A new study shows that adding selenium-rich Brazil nuts to an energy-restricted diet significantly reduces inflammation and improves gut health in women, making it a promising dietary strategy for managing obesity-related symptoms.
Brazil nut (Bertholletia excelsa HBK) consumption in an energy restriction intervention reduces proinflammatory markers and intestinal permeability in overweight/obese women: a controlled trial (The Brazil Nut Study). Image credit: Igor Dutina/Shutterstock
In a recent study published in The Journal of Nutrition, researchers evaluated the effects of daily consumption of selenium-rich Brazil nuts (BN) on inflammatory biomarkers and intestinal permeability (IP) in overweight/obese women following an energy-restricted diet.
background
Obesity is a metabolic disorder characterized by increased body fat, oxidative stress, and chronic low-level inflammation, which contributes to conditions such as hypertension, diabetes, and cardiovascular disease. This inflammatory state also promotes impaired intestinal permeability, further exacerbating inflammation. Management of obesity typically involves energy restriction and adopting a healthy diet. Certain foods, such as BN, are known to have anti-inflammatory properties due to their high selenium (Se) content, which plays an important role in antioxidant defense and inflammation control. However, the full impact of BN on gut health remains unknown and requires further investigation.
About the Research
This was a non-randomized, controlled, parallel, 8-week dietary intervention aimed at investigating changes in inflammatory biomarkers and IP in overweight and obese women. The study was conducted at the Department of Nutrition and Health, Federal University of Viçosa (UFV), Brazil, from June 2019 to September 2021.
Participants were adult women aged 20-55 years with a body mass index (BMI) ≥ 27kg/m² and < 30kg/m², elevated body fat (≥ 32%), waist circumference (WC) ≥ 80cm, and at least one other cardiometabolic risk factor. Obese women (BMI ≥ 30kg/m²) were also included, regardless of additional risk factors. Exclusion criteria included pregnancy, menopause, serious illness, use of certain medications, and regular consumption of nuts.
The study consisted of an energy restriction intervention, in which participants were assigned to either a nut-free diet (control group) or a BN group consuming 8 g of BN daily. The aim of the intervention was to reduce body weight by at least 4 kg. To ensure a balanced diet, both groups consumed a salad dressing with a restricted amount of fat, with the BN group receiving canola oil and the control group receiving soybean oil. Anthropometric measurements, dietary intake, body composition and blood samples were collected at baseline and at the end of the study. IP was assessed with the lactulose/mannitol (LM) test and inflammatory markers were measured in plasma.
Statistical analyses were performed to compare changes in variables within and between groups, and correlation and regression analyses were used to explore the relationships between Se concentrations, inflammatory cytokines, and IP. The study had 97% power to detect differences in IP results between groups.
Research findings
Of the 56 women assigned to the control (CO) or BN treatment group, 49 (87.5%) completed the intervention. Forty-six (82.1%) women were included in the analysis. The mean age of participants was 34.0 years, 17.4% were classified as overweight and 82.6% as obese. Of the obese participants, 60.9% were in class I, 10.9% in class II, and 10.8% in class III obesity categories. At baseline, no significant differences were observed between groups in anthropometric measurements, body composition, or serum Se concentrations.
Before the intervention, the CO group had a higher intake of polyunsaturated fatty acids (PUFA) compared to the BN group. During the intervention period, the CO group reduced their intake of saturated fatty acids (SFA) and the BN group increased their intake of PUFA and fiber. During the 8-week intervention period, the most significant difference between the groups was selenium intake.
No significant differences were observed between the groups in terms of energy restriction (CO group: −253.7 ± 169.4 kcal/day; BN group: −265.8 ± 141.8 kcal/day), weight loss (CO group: −2.4 ± 0.4 kg; BN group: −3.2 ± 0.4 kg), or waist circumference loss (CO group: −3.6 ± 0.6 cm; BN group: −5.2 ± 0.6 cm). However, the BN group had a significantly increased serum Se concentration (159.4 ± 17.1 μg/L) compared with the CO group (−1.8 ± 8.5 μg/L), confirming compliance with BN intake.
At the end of the 8-week intervention, the BN group showed greater reductions in inflammatory markers, including C-reactive protein (CRP), tumor necrosis factor (TNF), interleukin-1β (IL1-β), and interleukin-8 (IL-8), compared with the CO group. The percentage of women with normal CRP levels (<3 mg/L) increased from 24.0% to 36.0% in the BN group, whereas it decreased in the CO group (23.8% to 4.7%). Even BN participants who did not achieve their weight loss goal of 4 kg or more showed greater reductions in TNF, IL1-β, and IL-8 than the CO group. BN groups who lost more weight also showed greater reductions in CRP levels.
The BN group also showed lower lactulose excretion and LM ratio, but changes in IP variables were similar between the two groups. Small but significant correlations were found between changes in serum Se and IL1-β and IL-8 levels. Furthermore, changes in IL-8 were positively correlated with changes in LM ratio. Linear regression analysis further confirmed that increases in serum Se predicted decreases in IL-8, and decreases in IL-8 predicted improvements in LM ratio.
Conclusion
In summary, in this study, daily BN intake significantly reduced inflammatory markers, including CRP, TNF, IL1-β, and IL-8, urinary lactulose excretion, and LM ratio compared with the CO group. The BN group also showed a significant increase in serum Se levels, which correlated with a reduction in proinflammatory cytokines (IL-8 and IL1-β). Furthermore, improved intestinal permeability, as measured by the LM ratio, was associated with a reduction in IL-8. These findings suggest that the benefits of BN intake are a selenium-dependent mechanism, with potential implications for inflammation and gut health.
Journal References:
Brenda Kelly Souza Silveira, Alessandra da Silva, Daniela Mayumi Usuda Prado Rocha, et al. “Brazil nut (Bertholletia excelsa HBK) consumption in an energy restriction intervention reduces proinflammatory markers and intestinal permeability in overweight/obese women: a controlled trial (Brazil Nut Study)”, The Journal of Nutrition (2024), DOI – 10.1016/j.tjnut.2024.07.016, https://www.sciencedirect.com/science/article/pii/S0022316624003973
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