Effects of Adding Lean Red Meat to A Vegetarian Diet on Gut Microbiota in Young Adults: A Randomized Controlled Trial

OBJECTIVES: Diet strongly affects human metabolic health, partly by modulating gut microbiota. To date, limited research has assessed the effects of different types of red meat on gut microbiota in human adults. We aim to assess the effects of consuming a healthy US-style eating pattern, without or with unprocessed or processed lean red meats (LRM), on gut microbiota in generally healthy young adults. Secondary outcomes are fecal short-chain fatty acids (SCFAs) and cardiovascular risk factors. METHODS: We conducted a randomized-controlled, crossover trial with three 3-week dietary interventions, each separated by a 5-week washout with a habitual diet. Five females and 7 males (age 26.5 ± 1.5 years old, BMI 23.7 ± 0.9 kg/m(2)) consumed the following three diets in random order: a healthy lacto-ovo vegetarian diet (LOV), the LOV diet with 3 oz/day of cooked unprocessed LRM, or with 3 oz/day of cooked processed LRM. Fecal and blood samples were collected before and during the last 2 weeks of each diet. We measured changes in fecal microbial community structure using 16S amplicon sequencing targeting the V4 region (primers 515F-806R). Community diversity, structure, and taxonomic composition were computed using mothur v.1.39.3. RESULTS: After consuming a healthy vegetarian diet without or with adding unprocessed or processed LRM, community diversity and structure of gut microbiota were not significantly altered at the phylum level. However, the diets differentially affected bacterial abundances (2 of 14 families and 5 of 42 genera) with varied directionality. Adopting the prescribed healthy eating pattern for 3 weeks did not influence fecal SCFA contents, serum HDL-C or triglycerides concentrations, or blood pressures. Serum total cholesterol and LDL-C concentrations were reduced by diet, independent of LRM intake. CONCLUSIONS: These results suggest adding three ounces per day of unprocessed or processed lean red meats to a healthy vegetarian diet that improved blood lipids and lipoproteins in the short term does not influence the overall gut microbial composition but may influence the abundances of specific families or genera. Further research is warranted to assess potential effects of red meat on gut bacteria. FUNDING SOURCES: The Pork Checkoff, North Dakota Beef Commission, Beef Checkoff, and Foundation for Meat and Poultry Research and Education.