Meat Consumption and Gut Microbiota: a Scoping Review of Literature and Systematic Review of Randomized Controlled Trials in Adults

Abstract

Emerging research indicates the importance of gut microbiota in mediating the relationship between meat intake and human health outcomes. We aimed to assess the state of available scientific literature on meat intake and gut microbiota in humans (PROSPERO, International Prospective Register of Systematic Reviews, CRD42020135649). We first conducted a scoping review to identify observational and interventional studies on this topic. Searches were performed for English language articles using PubMed, Cochrane Library, Scopus, and CINAHL (Cumulated Index to Nursing and Allied Health Literature) databases from inception to August 2021 and using keywords related to meat (inclusive of mammalian, avian, and aquatic subtypes) and gut microbiota. Of 14,680 records, 85 eligible articles were included in the scoping review, comprising 57 observational and 28 interventional studies. One prospective observational study and 13 randomized controlled trials (RCTs) were identified in adults without diagnosed disease. We included the 13 RCTs, comprising 18 comparisons, in the systematic review to assess the effects of higher and lower intakes of total meat and meat subtypes on the gut microbiota composition. The bacterial composition was differentially affected by consuming diets with and without meat or with varied meat subtypes. For example, higher meat intake tended to decrease population sizes of genera Anerostipes and Faecalibacterium, but it increased the population size of Roseburia across studies. However, the magnitude and directionality of most microbial responses varied, with inconsistent patterns of responses across studies. The data were insufficient for comparison within or between meat subtypes. The paucity of research, especially among meat subtypes, and heterogeneity of findings underscore the need for more well-designed prospective studies and full-feeding RCTs to address the relationships between and effects of consuming total meat and meat subtypes on gut microbiota, respectively.

Keywords: animal-based protein sources; dietary pattern; fish; poultry; red meat; seafood.

FIGURE 1

PRISMA flow diagram of the search and screening process.

FIGURE 2

Percentages of (A) all, (B) primary, and (C) secondary comparisons that reported gut microbial outcomes at the specified levels, with (darker gray) or without (lighter gray) significant effects of diet on gut microbiota. The effects refer to whether significant changes or differences in microbiota composition were reported by authors of the included studies. The percentages and numbers of studies showing any significant effects out of the total number of studies that reported the specific outcome were denoted in percentages and n.

FIGURE 3

Percentages of primary comparisons that did vs. did not report significant effects of diet on gut microbiota based on the (A) type of randomized controlled trial (RCT), (B) length of RCT, (C) type of diet, and (D) level of dietary control. The partial level of dietary control (D) encompasses the studies in which partial foods were provided with or without control over basal dietary intake, as well as studies in which 1 group was controlled and 1 group followed a habitual diet. The significant effects refer to whether significant changes or differences in microbiota composition were reported by authors of the included studies. The percentages and numbers of studies showing any significant effects out of the total number of studies with the specific study characteristics were denoted in percentages and n.