Brazil Nuts - Beneficial Foods

Table of Contents

1. Introduction
2. A Wild Harvest from Standing Forest
3. The Tree, Its Bees and the Agouti
4. Nutritional Profile
5. Selenium per Nut: Why the Numbers Swing So Widely
6. Selenium and the Thyroid
7. Selenium Status and Antioxidant Enzymes
8. Cholesterol and Inflammation
9. Brain Aging and Cognition
10. A Selenium Tablet Is Not a Brazil Nut
11. Buying, Storing and the Aflatoxin Findings
12. Amounts Used in the Studies
13. Who the Research Raises Cautions For
14. Connections
15. Key Research Papers
16. Featured Videos

Introduction

The Brazil nut is the seed of Bertholletia excelsa, a large tree of the Amazon rainforest. Among everyday foods it is famous for one thing above all: selenium. A single kernel can carry more selenium than an adult's whole daily requirement, and in some batches far more. That one fact explains almost everything about how Brazil nuts are studied. Most of the research on them is really research on selenium delivered in a nut.

Selenium is a trace mineral, needed only in micrograms (millionths of a gram). The body builds it into a family of proteins called selenoproteins. They include the glutathione peroxidases, enzymes that break down damaging peroxides, and the deiodinases, enzymes that switch thyroid hormone between its stored and active forms. That is why Brazil nut trials keep measuring the same things: blood selenium, glutathione peroxidase activity, thyroid hormones, cholesterol and markers of inflammation.

The same chemistry sets the limits. Selenium has a narrow range between "enough" and "too much", and the selenium content of Brazil nuts varies so much from tree to tree and soil to soil that nobody can know exactly what one nut holds. This page covers the tree and its wild harvest, the measured nutrient profile, what the human trials found for each researched benefit, and what the research says about selenium overload, aflatoxin, natural radioactivity and allergy.

Back to Table of Contents

A Wild Harvest from Standing Forest

The Brazil nut tree grows in terra firme forest, the parts of the Amazon that do not flood, in Brazil, Bolivia, Colombia, the Guianas, Peru and Venezuela. The botanist A.J.A. Bonpland described it scientifically in 1808, placing it alone in its own genus, Bertholletia, in the Brazil nut family (Lecythidaceae). In Europe and the United States it has also been known as the Pará nut. These details come from a 2018 chapter on the Brazil nut in a pollination compendium published by the Food and Agriculture Organization of the United Nations (FAO, The Pollination of Cultivated Plants, 2018, section 9.3.1).

What makes the Brazil nut unusual among the world's traded nuts is where it comes from. The FAO chapter describes the seeds as sustaining "one of the most important extractive industries in the Neotropics": they are gathered from natural forest rather than orchards, and local people have traded them internationally for more than 120 years, earning income in Brazil, Bolivia and Peru. Collectors wait for the heavy fruits to drop from the canopy, gather them from the forest floor, and crack out the seeds. In the Brazilian Amazon the nut is a key product of the extractive reserves, protected forest areas where communities harvest forest products. The same chapter notes that logging and trading Brazil nut trees from natural forest is prohibited under Brazilian law.

People have tried to grow the tree in orchards. According to the FAO chapter, efforts to grow it outside the Amazon basin, in Indonesia, Malaysia, Sri Lanka and the West Indies, failed. Inside the Brazilian Amazon it has been planted in agroforestry systems and in large monocultures since the 1980s, but growers there report low and highly irregular yields. That is one reason most of the world's supply still comes from wild trees.

Botanically, the FAO chapter points out, the Brazil nut "is essentially a seed rather than a nut"; the name is a matter of tradition. For allergy labelling, though, it is grouped with the tree nuts (see cautions).

Back to Table of Contents

The Tree, Its Bees and the Agouti

Whether a Brazil nut forms at all depends on two animals: a bee that can get into the flower, and a rodent that buries the seed.

Flowers that only strong bees can open

From October to January, the FAO chapter reports, the trees carry flower clusters 14 to 45 cm long, with fewer than one flower opening per cluster each day, and the flowers open in the small hours of the night. The flower is closed off by a curved, hood-like structure made of fused sterile stamens, and the nectar sits deep at its base. Only bees strong enough to lift that hood, with tongues long enough to reach inside, can feed and carry pollen. The main pollinators named in the chapter are medium to large-bodied native bees of the genera Bombus, Centris, Xylocopa, Eulaema and Epicharis, the last two including long-tongued orchid bees. The tree is mostly outcrossing: it sets fruit far better when pollen comes from another tree.

