Mediterranean diet with lean beef shows no spike in heart-risk indicator: Study

By Admin

20 Nov, 2025

A new study from Penn State University is challenging long-held assumptions about red meat and heart health. For years, beef has carried a reputation for increasing cardiovascular risk but new evidence suggests that may not be the case when lean beef is eaten in moderation within a Mediterranean-style diet. According to findings published in the Journal of the American Heart Association, moderate portions of lean beef did not raise levels of trimethylamine N-oxide (TMAO), an emerging indicator linked to cardiovascular disease.

Understanding TMAO and Why It Matters
TMAO is a compound produced when the body breaks down certain foods, particularly animal products like beef. Elevated TMAO levels have been associated with a higher likelihood of heart disease, prompting researchers to explore how different eating patterns influence this marker. The Penn State team wanted clarity on whether lean beef often considered a healthier alternative would still raise TMAO when paired with an otherwise heart-friendly diet.

Kristina Petersen, associate professor of nutritional sciences at Penn State and senior author of the study, said the goal was “to better understand the relationship between lean beef consumption and TMAO levels in the context of a healthy, Mediterranean-style diet.”

Four Diets, One Group, and Highly Controlled Meals
The analysis drew from a tightly controlled feeding trial involving 30 adults. Every participant rotated through four distinct four-week diets, separated by one-week breaks. Because the same group tried every diet, researchers could confidently compare results without worrying about differences in participants’ health or habits.

The four diets included:

• A typical American diet high in saturated fats, low in fruits, vegetables, and olive oil featuring 2.5 ounces of regular (non-lean) beef per day.
• Three Mediterranean diet variations rich in plant foods and olive oil with participants eating either 0.5 ounces, 2.5 ounces, or 5.5 ounces of lean or extra-lean beef daily.

The results were eye-opening. When participants consumed Mediterranean diets containing either 0.5 ounces or 2.5 ounces of lean beef, their TMAO levels remained significantly lower than during the American diet phase. Meanwhile, the highest-beef Mediterranean diet (5.5 ounces daily) and the American diet showed no meaningful differences in TMAO levels. Petersen emphasized that “diet quality mattered more than the sheer amount of beef.”

What This Means for People Who Still Want Red Meat
Lead author Zachary DiMattia said the 2.5-ounce lean beef portion reflected what Americans typically eat daily. “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,” he noted.

The research team also monitored participants’ gut microbiomes. Interestingly, all three Mediterranean-style diets improved microbiome diversity compared to the American diet. However, more work is needed to understand how these microbiome shifts relate to TMAO.

A Balanced Takeaway Not a Free Pass
Experts caution that the findings should not be interpreted as permission to consume unlimited red meat. Petersen stressed that the study examined lean, unprocessed beef, not processed meats or high-fat cuts. The participants were also relatively young and healthy, meaning additional research is required to see if the outcomes apply to older adults or those with cardiovascular risk factors.

Conclusion
The study reinforces a key message in nutrition science: overall diet quality matters. A Mediterranean diet rich in fruits, vegetables, whole grains, legumes, nuts, and olive oil can accommodate moderate amounts of lean beef without raising certain heart-risk markers like TMAO. For people who enjoy red meat but want to protect their heart health, choosing lean cuts and pairing them with nutrient-rich plant-based foods may offer a sensible middle path.