In a recent study published in The Journal of Nutrition, a group of researchers estimated dietary polyphenol intake in healthy adults and investigated its associations with gastrointestinal (GI) and systemic inflammation markers.
Study: Fine-scale Dietary Polyphenol Intake is Associated with Systemic and Gastrointestinal Inflammation in Healthy Adults. Image Credit: Goskova Tatiana/Shutterstock.com
Background
Due to their antioxidant and anti-inflammatory properties, the intake of polyphenol-rich foods (polyphenols) may reduce systemic inflammation and cardiovascular risk factors. However, polyphenol absorption and metabolism vary based on their structure, with only 5-10% absorbed in the small intestine and the rest reaching the large intestine. Here, polyphenols can influence gut health by suppressing inflammation, enhancing microbial diversity, and promoting short-chain fatty acid production.
Given the complexity of their metabolism, absorption, and bioefficacy, further research is needed to fully understand the differential effects of various polyphenol types on GI and systemic inflammation.
About the study
The present study conducted a secondary analysis of data from the United States Department of Agriculture (USDA) Nutritional Phenotyping Study, an observational cross-sectional study performed between 2015 and 2019 with approval from the University of California, Davis Institutional Review Board. The sample comprised 350 generally healthy adults aged 18 to 65 years with body mass indices ranging from 18.5 to 45 kg/m², recruited from the Davis, California area and balanced across sex, age, and body mass index (BMI) categories.
Participants with conditions such as pregnancy, antibiotic use, chronic diseases, hypertension, recent surgeries, or medications affecting relevant outcomes were excluded. Dietary intake was assessed through multiple 24-hour recalls using the Automated Self-Administered 24-hour Dietary Assessment Tool, and the reported foods were systematically disaggregated into individual ingredients. These ingredients were then mapped to the FooDB database to estimate polyphenol content accurately.
Primary outcomes measured included markers of GI inflammation (myeloperoxidase, fecal calprotectin (CAL), neopterin), systemic inflammation (C-reactive protein (CRP)), and GI permeability (plasma lipopolysaccharide binding protein (LBP)). Demographic and lifestyle information was collected via electronic surveys, and all statistical analyses were performed using RStudio.
Study results
The study analyzed the characteristics of 350 generally healthy adults with an average age of 40 ± 14 years and an average BMI of 27 ± 5 kg/m². The cohort had a balanced gender representation, with 186 females and 164 males. The majority (over 60%) identified as white, while 14% identified as Latinx or Hispanic, and 11.7% as Asian or members of an Asian subgroup. Most participants had at least a bachelor’s degree, with a range of reported household incomes. The study also collected additional clinical information, including anthropometrics and blood lipid profiles, which are detailed in other analyses of this cohort.
The average total polyphenol intake for this cohort was approximately 914 ± 50 mg per 1000 kcal/day. Polyphenol intake was observed to increase with age and decrease with BMI, with males consuming less than females. Even after adjusting for total fiber intake and total Healthy Eating Index (HEI) scores, age and sex continued to show a significant relationship with polyphenol intake, whereas BMI did not. Of the 3063 polyphenols identified in the FooDB database, 1483 were detected in the dietary data, representing 57 classes. On average, participants consumed 44 ± 4 polyphenol classes, with flavonoids being the most significant contributor to total polyphenol intake at approximately 495 ± 38 mg per 1000 kcal/day.
Tea emerged as a major food source of polyphenols, with 41% of the cohort consuming it regularly. Other significant sources included coffee, wine, and various fruits such as grapes, apples, blueberries, oranges, and strawberries. Additionally, by "ingredientizing" foods with multiple ingredients, wheat was identified as a polyphenol source. The study highlighted the importance of specific polyphenols, particularly those in the highest quartiles of user frequency and polyphenol intake, such as wheat products, sweet oranges (including orange juice), and common beans.
In terms of inflammation, total polyphenol intake was found to be negatively associated with fecal CAL after adjusting for BMI, age, and sex. However, this relationship disappeared when total fiber intake and HEI score were considered. Although total fiber intake did not correlate with the inflammatory markers, the HEI score was negatively associated with CAL. No significant relationship was observed between total polyphenol intake and other inflammatory markers such as CRP and LBP. However, sex and BMI were significant predictors of these markers, with males generally having lower CRP and LBP levels, and a positive correlation was observed between BMI and these markers.
Conclusions
To summarize, total polyphenol intake was negatively associated with GI inflammation, while prenol lipids and phenylpropanoic acids were linked to reduced GI permeability, primarily from olive products.
Machine learning identified a positive association between "cinnamic acids and derivatives" and systemic inflammation. Tea, coffee, and fruits were key polyphenol sources, with flavonoids as the largest contributor.
The findings suggest that polyphenols have varying effects on inflammation, influenced by individual differences in metabolism and gut microbiome activity.
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