A genetic study of two natural populations in the Brazilian Amazon traced where pollen and seeds had actually travelled. Pollen moved between 36 and 2,060 metres and seeds between 30 and 1,742 metres, with most matings between nearby trees and most seeds landing near the mother tree. The authors concluded that breaking these forests into fragments could substantially reduce gene flow between trees (Baldoni 2017).

A hard fruit and a forgetful rodent

The fruit is a hard, round woody capsule 11 to 16 cm across and weighing 500 to 1,500 grams. Each holds 10 to 25 seeds about 3.5 to 5 cm long with a triangular cross-section: the "nuts". The fruit falls many metres to the ground when ripe. Fruit production per tree is extremely variable: in natural forest, the FAO chapter reports, trees produce anywhere from 0 to 800 fruits a year, with a mean of 66.

Under natural conditions, most Brazil nuts are eaten by agoutis (Dasyprocta), large rodents with teeth strong enough to gnaw through the capsule. Agoutis also bury seeds around the forest to eat later, and they forget many of them. The FAO chapter credits this burying habit with dispersing the tree and letting it regenerate. The animal that eats most of the crop is also the one that plants the next generation.

Back to Table of Contents

Nutritional Profile

The figures below are from USDA FoodData Central, entry "Nuts, brazilnuts, dried, unblanched" (FDC ID 170569, SR Legacy). USDA lists one kernel as 5 g and one ounce as 28.35 g (6 kernels). Percentages are calculated against the adult Daily Values the U.S. Food and Drug Administration uses on food labels (FDA Daily Values). The selenium figure is a single database average; the next section explains why real nuts differ widely from it.

A few points stand out. The fat is split roughly evenly between monounsaturated fat (almost all oleic acid, the main fat of olive oil) and polyunsaturated fat, which here is nearly all linoleic acid, an omega-6 fat; USDA lists only 0.018 g of the plant omega-3 ALA per 100 g, so Brazil nuts are not an omega-3 source. Saturated fat is about 16 g per 100 g. Beyond selenium, the nut is a strong source of copper and magnesium. USDA also lists gamma-tocopherol (another form of vitamin E) at 9.6 mg per 100 g and beta-sitosterol, a plant sterol, at 64 mg.

Laboratory analyses also find phenolic compounds in the nut, including catechin, epicatechin, gallic acid and ellagic acid, along with squalene and the tocopherols (Vasquez-Rojas 2021). Reviews of the nut's composition rank it among the richest food sources of selenium, alongside useful amounts of magnesium, copper and zinc (Cardoso 2017).

Back to Table of Contents

Selenium per Nut: Why the Numbers Swing So Widely

The USDA average works out to about 96 mcg of selenium in one 5 g kernel. The NIH Office of Dietary Supplements gives an average of 544 mcg per ounce and notes that values from other analyses vary widely (NIH ODS, Selenium Fact Sheet for Health Professionals). The research shows just how widely.

• Seed to seed. A study of two batches of nuts bought from shops measured mean selenium levels of 28 to 49 mg per kg, with up to an eight-fold difference between individual seeds in the same batch. The selenium was mainly in organic form (bound into compounds such as selenomethionine) and was most concentrated in a ring 1 to 2 mm below the seed's surface. The authors calculated that one 5 g seed from a high-selenium area meets the daily requirement, and that a 30 g serving could exceed the 400 mcg upper limit or even the 1,200 mcg level they cite as a toxicity threshold (Lima 2019).
• Lower than expected. In a New Zealand trial, two nuts a day were expected to supply about 100 mcg. When the study nuts were analysed, the actual intake averaged 53 mcg a day, with a possible range of 20 to 84 mcg for the two nuts (Thomson 2008).
• Far higher than expected. In a São Paulo trial, a single nut a day supplied an estimated 288.75 mcg (Cardoso 2016). In another São Paulo trial, one nut a day supplied about 1,261 mcg, roughly three times the adult upper limit in a single kernel (Duarte 2019).

A review of the agronomy explains the spread: how much selenium a plant can accumulate depends on the soil's selenium profile, both how much it holds and in what chemical form (Alcântara 2022). Germany's Federal Office for Radiation Protection draws the practical conclusion that because the selenium content of Brazil nuts "can fluctuate greatly", a targeted selenium supply from eating them "is thus not possible" (BfS).

Back to Table of Contents

Selenium and the Thyroid

The deiodinase enzymes that turn the storage hormone T4 into the active hormone T3 are selenoproteins. Glutathione peroxidases protect the gland from the hydrogen peroxide it produces while making hormone. Selenoprotein P, made in the liver, carries selenium in the blood and preferentially supplies the endocrine glands and the brain (Schomburg 2022). That biology is why Brazil nuts are so often discussed for autoimmune thyroid disease. A 2018 commentary noted that eating them is "often suggested as therapeutic" for people with autoimmune thyroid disease, and then set out the health concerns that come with it (Mazokopakis 2018).

