Steak is bad for the heart and now we know why

“Red meat is bad for your heart”, that is typically the story we hear from people. While some might take this as meat is bad for us, or that it is wrong to eat red meat, science has been trying to find a better answer to that question. After all it wouldn’t do for science to say, it just does. Well as luck may have it, new research provides details on how gut bacteria turn a nutrient found in red meat into metabolites that increase the risk of developing heart disease. The findings may lead to new strategies for safeguarding individuals’ cardiovascular health.

Previous research by this same team revealed a pathway by which red meat can promote atherosclerosis, or hardening of the arteries. Essentially, bacteria in the gut convert L-carnitine, a nutrient abundant in red meat, into a compound called trimethylamine, which in turn changes to a metabolite named trimethylamine-N-oxide (TMAO), which promotes atherosclerosis.

Now the team, through extend their earlier research, identified another metabolite, called gamma-butyrobetaine. This new metabolite is generated to an even greater extent by gut bacteria after L-carnitine is ingested, and it too contributes to atherosclerosis.

The researchers found that gamma-butyrobetaine is produced as an intermediary metabolite by microbes at a rate that is 1,000-fold higher than the formation of trimethylamine in the gut, making it the most abundant metabolite generated from dietary L-carnitine by microbes in the mouse models examined. Moreover, gamma-butyrobetaine can itself be converted into trimethylamine and TMAO.

Interestingly, however, the bacteria that produce gamma-butyrobetaine from L-carnitine are different from the bacterial species that produce trimethylamine from L-carnitine.

The discovery that metabolism of L-carnitine involves two different gut microbial pathways, as well as different types of bacteria, suggests new targets for preventing atherosclerosis—for example, by inhibiting various bacterial enzymes or shifting gut bacterial composition with probiotics and other treatments.

“The findings identify the pathways and participants involved more clearly, and help identify targets for therapies for interventions to block or prevent heart disease development,” says Dr. Stanley Hazen, lead researcher.

“While this is into the future, the present studies may help us to develop an intervention that allows one to ‘have their steak and eat it too’ with less concern for developing heart disease.”

Well I don’t know about you, but I do enjoy a good steak, so the idea that it could be healthier is one that I look forward to.

Sources: 
Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, DiDonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, & Hazen SL (2013). Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nature medicine, 19 (5), 576-85 PMID: 23563705

Robert A. Koeth, Bruce S. Levison, Miranda K. Culley, Jennifer A. Buff, Zeneng Wang, Jill C. Gregory, Elin Org, Yuping Wu, Lin Li, Jonathan D. Smith, W.H. Wilson Tang, Joseph A. DiDonato, Aldons J. Lusis, & Stanley L. Hazen (2014). g-Butyrobetaine is a proatherogenic intermediate in gut microbial metabolism of L-carnitine to TMAO Cell Press : 10.1016/j.cmet.2014.10.006.