National Cattlemen’s Beef Association funded research finds that Mediterranean-style eating with lean beef produces less trimethylamine N-oxide (TMAO) compared with a typical American diet that included the same amount of beef.
Cardiovascular risk has been linked to diet quality and to microbiome-derived metabolites such as TMAO. Eating beef has been shown to increase cardiovascular risk due to high saturated fats raising LDL cholesterol, and chemicals produced by gut bacteria from red meat that increase TMAO levels, promoting arterial plaque buildup, and inflammation. Consuming red and processed meats is linked to a higher risk of heart disease, heart attacks, strokes, and death.
Previous clinical trials have hinted that lean, unprocessed red meat can fit within heart-healthy patterns without worsening traditional risk factors.
In the study, “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,” published in Journal of the American Heart Association, researchers conducted a randomized four-round crossover controlled-feeding trial, researchers compared Mediterranean-style diets containing 14, 71, or 156 g/day per 2,000 kcal of lean beef with an average American diet containing 71 g/day per 2,000 kcal, and in a post hoc exploratory analysis evaluated gut microbiota and TMAO-related metabolites.
Each diet period lasted four weeks with at least a one-week washout. Participants included 30 generally healthy adults from the Penn State site who completed at least two full diet periods.
Blood, 24-hour urine, and fecal samples were collected at baseline and end of each period. Plasma, urine, and fecal metabolites were quantified by proton nuclear magnetic resonance and liquid chromatography–mass spectrometry.
Gut microbiota composition was profiled by 16S rRNA gene amplicon sequencing. Compliance exceeded 90%. Randomization followed an orthogonal Latin-square design with blinding of coordinators, investigators, analysts, and statisticians for outcome assessment and analysis.
Sodium was lower in the Mediterranean-style menus, with target values reported as below 2,300 mg per 2,000 kcal versus around 3,500 mg per 2,000 kcal in the average American diet.
Compared with the average American diet menu, Mediterranean-style menus differed on several reported components. Mediterranean-style was 20–31% higher in total fat, 7–13% higher in protein, 91–110% higher in monounsaturated fat, 13–23% higher in polyunsaturated fat, 15–30% higher in fiber, 8–28% higher in marine n-3, and 20–32% higher in α-linolenic acid. The American diet was higher in carbohydrates by 20–33% and saturated fat by 28–54%.
Compared with the average American diet, Mediterranean-style diets differed in several reported outcomes. The Mediterranean-style was higher in gut microbiota diversity, 1.78–2.04-fold lower in plasma TMAO with 14 g and 71 g of lean beef per 2,000 kcal, 1.76–2.15-fold lower in urinary TMAO across 14 g, 71 g, and 156 g, and higher in plasma l-carnitine with 71 g and 156 g.
The American diet was higher in fecal choline than the Mediterranean-style diet, with 71 g. TMAO concentrations remained below the reported clinical cut point across all study diets.
Findings from the randomized crossover trial show that with beef held constant (71 g per 2,000 kcal), the average American diet produced higher plasma and urinary TMAO than Mediterranean-style eating. Within the Mediterranean-style pattern, raising lean beef from 14 g to 156 g per 2,000 kcal did not raise TMAO. Interpretation restricted to these endpoints points to the overall diet pattern, not beef, as the driver of the observed TMAO differences in this cohort.
It is important to note that this study was funded by the National Cattlemen’s Beef Association. While the research was conducted with rigorous controls and blinding, readers should consider the funding source when interpreting the results, as industry funding can introduce potential bias.
Outcomes were short-term TMAO, exploratory and not the prespecified primary endpoints of the parent trial, which was powered for LDL-C.