Delving into the science behind Trimethylamine N-oxide (TMAO) and its potential link to cardiovascular disease.
Delving into the science behind Trimethylamine N-oxide (TMAO) and its potential link to cardiovascular disease.
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Hello and welcome to the Nutrition Diva podcast, a show where we take a closer look at nutrition research and trends so that you can make more informed decisions about what you eat. I’m your host, Monica Reinagel, and in addition to hosting this podcast, I am also a speaker, media expert, and behavioral health coach. If you’d like to learn more about having me speak or lead a workshop at your next live or virtual event, you can find more at my new website: wellnessworkshere.com
Today, I want to bring you up to date on a compound you may have started to hear more about: Trimethylamine N-oxide, or TMAO. People who eat meat and other animal products generally have higher TMAO levels in their blood–for reasons I’ll explain in a minute. And many people believe that this is part of the reason that diets high in animal products have been linked with higher risk of cardiovascular disease. In fact, if you have encountered this term, it’s very likely to have been from someone arguing that plant-based diets are healthier.
Before I go on, I want to acknowledge that health is only one of many reasons that people may have for choosing to avoid animal products. There are also valid concerns about environmental impacts and animal welfare. In this episode, however, I’m focusing on TMAO and its potential role in human health.
As I said earlier, those who eat vegetarian or vegan diets tend to have lower TMAO levels, so this is mostly a concern for people who eat meat. At the same time, eating more protein is one of the top priorities among consumers who are trying to change their dietary patterns, according to the most recent consumer survey from IFIC.
As I’ve talked about in several previous episodes, higher protein diets can help to mitigate age-related loss of muscle mass that can lead to frailty and decreased quality of life. Protein also promotes satiety. You’re likely to feel fuller for longer after a higher protein meal or snack than you would after eating a similar number of calories from lower-protein foods. That’s important for those who are trying to control their calorie intake in order to manage their weight.
Now, if you’re among those trying to get more protein, you’ll probably have noticed that animal foods are a lot more protein-dense than most plant sources, meaning that you’ll usually get quite a bit more protein per calorie (and per serving) from animal protein foods than plant protein foods. In addition, protein from animal sources (including eggs, dairy, fish, as well as meat) tend to be a higher quality protein, providing all of the essential amino acids in optimal ratios.
Of course, it’s not only about the protein. You may simply enjoy the flavor and texture of a grilled chicken breast or steak or a cheese omelet. For many, these foods are an important part of their cultural traditions.
Nonetheless, this whole TMAO thing has people worried. Do you have to choose between your heart health and your body composition? Do you have to give up foods you enjoy in order to enjoy a long and healthy life? Not necessarily.
First, let’s take a closer look at how TMAO is created. When we consume foods that are high in choline and L-carnitine–two nutrients that are found primarily in animal-based foods, bacteria in our gut transform these nutrients into a substance called trimethylamine, or TMA. This TMA then makes its way to our liver, where it is oxidized into TMAO.
Different animal foods vary significantly in their TMAO-producing potential. Red meat produces the highest levels, followed by fish, eggs, white meat, and dairy.
Fish is actually an interesting case. It is lower in L-carnitine than either red meat or poultry. However, it naturally contains TMAO. So the spike in TMAO blood levels after eating fish is less about the gut bacteria action and more from the fish itself.
As I said earlier, higher TMAO levels have been linked with higher risk of heart disease and other health issues. But you might be wondering, "Is TMAO really the villain here, or just an innocent bystander?” That's a great question, because most of the research linking elevated TMAO levels with health risks in humans is observational. And, as we never get tired of saying, correlation is not causation. However, animal studies have shown that directly administering TMAO can promote heart disease, evidence that certainly strengthens the case that high TMAO levels may play a causal role in cardiovascular disease.
If you are a committed vegan, you’re probably feeling pretty good about your choices right about now. If, on the other hand, you’re someone who sees benefits to incorporating some animal products into your diet, I bet you’re ready for some good news. And I do have some for you.
But first, let’s take a look at what we can learn from our vegan friends. As a rule, they have lower TMAO levels in their blood. They also tend to have lower rates of heart disease. Although, this is not as binary an equation as it might sound.
The association between meat consumption and increased health risks, for example, is most pronounced in those who eat a lot of meat–two or more servings every day. By contrast, those who eat just 1-2 servings of meat a week generally have the same health risks as those who never eat meat.
But, back to TMAO.
Plant-based foods provide no L-carnitine and a lot less choline than animal foods. So, with a plant-based diet, there are significantly fewer substrates for the gut bacteria to convert into TMA and that means there is less TMA to be oxidized into TMAO in the liver. But there’s something else going on as well.
Plant-based diets tend to be higher in fiber, thanks in part to the increased role of legumes, nuts, and seeds as protein sources. This fiber feeds beneficial bacteria in the gut, fostering strains of bacteria that produce less TMA, even when they do have those substrates or nutrients around. What’s more, they tend to crowd out the TMA-producing microbes.
So, could increasing fiber help reduce TMAO levels in meat eaters? After all, meat eaters who eat more fiber do have lower risks of heart disease, Type 2 diabetes, and colorectal cancer. How much of this has to do with the impact of fiber on TMAO production? A couple of studies have attempted to suss this out, albeit with mixed results.
One was a study in mice. First, researchers fed the mice a diet high in red meat, which led to increased TMAO levels. But when they added fiber to the red meat diet,.it reduced TMAO levels in the mice by 40-60%.
There was also a small pilot study in which human subjects took either a fiber supplement or a placebo for two weeks and then ate some beef. Compared to the placebo, the fiber supplement did seem to reduce TMAO formation in response to the meat, however the effect was most noticeable in people who didn't eat much meat in their regular diets.
There was also an intriguing study which found that the amount of meat people ate did not reliably predict TMAO levels in healthy individuals. But measures of their microbiome diversity did.
Obviously, we’re still unraveling the complex relationships between animal protein, fiber, TMAO production, and disease risks. But, if you choose to include animal products in your diet, here are a few tips that can help you balance the potential impact of that on your TMAO production and disease risk.
If you have a question you'd like me to answer in a future episode, you can email me at nutrition@quickanddirtytips.com. You can also leave me a message at 443-961-6206
I’d also like to invite you to check out my other podcast. It’s called the Change Academy, where we explore the art and science of creating positive behavior change, both in our own lives, and in our workplaces and communities. You can find it on all the major podcast platforms. Just search for Change Academy.
Nutrition Diva is a Quick and Dirty Tips podcast. Our team includes Brannan Goetschius, Nathan Semes, Davina Tomlin, Holly Hutchings, and Morgan Christianson.
That's all for this episode. Thanks for listening! I'll see you next week.