Brazil nuts reduce inflammation and improve gut health in women on restricted diets

By Vijay Kumar MalesuReviewed by Susha Cheriyedath, M.Sc.Sep 23 2024

New research shows that adding selenium-rich Brazil nuts to energy-restricted diets significantly reduces inflammation and enhances gut health in women, offering a promising dietary strategy for managing obesity-related conditions.

Brazil Nut (Bertholletia excelsa H.B.K.) Consumption in Energy-Restricted Intervention Decreases Proinflammatory Markers and Intestinal Permeability of Women with Overweight/Obesity: A Controlled Trial (Brazilian Nuts Study). Image Credit: Igor Dutina / Shutterstock

In a recent study published in The Journal of Nutrition, researchers evaluated the effects of daily selenium-rich Brazil nut (BN) consumption 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-grade inflammation, which contribute to conditions like hypertension, diabetes, and cardiovascular disease. This inflammatory state also promotes disruptions in intestinal permeability, further exacerbating inflammation. Managing obesity typically involves energy restriction and adopting a healthy diet. Certain foods, like BNs, are recognized for their anti-inflammatory properties due to their high selenium (Se) content, which plays a crucial role in antioxidant defenses and inflammation control. However, the full impact of BNs on intestinal health remains unclear and requires further exploration.

About the study 

The present study was a nonrandomized, controlled, parallel, 8-week dietary intervention aimed at investigating changes in inflammatory biomarkers and IP in women with overweight and obesity. The study was conducted at the Department of Nutrition and Health of the Universidade Federal de Viçosa (UFV) in Brazil between June 2019 and September 2021. 

Participants were adult women aged 20–55 years with a Body mass index (BMI) ≥27 kg/m² and <30 kg/m², increased body fat (≥32%), and waist circumference (WC) ≥80 cm, along with at least one other cardiometabolic risk factor. Women with obesity (BMI ≥30 kg/m²) were also included, regardless of additional risk factors. Exclusion criteria included pregnancy, menopause, serious illnesses, use of certain medications, and regular nut consumption.

The study consisted of an energy-restricted intervention, with participants assigned to either a control group following a nut-free diet or a BN group consuming 8 g of BNs daily. The intervention aimed to reduce body weight by at least 4 kg. To ensure dietary balance, both groups consumed salad dressings with controlled amounts 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 through the lactulose/mannitol (LM) test, and inflammatory markers were measured in plasma.

Statistical analyses were conducted to compare changes in variables within and between groups, with correlations and regression analyses used to explore the relationships between Se concentrations, inflammatory cytokines, and IP. The study had 97% power to detect differences in IP outcomes between groups.

Study results 

Of the 56 women assigned to the control (CO) or BN treatment groups, 49 (87.5%) completed the intervention. For the analysis, 46 (82.1%) women were included. The participants' average age was 34.0 years, with 17.4% classified as overweight and 82.6% as obese. Among 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 the groups in anthropometric measurements, body composition, or serum Se concentrations. 

Before the intervention, the CO group had a higher intake of polyunsaturated fatty acids (PUFAs) compared to the BN group. Throughout the intervention, the CO group reduced their saturated fatty acid (SFA) intake, while the BN group increased their intake of PUFA and fiber. The most notable difference between the groups during the 8-week intervention was in Se intake.

No significant differences were found between the groups regarding energy restriction (CO group: −253.7 ± 169.4 kcal/d; BN group: −265.8 ± 141.8 kcal/d), weight loss (CO group: −2.4 ± 0.4 kg; BN group: −3.2 ± 0.4 kg), or waist circumference reduction (CO group: −3.6 ± 0.6 cm; BN group: −5.2 ± 0.6 cm). However, the BN group exhibited a significant increase in serum Se concentrations (159.4 ± 17.1 μg/L) compared to the CO group (−1.8 ± 8.5 μg/L), confirming adherence to BN intake.

At the end of the 8-week intervention, the BN group showed significant reductions in inflammatory markers, including C-reactive protein (CRP), tumor necrosis factor (TNF), interleukin-1β (IL1-β), and interleukin-8 (IL-8), compared to the CO group. The percentage of women with normal CRP levels (<3 mg/L) in the BN group increased from 24.0% to 36.0%, while it decreased in the CO group (23.8% to 4.7%). Even participants in the BN group who did not achieve the target weight loss of ≥4 kg showed more significant reductions in TNF, IL1-β, and IL-8 than those in the CO group. Those in the BN group who lost more weight also demonstrated larger reductions in CRP levels.

The BN group also presented lower values for lactulose excretion and LM ratio, though the changes in IP variables were similar between the two groups. Modest but significant correlations were found between changes in serum Se and IL1-β and IL-8 levels. Additionally, changes in IL-8 were positively correlated with changes in the LM ratio. Linear regression analysis further confirmed that increases in serum Se were predictive of reductions in IL-8, while decreases in IL-8 were predictive of improvements in the LM ratio.

Conclusions 

To summarize, in this study, daily BN consumption significantly reduced inflammatory markers such as CRP, TNF, IL1-β, and IL-8, as well as urinary lactulose excretion and the LM ratio, compared to the CO group. The BN group also showed a substantial increase in serum Se levels, which correlated with reductions in proinflammatory cytokines (IL-8 and IL1-β). Additionally, improvements in intestinal permeability, as measured by the LM ratio, were linked to decreases in IL-8. These findings suggest a selenium-dependent mechanism for the benefits of BN consumption, with potential implications for inflammation and intestinal health.