How much do red and processed meats affect our gut health? Investigation of the gut microbiome following randomized controlled diets with and without red and processed meat: the EAT-WELL study

Abstract

Background: Red meat and processed meat are consumed globally and might be important sources of nutrients. However, in 2015 red meat was classified as a group 2A, a probable carcinogen, and processed meat was classified as group 1, a carcinogen by the International Agency for Research on Cancer. Despite the widespread availability and consumption of red and processed meat globally, their effect on the microbiome and health has yet to be fully elucidated. Methods: Data were obtained from the EAT-WELL Study (Effects on metabolism of AlTering protein sources in WELL-balanced meals), a randomized crossover feeding trial with two arms: a healthy diet following the 2015 Healthy Eating Index with 1 to 2 servings of red and processed meat per day (Diet A), and another one with no red and processed meat (Diet B). All diets were eucaloric and Diet B used other sources of protein such as fish, chicken, and plant protein. Each feeding period lasted 3 weeks, separated by a ~3-week washout period. A total of 20 healthy subjects completed the study (mean age 35.5). Stool samples were collected and 16S sequencing along with droplet digital polymerase chain reaction (ddPCR) were completed. ddPCR examined 3 genes for 2 bacterial enzymes: 1 for nitrate reductase (narG) and 2 for butyryl-CoA: acetate CoA-transferase (but). The main objective of this dissertation was to understand the effect of consumption of red and processed meats on the gut microbiome in healthy subjects under controlled conditions. Results: Differential abundance of taxa at the genus and family level was observed for the three targeted genes. Diet A increased narG counts when compared with baseline (p=0.032). Protein intake at baseline was a predictor of a decrease in alpha diversity following the dietary intervention (p=0.016 after Holm correction). In all the adjusted models that included baseline dietary intake, Diet B led to an increase in Streptococcus when compared with Diet A. No changes in beta diversity were observed in any of the models. Conclusion: While some taxa were found to be differentially abundant, red and processed meat did not lead to a broad shift in the microbiome community structure in the short term. However, longitudinal cohort studies are better suited to understand chronic dietary intake change. The interplay between host diet, bacteria, cross-feeding, and bacterial metabolism is highly complex and more studies with metatranscriptomics and metagenomic approaches are needed.