A study by a team of scientists from King’s College London has found that red wine drinkers had a greater diversity of bacteria in their digestive tracts, which is a marker of gastrointestinal health, compared to those who consumed other kinds of alcohol.

Their paper, published in the journal Gastroenterology on Wednesday, explored the effects of beer, cider, red wine, white wine and spirits on the gut microbiome (GM) and other health indicators in a group of 916 female twins in the UK.

Among the libations, red wine had the greatest positive impact on gut health — and it was also linked to lower levels of obesity and “bad” cholesterol. There were no such associations for beer, cider, or spirits, but a minor effect linked to white wine.

Lead author Caroline Le Roy told AFP that while there had been some previous research on animals and in lab experiments that showed that red wine expanded gut microbiota, there had never been a large human study.

“The more diversity there is, the better it is for us in some ways. You will be more able to fight disease and produce more metabolites from food,” she told AFP.

The microbiome refers to the collection of microorganisms living in the human gut, and plays an important role in health.

An imbalance between “good” and “bad” microbes can lead to adverse outcomes like reduced immunity, weight gain and high cholesterol.

– ‘Alcohol still bad’ –

One of the major drawbacks of so-called “association” studies that are based on observations about populations is that they do not demonstrate causation, and a one-off result that appears to show a positive correlation can be the result of luck.

The higher standard randomized clinical trials, in which researchers closely control the inputs given to subjects, are generally used to test new medicine but rarely applied to studies related to human diet because of ethical concerns.

The researchers therefore tested their findings in two more groups — in the US and in the Netherlands — both of about a thousand people each.

Recruiting twins for the initial UK-based group had the benefit of removing potential outside factors (known as “confounders”) such as genetic predisposition and socioeconomic background.

The team suspect polyphenols, micronutrients found in grape skin, were responsible for the greater GM diversity.

That conclusion is seemingly backed by the fact that white wine was also linked to a positive association with GM diversity, although to a far lesser extent. White wine has similar alcohol content to red, but with 6-7 times less concentration in polyphenols.

But Le Roy urged people not to start hitting the bottle, especially if they are non-drinkers.

“Potentially drinking one glass of red wine every two weeks is enough to have a beneficial effect, which is quite a good message because obviously alcohol is still bad for us,” she said, adding that several fruits and nuts are also rich in polyphenols.

“You don’t have to drink red wine and you don’t have to start drinking red wine if you don’t drink it,” Le Roy said.