Do Brazil nuts boost testosterone?

There is no evidence that they do. We found no study of any kind that gave people Brazil nuts and measured testosterone or any other male hormone. The idea rests on selenium, which Brazil nuts carry in large amounts. In the one placebo-controlled trial in healthy men that measured it, 36 men took 247 mcg of selenium a day for 9 months, their blood selenium doubled, and their testosterone did not change.

Myth. Selenium, the reason the claim exists, was tested on testosterone in healthy men and left it unchanged. That trial was a small pilot and used selenium yeast rather than nuts, so it is not the last word. It is the only direct test there is, and it came out flat.

Selenium, micrograms a day

The trial dose came from selenium yeast, not from nuts. The Brazil nut figure is an average, and the selenium content of the nuts depends on the soil they grew in, so a given bag can sit well above or below it. Sources: cards ev-bnt-01, ev-bnt-09 and ev-bnt-10 below.

What the trials found

The testosterone trial ran for 12 months. Men aged 19 to 43 took selenium-enriched yeast for 9 months and then placebo for 3, against a group on placebo throughout. Plasma selenium was twice as high at 3 and 9 months. Testosterone, dihydrotestosterone and the ratio between them did not change in either group.

Most selenium research in men is about sperm rather than hormones, and it is mixed. A meta-analysis of 50 placebo-controlled trials in infertile men found no convincing evidence that any supplement helps male infertility. It reported better sperm motility with selenium, carnitine and coenzyme Q10 only on low or very low certainty evidence, and no supplement improved pregnancy or live birth. A network meta-analysis of 29 trials in 2,045 subfertile men ranked vitamin E with selenium, or zinc, highest for sperm motility, which is a ranking and not a measure of how much. A US trial in 174 men with male factor infertility found a daily antioxidant pill containing 200 mcg of selenium did not improve sperm motility, shape or DNA damage after 3 months.

Nuts as a food have a little more behind them, and none of it involves Brazil nuts. A meta-analysis of 2 randomized trials in 223 healthy men found that at least 2.1 oz (60 g) of nuts a day improved sperm motility, vitality and shape, with no change in sperm concentration. One of those trials, FERTINUTS, gave 119 healthy men aged 18 to 35 a 60 g daily mix of nuts for 14 weeks, and the mix did not include Brazil nuts. Sperm quality is not testosterone, and testosterone was not the main outcome of that trial.

Unsettled. Whether a handful of nuts does anything for male hormones is open, and the reason is that nobody has measured it properly. The only hormone data on nuts comes from US survey data on 2,699 women, where tree nut eaters had higher SHBG, a protein that binds sex hormones in the blood, and no difference in testosterone. That is observational, in women, and cannot answer a question about men.

Who should be careful

The real issue with Brazil nuts is too much selenium. The NIH puts Brazil nuts at an average of 544 mcg of selenium per ounce, which is more than the adult upper limit of 400 mcg a day, and values from other analyses vary widely. The upper limit covers food and supplements together. For children it is lower, from 45 mcg depending on age. Signs of too much selenium include hair loss, brittle nails, rash, nausea, diarrhea and fatigue.

More selenium is not better in people who already have enough. In a randomized trial in 55 women with obesity in Sao Paulo, none of them short of selenium, one Brazil nut a day for 2 months raised every selenium marker and also raised the activity of several inflammation genes. Blood markers of inflammation did not change, so this is a signal in gene expression and not a measured harm.

Tree nut allergy is the other caution. A systematic review of 36 studies found allergy confirmed by a food challenge in under 2 percent of people, though only seven of the studies used a challenge.

Not for everyone. A handful of Brazil nuts a day, or Brazil nuts on top of a selenium or multivitamin supplement, can take an adult past the upper limit. Children reach their limit on far less. Anyone with a tree nut allergy should avoid them.

What expert bodies say

We found no expert body position on Brazil nuts and testosterone. The NIH Office of Dietary Supplements says trials of selenium supplements on sperm quality conflict, and that there is not enough data to say whether selenium supplements significantly affect male fertility. Its fact sheet does not address testosterone. It sets the adult upper limit for selenium at 400 mcg a day.