What the trials measured, and what they did not

Almost all of the evidence comes from trials of selenium supplements, not Brazil nuts, mostly in Hashimoto's thyroiditis (the autoimmune disease that is the most common cause of an underactive thyroid in iodine-sufficient countries). The main thing they measured was blood levels of antibodies against the thyroid, especially thyroid peroxidase antibodies (TPOAb), rather than how patients felt.

• A 2024 meta-analysis of 35 studies found that selenium supplements lowered TPOAb and slightly lowered TSH (the pituitary hormone that drives the thyroid) in patients not taking thyroid hormone. It found no significant changes in the thyroid hormones themselves (T4 and T3), in thyroglobulin antibodies or in thyroid volume. Side effects were similar to placebo (Huwiler 2024).
• A 2016 meta-analysis found lower TPOAb with selenium after 3, 6 and 12 months in patients on thyroid hormone, but only at 3 months in untreated patients. It rated the quality of evidence as generally low, found a higher rate of reported side effects in the selenium groups, and stated that whether the antibody changes matter clinically "remains to be demonstrated" (Wichman 2016).
• A companion 2017 meta-analysis by the same group looked at outcomes patients would notice. In patients not on thyroid hormone it found no effect on TSH, on quality of life or on thyroid ultrasound, and titled its paper "Insufficient documentation for clinical efficacy" (Winther 2017).
• A 2013 Cochrane review found only four trials it could include (463 participants), at unclear to high risk of bias, and could not pool them (van Zuuren 2013). A 2023 overview of six systematic reviews rated the certainty of the antibody findings as low to very low (Wang 2023).

The Brazil nut evidence itself

Direct Brazil nut data on the thyroid are thin. In a Rio de Janeiro trial in people with high cholesterol and high blood pressure who had normal thyroid function, 13 g a day of partially defatted Brazil nut flour (about 227.5 mcg selenium) for 90 days was compared with a cassava-flour placebo. Free T3 fell in the placebo group but not in the Brazil nut group, which the authors read as the nut helping maintain T3 levels (Carvalho 2015). A systematic review of Brazil nut trials also reported improved thyroid function among the results in hemodialysis patients (da Silva 2022). None of the studies reviewed for this page tested Brazil nuts as a treatment for Hashimoto's or Graves' disease, and none shows that eating them treats thyroid disease.

The full trial-by-trial account is in the deep dive: Brazil Nuts: Selenium and Thyroid.

Back to Table of Contents

Selenium Status and Antioxidant Enzymes

The best-established finding is the simplest: eating Brazil nuts raises the amount of selenium in the blood and increases the activity of the selenium-dependent glutathione peroxidase (GPx) enzymes. A 2022 systematic review of 24 Brazil nut trials (15 of them non-randomized) found improved antioxidant status, measured as higher selenium and/or GPx activity, in every study that measured it, regardless of the participants' health (da Silva 2022).

• Nuts versus a selenium supplement. In a randomized trial in 59 New Zealand adults, a population with relatively low selenium intake, two Brazil nuts a day for 12 weeks raised plasma selenium by 64.2%, compared with 61.0% for 100 mcg of selenomethionine and 7.6% for placebo. Whole-blood GPx rose 13.2% with the nuts, more than with the supplement (5.3%) or placebo (1.9%). The authors concluded the nuts were as effective as the supplement for raising selenium status (Thomson 2008).
• High blood pressure and cholesterol. In a double-blind crossover trial in 91 people, 13 g a day of partially defatted Brazil nut flour for 12 weeks raised plasma selenium from about 87 to about 181 mcg/L, raised GPx3 activity by 24.8% and lowered oxidized LDL by 3.25% (Huguenin 2015).
• Hemodialysis. In 40 hemodialysis patients given one nut a day for 3 months, without a control group, plasma selenium and GPx rose while markers of oxidative damage (8-isoprostane and the DNA-damage marker 8-OHdG) fell (Stockler-Pinto 2014).
• A null result. In patients with coronary artery disease, one nut a day for 3 months did not change TMAO, a gut-derived compound linked to heart disease, and the 41% rise in GPx activity was not statistically significant (Coutinho-Wolino 2022).

Genes affect how people respond. Studies in healthy adults and in statin users found that common variants in the gene for selenoprotein P changed how GPx activity, blood fats or glucose responded to a daily nut (Donadio 2018; Watanabe 2022). The deep dive covers the biomarkers, the genetics and what "selenium status" does and does not tell you: Brazil Nuts: Selenium Status and Antioxidant Enzymes.

