I always cringe when I read something on the lines of "I refuse to deprive my body of something it needs, so I take iron supplements." I personally have a disease called hereditary hemochromatosis. My body is extremely efficient at extracting iron from food. Before I started getting treatment for having too much iron, I developed heart disease, joint disease, chronic migraine headaches, chronic bacterial and fungal infections, and diabetes, all of them related to iron overload. Oh, and I'm overweight, too.
There really are people who, totally unlike me, need more iron, not less. One group of people who need more iron is people who have iron-deficiency anemia. The only way you can know you have iron-deficiency anemia is to have a blood test, or actually several blood tests.
If you have anemia, you will have abnormalities in your red blood cells.
They will be too small, that is, mean-corpuscular volume or MCV will be low. They won't have enough hemoglobin, the iron-based protein that carries oxygen through the bloodstream. The mean corpuscular hemoglobin concentration or MCHC will also be low.
Anemia isn't always caused by low iron levels. If you have MCV and low MCHC, then the doctor looks for total serum iron and serum ferritin, ferritin being a protein that "binds" iron until it is used to make hemoglobin. If MCV, MCHC, and total iron are all low, then you probably have anemia. Your ferritin levels may or may not be low, since ferritin levels go up when you have inflammation. Only when all of these tests agree is it a good idea to take iron for anemia. Even when you aren't getting "enough" iron in your diet, if you still have enough iron in your body, you aren't anemic and you don't need iron, at least not yet. Taking iron you don't need can cause all the problems I mentioned in the first paragraph.
Really severe iron-deficiency anemia is almost always associated with being too thin. Iron deficiency causes changes in mucous membranes. The membrane at the bottom of the esophagus can become "webbed," so it is hard to swallow food. The villi in the small intestine, which are tiny receptacles for nutrients, can flatten out. If you don't have enough iron, you can't absorb other nutrients, either.
On the other hand, getting too much iron can cause the opposite problem. Too much iron interferes with the body's ability to respond to insulin for storing sugar, but doesn't interfere with the body's ability to respond to insulin for storing fat. Before iron overload causes full-blown diabetes, it forces the pancreas to make more and more insulin to transport less and less glucose. However, while it's moving less and less glucose, the body is also storing more and more fat.
In theory, you could diet and avoid weight gain even if your iron levels are high. However, there are a lot of things going on when your iron levels go up.
One is increased susceptibility to infections. You need iron, but bacteria need iron, too. Certain gastrointestinal "bugs" thrive on excess iron, as do bacteria that cause urinary tract infections (UTIs). The effect can be extreme. In the 1970's, a well-intentioned missionary group handed out iron pills to "anemic" children in Tanzania. Hundreds then died of malaria. In the early 2000's, researchers tried the same experiment once again, this time recruiting over 24,000 children. They stopped the study when they found that children who were given iron supplements were 15% more likely to die of infections.
Another thing that is going on with high iron levels is changes in thyroid hormone production. (This explanation is not what you will find in most articles on losing weight and iron levels, because they get it wrong.) Iron accumulates in the hypothalamus, the "master gland" in the brain. The hypothalamus sends thyroid-stimulating hormone (TSH) to the thyroid. When the thyroid does not get enough TSH, even when TSH levels are still "low normal," the body does not burn sugars as efficiently. The metabolism slows down and it becomes harder and harder to lose weight with exercise, and easier and easier to put on weight by eating too much. This is, however, a long-term effect. It takes years, not months or weeks.
Once you are overweight, your liver makes less of a hormone called hepcidin, which helps your body absorb iron. Your body absorbs less iron from your food, and this makes it harder for your body to use the thyroid hormone it makes. (It is already making less because of high iron. In effect, this helps it lower iron.) The solution to this problem isn't to take more iron. It's to eat less. If you take iron because you're overweight, your overweight can get worse. If you take iron because you need iron, then your weight can normalize. It would be nice if all you needed to do to lose weight was to take iron supplements, but it doesn't actually work that way.
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