Brazil Nut
Best for
Improve thyroid function
Faint early signal 13 g/day 13 weeks 1 study, n=77 #3 of 7 studied
- 3 papers
- 2 of 21 outcomes
- 2 positive
Brazil nuts show a faint early signal for thyroid-related outcomes, including maternal and fetal thyroid needs, but evidence is too limited to establish a proven supplement benefit.
What brazil nut actually does
Thyroid hormones help regulate energy use, body temperature, heart rate, and digestion. 26077768
During pregnancy, the thyroid makes hormones that regulate metabolism and support fetal development. 26077768
| Outcome | Effect | Evidence | Dose | Time | Rank |
|---|---|---|---|---|---|
| Early research 2 | |||||
| Improve thyroid function Faint early signal Thyroid hormones help regulate energy use, body temperature, heart rate, and digestion. | | 1 RCT 1 papers · n=77 | 13 g | 13 wk | #3 /7 |
| Healthy thyroid function in pregnancy Faint early signal During pregnancy, the thyroid makes hormones that regulate metabolism and support fetal development. | | 1 RCT 1 papers · n=77 | 13 g | 13 wk | #4 /8 |
Effect tiers come from native-unit MCID where available, Cohen's d otherwise.
Dose, timing & forms
How much
The only thyroid-focused protocol used 13 g daily of Brazil nuts for about 13 weeks.3 That is a small weighed portion, not an invitation to snack freely from a bag. Since the thyroid signal is faint and the measured thyroid outcomes did not show a clear significant effect, there is no evidence-based higher dose to chase.3
When and how long
Use Brazil nuts as a consistent daily food if you choose to follow the studied approach, rather than taking them only when you feel low on energy.3 The trial duration was roughly three months, so thyroid blood markers, not same-day sensations, were the relevant outcome.3 Taking them with a meal is a practical choice, although the trial evidence does not establish a best time of day.3
Forms & standardisation
The research uses whole Brazil nuts, not a standardized Brazil nut extract.23 A food scale gives more control than counting nuts because their selenium content varies sharply by origin.12 If you want a predictable selenium dose, a labeled selenium product is easier to quantify than a variable whole food, but it is not interchangeable with the Brazil nut trials.
Studied range, by outcome
| Outcome | Studied range | Median effective | Duration | Evidence |
|---|---|---|---|---|
| Bring thyroid levels into range | 13 g | — | 13 wk | 1 paper |
What this is and how it works
- One study (n=77) reported positive thyroid-related endpoints for healthy thyroid balance and maternal-fetal thyroid needs.2
- Three papers reviewed here span 21 outcomes, with thyroid findings limited to early evidence.
- Brazil nuts deliver selenium in a concentrated food dose, making added supplements worth discussing with a clinician.
Brazil nuts are large seeds from a rainforest tree in South America. Their standout nutrient is selenium, a mineral your body uses in several protective enzymes and in thyroid hormone processing.1 The catch is that selenium levels swing widely from nut to nut because soil selenium differs across growing regions.12
Selenium helps build enzymes that switch thyroid hormone into its active form and help shield thyroid tissue from normal oxygen-related wear and tear.1 Think of selenium as a tiny replacement part in both the thermostat's control circuit and its surge protector. Brazil nuts raise selenium status efficiently, but the available thyroid trials remain small and early.23
Bottom line
Brazil nuts make sense for someone who enjoys them and wants a food source of selenium, but they are not a proven thyroid supplement. The thyroid evidence is early, small in effect, and too thin to guide treatment decisions.3 Skip the do-it-yourself high-dose approach if you already take selenium or are pregnant and have thyroid concerns. Get individualized guidance from your prenatal clinician.
Common questions
Do Brazil nuts support thyroid health?
How many Brazil nuts should you eat for selenium?
Can you eat Brazil nuts every day?
Are Brazil nuts useful during pregnancy?
Sources
Sources
Generated August 27, 2026