study, which found that the intake of heme iron–but not non-heme iron–was associated with an increased risk of stroke, as well as diabetes. Higher heme iron (animal iron) intake was significantly associated with greater risk for type 2 diabetes, but not total or non-heme iron (plant iron); 16% increase in risk for every daily milligram of heme iron consumed. And the same for cancer, with up to 12% increased risk for every milligram of daily heme iron exposure. In fact, you can actually tell how much meat someone is eating by looking at their tumors. To characterize the mechanisms underlying meat-related lung cancer development, they asked lung cancer patients how much meat they ate, and examined the gene expression patterns in their tumors, and identified a signature pattern of heme-related gene expression. Though they just looked at lung cancer, they expect these meat-related gene expression changes may occur in other cancers as well.
We do need to get enough iron. Only about 3% of premenopausal white women have iron deficiency anemia these days, but the rates are worse in African- and Mexican-Americans. Taking our leading killers into account—heart disease, cancer, diabetes—the healthiest source of iron appears to be non-heme iron, found naturally in abundance in whole grains, beans, split peas, chickpeas, and lentils, dark green leafy vegetables, dried fruits, and nuts and seeds. But how much money can be made on beans? So the industry came up with a blood-based crispbread, made out of rye and cattle and pig blood–one of the most concentrated sources of heme iron, about two thirds more than chicken blood. If blood-based crackers don’t sound appetizing, there’s always cow-blood cookies and blood-filled biscuits. The filling ends up a dark-colored, chocolate-flavored paste with a very pleasant taste; dark-colored because spray-dried pig blood can have a darkening effect on the food product’s color. But the worry is not the color or taste; it’s the heme iron, which, because of its potential cancer risk, is not considered safe to add to foods intended for the general population.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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