Back to Table of Contents

Cholesterol and Inflammation

The cholesterol and inflammation trials are small, often uncontrolled, and point in different directions. Read one at a time, several look positive. Read together, they are mixed.

Cholesterol and blood fats

• In the Rio de Janeiro flour trial (77 patients already on cholesterol-lowering drugs, 13 g a day for 90 days), the Brazil nut group's total cholesterol fell by about 20.5 mg/dL and non-HDL cholesterol by about 19.5 mg/dL. However, the trial found no statistical difference in blood fats or blood pressure between the Brazil nut group and the placebo group (Carvalho 2015).
• In 130 healthy volunteers in São Paulo, one nut a day for 8 weeks was followed by lower total cholesterol and fasting glucose. There was no separate control group (Donadio 2018).
• In the hemodialysis study, HDL ("good") cholesterol rose and LDL fell after 3 months of one nut a day, again without a control group (Stockler-Pinto 2014).
• Brazil nut oil behaved differently from the whole nut. In 31 people with metabolic syndrome given 10 mL a day of Brazil nut oil or soybean oil for 30 days, the Brazil nut oil group's HDL fell and triglycerides rose. Its one favourable change was lower malondialdehyde, a marker of fat oxidation (Costa e Silva 2019).

Inflammation: two trials that disagree

• In a non-randomized controlled trial of 56 women with overweight or obesity on a calorie-reduced diet, those who ate 8 g of Brazil nuts a day (about 347 mcg selenium) for 8 weeks ended with lower C-reactive protein, TNF, IL-1β and IL-8 (inflammatory signalling proteins) and lower gut permeability than the nut-free group. The authors noted the effects seemed to depend on selenium status (Silveira 2024).
• In a randomized trial of 55 women with obesity, one very high-selenium nut a day (about 1,261 mcg) for 2 months did not change inflammatory markers in the blood. However, it increased the activity of the genes for several inflammatory signals (IL-6, TNF-α and the immune receptors TLR2 and TLR4). The authors read this as a possible pro-inflammatory effect of nuts this high in selenium (Duarte 2019).

In type 2 diabetes, 6 months of Brazil nuts raised blood selenium and made blood cells more resistant to laboratory-induced DNA damage. Fasting blood glucose rose significantly over the same period, while HbA1c (a three-month average of blood sugar) did not change (Macan 2022). The trial-by-trial detail is in the deep dive: Brazil Nuts: Cholesterol and Inflammation.

Back to Table of Contents

Brain Aging and Cognition

The brain is one of the organs that selenoprotein P supplies first when selenium is scarce (Schomburg 2022). This, and the brain's sensitivity to oxidative damage, is the reason researchers have tested Brazil nuts in older adults with memory problems.

The human evidence is a single pilot trial. In São Paulo, 31 older adults with mild cognitive impairment (memory or thinking problems that are noticeable but not dementia) were randomly assigned to one Brazil nut a day, an estimated 288.75 mcg of selenium, or no nut for 6 months. Only 11 people in the nut group and 9 controls completed the study. Blood selenium rose in the nut group, and of the antioxidant measures only erythrocyte GPx activity differed between groups. On cognitive testing, two measures improved more in the nut group: verbal fluency (naming as many words in a category as possible) and constructional praxis (copying drawings). The authors called this "preliminary evidence" (Cardoso 2016).

That is a small, early signal from 20 completers. It does not show that Brazil nuts prevent or slow dementia, and no larger trial of Brazil nuts and cognition appears in the research reviewed for this page. The deep dive covers the trial and what remains unknown: Brazil Nuts: Brain Aging and Cognition.

Back to Table of Contents

A Selenium Tablet Is Not a Brazil Nut

Articles about Brazil nuts often borrow results from selenium supplement trials. They are different exposures, and the large supplement trials did not find what early hopes predicted.

• Dose. A tablet delivers a fixed, labelled dose. A nut delivers anything from a few tens of micrograms to over a thousand (see selenium per nut).
• Form. Thyroid trials used sodium selenite or selenomethionine. Brazil nut selenium is mostly organic, bound into seed proteins (Lima 2019). A nut also brings fat, fiber, magnesium and other compounds.
• Large supplement trials. The Selenium and Vitamin E Cancer Prevention Trial (SELECT) randomized 35,533 men to 200 mcg a day of selenium as L-selenomethionine, vitamin E, both, or placebo. It found no reduction in prostate cancer with selenium (Klein 2011). In the earlier Nutritional Prevention of Cancer Trial, 200 mcg a day of selenium yeast in 1,312 people with a history of skin cancer did not prevent basal cell carcinoma and was linked to a higher risk of squamous cell carcinoma (hazard ratio 1.25) and of total nonmelanoma skin cancer (hazard ratio 1.17) (Duffield-Lillico 2003).

