Brazil nuts are by far the richest nut source of selenium, packing 68 to 91 mcg in a single nut and about 544 mcg per ounce. That one nut alone can deliver more than the full daily requirement for an adult (55 mcg). Other nuts contain selenium too, but in dramatically smaller amounts. Cashews come in a distant second, followed by peanuts and walnuts, with almonds trailing far behind.
Brazil Nuts: The Standout Source
No other food comes close to Brazil nuts for selenium density. At 544 mcg per ounce (roughly six nuts), a single serving can contain nearly 10 times the recommended daily intake. This makes Brazil nuts both incredibly useful and something to be cautious about.
The selenium content in Brazil nuts varies enormously depending on where the trees grow. Nuts from the Amazonas state of Brazil can contain over 30 times more selenium than those from Mato Grosso state, because the soil in Amazonian regions is naturally richer in selenium. A single nut from a high-selenium region could supply nearly three times your daily requirement, while one from a low-selenium area might only cover about 11%. You have no way of knowing which type you’re buying, so it’s smart to treat every Brazil nut as if it’s a high-selenium one.
How Other Nuts Compare
After Brazil nuts, the drop-off is steep. A large-scale analysis of mineral content across nut varieties found that Brazil nuts contain about 12 times more selenium than cashews and 121 times more than almonds. Here’s how the most common nuts rank:
- Cashews: The second-best nut source, with a median of about 354 mcg per kilogram. In practical terms, an ounce of cashews provides a modest but meaningful amount of selenium.
- Peanuts: A median of roughly 164 mcg per kilogram. A full cup of dry-roasted peanuts delivers about 14 mcg, which covers roughly a quarter of daily needs.
- Walnuts: Similar to peanuts, with a median around 151 mcg per kilogram.
- Almonds: The lowest among common nuts at just 37 mcg per kilogram. A cup of dry-roasted almonds contains only about 3 mcg of selenium, making them a negligible source.
If you’re eating a mixed nut snack, the selenium you get will depend heavily on whether Brazil nuts or cashews are in the mix. A handful of almonds or walnuts alone won’t move the needle much.
Why Selenium Matters
Selenium is a trace mineral your body needs in small amounts for several critical functions. It plays a key role in thyroid hormone production, helping convert the inactive form of thyroid hormone into its active form. It also supports your body’s antioxidant defenses and immune function. Most adults need about 55 mcg per day, an amount easily met through a varied diet that includes seafood, meat, eggs, or even one Brazil nut.
The Risk of Getting Too Much
Because Brazil nuts are so selenium-dense, overconsumption is a real concern. The tolerable upper limit for selenium is 400 mcg per day. A standard recommended serving of Brazil nuts is about 30 grams (six nuts), but researchers have found that this serving size can deliver between 840 and 1,470 mcg of selenium depending on the batch. That’s two to nearly four times the safe upper limit in a single handful.
Chronic selenium excess, called selenosis, causes brittle or discolored nails, hair loss, and eventually loss of nails and hair entirely. Acute overexposure brings nausea, diarrhea, skin rash, fatigue, irritability, and nervous system problems. Toxicity has been estimated to begin around 1,200 mcg per day with sustained intake.
Researchers have recommended limiting Brazil nut consumption to about three nuts (15 grams) per sitting to stay within safe limits, since there’s no reliable way to tell how much selenium any given batch contains. One to two Brazil nuts per day is a common practical guideline for people using them as a selenium supplement.
Practical Approach to Selenium From Nuts
If your goal is to boost selenium intake through nuts, Brazil nuts are the only variety that makes a significant difference on their own. Eating one or two daily is enough to meet or exceed your requirement without risking overexposure. Treat them like a supplement rather than a snack you eat by the handful.
Cashews and peanuts contribute smaller amounts that add up over time, especially as part of a broader diet that includes other selenium sources like fish, poultry, and eggs. Almonds and walnuts are nutritional powerhouses for other reasons (healthy fats, magnesium, vitamin E), but they’re not worth counting on for selenium.