Guide · Oct 13, 2026
Brazil Nuts and Selenium: How Many Brazil Nuts a Day Is Safe?
How much selenium is in one Brazil nut, how many fit under the 400 mcg upper limit, and what the big SELECT trial found about selenium and prostate cancer.
By Michael Gonzales · Last updated
By Michael Gonzales · Last updated October 13, 2026
Short answer: One or two Brazil nuts a day is plenty for most adults. A single nut has roughly 68 to 91 mcg of selenium according to NIH, more than the 55 mcg adults need in a day [1]. The adult upper limit is 400 mcg a day from all sources, so a daily handful of six or more can put you over it [1].
Brazil nuts are the richest food source of selenium by a wide margin. That makes them handy, and also easy to overdo. Here's how the numbers work out, why one nut can differ so much from the next, and what the research on selenium and the prostate found.
How many Brazil nuts a day?
| Serving | Weight | Selenium (USDA average) | vs. adult RDA (55 mcg) | vs. upper limit (400 mcg) |
|---|---|---|---|---|
| 1 nut | 5 g | 96 mcg | 174% | 24% |
| 2 nuts | 10 g | 192 mcg | 349% | 48% |
| 3 nuts | 15 g | 288 mcg | 523% | 72% |
| 1 ounce (about 6 nuts) | 28 g | 543 mcg | 988% | 136% |
Source: USDA FoodData Central SR Legacy, "Nuts, brazilnuts, dried, unblanched," 1,917 mcg selenium per 100 g, with USDA's 5 g per kernel and 28.35 g per ounce [2].
In practice:
- 1 nut a day covers the RDA with room to spare.
- 2 nuts a day is still under half the upper limit for most nuts.
- 3 or more every day starts to crowd the limit once you add selenium from bread, eggs, meat, fish and any multivitamin.
- An occasional handful isn't a problem. The upper limit is about long-term daily intake.
Why one nut can be very different from the next
Brazil nut trees take up selenium from the soil, and soil selenium varies hugely across the Amazon. NIH notes that selenium in plant foods varies widely by location, and that Brazil nut values from different analyses vary widely too [5]. That's why the USDA average (about 96 mcg per nut) sits a little above NIH's 68 to 91 mcg range. The label can't tell you which end of the range your bag is on, which is one more reason to keep it to one or two.
What happens if you eat too many?
Getting too much selenium over time is called selenosis. NIH lists signs such as a garlic smell on the breath, a metallic taste in the mouth, hair and nail loss or brittleness, skin rashes, nausea, diarrhea, fatigue, irritability and nervous system problems [1][5]. Very large amounts can be serious.
The U.S. upper limit for adults is 400 mcg a day [1]. In 2023 the European Food Safety Authority set a lower limit of 255 mcg [1]. By that measure, three average nuts a day is already over.
Brazil nuts vs. selenium pills
Most people in the United States get enough selenium, according to NIH [5], so most people don't need either. If you're choosing:
- A nut comes with fat, fiber, magnesium and other nutrients. A pill doesn't.
- A pill gives a known dose. A nut doesn't, because of the soil issue above.
- Doubling up is the real risk: a Brazil nut habit plus a multivitamin plus a "men's health" supplement can add up fast. Check labels.
Selenium and the prostate: what the SELECT trial found
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) gave more than 35,000 men selenium, vitamin E, both, or a placebo. Selenium supplements did not lower prostate cancer risk [3]. Longer follow-up found that vitamin E supplements were linked to a higher risk [4]. The takeaway: a nutrient that sounds protective in theory may not be, and more is not better.
Brazil nuts and the thyroid
Your thyroid needs selenium to make its hormones [1]. But NIH says a few studies found selenium supplements don't do much for the thyroid, and more research is needed on selenium and thyroid disease [1]. If you have a thyroid condition, talk to your doctor rather than adding Brazil nuts for it.
How to eat and store them
- Chop one into oatmeal or yogurt, or onto a salad.
- Keep them in a mixed-nut jar so you're not eating them by the handful.
- Store them cold. Their oils go rancid fast. Keep them in a sealed jar in the fridge for a few months, or the freezer for longer.
- Toss any that taste bitter or smell off.
Forest Up raw, unsalted Brazil nuts are one option.
For other ways to get selenium, see foods high in selenium. For zinc and magnesium, see pumpkin seeds nutrition.
Sources
- NIH Office of Dietary Supplements. Selenium: Fact Sheet for Consumers. https://ods.od.nih.gov/factsheets/Selenium-Consumer/
- U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, SR Legacy (2018). https://fdc.nal.usda.gov/
- Lippman SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39-51. https://pubmed.ncbi.nlm.nih.gov/19066370/
- Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: SELECT. JAMA. 2011;306(14):1549-56. https://pubmed.ncbi.nlm.nih.gov/21990298/
- NIH Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/
ProstateFoods writes about food, not treatment. Nothing here is medical advice or a claim that any food treats, cures or prevents a disease. Talk to your doctor before changing how you eat, especially if you take medication or have a health condition. See our medical disclaimer. Photo: Bertholletia excelsa seeds closeup by רנדום, CC BY-SA 3.0, via Wikimedia Commons.
Frequently asked questions
Can I eat 1 Brazil nut daily?
Yes, for most adults one Brazil nut a day is a reasonable amount. NIH puts a single nut at about 68 to 91 mcg of selenium, which covers the 55 mcg adult RDA and stays well under the 400 mcg upper limit. Count any selenium in your multivitamin or other supplements too.
How many Brazil nuts a day is safe?
For most adults, one or two. Each nut can have about 68 to 91 mcg of selenium, and the U.S. upper limit is 400 mcg a day from all sources. Europe's 2023 limit is lower, at 255 mcg. A daily handful of six or more can put you over either one.
Is there a downside to eating Brazil nuts?
The main downside is too much selenium. Eaten by the handful every day, Brazil nuts can push you past the upper limit, and over time that can cause garlic breath, a metallic taste, brittle nails, hair loss and other problems. They're also high in calories, and their oils go rancid if stored warm.
Are Brazil nuts good for your thyroid?
Your thyroid needs selenium to make hormones, and Brazil nuts are a rich source. But NIH says a few studies found selenium supplements don't do much for the thyroid, and more research is needed. If you have a thyroid condition, ask your doctor before adding Brazil nuts or selenium for it.
How should I eat Brazil nuts?
Eat one or two at a time, plain or chopped into oatmeal, yogurt or a salad. Keep them in the fridge or freezer in a sealed jar, because their oils spoil quickly at room temperature. Throw out any that taste bitter or smell off.
Does selenium prevent prostate cancer?
That hasn't been shown. The large SELECT trial gave over 35,000 men selenium, vitamin E, both, or a placebo, and selenium supplements did not lower prostate cancer risk. Later follow-up linked vitamin E supplements to a higher risk.
Written by
Michael Gonzales
Founder & Editor
Michael Gonzales is the founder of Cloudalien Technologies LLC, the company that owns ProstateFoods, and he edits every page on the site. ProstateFoods publishes everyday recipes, food lists and grocery guides for men who want to eat well. Michael is not a doctor or registered dietitian, so nothing on ProstateFoods is medical advice.