Neither of those trials studied Brazil nuts, and their results cannot be transferred to the nut directly, in either direction. What they show is that more selenium is not automatically better once a person already has enough. This page states, for each result, whether it came from nuts or from tablets.

Back to Table of Contents

Buying, Storing and the Aflatoxin Findings

Rancidity

With about 67 g of fat per 100 g, roughly a third of it polyunsaturated, Brazil nuts are more prone to going rancid than lower-fat nuts. Oxidized nuts taste bitter or paint-like. Oxidation is driven by air, light and warmth, so cool, dark, airtight storage, including the refrigerator or freezer, slows it.

Mould and aflatoxin

Brazil nuts are gathered from the forest floor in a hot, humid climate, so mould is the main food-safety question. The concern is aflatoxin, a liver-damaging and cancer-causing toxin made by moulds of the Aspergillus section Flavi group.

• A study that tested 110 stored samples (55 of nuts and 55 of shells) collected monthly for 11 months in the state of Amazonas often found aflatoxin-producing moulds, mainly Aspergillus flavus. It detected no aflatoxin or cyclopiazonic acid (another mould toxin) in any sample. The authors credited the low moisture of the stored nuts for the absence of toxin, and said the persistence of toxin-producing moulds showed why good handling practices matter (Baquião 2013).
• In 25 samples of Brazil nut oil from northern Brazil, including oils made by local producers from nuts the industry had discarded and factory-made oils, 7 (28%) contained aflatoxin, at up to 50.87 mcg per kg (Kluczkovski 2022).

In the stored-nut study, dryness was the factor that kept moulds present on the nuts from producing toxin. A broader overview of mould toxins is on the Mold and Mycotoxins page, and the peanut version of the same problem is covered under Peanuts: Aflatoxin and Safe Sourcing.

In the kitchen

Brazil nuts are eaten raw or roasted, chopped into baking, or blended into a plant "milk". A study of Brazil nut beverages found that selenium and phenolic compounds carried over into the drink at high levels (Vasquez-Rojas 2021), so a nut milk is not a way around the selenium content.

Back to Table of Contents

Amounts Used in the Studies

These are the amounts the trials gave, reported as facts about the studies. Because selenium per nut varies so much, the same number of nuts meant very different selenium doses in different trials.

• 1 nut a day: for 2 months (about 1,261 mcg selenium, Duarte 2019); 8 weeks (Donadio 2018); 3 months (Stockler-Pinto 2014; Coutinho-Wolino 2022; Watanabe 2022); 6 months (estimated 288.75 mcg, Cardoso 2016).
• 2 nuts a day for 12 weeks: measured intake averaged 53 mcg selenium, range 20 to 84 mcg (Thomson 2008).
• 8 g a day (about two nuts) for 8 weeks: about 347 mcg selenium (Silveira 2024).
• 13 g a day of partially defatted Brazil nut flour for 90 days or 12 weeks: about 227.5 mcg selenium (Carvalho 2015; Huguenin 2015).
• 15 g of Brazil nuts plus 30 g of cashews a day in a calorie-reduced diet for 8 weeks: the meal had no immediate effect on appetite, but after 8 weeks ghrelin (a hunger hormone) after meals was lower than in the nut-free group (Rocha 2023).
• 10 mL a day of Brazil nut oil for 30 days (Costa e Silva 2019).

For reference against an authority's figures: the NIH Office of Dietary Supplements lists the adult Recommended Dietary Allowance for selenium as 55 mcg a day and the adult Tolerable Upper Intake Level as 400 mcg a day, values that come from the U.S. Institute of Medicine's 2000 Dietary Reference Intakes (Institute of Medicine 2000; NIH ODS). By the USDA average, one ounce (about 6 nuts) already supplies more than the adult upper limit. Germany's Federal Office for Radiation Protection bases its dose estimates on two nuts, about 8 g, a day (BfS, Natural radioactivity in Brazil nuts).

Back to Table of Contents

Who the Research Raises Cautions For

Selenium overload

The NIH Office of Dietary Supplements sets the selenium upper limit at 400 mcg a day for adults. For infants, children and adolescents the limit ranges from 45 to 400 mcg depending on age, which a single high-selenium nut can exceed. ODS describes chronic selenium excess (selenosis) as most commonly causing hair loss and brittle or lost nails, along with garlic-smelling breath, a metallic taste, skin rash, nausea, diarrhea, fatigue, irritability and nervous-system problems (NIH ODS). A 2018 commentary on Brazil nut concerns listed selenium toxicity first, together with a possible link between high selenium intake and type 2 diabetes (Mazokopakis 2018). The type 2 diabetes trial above reported a rise in fasting glucose (Macan 2022).

