Brazil nuts: the one food where a handful can be too much

One Brazil nut holds 68 to 91 micrograms of selenium and the tolerable upper intake level for an adult is 400 micrograms a day. That arithmetic makes this one of the very few foods where a handful is genuinely too much. Our own records show why it is hard to be precise: two USDA entries for raw Brazil nuts differ sevenfold in selenium, because the nut takes up whatever the soil holds. In one trial a single nut supplied 1261 micrograms, three times the ceiling. Nobody can tell you what is in your packet, which is exactly why the advice is a small number of nuts rather than a weight.

What a real portion looks like

• One Brazil nut holds most of a day's selenium, and the safe ceiling is about four or five of them. — — Evidence E source
  The tolerable upper intake level for selenium is 400 mcg a day for adults, ranging from 45 to 400 mcg for infants, children and adolescents by age; Brazil nuts contain 68 to 91 mcg per nut and could cause selenium toxicity if eaten regularly; selenosis presents as hair loss and brittle nails, with garlic breath and a metallic taste as early signs

What your body absorbs

• As a way to top up selenium, Brazil nut butter worked exactly as well as a supplement pill. — 44 vegans and 42 omnivores (n = 86) Evidence B source
  Estimated selenium intake was lower in vegans and correlated with all three biomarkers; both the nut butter and the supplement raised serum selenium and selenoprotein P significantly with no change in placebo, and the two were equally effective; the selenoprotein P rise was larger in vegans

What cooking and storage change

• Defatted Brazil nut flour lowered cholesterol against its own baseline and not against the placebo. — 77 dyslipidaemic and hypertensive patients already taking lipid-lowering drugs (n = 77) Evidence B source
  The Brazil nut group showed falls in total cholesterol (-20.5 mg/dL, p = 0.02), non-HDL cholesterol (-19.5, p = 0.02) and apolipoprotein A-1 (-10.2, p = 0.03) without change in the ApoB to ApoA-1 ratio; the placebo group showed a fall in free T3 and a rise in lipoprotein(a); there were no statistical differences in blood pressure or serum lipids between the two groups

Safety, limits and interactions

• A single Brazil nut a day for two months raised inflammatory gene expression in women who already had enough selenium. — 55 women with obesity recruited at a clinical hospital in Sao Paulo, none selenium deficient at baseline (n = 55) Evidence B source
  All selenium biomarkers rose significantly in the nut group, together with gene expression of interleukin-6, tumour necrosis factor alpha and Toll-like receptors 2 and 4 (p<0.05)

What people believe that the data does not support

• The European nut heart-health claim names five nuts and specifically excludes the Brazil nut. — — Evidence E source
  The submitted claim covered peanuts and tree nuts (almonds, hazelnuts, pecans, pistachios and walnuts) while excluding Brazil, macadamia and cashew nuts, proposing that 30 g of nuts a day helps maintain heart health; its status is Non-authorised

Who this works differently for

• Six months of one nut a day in older adults with memory problems moved one antioxidant enzyme and little else. — 31 older adults with mild cognitive impairment, mean age 77.7, of whom 11 treated and 9 control completed (n = 31 enrolled, 20 completed) Evidence B source
  Selenium levels rose in the treated group with no change in controls; among antioxidant measures only erythrocyte glutathione peroxidase activity differed significantly between groups (p = 0.006); improvements in verbal measures were reported

The bottom line

More selenium is not better once you have enough. In 55 women with obesity and no deficiency, one nut a day for two months raised every selenium marker and also raised the expression of several inflammatory genes. For people who are short of selenium the nut works, and so does a pill: 55 micrograms a day as Brazil nut butter or as a supplement raised blood selenium equally in 86 vegans and omnivores. Selenosis, the condition caused by chronic excess, shows up as hair loss and brittle nails, with garlic breath and a metallic taste as the early signs. Europe has refused both health claims ever filed for Brazil nuts, and the nut industry's own heart-health dossier specifically excluded them.

Sources

1. brz-dr-01 · expert body fact sheet
   As discussed earlier, Brazil nuts contain very high amounts of selenium (68–91 mcg per nut) and could cause selenium toxicity if consumed regularly.
   NIH Office of Dietary Supplements, Selenium fact sheet for health professionals, знімок 2026-09-21 · checked 2026-09-22
2. brz-dr-03 · randomised controlled trial
   Independent of the dietary pattern (vegan or omnivore), Brazil nut butter as well as supplement significantly increased serum selenium and SELENOP concentrations, while there were no changes in the placebo groups.
   Eur J Nutr, 2025 · checked 2026-09-22
3. brz-dr-04 · randomised placebo-controlled double-blind trial
   There were no statistical differences in blood pressure and serum lipids between Brazil nut and placebo group.
   Nutr J, 2015 · checked 2026-09-22
4. brz-dr-02 · randomised controlled trial
   In the BN group, a significant increase (P < 0.05) in all Se biomarkers and in gene expression of several proinflammatory parameters (interleukin-6, tumor necrosis factor-α, and Toll-like receptors 2 and 4) were observed
   Nutrition, 2019 · checked 2026-09-22
5. brz-dr-06 · regulatory register entry
   POL-HC-7666 Nuts - peanuts and tree nuts (almonds, hazelnuts, pecans, pistachios and walnuts), excluding brazil, macadamia and cashew nuts Eating 30g of nuts per day as part of a balanced diet helps maintain heart health. Non-authorised
   EU Register on nutrition and health claims, заява POL-HC-7666, знімок 2026-09-21 · checked 2026-09-22
6. brz-dr-05 · randomised controlled pilot trial
   Among the parameters related to the antioxidant system, only erythrocyte GPx activity change was significantly different between the groups (p = 0.006).
   Eur J Nutr, 2016 · checked 2026-09-22