A new clinical trial from Penn State offers a more nuanced look at how lean red meat fits into a heart-healthy eating pattern. In a tightly controlled crossover study, researchers found that moderate amounts of lean, unprocessed beef did not raise levels of trimethylamine N-oxide, or TMAO, when the meat was included in a Mediterranean-style diet. TMAO is an emerging biomarker that has been linked in some studies to cardiovascular disease risk.
Because the study was funded in part by the National Cattlemen’s Beef Association, a contractor to the Beef Checkoff, readers should interpret the findings within that context. The research design itself was rigorous: every participant completed four different four-week diet phases, and all meals and snacks were provided to ensure accuracy in what people actually ate.
“Observational evidence shows higher levels of TMAO are associated with higher cardiovascular risk,” said Kristina Petersen, associate professor of nutritional sciences and senior author of the study, which was published in the Journal of the American Heart Association. “In this study we wanted to better understand the relationship between lean beef consumption and TMAO levels in the context of a healthy, Mediterranean style diet.”
The Mediterranean diets used in the trial were rich in fruits, vegetables and olive oil and lower in saturated fat than the average American diet. Participants ate either 0.5 ounces, 2.5 ounces or 5.5 ounces of lean beef per day while following these patterns. For comparison, they also completed a four-week period eating an average American diet that included 2.5 ounces of regular, non-lean beef.
When participants ate 0.5 or 2.5 ounces of lean beef in a Mediterranean diet, their TMAO levels were lower than when they ate the American diet. When they consumed the highest amount of lean beef, or 5.5 ounces per day, their TMAO levels were similar to those seen in the American diet. According to the researchers, this suggests the overall quality of the diet may matter more than the amount of lean beef in it.
“We chose 2.5 ounces of lean beef because that approximates the amount of beef that the average American consumes each day,” said Zachary DiMattia, doctoral candidate in nutritional sciences and lead author on the study. “This study suggests that, in the context of a healthy dietary pattern, people may be able to include similar amounts of lean beef without increasing their TMAO levels.”
The team also looked at the gut microbiome and found that all Mediterranean diet periods improved microbiome diversity compared with the American diet. That adds to a growing body of research showing that dietary patterns rich in plants and unsaturated fats support a healthier gut environment.
This trial focused specifically on TMAO, so the findings should not be taken to mean that any amount of beef is risk-free for everyone. Petersen noted that the work was done in younger, generally healthy adults and did not include processed meats.
“Lean, moderately sized, unprocessed cuts of beef can be included as part of a healthy diet when people are consuming plenty of fruits, vegetables and healthy fats like olive oil,” DiMattia said.
For people aiming to improve heart health, the researchers said the most consistent advice remains the same: build meals around vegetables, fruits, whole grains and healthier fats, and include animal proteins in reasonable amounts.
This research was funded by the National Cattlemen’s Beef Association, a contractor to the Beef Checkoff, and Penn State. According to the authors, the funders did not influence the study design, data collection, analysis or publication.