A red meat nutrient sold as a supplement for weight loss and muscle growth may damage the heart and arteries, new research suggests.
Capsules of L-carnitine are widely available in health food stores and online.
They are advertised as a fat-burning slimming aid and powerful muscle builder - and are also said to help people with heart conditions.
But new research indicates a link between L-carnitine and heart disease. It may be a key reason why eating too much red meat can damage the heart, separate from the effects of saturated fat or cholesterol, say experts.
The studies show that L-carnitine is broken down by certain gut bacteria to produce a potentially harmful compound, trimethylamine N-oxide (TMAO).
Scientists found that high levels of L-carnitine in the blood were associated with heart disease, but only in individuals with raised TMAO.
Omnivorous individuals were found to produce more TMAO than vegetarians and vegans after consuming L-carnitine.
This suggests that, as well as containing L-carnitine, red meat favours the growth of gut bacteria that use the nutrient as an energy source, said the researchers.
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Hot dogs, bacon, sausage and deli meats -- even lean ones like turkey -- are made with loads of sodium and preservatives, often including nitrates and nitrites, both of which have been linked to heart problems. "With processing, you lose control over the quality of the ingredients," says Cynthia Thaik, M.D., a Los Angeles-based cardiologist. Processed meats are also higher in saturated fat and lower in protein than any red meat you could prepare yourself, writes director of the Yale Prevention Research Center and HuffPost blogger, David Katz. Not convinced to stay away? Processed meats have also been linked to a higher risk of diabetes and pancreatic cancer.
Yes, the processed picks are worse for your heart, but that doesn't mean you should go wild for steak. Instead, consider it more of a treat than a staple in your diet: It's still high in saturated fat, even when it's unprocessed. "I don't want to suggest that we have to go [completely] plant-based," says Thaik, "but moderation is always the key." If you're not planning on changing your carnivore ways anytime soon, at the very least pick a lean cut of beef, which, according to the USDA, contains less than 10 grams of total fat and 4.5 grams of saturated fat. Or opt for extra-lean, with 5 grams of total fat and less than 2 of saturated fat. Of the 29 cuts that meet these regulations, five are extra-lean, according to the Mayo Clinic, including eye of round roast or steak, sirloin tip side steak, top round roast and steak, bottom round roast and steak and top sirloin steak.
That cheesy slice may contain as much as two thirds of your daily recommended limit of saturated fat, according to Real Age, which is found mostly in animal products like beef, pork, butter, cream and milk. The American Heart Association recommends getting no more than 7 percent of total daily calories from saturated fat. (Based on a 2,000-calories-a-day diet, that totals out to about 15 grams a day of saturated fat). And even though you may think it's "just cheese," many dairy products are actually highly processed, says Thaik. To lighten up, skip extra cheese and top with veggies instead of pepperoni or sausage.
These fatty acids are created through processes that make vegetable oils more solid, according to the American Heart Association. They're cheap to produce, are used to make packaged and prepared foods last longer and can be re-used in frying. But trans fats raise LDL or "bad" cholesterol while also lowering HDL or "good" cholesterol, thereby putting your heart at risk. While a number of manufacturers have cut back on trans fat use in light of these health risks, packaged snacks, baked goods and some margarines may still contain it, according to EatingWell. Look for hydrogenated or partially hydrogenated oils on ingredients lists and beware the "zero trans fat" labels -- many are hiding .5 grams and rounding down to zero. But considering that the AHA recommends getting no more than 2 grams a day, that adds up, and fast!
As restaurants use their frying oil over and over again, the fat becomes more and more saturated, according to Live Science. And, as mentioned previously, trans fats are often lurking. Even though some restaurants may have cut back in the face of mounting health concerns, a number of joints still fry with solid oils like shortening, says Thaik. However, a 2012 found that how you fry makes a big difference. Among 41,000 Spanish adults, researchers found no link between fried food consumption and heart problems, likely because cooking with heart-healthy olive oil is more common than in the U.S, Time.com reported.
"When we think of heart disease, a lot of people think cholesterol and fat, but we know that sugar, as it relates to obesity and the effect it has on insulin, has a lot to do with the development of artherosclerosis," says Thaik. In fact, drinking one sugary beverage a day leads to a 20 percent increase in a man's risk of having a heart attack, according to a 2012 study, even if those empty calories aren't causing weight gain, CNN reported. Soda has previously been linked to increased rates of heart disease in women, as well. And diet soda isn't any better. A 2012 study found that a daily diet soda increased risk for stroke, heart attack and death, although the exact cause is not yet fully understood.
There's little on the drive-thru menu that isn't loaded with saturated fat, trans fat, sugar or sodium, making most of your orders recipes for disaster. And the consequences for the heart are nearly immediate. A 2012 study examined the effects of fast food on the arteries after just one meal and found that the ability of the blood vessels to dilate dropped by 24 percent, YouBeauty reported. "Not just fast food but processed food in general has a very high sodium content just by the pure nature of having to do the preservation," says Thaik. Soups and soy sauce are obvious culprits, she says, but saltwater sushi and even bread can be more surprising sources of salt.
A study of 2,595 patients undergoing heart check-ups showed "significant dose-dependent associations" between L-carnitine levels and the risk of coronary artery disease.
Links were also seen between L-carnitine and major events such as heart attacks, strokes and death.
In mice, L-carnitine supplements markedly increased TMAO levels and artery damage, but not if their gut bacteria was suppressed.
The scientists, led by Dr Stanley Hazen from the Cleveland Clinic in Ohio, US, wrote in the journal Nature Medicine: "Discovery of a link between L-carnitine ingestion, gut microbiota metabolism and CVD (cardiovascular disease) risk has broad health-related implications.
"Our studies reveal a new pathway potentially linking dietary red meat ingestion with atherosclerosis (narrowing of the arteries)."
They added: "Our studies have public health relevance as L-carnitine is a common over-the-counter dietary supplement. Our results suggest that the safety of chronic L-carnitine supplementation should be examined, as high amounts of orally ingested L-carnitine may under some conditions foster growth of gut microbiota with an enhanced capacity to produce TMAO and potentially advance atherosclerosis."
Victoria Taylor, senior dietitian at the British Heart Foundation, said: "This is certainly an interesting discovery and sheds some light on why red meat might have an impact on heart health.
"While the findings won't necessarily mean a change to existing recommendations, these scientists have served up a good reminder for us to think about alternative sources of protein if we regularly eat a lot of red or processed meats.
"The odd meat-free day isn't such a bad thing and eating less meat automatically leaves room in your diet for other foods high in protein like fish, pulses, nuts and eggs, all of which should be part of a nutritious and varied diet.
"Unless told otherwise by a doctor or qualified health professional, we should be able to get all the nutrients we need from a healthy, balanced diet without additional supplements."
See also: Baldness Linked To Heart Disease In Men
Nutrition expert Professor Brian Ratcliffe, from Robert Gordon University in Scotland, said: "Dietary intakes of saturated fatty acids do not explain all the variation in blood cholesterol levels and these in turn do not explain all the variation in the occurrence of cardiovascular diseases (CVD).
"These diseases are complex and multi-factorial and this study provides another piece in the jigsaw puzzle showing the links between atherosclerosis and diet and lifestyle. The study is comprehensive and demonstrates a mechanism that may help to explain the observed associations between the consumption of red meat and the risk of CVD.
"This does not mean that we need to change current dietary recommendations because the advice is to limit the intake of red meat anyway. However, people who take supplements of L-carnitine for non-medical reasons may need to have some second thoughts."