Spectroscopic methods, such as laser fluorescence spectroscopy, can be used to determine the chemical binding form of metal ions to various inorganic and organic substances from Brazil nuts and the body’s digestive juices. Credit: B. Schröder/HZDR

Brazil nuts are an especially nutrient-rich source of food: They contain important minerals like calcium and magnesium, essential amino acids and unsaturated fatty acids. Brazil nuts are characterized by very high selenium levels, an essential trace element that supports the immune system and protects cells from oxidative stress. A single Brazil nut can cover the recommended daily requirement of 55 to 70 micrograms. However, they not only contain this essential nutrient, but also traces of potentially problematic metals like barium and radioactive radium.

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the VKTA—Radiation Protection, Analytics & Disposal Rossendorf Inc. have now conducted the first systematic study on the amounts of these elements that could actually enter the body during the digestive process and has some good news for lovers of the nut-like seed.

"Our study confirms the extremely high selenium content in Brazil nuts. At the same time, we were also able to show that around 85% of the selenium is released during digestion and can then be taken up by the body," says Dr. Astrid Barkleit from the Institute of Resource Ecology at HZDR, summarizing a core finding of the study published in the International Journal of Molecular Sciences.

Using nuclear magnetic resonance (NMR) spectroscopy, the researchers identified the main form of selenium in the nuts: selenomethionine, an amino acid that is particularly well absorbed by the body. Thus, Brazil nuts really provide a selenium compound that is of high value to the human organism.

Unexpected companions

Besides the healthful nutrients, Brazil nut trees also extract and store other elements from the soil. Because the soils in the South American rainforests—home to the trees—are relatively low in calcium, chemically similar elements like barium and radium partially replace the calcium. Similar to calcium, these metals can accumulate in bones and potentially cause harm. Radium, for instance, is radioactive and thus is suspected of causing bone damage and increasing cancer risk. However, the study revealed that both substances are barely dissolved in the digestive tract. Only about 2% of barium and radium in the nut kernel are bioavailable, that is, released in the digestive tract.

"The calculations show that, due to the very low bioavailability, a daily consumption of one Brazil nut would result in a radiation dose of about 2.4 microsieverts per year. That is only about a thousandth of the natural annual radiation exposure in Germany, which is given to 2.1 millisieverts per year on average by the Federal Office for Radiation Protection. Of this, about 10% are ingested with food. Therefore, the radiation exposure caused by radium in Brazil nuts is significantly less than previously assumed," explains Dr. Diana Walther from VKTA.

The researchers suspect that the low solubility is due to substances the plant stores in its seeds: They found phytic acid, which binds minerals and metals strongly and thus prevents the body from absorbing them.

They analyzed other trace elements like strontium, lanthanum and europium. Strontium behaves chemically similar to calcium and is bioavailable to approximately 50%, however, only present in such small amounts that it is not toxicologically relevant. Lanthanum and europium belong to the so-called rare earths and were detected in only the smallest amounts. Their bioavailability is about 25%, however, the intake levels remain well below the established limit values.

This is because not every element in a food is actually absorbed by the body. The decisive factor is how much is released during digestion—this fraction is considered as "bioavailable." To test this, the researchers simulated the digestion process in the lab using artificial saliva, gastric juice and digestive enzymes at body temperature. This allowed them to see which substances dissolve and could potentially be absorbed by the small intestine.

Modern analytics for an ancient food

The team used mass spectrometry to determine the concentrations of the elements, gamma and alpha spectrometry for radioactive isotopes, and NMR and laser fluorescence methods for characterizing the chemical binding form of the elements.

Moreover, the researchers were interested in discovering whether components of the Brazil nut influence the efficacy of so-called decorporation agents—compounds that are used to remove radioactive material in cases of contamination from the body. The results showed that the composition of Brazil nuts only had a minimal impact on the efficacy of these substances.

"Our results confirm that Brazil nuts are a valuable food—especially as a natural source of selenium," Barkleit summarizes. "At the same time, they show that, thanks to their low solubility, the potentially harmful elements they contain hardly affect the body when the nuts are consumed."

More information: Astrid Barkleit et al, In Vitro Bioaccessibility and Speciation of Toxic and Nutritional Trace Elements in Brazil Nuts, International Journal of Molecular Sciences (2025). DOI: 10.3390/ijms26178312

Citation: How healthy are Brazil nuts? New study elucidates trace elements in the seeds (2025, December 22) retrieved 22 December 2025 from https://phys.org/news/2025-12-healthy-brazil-nuts-elucidates-elements.html

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