The study, named SWAP-MEAT (The Study With Appetizing Plant food – Meat Eating Alternatives Trial) was published in the American Journal of Clinical Nutrition, and involved participants who alternated between a plant-based alternative meat diet -- using Beyond Meat products -- and animal meat diet for 8-week phases.
The single-site, randomized crossover trial study involved 36 participants who were instructed to consume two or more servings per day of plant protein for 8 weeks. They then switched and ate animal meat for another 8-week phase. Comparisons were then made between the two phases of the diets. Participants were told to keep all other foods and beverages as similar as possible between the 2 phases, according to the study.
The study, which was funded by an unrestricted gift from Beyond Meat, which makes plant-based meat alternatives, used products from the company to compare the health effects of meat with plant-based alternatives. The company was not involved in actually conducting the study. To eliminate bias throughout, the researchers worked with a third party, the Quantitative Sciences Unit, to analyze the data once all participants had finished their 16-week diet.
The researchers found the group who ate the red-meat diet during the first eight-week phase had an increase in TMAO concentrations (a substance produced during digestion and metabolism that has been linked to higher risk for cardiovascular disease in some studies), while those who ate the plant-based diet first did not. A notable finding was when they switched diets, those who changed from meat to plant had decreased levels of TMAO, but those who switched from plant to meat did not see an increase in TMAO, according to the news release by the university.
“It was pretty shocking; we had hypothesized that it wouldn’t matter what order the diets were in,” Christopher Gardner, PhD, professor of medicine at the Stanford Prevention Research Center said in the news release. Bacterial species are said to be responsible for the initial step of creating TMAO in the gut and this bacteria is believed to flourish in people whose diets include red-meat.
“So for the participants who had the plant-based diet first, during which they ate no meat, we basically made them vegetarians, and in so doing, may have inadvertently blunted their ability to make TMAO,” Gardner stated.
However, Gardner also cautioned that more research was needed into the relationship between TMAO and potential cardiovascular risk, saying: “At this point we cannot be sure that TMAO is a causal risk factor or just an association.”
Besides the effect on TMAO levels, the plant-based alternative diet also showed other health benefits. An average 2-pound weight loss was seen during the plant-based diet phase and participants’ levels of LDL cholesterol dropped an average 10 milligrams per deciliter. It's also possible that other factors led to the weight loss, such as exercise or basic daily movement.
“The modest weight loss observed when participants substituted the plant-based meats in place of the red meats is an unexpected finding, since this was not a weight-loss study,” Anthony Crimarco, PhD, also involved in the study was quoted in the news release. “I think this indicates the importance of diet quality.”
Gardner hopes to continue studying the relationship between health and plant-based meat alternatives, particularly as it pertains to changes in the microbiome, and indicated he may investigate alternative dairy products next.