& Joannie Dobbs Tuesday, April 23, 2013
New report on heart risks and beef is seriously flawed
News reports on the latest nutrition and health research often sound as if the findings are clear and straightforward. But about two weeks ago, a number of newspaper articles and news reports touted headlines like, "Red Meat's Heart Risk Goes Beyond the Fat" and although the headline may not be completely wrong, it is gravely misleading. Below we provide an example of how researchers and journalists can use research to intentionally or unintentionally support their beliefs related to health.
Based on a new study published in the prestigious journal Nature Medicine, carnitine, a naturally occurring compound in beef, can be converted by human intestinal bacteria to a compound called TMA (trimethylamine). TMA is then absorbed into the blood, and converted by the liver to another compound called TMAO (trimethylamine oxide). TMAO has been shown to cause cardiovascular disease in genetically prone mice.
The researchers clearly demonstrated that there are bacteria in the lower intestines of meat-eating people that produce this TMAO compound. They also found one man consuming a vegan diet who was willing to eat a steak for the sake of science. In this one person, TMA did not increase after eating the steak, possibly indicating that he had a low level of the carnitine-metabolizing bacteria. Of course, measurements on one individual, though interesting, may not mean much and definitely cannot provide any statistically significant conclusions.
QUESTION: Do we finally have a good explanation for the claim that red meat causes heart and blood vessel diseases?
ANSWER: Although the research was scientifically interesting and provided some new perspectives on the metabolism of carnitine in humans, making the cause-and-effect link between carnitine and cardiovascular disease is not so clean. First of all, despite "common knowledge," it should be pointed out that a number of large well-designed studies do not indicate associations between red meat consumption and cardiovascular disease. So, this link should not be considered to be a scientific fact.
Secondly, if the TMAO compound produced from the carnitine in beef is a key cause of heart and blood vessel disease, then you would expect that other foods that we consider heart-healthy would cause less TMAO production. However, this is not the case. Based on a study published in 1999, and cited in the Nature Medicine article, peas, cauliflower, mushrooms and bread all produced slightly greater amounts of TMAO than beef did.
But, the biggest problem with the red meat and TMAO production theory is based on a very big contradiction with other heart-health information. The 1999 study showed that most types of fish and other seafood caused 10 to 50 times as much TMAO production as beef. But, fish consumption has been repeatedly linked with heart health. Therefore if the carnitine/TMAO heart disease theory is correct, fish should be very harmful to cardiovascular health.
It is important for those of us who write articles on health topics to put new research into a broader perspective. Of course, the researchers should have pointed out the limitations of their study in their publication and addressed the contradiction presented by the glaring issue related to fish consumption.
Alan Titchenal, PhD, CNS and Joannie Dobbs, PhD, CNS
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa. Dr. Dobbs also works with the University Health Services.
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