April 7, 2013

expert reaction to new research on red meat and cardiovascular disease

Nature Medicine published a study suggesting the nutrient l-carnitine, found in red meat, is associated with cardiovascular disease, but that gut bacteria played a role in disease susceptibility.

Catherine Collins, Principal Dietitian, St George’s Hospital NHS Trust, said:

“The authors performed a number of studies on humans and mice models that showed an increased blood level of TMA-O in the diet of meat eaters. TMA-O is a breakdown product of L-carnitine, found naturally in meats, but when present in the bloodstream of mice is associated with accelerated atherosclerosis. In a rather elegant series of tests, they proved that meat-eaters have different bacterial strains in their gut, and that these different bacteria appeared responsible for converting L-carnitine to TMA-O, a process that didn’t occur if vegan or vegetarian subjects set their dietary objections aside and ate meat, or if meat eaters were given antibiotics to kill of specific bacterial groups.

“The authors suggest that L-carnitine (found naturally in meat) and a similar food component choline (found in eggs, soya and other beans, and brassica vegetables) may be the link with heart disease in meat eaters, rather than other components such as saturated fat, or excessive iron intake from red meat.

“It’s a very persuasive argument, but we know that eating a couple of portions of red meat weekly is of no risk, heart wise. We also know including seafish in the diet is beneficial for heart health – yet seafish contain TMA and TMA-O naturally. And that eating beans and brassicas also seem protective in an omnivorous diet – which goes against this hypothesis in a meat-eaters diet.

“There’s no need to change our dietary recommendations from this – a Mediterranean style diet with modest meat, fish, dairy and alcohol intake, coupled with more pulses, vegetables fruits, wholegrains and mono-unsaturated fats, remains the nutritional blueprint for a healthy and healthful life. But I would strongly recommend that unless you’re a vegetarian or vegan, there is a potential risk from taking L-carnitine, lecithin, choline or betaine supplements in an attempt to ward off cognitive decline or improve fat metabolism. If the evidence is confirmed these supplements would do more to damage arteries than provide health benefits.”

Professor Brian Ratcliffe, Professor of Nutrition, Robert Gordon University, 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.” 

‘Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis’ by Robert Koeth et al. published in Nature Medicine on Sunday 8 April.