How we searched

Searched: a local copy of PubMed, across all study types, for selenium or Brazil nut with testosterone, androgens, sperm, semen or male fertility, which returned 114 records. Brazil nuts alone returned 62, and none of those studies measured a hormone. Selenium with testosterone returned 40, mostly about women with polycystic ovary syndrome, the prostate or animals. Nuts with sperm, semen or testosterone returned 13. We also searched the NIH selenium fact sheet, ClinicalTrials.gov, which lists no Brazil nut trial, the open web and the retraction database. Search run on 7 October 2026.

Included: one placebo trial of selenium and testosterone, three meta-analyses and two trials on supplements or nuts and sperm, and one survey analysis of nuts and hormones in women. For safety, one trial of a Brazil nut a day, one review of tree nut allergy and three sections of the NIH selenium fact sheet. None of the included papers is retracted.

Excluded: a 2009 trial reporting that selenium with N-acetylcysteine raised testosterone, because it carries an expression of concern from 2023. Studies of selenium in women with polycystic ovary syndrome, which ask a different question. Studies in dogs, goats and mice. A study of other trace elements in Brazil nuts. Supplement blogs.

What we read: abstracts for the papers and the relevant sections of the NIH fact sheet.

What we could not get: any study of Brazil nuts and testosterone or any male hormone, because none exists that we could find. Any agency position on the question. The full texts of the papers.

What would change this answer

A controlled trial of 1 to 3 Brazil nuts a day in men with low selenium status that measures total and free testosterone. We found no such trial registered.
A meta-analysis pooling the testosterone results of selenium trials in men. We found none.

More on the nut itself is on the Brazil nuts page, and the nutrient behind the claim has its own selenium guide.

The food behind this question

Brazil nuts: the one food where a handful can be too much — numbers, evidence and safety

The same question for other foods (testosterone)

