The Brazil nut (Bertholletia excelsa) is a South American tree in the family Lecythidaceae, and it is also the name of the tree’s commercially harvested edible seeds. It is one of the largest and longest-lived trees in the Amazon rainforest. The fruit and its nutshell – containing the edible Brazil nut – are relatively large, possibly weighing as much as 2 kg (4 lb 7 oz) in total weight. As food, Brazil nuts are notable for diverse content of micronutrients, especially a high amount of selenium. The wood of the Brazil nut tree is prized for its quality in carpentry, flooring, and heavy construction.

The Brazil nut is a large tree, reaching 50 m (160 ft) tall and with a trunk 1 to 2 m (3 ft 3 in to 6 ft 7 in) in diameter, making it among the largest of trees in the Amazon rainforest. It may live for 500 years or more, and can often reach a thousand years of age.[7] The stem is straight and commonly without branches for well over half the tree’s height, with a large, emergent crown of long branches above the surrounding canopy of other trees.

The bark is grayish and smooth. The leaves are dry-season deciduous, alternate, simple, entire or crenate, oblong, 20–35 cm (8–14 in) long, and 10–15 cm (4–6 in) broad. The flowers are small, greenish-white, in panicles 5–10 cm (2–4 in) long; each flower has a two-parted, deciduous calyx, six unequal cream-colored petals, and numerous stamens united into a broad, hood-shaped mass.

Range

The Brazil nut is native to the Guianas, Venezuela, Brazil, eastern Colombia, eastern Peru, and eastern Bolivia. It occurs as scattered trees in large forests on the banks of the Amazon River, Rio Negro, Tapajós, and the Orinoco.

As a result, they can be found outside production areas, in the backyards of homes and near roads and streets in the Northern and Northeastern Brazil. The fruit is heavy and rigid; when the fruits fall, they pose a serious threat to vehicles and people passing under the tree. 

A freshly cut Brazil nut fruit

Brazil nut trees produce fruit almost exclusively in pristine forests, as disturbed forests lack the large-bodied bees of the genera Bombus, Centris, Epicharis, Eulaema, and Xylocopa, which are the only ones capable of pollinating the tree’s flowers, with different bee genera being the primary pollinators in different areas, and different times of year. Brazil nuts have been harvested from plantations, but production is low and is currently not economically viable.

The fruit takes 14 months to mature after pollination of the flowers. The fruit itself is a large capsule 10–15 cm (4–6 in) in diameter, resembling a coconut endocarp in size and weighing up to 2 kg (4 lb 7 oz). It has a hard, woody shell 8–12 mm (3⁄8–1⁄2 in) thick, which contains eight to 24 wedge-shaped seeds 4–5 cm (1+5⁄8–2 in) long (the “Brazil nuts”) packed like the segments of an orange, but not limited to one whorl of segments. Up to three whorls can be stacked onto each other, with the polar ends of the segments of the middle whorl nestling into the upper and lower whorls (see illustration above). 

The capsule contains a small hole at one end, which enables large rodents like the agouti to gnaw it open. They then eat some of the seeds inside while burying others for later use; some of these are able to germinate into new Brazil nut trees. Most of the seeds are “planted” by the agoutis in caches during wet season, and the young saplings may have to wait years, in a state of dormancy, for a tree to fall and sunlight to reach it, when it starts growing again. Capuchin monkeys have been reported to open Brazil nuts using a stone as an anvil.

Brazil nuts contain 14% protein, 12% carbohydrate, and 66% fat by weight; 85% of their calories come from fat, and a 100-gram (3+1⁄2-ounce) amount provides 2,740 kilojoules (656 kilocalories) of food energy.[22] The fat components are 23% saturated, 38% monounsaturated, and 32% polyunsaturated. Due to their high polyunsaturated fat content, primarily omega-6 fatty acids, shelled Brazil nuts may quickly become rancid.

Nutritionally, Brazil nuts are a rich source (20% or more of the Daily Value, DV) of dietary fiber (30% DV) and various vitamins and dietary minerals. A 100 g (3+1⁄2 oz) amount (75% of one cup) of Brazil nuts contains rich content of thiamin (54% DV), vitamin E (38% DV), magnesium (106% DV), phosphorus (104% DV), manganese (57% DV), and zinc (43% DV). Brazil nuts are perhaps the richest dietary source of selenium, with a 28 g (1 oz) serving of six nuts supplying 774% DV.[22] This is 10 times the adult U.S. Recommended Dietary Allowance, more even than the Tolerable Upper Intake Level, although the amount of selenium within batches of nuts varies greatly. A 200 grams bag of Brazil nuts from the supermarket has a selenium content of around 20,000 micrograms. That is almost 300 times the amount that the German Nutrition Society (GNS) recommends for healthy adults (70 micrograms per day for men, 60 micrograms per day for women).[25] The most common signs of a chronical overdose are hair and nail loss or brittleness.

The high selenium content is used as a biomarker in studies of selenium intake and deficiency. Consumption of just one Brazil nut per day over 8 weeks was sufficient to restore selenium blood levels and increase HDL (good) cholesterol in obese women.

The selenium which is contained in Brazil nuts comes in organic compounds, mainly in the form of selenomethionine. The body confuses this form of selenium with the protein element methionine. That means that it incorporates the organic compound uncontrollably into proteins that should contain sulfur. A part of the selenium is regenerated later but does occur as a function of protein metabolism and not as needed. Instead of having the positive effects, the regular consumption of Brazil nuts can have negative effects.

Phytochemicals

The shells of Brazil nuts contain high levels of aflatoxins, which are produced by molds, and can cause liver damage, including possible cancer, if consumed. Aflatoxin levels have been found in Brazil nuts during inspections that were far higher than the limits set by the EU.
The nuts contain small amounts of radium, a radioactive element, with a kilogram of nuts containing an activity between 40 and 260 becquerels (1 and 7 nanocuries). This is about 1000 times higher than in several other common foods. According to Oak Ridge Associated Universities, elevated levels of radium in the soil does not directly cause the concentration of radium, but “the very extensive root system of the tree” can concentrate naturally occurring radioactive material, when present in the soil. The material must still be present in the soil in order to concentrate in the trees.

Brazil nuts also contain barium, a metal with a chemical behavior quite similar to radium, which can have toxic effects, such as weakness, vomiting or diarrhea, after intentional or accidental ingestion.