Effect of Varying Quantities of Lean Beef as Part of a Mediterranean-Style Dietary Pattern on Gut Microbiota and Plasma, Fecal, and Urinary Metabolites: A Randomized Crossover Controlled Feeding Trial

BACKGROUND: Consumption of trimethylamine N-oxide (TMAO) precursors, such as carnitine found in lean beef, raises circulating TMAO concentrations; however, a healthy dietary pattern may attenuate these effects. METHODS: This randomized, 4-period crossover, controlled-feeding study investigated the effects of Mediterranean-style (MED) diets (carbohydrate 42%, protein 17%, fat 41%) with 14 (MED0.5; 0.5 oz), 71 (MED2.5; 2.5 oz), and 156 (MED5.5; 5.5 oz) g/day/2000 kcal of lean beef, compared with an average American diet (AAD; carbohydrate 52%, protein 15%, fat 33%; 71 g/day/2000 kcal beef), on gut microbiota composition and plasma, urinary, and fecal metabolites including TMAO and precursor molecules. Thirty generally healthy individuals consumed each diet for 4 weeks with a ≥1-week washout. Fasting blood samples, 24-hour urine samples, and fecal samples were collected at baseline and at the end of each 4-week diet period. Metabolites were measured by proton nuclear magnetic resonance and liquid chromatography/mass spectrometry. Gut microbiota composition was measured using amplicon sequencing of the 16S rRNA gene. RESULTS: The 3 MED diets increased gut microbiota diversity compared with the AAD. Plasma TMAO was higher following the AAD compared with the MED0.5 (mean fold difference, 1.78 [95% CI, 1.05–3.06]) and MED2.5 (2.04 [95% CI, 1.18–3.52]). Urinary TMAO was higher following the AAD compared with the MED0.5 (1.88 [95% CI, 1.19–2.97]), MED2.5 (2.15 [95% CI, 1.37– 3.39]), and MED5.5 (1.76 [95% CI, 1.12–2.77]). CONCLUSIONS: Compared with an AAD, inclusion of up to 71 g/day of lean beef in a Mediterranean-style diet increased gut microbiota diversity and lowered TMAO concentrations in healthy adults.