Can Iron Supplements Make You Gain Weight?

Iron deficiency is one of the most common nutrient deficiencies in the U.S. While it's typically found in people who menstruate or are pregnant, per the American Society of Hematology, anyone can have trouble absorbing iron, especially if they have certain medical conditions.

The symptoms of iron deficiency include fatigue, restless legs, pale skin, brittle nails, inflamed or sore tongue, cold hands and feet, headaches and lightheadedness, per the Mayo Clinic.

But why is iron important? It's a mineral your body needs to grow and develop, to make healthy red blood cells and to make certain hormones, per the National Institutes of Health (NIH).

If you have low iron, then, your doctor may recommend taking an iron supplement.

Anecdotally, weight gain may be a side effect of iron supplementation for some people. But it's more likely that iron deficiency itself is causing your weight gain. Read on to learn more.

There are no reputable sources that link iron tablets with weight gain. In fact, it's not even listed as a rare side effect.

A common side effect of iron supplements, though, is constipation, according to the National Library of Medicine (NLM), which may make you ‌feel‌ like you've gained weight if you're also bloated (which often accompanies constipation) and your clothes feel tighter than usual.

In general, anecdotal reports of people who claim their iron supplements cause weight gain aren't supported by much scientific research.

That said, one small April 2016 study in the ‌Egyptian Journal of Haematology‌ reported an interesting finding in regards to iron pills and weight gain. Thirty-three patients on iron therapy were observed for three months, during which time 30 patients gained weight.

In the three who did not gain weight, no increase in hemoglobin — the iron-rich protein that carries oxygen in the blood, per Mount Sinai — was observed. The rest of the patients gained weight, and the amount of weight gained was associated with the level of increase in hemoglobin.

This was just one small study, though, and much more research needs to be done to support this possible connection.

Weight gain is more likely to be a side effect of iron-deficiency anemia itself than the supplement used to treat it. Sufficient iron is needed to activate the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine), which are involved in metabolism, per an April 2019 report in the ‌Journal of the Endocrine Society.‌

Low levels of thyroid hormone due to iron deficiency — or another reason — can also cause stubborn weight gain that may persist until your blood levels are back to normal, per NHS Inform.

Some of the side effects of iron deficiency could also make it hard for you to maintain your weight. Fatigue, weakness and lightheadedness can make it difficult to exercise, which is an important component of managing your weight. It can also make it harder to prepare nutritious meals and avoid food cravings, because tiredness can increase food cravings, per the Cleveland Clinic.

If you noticed weight gain before starting supplementation and you continue to gain weight, watch your symptoms. If you're still feeling fatigue and weakness, then your iron blood levels may not be high enough yet.

It's not likely that your iron supplements are causing weight gain, but if you think they are, talk to your doctor. They can help figure out the underlying cause and come up with treatment options.

As you continue to take iron pills, you should start to notice your energy levels increasing, too. This means you may have more energy to exercise and make yourself nutritious meals, which can help you lose weight or maintain a healthy weight.

While taking iron supplements, aim to get at least 150 minutes of moderate-intensity exercise each week, like brisk walking, jogging or swimming, per the Centers for Disease Control and Prevention (CDC). If you're looking to lose weight gained from anemia, you may need to increase this daily amount.

The CDC also recommends doing strength-training activity two days a week to build muscle, which will help you burn body fat.

Additionally, try to eat mostly whole foods like fresh fruits and vegetables, lean protein, whole grains, low-fat dairy, healthy oils — such as olive oil — and nuts and seeds. These nutrient-rich foods can help you lose weight and help you keep your vitamin and mineral levels in a healthy range.

Iron-deficiency anemia is more likely to cause weight gain than iron pills or supplements.

Though, if you think your iron pills are causing you to gain weight (or you feel you're gaining weight for no reason), talk to your doctor.

Plus, if you're feeling symptoms like fatigue, lightheadedness, weakness or a sore tongue, ask your doctor about getting blood work done to see if you're iron-deficient, which can help determine whether you should take iron supplements in the first place.