Scientists for long have looked for a link between consumption of red meats, especially processed meats, and an increased risk of developing cardiovascular disease. But they have always come up short.
Factors such as stress, alcohol consumption, smoking and sedentary lifestyles – which we now know play a role in increasing the risk of developing cardiovascular disorders (CVDs) – have always muddied up the data.
There has also been a lack of evidence for the mechanisms of how eating foods rich in cholesterol, trans- and saturated fats increases the risk of developing CVDs.
But now, scientists at the Cleveland Clinic and Friedman School of Nutrition and Policy at Tufts University may have uncovered the most convincing answer yet; and it has to do with the way the microbes in our gut digest red and processed meats.
A potential biomarker emerges
In a study published in one of the American Heart Association’s peer-reviewed journals, the researchers pointed out how the secretion of certain metabolites has been found to be associated with increased risks of heart failure.
They identified an amino acid – carnitine – which is converted into a compound called Trimethylamine N-oxide, or TMAO in short, in the gut.
In recent years TMAO has been identified as a potential biomarker for cardiac disorders.
The study, which involved almost 4,000 American men and women above the age of 65, found that consuming 1.1 servings of red meat daily was linked with a 22% increase in risk of developing atherosclerotic cardiovascular disease. About 10% of this risk was due to increased levels of metabolites produced by the gut bacteria when breaking down proteins in meat.
The researchers added that this increased production of TMAO was not seen when consuming poultry, eggs, or fish.
A lingering question
“These findings help answer long-standing questions on mechanisms linking meats to risk of cardiovascular diseases,” Meng Wang, a post-doctoral fellow at the Friedman School and co-author of the study, said in a statement.
The researchers added that the interaction between red meat, the gut microbiome, and the metabolites they produce seems to be an important pathway leading to increased risk of CVD. Understanding it will help in creating new possible targets for drugs to reduce the risk of developing a heart disease.
Significantly high risk
In fact, the study found that the risk of developing CVD from the metabolites produced due to red meat was more than the risks caused by bad levels of blood cholesterol and blood pressure.
“This suggests that, when choosing animal-source foods, it’s less important to focus on differences in total fat, saturated fat, or cholesterol, and more important to better understand the health effects of other components in these foods, like L-carnitine and heme iron,” said Dariush Mozaffarian, dean for policy at the Friedman School and a co-author of the study.
How to reduce TMAO levels?
TMAO is a metabolite produced by certain bacteria in our gut. It is a by-product of the breakdown of carnitine, and nutrients called choline and lecithin that are present in many foods. These substances are found in abundance in red meat and full-fat dairy products.
In fact, carnitine is a supplement most seen added to energy drinks and touted for its fat burning properties. But scientists have found that TMAO is responsible for regulating physiological processes associated with the development of atherosclerosis.
But there are ways to reduce TMAO levels in the body. Apart from individuals consciously reducing the consumption of foods rich in carnitine, it has been found that cold-pressed olive oil, balsamic vinegar and red wine can stop TMAO production. This is mainly due to the presence of a compound commonly called DMB, short for 3,3-dimethyl-1-butanol, in these foods.
The DMB factor
Scientists are also researching on medication that can inhibit TMAO pathways, one such research works by producing in labs DMB that can be potentially ingested. However, this is a study in progress and has not reached human trials yet.
“Present studies suggest that targeting gut microbial production of TMAO specifically and non-lethal microbial inhibitors in general may serve as a potential therapeutic approach for the treatment of cardiometabolic diseases,” a paper on the subject says.
Should carnitine be avoided?
While consuming foods rich in carnitine has been implicated in increasing CVD risk, the substance does have several benefits as well. A September 2020 meta-analysis found that carnitine could help to increase physical performance, make good use of carbohydrates in the body, and lead to overall wellbeing.
But as is with the case with most foods, the issue lies with overconsumption.
“The problem mostly arises when carnitine is consumed in excess and when an individual already has conditions such as hypertension, muscle loss and excess inflammatory markers in circulation,” says Dr Shruthi S, a research scholar at the department of genetics at Dr A L Mudaliar Post Graduation Institution of Basic Medical Sciences, University of Madras.
She adds that the carnitine obtained from meat and that consumed as a supplement may together increase TMAO in the circulation. This could in turn alter an individual’s cellular functions in an unfavourable manner.
Carnitine in non-meat sources
While carnitine is also present in non-meat sources of food, vegans and vegetarians may not need to worry as much about consuming such foods. A 2018 study found that vegans could have a lower risk of TMAO-induced CVD than meat eaters despite consuming the same level of carnitine through supplementation.
At baseline, vegans and vegetarians exhibited a limited ability to produce TMAO from carnitine, while meat-eaters rapidly produced TMAO. It is interesting to note that TMAO levels with the same supplementation can vary drastically among vegetarians and meat eaters.
Nevertheless, scientists believe the new TMAO pathway can provide new insights into how CVD comes to be in the human body, and also ultimately could help in developing novel ways to prevent it.