Dear Doctor: I’ve always heard that it’s the saturated fat in red meat that leads to a heart attack. But now I’m reading that it has something to do with the gut? Does that mean probiotics will make it OK to eat steak, which my wife and I just love?
Dear Reader: You’re referring to a study published earlier this year that found a connection between a diet heavy in red meat and a marked increase in a certain compound produced by gut bacteria, which has been linked to an increased risk of heart attack and stroke. That byproduct is trimethylamine N-oxide, also referred to as TMAO. In earlier studies, researchers uncovered a link between elevated levels of TMAO in the blood and the development of arterial plaque, which can block blood vessels and lead to heart disease.
The study you’ve been reading about, which was published in the European Heart Journal last February, analyzed how each of 113 volunteers responded to three different diets. The diets, which the volunteers followed for four weeks, used either red meat, white meat from poultry, or non-meat products such as legumes, nuts and grains as a source of protein. Every aspect of the meals, from portion size to ingredients to preparation methods, was uniform and highly controlled. The volunteers followed the three different diets in random order.
Only the red meat diet resulted in increased levels of TMAO, both in the blood and in the urine. The majority of volunteers following the red meat diet had levels of TMAO that measured two to three times higher than volunteers who were getting their protein from white meat poultry or vegetal sources. In some cases, the levels of TMAO in blood and urine were as much as 10 times higher in the red meat group than in the white meat and vegetal groups.
Researchers also discovered that the red meat diet interfered with the kidneys’ ability to excrete TMAO. That kept the circulating levels of the potentially damaging bacterial byproduct high. The good news is that a month after they stopped eating a diet rich in red meat, both blood and urine levels of TMAO had fallen significantly. The researchers speculated that the metabolic pathways suggested by this study might account for why the Mediterranean diet, which is low in red meat, is associated with lower risk of heart attack and heart disease.
Since the study shows that red meat causes the gut bacteria to produce potentially harmful compounds, your idea about taking probiotics as protection won’t actually work. However, if it’s only as an occasional splurge, it’s probably fine for you to have that juicy steak.
(Send your questions to email@example.com, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)