Sources

ev-bnt-01 · Randomized controlled trial(s) · double-blind randomized placebo-controlled pilot trial, 12 months · n = 36
No changes were observed in either group for plasma T, dihydrotestosterone (DHT) or DHT:T ratios, suggesting that selenium had no effect on the alpha-reductase involved in the conversion of T to DHT.
Who: healthy adult males aged 19-43 years, selenium-enriched yeast 247 mcg/day for 9 months then placebo for 3 months
Effect: plasma selenium 2-fold higher at 3 and 9 months; no change in plasma testosterone, DHT or DHT:T in either group
Certainty: Small pilot; selenium yeast, not Brazil nuts.
Cancer Epidemiol Biomarkers Prev, 2002 · checked 2026-10-07 · we read the abstract
ev-bnt-02 · Position of an expert body · agency fact sheet · n = —
There is currently not enough data to determine whether selenium supplements significantly affect male fertility.
Who: men; NIH Office of Dietary Supplements selenium fact sheet, male fertility section
Effect: conflicting trials; no conclusion on male fertility
Certainty: About supplements and fertility; the sheet does not address testosterone.
NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
ev-bnt-03 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 50 studies
This study found no convincing evidence of an effect of any dietary supplements on male infertility.
Who: men with infertility in placebo-controlled RCTs of at least 12 weeks
Effect: selenium, carnitine and CoQ10 improved motility; no effect on pregnancy or live birth; certainty low or very low
Certainty: Most trials at some concern or high risk of bias; testosterone not an outcome.
Nutrients, 2025 · checked 2026-10-07 · we read the abstract
ev-bnt-04 · Meta-analysis or systematic review · network meta-analysis of randomized controlled trials · n = 2045
Vitamin E+selenium or zinc had the highest SUCRA for total motility.
Who: men with idiopathic oligo-astheno-teratozoospermia, mean age 33.5 years, 19 antioxidant preparations
Effect: vitamin E + selenium or zinc: highest SUCRA for total motility; L-carnitine highest for concentration and morphology
Certainty: Ranking, not effect size; supplements, not food; sperm, not testosterone.
Andrology, 2024 · checked 2026-10-07 · we read the abstract
ev-bnt-05 · Randomized controlled trial(s) · multicentre double-blind randomized placebo-controlled trial · n = 174
However, there were no statistically significant differences between the two groups for changes in sperm morphology, motility, or DNA fragmentation.
Who: men with low sperm concentration, motility or morphology or high DNA fragmentation; daily vitamin C, E, 0.20 mg selenium, L-carnitine, zinc, folic acid, lycopene vs placebo
Effect: no significant differences vs placebo in morphology, motility or DNA fragmentation at 3 months
Certainty: Combination product; cannot isolate selenium.
Fertil Steril, 2020 · checked 2026-10-07 · we read the abstract
ev-bnt-06 · Meta-analysis or systematic review · systematic review and meta-analysis · n = 223
Meta-analysis of 2 RCTs involving 223 healthy males indicated consumption of ≥ 60g nuts/d increased sperm motility, vitality, and morphology in comparison to controls but had no effect on sperm concentration.
Who: healthy males of reproductive age on a Western-style diet, nuts for at least 3 months
Effect: motility, vitality and morphology improved vs control; sperm concentration unchanged
Certainty: Only 2 RCTs; mixed nuts and walnuts, not Brazil nuts; hormones not pooled.
Adv Nutr, 2024 · checked 2026-10-07 · we read the abstract
ev-bnt-07 · Randomized controlled trial(s) · randomized controlled parallel trial, 14 weeks · n = 119
Compared with the control group, improvements in total sperm count (P = 0.002) and vitality (P = 0.003), total motility (P = 0.006), progressive motility (P = 0.036), and morphology of sperm (P = 0.008) were observed in the nut group.
Who: healthy men aged 18-35 years on a Western-style diet, 60 g/day mixed nuts vs no nuts, 14 weeks
Effect: total sperm count P = 0.002, vitality P = 0.003, total motility P = 0.006, morphology P = 0.008 vs control
Certainty: Nut mix did not include Brazil nuts; testosterone not a primary outcome.
Am J Clin Nutr, 2018 · checked 2026-10-07 · we read the abstract
ev-bnt-08 · Observational data · cross-sectional analysis of national survey data · n = 2699
Tree nut consumption was positively associated with circulating SHBG (β = 0.041, P = .018) but not testosterone nor estradiol after adjustment for all tested confounders.
Who: adult women in NHANES 2013-2016; tree nut consumers on either of two 24-hour recalls
Effect: SHBG beta = 0.041 (P = .018); no association with testosterone or estradiol after adjustment
Certainty: Women only; tree nuts as a group; single-day recalls.
Nutr Res, 2021 · checked 2026-10-07 · we read the abstract
ev-bnt-09 · Position of an expert body · agency fact sheet · n = —
The Tolerable Upper Intake Level for selenium is 400 mcg for adults, and it ranges from 45 mcg to 400 mcg for infants, children, and adolescents, depending on age.
Who: adults; children and adolescents 45 to 400 mcg depending on age
Effect: UL 400 mcg/day adults; selenosis signs: hair loss, nail brittleness, rash, nausea, diarrhea, fatigue
Certainty: UL covers food and supplements together.
NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
ev-bnt-10 · Position of an expert body · agency fact sheet · n = —
For example, according to FoodData Central from the U.S. Department of Agriculture (USDA), Brazil nuts have an average of 544 mcg selenium/ounce, but values from other analyses vary widely [16-18].
Who: Brazil nuts; NIH ODS citing USDA FoodData Central
Effect: average 544 mcg selenium per ounce (28 g); values from other analyses vary widely
Certainty: Soil selenium drives large variation between batches.
NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
ev-bnt-11 · Randomized controlled trial(s) · randomized controlled trial, 2 months · n = 55
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 after the intervention period.
Who: women with obesity in Sao Paulo, not selenium deficient at baseline; 1 Brazil nut/day vs no intervention, 2 months
Effect: all selenium biomarkers up; IL-6, TNF-alpha, TLR2 and TLR4 gene expression up; plasma inflammatory markers unchanged
Certainty: Gene expression only; unblinded no-intervention control.
Nutrition, 2019 · checked 2026-10-07 · we read the abstract
ev-bnt-12 · Observational data · systematic review of prevalence studies · n = 36 studies
Challenge-confirmed IgE-mediated tree nut allergy prevalence was less than 2 % (although only seven studies used this gold standard) while probable tree nut allergy prevalence ranged from 0.05 to 4.9 %.
Who: children and adults in population studies, mostly Europe, UK and USA, 1996-2014
Effect: challenge-confirmed tree nut allergy <2%; probable 0.05 to 4.9%
Certainty: Only 7 studies used food challenge.
Curr Allergy Asthma Rep, 2015 · checked 2026-10-07 · we read the abstract

How this page was made. Evidence was extracted from primary sources into cards, every number was re-checked against the source, and the text was written from those cards. Bioma Learn has no human medical reviewer at this time, and we say so rather than invent one. Methodology. This is information, not medical advice.