Swapping red meat for certain plant-based meat alternatives may improve some cardiovascular risk factors, according to a new study by researchers at Stanford Medicine.
The small study was funded by an unrestricted gift from Beyond Meat, which makes plant-based meat alternatives, and used the company’s products to compare the health effects of meat with plant-based alternatives. Beyond Meet was not involved in the design or conduct of the study and did not participate in data analysis.
It may seem obvious that plant-based patties are a healthier alternative to hamburgers. But many new meat alternatives, such as Beyond Meat, are relatively high in saturated fat and added sodium and are considered highly processed foods, meaning they are made with food isolates and extracts, as opposed to whole beans or chopped mushrooms. All of these factors have been shown to contribute to the risk of cardiovascular disease, says Christopher Gardner, PhD, professor of medicine at the Stanford Prevention Research Center.
“There’s been this kind of backlash against these new meat alternatives,” Gardner said. “The question is, if you add sodium and coconut oil, which is high in saturated fat, and use processed ingredients, is the product actually healthy?” To find out, Gardner and his team gathered a group of more than 30 people and assigned them to two different diets, each for eight weeks. One diet called for at least two daily servings of meat — the options available were primarily red meat — and one called for at least two daily servings of plant-based meat.
Specifically, the researchers measured levels of one molecule, trimethylamine N-oxide, or TMAO, in the body; TMAO has been linked to an increased risk of cardiovascular disease. They found that TMAO levels were lower when study participants were eating plant-based meats.
A paper describing the study’s findings will be published on August 11 American Journal of Clinical Nutrition. Gardner is the paper’s senior author. Postdoctoral scholar Anthony Krimerko, PhD, is the lead author.
Comparison of burgers
Gardner, a longtime vegetarian, is a staunch advocate of eating whole foods with an emphasis on vegetables. Because almost all plant-based meats contain saturated fat and are classified as highly processed foods — including those outside of meat — Gardner wanted to study how they affect the body compared to red meat.
He and his team conducted a study that enrolled 36 participants for a 16-week dietary experiment. Gardner designed the research as a crossover study, meaning the participants served as their own controls. For eight weeks, half of the participants ate a plant-based diet, while the other half ate a meat-based diet that consisted primarily of red meat, although some participants ate a small amount of chicken. Then they switch. Regardless of the diet participants were on, both groups had an average of two meat or plant-based options per day, carefully tracking their food in journals and working with members of Gardner’s team to record their eating habits.
The team took precautions to eliminate bias throughout the study, including working with a third party at Stanford, Quantitative Sciences Unit, to analyze the data after all participants had completed their 16-week dietary intervention. “QSU helped us develop a statistical analysis plan, which we published online before the study was completed,” Gardner said. “Thus our plan was public, and we were accountable for the specific primary and secondary outcomes that we initially said we wanted to pursue — namely, participants’ TMAO, blood cholesterol, blood pressure and weight.”
An emerging risk factor
The main outcome the team was interested in tracking, Gardner said, was levels of TMAO.
Gardner called TMAO “an emerging risk factor,” meaning that there appears to be a link between high levels of TMAO and an increased risk of cardiovascular disease, but the link has not yet been conclusively proven. Two of TMAO’s precursors, carnitine and choline, are found in red meat, so it’s possible that people who regularly eat beef, pork, or lamb for dinner will have higher levels of TMAO.
“At this point we can’t be sure if TMAO is a causal risk factor or just an association,” Gardner said. However, he sees a reason to pay attention to TMAO readouts. In the past few years, studies have shown that high levels of TMAO correlate with inflammation and blood clotting, among other health concerns. Gardner points to another study in which researchers found that people with elevated TMAO had a 60% higher risk for adverse cardiovascular events, such as heart attack.
In Gardner’s study, researchers found that participants who ate a red-meat diet during the first eight-week phase also had an increase in TMAO, while those who ate a plant-based diet first did not. But something strange happened when the groups switched diets. Those who switched from meat to plants had decreased TMAO levels, which was expected. Those who switched from plant to meat, however, did not see an increase in TMAO.
“It was quite surprising; we hypothesized that it didn’t matter what order the diets were in,” Gardner said. It appears that the gut contains the bacterial species responsible for the initial step in TMAO production. These species are thought to thrive in people whose diets are heavy on red-meat, but probably not in those who avoid meat.
“So for the participants who were initially on a plant-based diet, at which point they didn’t eat any meat, we essentially made them vegetarian, and in doing so, may have inadvertently blunted their ability to make TMAO,” he said. Whether this type of approach can be used as a strategy to reduce the risk of cardiovascular disease remains to be seen.
Beyond TMAO
Beyond TMAO, health benefits from plant-based options extend to weight and LDL cholesterol levels – or “bad” cholesterol. Regardless of which diet was started, participants’ LDL cholesterol levels dropped by an average of 10 milligrams per deciliter, which was not only statistically significant, but also clinically significant, Gardner said. Also, participants lost an average of 2 pounds during the plant-based portion of the diet.
“The modest weight loss when participants substituted plant-based meat for red meat was an unexpected finding, since this was not a weight-loss study,” Krimerko said. “I think this points to the importance of food quality. Not all highly processed foods are created equal.”
Gardner hopes to continue studying the relationship between health and plant-based meat alternatives, particularly as it relates to changes in the microbiome. Gardner says she’s interested in expanding her research into diet patterns overall. “Maybe next time we’ll see a combination of dietary factors on health — perhaps alternative meats combined with alternative dairy products,” he said.