As little as one glass of red wine a week can increase the diversity of the good bacteria in your microbiome, which can help lower bad cholesterol and keep your weight down, researchers say.
"The more people drink, the higher the diversity. But even small amounts, such as one glass of red wine every week, shows a benefit," said study first author Caroline Le Roy. She's a research associate in the department of twin research and genetic epidemiology at King's College London.
Le Roy cautioned that while the findings in the study were robust, they can't prove that red wine improves the microbiome, only that the two are associated.
It's not the alcohol that has this effect, but rather the polyphenols in red wine. Polyphenols help feed the good bacteria in the microbiome, the researchers explained.
Polyphenols are also found in fruits and vegetables, and include antioxidants.
For the study, Le Roy and her colleagues looked at the effect of beer, cider, red wine, white wine and whiskey on the gut microbiome of 916 female twins.
Only red wine resulted in a more diverse microbiome, the investigators found.
The microbiome is a collection of bacteria in the gut that has an important role in health. A healthy microbiome helps digest food and keeps some diseases at bay.
An unhealthy microbiome can lead to poor functioning of the immune system, weight gain and high cholesterol, Le Roy said.
A microbiome with lots of different bacteria is a healthy microbiome, she added.
Le Roy's team found that red wine improved the number of different bacteria in the microbiome, compared with those who didn't drink wine.
The researchers were able to confirm their findings in three other groups in Britain, the Netherlands and the United States, which brought the total number of participants to nearly 3,000.
Moreover, the results remained constant even after accounting for factors such as diet, socioeconomic status and age.
Samantha Heller, a senior clinical nutritionist at NYU Langone Medical Center in New York City, thinks that drinking red wine may be a marker of a healthy lifestyle, so the health benefits may be due to other factors.
"Do they, in general, lead healthier lives, such as not smoking, eating more of a plant-based diet and exercising?" she asked.
Wine comes from grapes, which like a lot of plant foods, are rich in polyphenols, Heller said.
But polyphenols are also found in vegetables, fruits, grains, nuts, legumes and teas that don't contain alcohol, she noted.
"In addition, plants are our only source of dietary fiber, which is the favorite food for the microbes that live in our gut. When they are healthy, they help keep our bodies healthy," Heller said.
While drinking small amounts of red wine has apparent health benefits, there are also unhealthy effects of drinking too much, such as liver disease, certain cancers, pancreatitis and a depressed immune system, she said.
"Guzzling red wine, or any alcoholic beverage, is not the miracle we have been led to believe," Heller said.
For those who drink, the American Heart Association recommends an average of one to two drinks per day for men, and one drink per day for women (one 12-ounce beer, 4 ounces of wine, 1 ounce of 100 proof spirits).
"Let's be honest, most of us probably drink more than that. If you do not drink alcohol, there is no reason to start," Heller said.
The report was published Aug. 27 in the journal Gastroenterology.