Once again, a new study suggests a correlation between a metabolite trimethylamine N-oxide (TMAO) and heart disease risk. But does TMAO cause heart disease or is it a marker of other conditions that often go along with heart disease?
Another study, published in Journal of the American College of Cardiology (JACC), suggests an association between TMAO and risk of heart disease. As we have covered before, TMAO is produced by our gut bacteria and changes based on our diet. Eating more vegetables can decrease TMAO, and eating more meat can increase TMAO. But is TMAO causative of heart disease?
Some interpret the body of evidence as confirming that TMAO is causative.
But, as with most epidemiology research, this study does not support that claim.
In the JACC study, scientists measured baseline TMAO levels in 760 healthy women in 1989, and again ten years later. The authors determined how many women had heart attacks and then tried to correlate heart attack risk with blood levels of TMAO. Those with the highest baseline level of TMAO and the greatest increase in TMAO had a risk of heart disease of between 1.33 and 1.79.
However, women with the highest TMAO levels who had a heart attack, compared to those who did not have heart attacks, were also much more likely to have hypertension (32% vs 19%), diabetes (7.9% vs 1.3%), and to be a current smoker (4.5% vs 1.8%). [Note that this data is only available in the supplemental tables and is not included in the article.] So, once again, it is unclear if the TMAO level had anything to do with the increased risk of heart events, or if it was simply a marker that coincided with unhealthy lifestyles or “unhealthy user bias.”
TMAO advocates commonly point out that levels rise as subjects eat more red meat. Therefore, many will conclude this study shows we need to avoid meat to reduce our heart risk. But that is not what the study shows; it’s a gross misinterpretation of the results.
Why did some with elevated TMAO have heart attacks and others did not? It appears to be related to other known risk factors (like hypertension, diabetes, and smoking status), rather than to the absolute elevation of TMAO levels.
Does this mean that we can ignore TMAO? Not necessarily. If someone has hypertension, diabetes, or is a current smoker, then TMAO may be a marker of increased risk. But in the absence of those comorbid conditions, it is not clear that the impact is significant enough to alter an already healthy lifestyle, even (especially?) if it includes eating meat.
Thanks for reading,
Bret Scher, MD FACC
MeatWhy more protein is better15:17Dr. Ted Naiman is one of the individuals who believes more protein is better and recommends a higher intake. He explains why in this interview.45:29Although it is new in popularity, people have been practicing a carnivore diet for decades, and possibly centuries. Does that mean it is safe and without concern?Is low carb bad for the environment?07:09Won’t low carb contribute to global warming and pollution? Top low-carb doctors answer this question.Diet, health and the environment50:49Dr. Peter Ballerstedt explains how ruminants can be part of the solution to climate change and environmental degradation.Is fear of protein the new fear of fat?35:03Could protein restriction on a low-carb or keto diet cause problems?Diet Doctor Podcast #30 – Dr. Gary Fettke55:07Dr. Fettke, along with his wife Belinda, has made it his mission to uncover the truth behind the anti-meat establishment and much of what he has discovered is shocking.Can red meat kill you?14:55Where does the fear of red meat come from? And how much meat should we really eat? Science-writer Nina Teicholz answers.What about red meat and health?34:15Does red meat really cause type 2 diabetes, cancer and heart disease?Why you shouldn’t fear protein on keto20:15Do you really need to worry about protein on a ketogenic diet? Dr. Ben Bikman shares a new way of thinking about this.
Read more: dietdoctor.com