The real-world picture is more complicated. In 448 people from 12 riverside communities on the Tapajós River in the Brazilian Amazon, whose traditional diet includes Brazil nuts, blood selenium reached as high as 1,500 mcg/L, above the level the U.S. Environmental Protection Agency considers toxic. Yet a nurse's examination of hair, nails, skin and breath found no signs of selenosis linked to selenium levels. The authors called for toxicity limits to be re-examined with the form of selenium and the food it comes in taken into account (Lemire 2012). That is one population eating a traditional diet; it is not evidence that unlimited intake is safe for everyone. The deep dive covers the case findings, the upper-limit reasoning and the open questions: Brazil Nuts: Selenium Overload and Safety. See also Selenosis.

People already taking selenium

Selenium from nuts adds to selenium from multivitamins, thyroid or "immune" supplements and selenium-rich foods such as fish, eggs and organ meats. The upper limit applies to total intake. The supplement trials summarized above, which gave 200 mcg on top of the diet, are the reason researchers stress the total.

Natural radioactivity: radium

Germany's Federal Office for Radiation Protection (BfS) reports that Brazil nuts concentrate natural radium from the soil far more than most foods do: several tens of becquerels per kilogram each of radium-226 and radium-228, about 1,000 times the radium content of the average German diet per kilogram. Its explanation is that the trees grow in calcium-poor rainforest soils and take up radium, which is chemically similar to calcium, through their wide root systems. In the body, radium behaves like calcium and part of the absorbed amount is stored in bone. In BfS model calculations, two nuts a day (about 8 g) give an adult about 160 microsieverts a year and a child in the second year of life about 1,000 microsieverts a year. For comparison, natural radionuclides in an average diet give an adult about 300 microsieverts a year, and total natural background radiation in Germany averages 2,100. The BfS describes moderate adult consumption as harmless. As a precaution, it advises women not to eat Brazil nuts during pregnancy and breastfeeding, and children and adolescents not to eat them, because radium is laid down in growing bone (BfS). Radioactivity is also among the concerns listed in the 2018 commentary (Mazokopakis 2018).

Barium

The U.S. Agency for Toxic Substances and Disease Registry names Brazil nuts, along with seaweed, fish and certain plants, as foods that "may contain high amounts of barium", and lists Brazil nuts among the land plants that can concentrate it (ATSDR Barium ToxGuide). ATSDR also states that the soluble barium compounds are the ones of greater health concern. None of the human trials on this page measured barium. Background on barium is on the Barium Toxicity page.

Tree-nut allergy

Tree-nut allergy affects up to 4.9% of people worldwide in reported estimates. Reactions are IgE-mediated (the antibody type behind fast allergic reactions) and can be serious or life-threatening. Brazil nut allergy is less well mapped than walnut or hazelnut allergy, with only individual allergens identified so far (Geiselhart 2018). Its major allergen, Ber e 1, is very stable: it resists breakdown by stomach enzymes in laboratory tests and does not fully unfold until about 110°C at the acidity of most foods, so cooking or roasting is unlikely to destroy all of it (van Boxtel 2008). Brazil nut allergy is reported less often than allergy to cashew, walnut, hazelnut or almond (Roux 2003). See Food Allergy and Anaphylaxis.

Calories

At 659 kcal per 100 g, Brazil nuts are among the most energy-dense nuts. In the weight-loss trials above they were eaten as part of a calorie-reduced diet, not added on top of one (Silveira 2024; Rocha 2023).

Decisions about selenium intake, especially for people with thyroid disease, kidney disease, diabetes, or those who are pregnant, breastfeeding or feeding children, belong with a clinician, who can also order a selenium blood test.

Back to Table of Contents

Connections

• Nuts — all nut pages on this site
• Brazil Nuts — Benefits Deep Dive
• Selenium and Thyroid
• Selenium Status and Antioxidant Enzymes
• Cholesterol and Inflammation
• Brain Aging and Cognition
• Selenium Overload and Safety
• Selenium — the mineral in full
• Selenium for Thyroid Function
• Selenium Deficiency
• Selenosis — when selenium becomes toxic
• Selenium Test
• Hashimoto's Thyroiditis
• Thyroid Panel
• Glutathione — partner of the GPx enzymes
• Barium Toxicity
• Food Allergy
• Walnuts
• Cashews
• Peanuts

