How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Brazil nut
A single Brazil nut per day boosts blood selenium, including in vegans. On cholesterol, however, the meta-analysis of the trials finds no effect.
Benefits
- Boosts selenium in those who are deficient: one nut per day (about 5 g) for 3 months increased plasma selenium from 18.8 to 104.0 µg/L in deficient dialysis patients.
- Across eight randomized trials, the meta-analysis finds a sharp rise in blood selenium and an increase in the activity of glutathione peroxidase, an antioxidant enzyme.
- Performs as well as a supplement: in vegans as in omnivores, 55 µg of selenium per day in the form of Brazil nut butter raised blood selenium as much as a supplement, in two weeks.
- With 13 g per day of granulated nuts for twelve weeks, plasma selenium went from 87.0 to 180.6 µg/L and glutathione peroxidase activity increased by 24.8% in people with hypertension and high cholesterol.
- In a diet at −500 kcal per day, 8 g of Brazil nuts per day for 8 weeks lowered C-reactive protein, TNF and two interleukins, and improved gut permeability, compared to the same diet without nuts, in overweight women.
- In obese adolescent girls, 15 to 25 g per day for 16 weeks lowered total cholesterol, triglycerides and oxidized LDL compared to placebo.
- In elderly people with mild cognitive impairment, one nut per day for 6 months improved verbal fluency and the ability to reproduce drawings more than the absence of nuts (pilot trial: 11 treated individuals versus 9 controls at the end).
Precautions
A nut very rich in selenium (about 1261 µg) each day for 2 months increased the expression of inflammation genes in obese women who were not selenium-deficient, without changing inflammation markers in the blood. One nut per day for 2 months increased cadmium, a toxic metal, in the plasma of obese women; the authors nevertheless consider the heavy metal content of the nuts to be safe. Limitations: on cholesterol, the meta-analysis of eight randomized trials finds no effect on total cholesterol, HDL or LDL. In treated hypertensive patients with high cholesterol, 13 g per day for 90 days did no better than placebo, either on cholesterol or on blood pressure. In hypertensive patients with high cholesterol taking multiple medications, 13 g per day improved neither the reactivity nor the density of small vessels. In people with coronary heart disease, one nut per day for 3 months changed neither TMAO nor glutathione peroxidase activity. A shake with 15 g of Brazil nuts and 30 g of cashews was no more satiating than a shake of the same composition without nuts. Many trials are small; the effect on inflammation comes from a non-randomized trial, and the rise in thyroid hormones in dialysis patients from a trial without a control group. The selenium and glutathione peroxidase response to nuts varies according to genetic variants, according to a small pilot trial.
Recommended dosage
1 nut per day (about 5 g) in most trials; 8 g, 13 g or 15 to 25 g per day in others.
How to take it
- For whom: most trials involve sick people (dialysis, coronary heart disease, hypertension with high cholesterol, mild cognitive impairment) or overweight women; few involve healthy adults.
- Dose: one nut per day is the most tested dose. Its selenium content varies enormously: about 48 µg per day for six nuts in one trial, about 1261 µg for a single nut in another.
- Duration: from a single dose to 6 months; 3 months in most trials.
- Regularity: 12 months after stopping, the selenium of dialysis patients remained higher than before the nuts, but significantly lower than at the end of the cure.
- Form: whole nuts, nut butter or partially defatted flour depending on the trials; at an equal selenium dose, the butter performed as well as a supplement.
Did you know?
The selenium content of a Brazil nut varies enormously: in one trial, six nuts provided approximately 48 µg per day; in another, a single nut provided approximately 1261 µg.
What the studies say
This systematic review and meta-analysis of randomized clinical trials evaluated the effects of Brazil nuts on health. The results show a significant positive effect on blood selenium concentration and the activity of glutathione peroxidase, an antioxidant enzyme. In contrast, no significant effect was found on blood lipid levels such as total cholesterol, HDL, or LDL. The consumption of Brazil nuts could therefore improve selenium status and have antioxidant effects.
Godos J, Giampieri F, Micek A, Battino M, Forbes-Hernández TY, Quiles JL, Paladino N, Falzone L, Grosso G. — Antioxidants (Basel, Switzerland) (2022) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more