The Impact of Egg Consumption on Gastrointestinal Health: A Systematic Literature Review and Meta-Analysis

Objective: Eggs are a valuable source of nutrients and bioactive compounds that may influence the gastrointestinal tract by modulating the microbiome, promoting the production of gastrointestinal-related metabolites, and mediating inflammation. Limited human studies have explored the effects of whole egg intake on indices of gastrointestinal health. This systematic literature review aimed to synthesise research investigating the impact of whole egg consumption on markers of gastrointestinal health. Methods: Five databases were searched from inception until July 2024. Studies were included if they examined the link between whole egg consumption and gastrointestinal markers, including symptoms, gut microbiome composition, inflammation, colonic fermentation, and egg-derived metabolites such as trimethylamine N-oxide (TMAO) in healthy adults. Two reviewers independently conducted title and abstract and full-text screening, with conflicts resolved by a third reviewer. Similarly, two authors conducted data extraction, which was verified by a third. A risk of bias assessment was conducted using validated tools. Random effects meta-analyses were performed to summarise the effect of egg consumption on TMAO, choline, and C-reactive protein (CRP). Results: Twenty-two studies were included in a narrative synthesis and ten in the meta-analyses. Nine were randomised controlled trials (RCTs), three were non-randomised intervention trials, eight were cross-sectional, and two were prospective cohort studies. Meta-analyses indicated that egg consumption did not impact plasma TMAO (n = 6, p = 0.22) or CRP (n = 3, p = 0.45) concentrations but did increase plasma choline (n = 5, p < 0.001) in the short term (≤4 weeks). Four studies found correlations between habitual egg consumption and specific gut bacteria, although results varied as egg consumption was both positively and negatively associated with butyrate-producing genera. Conclusions: This review found conflicting results regarding egg consumption and most gastrointestinal outcomes, highlighting that future studies are needed to explore links between habitual egg intake and plasma TMAO, microbial diversity, and inflammation (PROSPERO registration: 408532).