Back to Table of Contents

Key Research Papers

1. da Silva A, Silveira BKS, de Freitas BVM, et al. Effects of Regular Brazil Nut (Bertholletia excelsa H.B.K.) Consumption on Health: A Systematic Review of Clinical Trials. Foods (Basel, Switzerland). 2022;11(18):2925. PubMed PMID: 36141050
2. Cardoso BR, Duarte GBS, Reis BZ, et al. Brazil nuts: Nutritional composition, health benefits and safety aspects. Food research international (Ottawa, Ont.). 2017;100(Pt 2):9-18. PubMed PMID: 28888463
3. Alcântara DB, Dionísio AP, Artur AG, et al. Selenium in Brazil nuts: An overview of agronomical aspects, recent trends in analytical chemistry, and health outcomes. Food chemistry. 2022;372:131207. PubMed PMID: 34634585
4. Lima LW, Stonehouse GC, Walters C, et al. Selenium Accumulation, Speciation and Localization in Brazil Nuts (Bertholletia excelsa H.B.K.). Plants (Basel, Switzerland). 2019;8(8):289. PubMed PMID: 31426292
5. Vasquez-Rojas WV, Martín D, Miralles B, et al. Composition of Brazil Nut (Bertholletia excels HBK), Its Beverage and By-Products: A Healthy Food and Potential Source of Ingredients. Foods (Basel, Switzerland). 2021;10(12):3007. PubMed PMID: 34945560
6. Baldoni AB, Wadt LHO, Campos T, et al. Contemporary pollen and seed dispersal in natural populations of Bertholletia excelsa (Bonpl.). Genetics and molecular research : GMR. 2017;16(3). PubMed PMID: 28973737
7. Thomson CD, Chisholm A, McLachlan SK, et al. Brazil nuts: an effective way to improve selenium status. The American journal of clinical nutrition. 2008;87(2):379-84. PubMed PMID: 18258628
8. Huguenin GV, Oliveira GM, Moreira AS, et al. Improvement of antioxidant status after Brazil nut intake in hypertensive and dyslipidemic subjects. Nutrition journal. 2015;14:54. PubMed PMID: 26022214
9. Carvalho RF, Huguenin GV, Luiz RR, et al. Intake of partially defatted Brazil nut flour reduces serum cholesterol in hypercholesterolemic patients--a randomized controlled trial. Nutrition journal. 2015;14:59. PubMed PMID: 26077768
10. Stockler-Pinto MB, Mafra D, Moraes C, et al. Brazil nut (Bertholletia excelsa, H.B.K.) improves oxidative stress and inflammation biomarkers in hemodialysis patients. Biological trace element research. 2014;158(1):105-12. PubMed PMID: 24504745
11. Coutinho-Wolino KS, da Cruz BO, Cardozo LFMF, et al. Brazil nut supplementation does not affect trimethylamine-n-oxide plasma levels in patients with coronary artery disease. Journal of food biochemistry. 2022;46(8):e14201. PubMed PMID: 35467017
12. Donadio JLS, Rogero MM, Guerra-Shinohara EM, et al. SEPP1 polymorphisms modulate serum glucose and lipid response to Brazil nut supplementation. European journal of nutrition. 2018;57(5):1873-1882. PubMed PMID: 28501922
13. Moriguchi Watanabe L, Bueno AC, de Lima LF, et al. Genetically determined variations of selenoprotein P are associated with antioxidant, muscular, and lipid biomarkers in response to Brazil nut consumption by patients using statins. The British journal of nutrition. 2022;127(5):679-686. PubMed PMID: 33947487
14. Costa E Silva LM, Pereira de Melo ML, Faro Reis FV, et al. Comparison of the Effects of Brazil Nut Oil and Soybean Oil on the Cardiometabolic Parameters of Patients with Metabolic Syndrome: A Randomized Trial. Nutrients. 2019;12(1):46. PubMed PMID: 31877968
15. Silveira BKS, Silva AD, Rocha DMUP, et al. Brazil Nut (Bertholletia excelsa H.B.K.) Consumption in Energy-Restricted Intervention Decreases Proinflammatory Markers and Intestinal Permeability of Women with Overweight/Obesity: A Controlled Trial (Brazilian Nuts Study). The Journal of nutrition. 2024;154(9):2670-2679. PubMed PMID: 39025334
16. Duarte GBS, Reis BZ, Rogero MM, et al. Consumption of Brazil nuts with high selenium levels increased inflammation biomarkers in obese women: A randomized controlled trial. Nutrition (Burbank, Los Angeles County, Calif.). 2019;63-64:162-168. PubMed PMID: 31026738
17. Mayumi Usuda Prado Rocha D, Paula Silva Caldas A, Simões E Silva AC, et al. Nut-enriched energy restricted diet has potential to decrease hunger in women at cardiometabolic risk: a randomized controlled trial (Brazilian Nuts Study). Nutrition research (New York, N.Y.). 2023;109:35-46. PubMed PMID: 36577255
