Brazil nuts, selenium and blood fats in trials
What it found
In people, eating Brazil nuts raised selenium levels in the blood and increased the activity of an antioxidant enzyme called glutathione peroxidase.
The trials found no clear change in total, HDL or LDL cholesterol.
What they found
Studies in people
Selenium in blood
Brazil nut intake clearly raised selenium levels in blood serum or plasma. In one crossover trial in people with high blood pressure and high blood fats, granulated Brazil nuts raised plasma selenium by 119% over 12 weeks.
Glutathione peroxidase activity
Brazil nut intake increased the activity of glutathione peroxidase, an antioxidant enzyme, in serum, plasma or red blood cells. Three of four parallel trials found a significant rise in the Brazil nut group but not in the placebo group.
Blood cholesterol
The pooled results showed no significant change in total cholesterol, HDL cholesterol or LDL cholesterol with Brazil nut intake. One trial in obese female adolescents found lower total and LDL cholesterol and triglycerides in the Brazil nut group at the end of follow-up, but two other trials found no differences.
Oxidised LDL and other markers
One trial in obese female adolescents found significantly lower oxidised LDL in the Brazil nut group compared to placebo. Another trial in people with high blood pressure and high blood fats found a 3.2% reduction in oxidised LDL after 3 months. No significant changes were seen for 8-epi PGF2α or MDA.
Inflammation marker CRP
Three trials looked at C-reactive protein (CRP) and found no effect of Brazil nut intake on its levels.
Side effects
None of the included studies reported any adverse effects related to eating Brazil nuts.
What the authors conclude
“In conclusion, the findings from this meta-analysis of RCTs demonstrate that Brazil nut consumption increases selenium blood levels and GPx activity, suggesting their antioxidant effects.”
Also in their conclusions
- They conclude that Brazil nut consumption increases selenium blood levels and glutathione peroxidase activity, suggesting antioxidant effects.
- They state that there is no consistent evidence that this antioxidant effect improves blood lipid profiles.
- They call for further research on Brazil nut consumption and cardiovascular health, using more valid biomarkers.
How it was done
Tree nuts like Brazil nuts have been suggested to affect heart health by changing oxidative stress and inflammation, but no one had combined the numbers from the trials to see the size of these effects.
The authors pooled eight randomised clinical trials that gave people Brazil nuts, granulated Brazil nuts or Brazil nut flour. The trials lasted 1.5 to 6 months and included healthy volunteers, obese female adolescents, people with high blood pressure and high blood fats, older adults with mild cognitive impairment, people at risk of colorectal cancer, and obese women.
What it can’t tell you
- The trials used different groups of people and different amounts of Brazil nuts, so the results may not apply to everyone.
- The review cannot show whether the changes in selenium and glutathione peroxidase lead to fewer heart problems over time.
- Some trials had a high risk of bias, and the analysis found signs of small-study effects for selenium, so the size of the effect may be uncertain.
Who paid
- Conflicts
- The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
- Authors work at
- University of Catania, Italy; Jagiellonian University, Poland; Polytechnic University of Marche, Italy
The paper
- Title
- Effect of Brazil Nuts on Selenium Status, Blood Lipids, and Biomarkers of Oxidative Stress and Inflammation: A Systematic Review and Meta-Analysis of Randomized Clinical Trials
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Godos J, Giampieri F, Micek A, et al (2022). Effect of Brazil Nuts on Selenium Status, Blood Lipids, and Biomarkers of Oxidative Stress and Inflammation: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Antioxidants (Basel, Switzerland). doi:10.3390/antiox11020403Free full textPubMed 35204285DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error