Plant-based meat products reduce trimethylamine-N-oxide, other CVD risk factors
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Replacing animal meat with plant-based alternatives improved several CVD risk factors, including trimethylamine-N-oxide, in generally healthy participants compared with a diet with animal meat, researchers found in the SWAP-MEAT trial.
“This is one alternative to red meat,” Christopher Gardner, PhD, professor of medicine at the Stanford Prevention Research Center at Stanford University School of Medicine, told Healio. “I have some people who are resistant and they are resistant to cutting back on meat because they like the taste, it’s familiar to them, it’s their social or cultural norm. It creates a different option for lowering red meat that may be more acceptable to some target audiences. It could also be a gateway to more vegetables. Maybe if you cut back on your red meat and try these, you’re also later more willing to try a whole-food, plant-based diet. This just gives [clinicians] another tool ... to reduce [patients’] red meat consumption.”
Plant-based vs. animal-based meats
In this single-site, randomized crossover trial published in the American Journal of Clinical Nutrition, Gardner and colleagues, including Anthony Crimarco, PhD, postdoctoral scholar at the Stanford Prevention Research Center, analyzed data from 36 participants (mean age, 50 years; 67% women; mean BMI, 28 kg/m2) who were generally healthy and reported consuming one or more servings of meat per day and were willing to consume approximately two servings per day of both plant-based and animal meat products.
Participants were randomly assigned a diet sequence of plant-based to animal meat products (n = 18) or animal meat to plant-based meat products (n = 18). The two phases for each intervention lasted 8 weeks. During the plant-based meat phase, participants were asked to consume two or more plant-congruent-type meat products per day and to avoid other sources of plant-meat alternatives, including tempeh and tofu. Animal products during the meat phase of the trial were supplied by an organic food delivery service.
Three types of dietary data were assessed during the study, including a brief questionnaire about habitual meat intake, a log of food intake and two unannounced 24-hour multiple-pass diet recall interviews. Researchers also took samples at baseline and periodically throughout the trial to measure fasting blood concentrations of insulin-like growth factor I, trimethylamine-N-oxide (TMAO), glucose, lipids and insulin.
The primary outcome was fasting serum TMAO. Secondary outcomes included lipids, fasting insulin-like growth factor I, insulin, glucose, weight and BP.
Servings per day for both treatment phases were similar in participants assigned the plant-based diet first and the animal meat diet first (2.5 vs. 2.6, respectively; P = .76).
“We asked them to eat two servings a day and they ate two and a half servings a day on average,” Gardner said in an interview. “They got about 25% of their calories per day from these products, which means the participants had good adherence, and 36 out of 38 people who started the study finished it, which means we had good retention. This helps make the case that the study was effectively conducted. But realistically to know more about the impact of the alternative meat products, we definitely need more people to do more studies and different permutations on the same theme.”
For the primary outcome, TMAO concentrations were lower in participants assigned the plant-based diet first compared with animal meat diet first (2.7 µM vs. 4.7 µM; mean difference, 2 µM; 95% CI, 3.6 to 0.3; P = .012), although a significant order effect was observed (P = .023).
In participants who received the animal-based diet first, TMAO concentrations were lower during the plant-based phase compared with the animal-based phase (2.9 µM vs. 6.4 µM; P = .007). This did not occur for participants who received the plant-based diet first (2.5 µM vs. 3 µM; P = .28).
“The possibility here is that we changed their microbiome in such a way that they couldn’t make TMAO when we switched them back,” Gardner told Healio.
Exploratory analyses that focused on the microbiome did not identify meaningful differences between possible responder factors compared with nonresponder factors, but more extensive analyses and a deeper dive into the microbiome are planned, Gardner said.
Several measurements were lower during the plant-based meat phase compared with the animal meat phase, including weight (78.7 kg vs. 79.6 kg; P < .001) and LDL (109.9 mg/dL vs. 120.7 mg/dL; P = .002).
Motivator for future research
Gardner said that although more research is needed in this area, “I hope this partially encourages other people to try to replicate it.”
For more information:
Christopher Gardner, PhD, can be reached at cgardner@stanford.edu; Twitter: @gardnerphd.
Perspective
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Monica Aggarwal, MD, FACC
Based on multiple studies and meta-analyses, prevention guidelines advocate toward reducing red meat and moving toward lean meats, fish and large quantities of plants. As a result, multiple plant-based alternative meats have come on the market that are beneficial for environmental reasons, although it has been less clear whether they have health benefits. These plant-based meats remain high in fat and are highly processed, allaying a significant concern from health care providers. This study was conducted to answer some of these health-related concerns.
This study, albeit small, did a nice job trying to address this question. The study showed that plant-based alternatives appear to be “not as bad” and likely better than red meat. There are some issues with the washout period and maintaining stricter adherence to other dietary components that need to be hashed out in a larger study, but the results are promising.
I remind patients that plant-based meats such as the Beyond Meat and Impossible Burger are good transition foods but not the end goal. While there is no cholesterol and less saturated fat, there is a still a lot of fat in these products. I have many patients that are not changing other habits and are not having changes in their weight and cholesterol. We need more and larger studies. I like these products as transition foods with the goal of getting to as many whole plant foods as they can.
The TMAO data were interesting in this study, especially with the chronological variation, which needs further study because there is a lot inconsistency in TMAO results and the timing of change in TMAO. I would like to see the same study with a washout and with a control group to look at changes in the microbiome from control.
In general, we need more data on diet, which is so challenging because adherence and accuracy in reporting continue to be real issues. I would love to be able to tell my patients more about oil intake, whether fish is good for you or just less bad for you, whether plant-based omega-3 fatty acids have benefit. I would like to understand changes in the microbiome with diet. There are so many questions. Ultimately, the majority of people will do better eating less meat and more plants. More of these types of studies that show this will keep us moving in the right direction.
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