18. Macan TP, de Amorim TA, Damiani AP, et al. Brazil nut prevents oxidative DNA damage in type 2 diabetes patients. Drug and chemical toxicology. 2022;45(3):1066-1072. PubMed PMID: 32811197
19. Rita Cardoso B, Apolinário D, da Silva Bandeira V, et al. Effects of Brazil nut consumption on selenium status and cognitive performance in older adults with mild cognitive impairment: a randomized controlled pilot trial. European journal of nutrition. 2016;55(1):107-16. PubMed PMID: 25567069
20. Schomburg L. Selenoprotein P - Selenium transport protein, enzyme and biomarker of selenium status. Free radical biology & medicine. 2022;191:150-163. PubMed PMID: 36067902
21. Huwiler VV, Maissen-Abgottspon S, Stanga Z, et al. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Thyroid : official journal of the American Thyroid Association. 2024;34(3):295-313. PubMed PMID: 38243784
22. Wichman J, Winther KH, Bonnema SJ, et al. Selenium Supplementation Significantly Reduces Thyroid Autoantibody Levels in Patients with Chronic Autoimmune Thyroiditis: A Systematic Review and Meta-Analysis. Thyroid : official journal of the American Thyroid Association. 2016;26(12):1681-1692. PubMed PMID: 27702392
23. Winther KH, Wichman JE, Bonnema SJ, et al. Insufficient documentation for clinical efficacy of selenium supplementation in chronic autoimmune thyroiditis, based on a systematic review and meta-analysis. Endocrine. 2017;55(2):376-385. PubMed PMID: 27683225
24. van Zuuren EJ, Albusta AY, Fedorowicz Z, et al. Selenium supplementation for Hashimoto's thyroiditis. The Cochrane database of systematic reviews. 2013;2013(6):CD010223. PubMed PMID: 23744563
25. Wang YS, Liang SS, Ren JJ, et al. The Effects of Selenium Supplementation in the Treatment of Autoimmune Thyroiditis: An Overview of Systematic Reviews. Nutrients. 2023;15(14):3194. PubMed PMID: 37513612
26. Mazokopakis EE, Liontiris MI. Commentary: Health Concerns of Brazil Nut Consumption. Journal of alternative and complementary medicine (New York, N.Y.). 2018;24(1):3-6. PubMed PMID: 28805450
27. Lemire M, Philibert A, Fillion M, et al. No evidence of selenosis from a selenium-rich diet in the Brazilian Amazon. Environment international. 2012;40:128-136. PubMed PMID: 21856002
28. Institute of Medicine (US) Panel on Dietary Antioxidants and Related Compounds. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington (DC): National Academies Press (US). 2000. PubMed PMID: 25077263
29. Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011;306(14):1549-56. PubMed PMID: 21990298
30. Duffield-Lillico AJ, Slate EH, Reid ME, et al. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. Journal of the National Cancer Institute. 2003;95(19):1477-81. PubMed PMID: 14519754
31. Baquião AC, De Oliveira MM, Reis TA, et al. Monitoring and determination of fungi and mycotoxins in stored Brazil nuts. Journal of food protection. 2013;76(8):1414-20. PubMed PMID: 23905798
32. Kluczkovski A, Bezerra L, Januário B, et al. Nuclear Magnetic Resonance Approach in Brazil Nut Oil and the Occurrence of Aflatoxins. Journal of oleo science. 2022;71(10):1439-1444. PubMed PMID: 36089397
33. Geiselhart S, Hoffmann-Sommergruber K, Bublin M. Tree nut allergens. Molecular immunology. 2018;100:71-81. PubMed PMID: 29680588
34. van Boxtel EL, Koppelman SJ, van den Broek LA, et al. Heat denaturation of Brazil nut allergen Ber e 1 in relation to food processing. Food chemistry. 2008;110(4):904-8. PubMed PMID: 26047277
35. Roux KH, Teuber SS, Sathe SK. Tree nut allergens. International archives of allergy and immunology. 2003;131(4):234-44. PubMed PMID: 12915766

PubMed Topic Searches

1. PubMed: Brazil nut selenium trials
2. PubMed: Brazil nuts and the thyroid
3. PubMed: Selenium supplementation in Hashimoto's thyroiditis
4. PubMed: Brazil nuts, cholesterol and inflammation
5. PubMed: Radium in Brazil nuts
6. PubMed: Aflatoxin in Brazil nuts
7. PubMed: Brazil nut tree pollination and seed dispersal

Back to Table of Contents

Featured Videos