Eating Brazil nuts daily may reduce inflammation, improve gut health

Researchers from the Department of Nutrition and Health at Universidade Federal de Viçosa, Brazil, conducted an eight-week non-randomized controlled trial between June 2019 and September 2021. It involved 56 adult women ages 20–55, with an average age of 34.

Participants included those who were overweight with specific cardiometabolic risk factors (17.4%) or had obesity (82.6%), regardless of risk factors.

The researchers excluded people who were pregnant, lactating, in menopause, athletes, vegan, had certain medical conditions, were using specific medications, experienced significant weight changes, consumed nuts regularly, and had other potential study interferences.

They split participants into control and Brazil nut groups, both of which received customized menu options with about 500 fewer calories than their estimated daily needs.

The researchers’ macronutrient distribution was 50% carbohydrates, 30% fats, and 20% proteins, following established obesity management guidelines. They aimed for participants to lose at least 4 kilograms over 8 weeks.

The researchers also provided each group with controlled-ingredient salad dressings to balance fat and calorie intake between groups.

The diets were as follows:

• control group — followed a nut-free diet with 10 grams of soybean oil-based salad dressing with lemon daily
• Brazil nut group — consumed 8 grams of Brazil nuts (347.2 micrograms of selenium) as a morning snack and 5 grams of canola oil-based salad dressing with lemon daily.

A nutritionist provided individualized counseling and monitored diet adherence biweekly, including alcohol consumption. Participants who did not adhere to the study protocol were excluded from the final sample.

Researchers analyzed inflammatory markers in the blood and selenium levels. They also tested intestinal permeability using the lactulose/mannitol test (LM ratio).

They used statistical analyses to assess group changes and relationships among the variables, with a 97% power to detect differences in intestinal permeability.

Of the 56 recruited women, 46 (82.1%) were included in the final sample. At baseline, the control group had a higher intake of polyunsaturated fats than the Brazil nut group.

During the intervention, the control group had reduced saturated fat, while the Brazil nut group increased their intake of polyunsaturated fats and dietary fiber.

Both groups achieved similar calorie restrictions, weight loss (about 3 kilograms), and small reductions in waist circumference.

The researchers noted that the group consuming Brazil nuts showed a significant increase in selenium levels compared to the control group, demonstrating adherence to their Brazil nut intake.

Compared to the control group, the Brazil nut group also exhibited lower values of inflammatory markers, including C-reactive protein, tumor necrosis factor, interleukin-1β (IL1-β), and interleukin-8 (IL-8), indicating an improvement in systemic inflammation.

In the Brazil nut group, C-reactive protein levels decreased from 7.1 mg/L to 5.6 mg/L at the end of 8 weeks. In contrast, the control group saw an increase from 8.0 to 9.4 mg/L. The mechanism behind the changes in C-reactive protein levels remains unclear, but they may be linked to intestinal permeability and gut inflammation.

Additionally, women in the Brazil nut group who lost more weight showed more significant reductions in C-reactive protein levels.

The Brazil nut group also showed lower lactulose excretion and LM ratio values, indicating slightly improved intestinal permeability markers compared to the control group. However, the changes were statistically similar across both groups.

In further analyses, researchers found that higher blood selenium levels were linked to lower inflammation markers, particularly IL1-β and IL-8, with IL-8 also relating to changes in the LM ratio. These results suggest selenium levels could predict shifts in markers of systemic inflammation and gut permeability.

This study had a small sample size and a short duration. It was limited to young and middle-aged women recruited in Brazil, so the findings might not be generalizable to other populations.

The study participants were not blinded to the interventions, were not randomized, and could not follow their intended calorie restrictions. Additionally, diet adherence was mainly monitored through self-reports, which can introduce errors.

Alyssa Simpson, RDN, CGN, CLT, a registered dietitian, certified gastrointestinal nutritionist, and owner of Nutrition Resolution in Phoenix, AZ, who was not involved in the study, calls for further research to isolate diet variables to clarify their effects and interactions.

She told Medical News Today that “the findings indicate that selenium from Brazil nuts significantly influences inflammation and intestinal permeability,” but “the simultaneous increases in polyunsaturated fats and fiber intake complicate attributing the effects solely to selenium.”

“A more controlled study design that treats selenium, polyunsaturated fats, and fiber as separate interventions would help identify how each factor independently affects inflammation and intestinal health,” she proposed.

Simpson explained that Brazil nuts may reduce inflammation and improve gut health in women who are overweight or obese on calorie-restricted diets primarily due to their high selenium content.

“Selenium acts as a powerful antioxidant, boosting selenoproteins that neutralize oxidative stress and reduce pro-inflammatory cytokines, thereby improving intestinal permeability. The nuts also provide polyunsaturated fats and fiber, which independently support anti-inflammatory processes and gut health, likely working synergistically with selenium.”

— Alyssa Simpson, RDN, CGN, CLT

MNT also spoke with Thomas M. Holland, MD, MS, a physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, who was not involved in the study.

He provided a similar explanation of the mechanisms underlying the study results, noting that “in this study, increased selenium levels correlated with reductions in inflammatory cytokines like IL-8 and IL1-β and improvements in intestinal permeability — which can lead to more complete absorption of digested foods.”

“The effects may apply to men as well, given the universal role of selenium in inflammatory pathways, though further research would be needed to confirm this,” he said.

Kiran Campbell, RDN, a registered dietitian and medical nutrition advisor at Dietitian Insights, who was not involved in the study, told MNT that our bodies can’t produce selenium.

So, we must get selenium from animal-based sources such as fish and seafood, poultry, meat, or plant-based sources like sunflower seeds and Brazil nuts, she said.

Campbell pointed out that a single Brazil nut (about 5 grams) provides approximately 96 micrograms of selenium, nearly double the daily recommended intake of 55 micrograms for most adults.

Still, according to Simpson, the typical recommendation is about 1–2 Brazil nuts per day for most people, which aligns with the safe upper limit of 400 micrograms per day as per the National Institute of Health.

However, “consuming 4–5 Brazil nuts daily or more could risk exceeding this limit,” she warned.

Campbell highlighted that the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) has set a lower recommended upper limit for selenium in 2023 — a maximum of 255 micrograms daily for adult men and women.

She advises monitoring selenium intake from supplements and foods to avoid selenium toxicity, especially if you eat Brazil nuts and other selenium sources regularly.

Symptoms of selenium toxicity can include “brittle nails, hair loss, skin rashes, and intestinal and neurological issues, among other things,” Campbell said.

Ultimately, both dietitians, along with Holland, suggest that mindfully incorporating 1–2 Brazil nuts per day may be practical and beneficial, as it may help reduce inflammation and improve gut health.

For those concerned with what type of Brazil nut to purchase, organic and raw options might be best, but the difference in nutrients between raw versus roasted nuts may be minimal.

The experts emphasized that Brazil nuts should not be considered a standalone solution. Instead, they should be included alongside other gut-health-promoting foods as part of a healthy dietary pattern, such as the Mediterranean or MIND diet.