When trying to lose weight, it can be tempting to look for supplements that can speed up the process.

Selenium is a mineral with many important jobs in your body, one of which is making thyroid hormones that help regulate your metabolism. Thus, it’s often touted as being helpful for weight loss (1).

Although it’s essential, you only need a tiny amount in your diet, and deficiency is uncommon (1).

This article explores if you may gain any benefits from taking selenium supplements and whether they might aid weight loss.

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Effectiveness for weight loss

Your thyroid contains high levels of selenium, which is used to make and metabolize thyroid hormones. These hormones regulate many metabolic functions in your body, including how many calories you burn (2).

Supplements

Selenium deficiency is linked with a higher risk of thyroid disease. Studies have shown that taking selenium supplements improves thyroid function in people with mild hypothyroid disease and autoimmune thyroid disease (2, 3).

The supplements may also benefit those with normal thyroid function.

In a small 12-week study in 37 adults with overweight, those who took a daily 240-mcg selenium supplement combined with a calorie-restricted diet lost more weight than a group who tried only the calorie restriction (4).

Those who took the daily supplement also lost more fat and had lower levels of leptin, which is a hormone that helps regulate fat storage (4).

The Recommended Dietary Allowance (RDA) — which is the average daily amount of a nutrient that meets most people’s daily needs — for selenium is 55 mcg per day. In North America, most people get more than this in their diet (1).

Selenium-containing foods

Selenium is a mineral that occurs naturally in soil and water. It’s transferred to plants and then throughout the food system. As such, it’s available in a wide variety of whole foods (1).

Good sources of selenium include (1, 5):

FoodAmount of selenium% of the Daily Value (DV)1 Brazil nut98 mcg1403 ounces (85 grams) yellowfin tuna92 mcg1673 ounces (85 grams) halibut47 mcg853 ounces (85 grams) chicken breast22 mcg401 cup (210 grams) low fat cottage cheese20 mcg361 cup (195 grams) brown rice19 mcg351 cup (198 grams) lentils6 mcg111 large egg15 mcg271 slice whole wheat bread13 mcg241 cup cooked oatmeal13 mcg24

Brazil nuts are an exceptional source of this nutrient. Eating just two a day can raise blood selenium levels more than taking a selenium supplement (6).

On the other hand, ultra-processed foods — those that are packaged, ready to eat, and have a long ingredients list — tend to be lower in selenium (7).

In a study of more than 3,200 people, those who consumed less selenium from their diet had a higher body mass index (BMI). Researchers also noted that every 0.45 mcg/pound/day (1 mcg/kg/day) increase in dietary selenium corresponded to a 3–6% decrease in body fat (8).

Because selenium is found in many foods, it’s possible to plan a diet that’s high in the nutrient. This may provide you with similar weight loss benefits as taking a supplement.

Summary

Your body needs selenium to make thyroid hormones that help regulate your metabolism. Most people aren’t deficient in this nutrient, but studies suggest that getting a bit more may help you lose body fat.

Risks

For selenium to work the best in your body, you shouldn’t get too little or too much. The safe upper limit for the mineral is set at 400 mcg per day (1).

If you frequently take a high dose selenium supplement on top of a selenium-rich diet, you might risk toxicity. In severe cases, this can cause kidney or heart failure (1, 2).

Symptoms that you’re getting too much selenium include hair and nail loss, nail brittleness, a metallic taste in your mouth, and a garlic odor on your breath. It can also cause nausea, vomiting, and diarrhea (1, 2).

Selenium poisoning from taking a mislabeled supplement has been reported. In 2008, a product labeled as containing 200 mcg of selenium per ounce (30 mL) was found to contain 200 times that (9).

Note that supplements, including selenium supplements, are not regulated by the Food and Drug Administration (FDA). If you are interested in trying a selenium supplement, look for one that has been analyzed or verified by an independent lab.

The most common symptoms reported after using the product for less than a month were diarrhea, fatigue, hair loss, and joint pain. Of the people who reported hair loss, 18% lost all the hair on their head (9).

Summary

It’s possible and even dangerous to get too much selenium from supplements. At levels over 400 mcg per day, you might experience symptoms like a garlic odor on your breath, brittle nails, diarrhea, hair loss, fatigue, and joint pain.

Dosing

Before taking a selenium supplement, you can first try to optimize your diet to include more of the nutrient.

If opting for a stand-alone selenium supplement, make sure to check that the nutrient isn’t added to any other supplements you’re taking. For example, it’s often added to multivitamin and mineral supplements (1).

According to older and newer research, selenium supplements are considered safe to take in regular doses, usually around 100–200 mcg per day (1, 2, 10).

If you prefer to go the diet route, eating two Brazil nuts each day provides the same amount. Since these nuts are also rich in other minerals and healthy fats, they may also provide other health benefits (5, 11).

Just keep in mind that since they’re so high in selenium, avoid eating more than five Brazil nuts, which contain about 400 mcg, in a day.

That being said, one study found no signs of selenium toxicity in people who regularly eat Brazil nuts and live in the Brazilian Amazon — even though their blood levels of the mineral were high (12).

Summary

Regular doses of selenium from supplements at up to 200 mcg per day are likely safe. You can get this same dose from eating two Brazil nuts.

The bottom line

The mineral selenium has many health benefits and is essential for healthy thyroid function. Among other things, your thyroid helps regulate your weight.

Studies suggest that taking a selenium supplement or getting more of the mineral from your diet might promote fat loss.

However, taking too much can have side effects like hair loss, brittle nails, or a garlic odor on your breath.

If you want to increase your selenium intake to promote weight loss, try adding high selenium foods like Brazil nuts and yellowfin tuna to your diet. If opting for a supplement, stick to one that provides no more than 200 mcg of selenium.