Fatty Liver

The Alcohol Your Gut Makes Without You Drinking

There's strong evidence here, and it includes the step most gut research never reaches, where removing one bacterium prevented the disease. Fatty liver means fat building up inside liver cells in people who drink little or no alcohol. The name has always been slightly misleading. Some people with the condition have measurable alcohol in their blood, and it isn't coming from a glass.

A bacterium that ferments sugar into alcohol

Certain gut bacteria break down carbohydrate and release ethanol as a by-product. Ethanol is ordinary drinking alcohol. Most people carry strains that produce trace amounts, which the liver clears without difficulty.

Researchers studying a Chinese cohort found something different. Up to 60% of the people with fatty liver carried a strain of Klebsiella pneumoniae that produced alcohol at high levels. The more of it someone carried, the more severe their liver disease.

The liver processes that alcohol exactly as it would a drink. It also sits directly downstream of the gut. Blood from the intestines reaches the liver before it reaches anywhere else, so the liver takes the full concentration.

Source: Fatty liver disease caused by high-alcohol-producing Klebsiella pneumoniae

The experiment that made it convincing

An association like that could still be a by-product of the disease. The researchers ran three steps to find out.

First, they took the alcohol-producing strain from patients and gave it to healthy mice by mouth. The mice developed fatty liver.

Second, they transplanted a whole bacterial community from a person with the disease into mice. Those mice developed it too.

Third, and this is the step that settles it, they removed just that one strain from the community before transplanting it. The mice stayed healthy.

Same community, one bacterium taken out, different outcome. That's about as close to demonstrating cause as this kind of work gets.

Measuring the alcohol in people

Mouse work needs confirming in humans, and researchers went looking for the alcohol itself.

They measured ethanol in 146 people, both while fasting and for two hours after a mixed meal. In a smaller group of 37, they sampled blood from the portal vein, the vessel carrying blood straight from the intestines to the liver, which is where gut-produced alcohol would be most concentrated.

They then ran an intervention. Ten people with fatty liver and ten overweight but otherwise healthy volunteers took part. Each was given a drug blocking the enzyme that breaks alcohol down. Any ethanol present would then accumulate rather than disappear, making it measurable.

The work confirmed that gut bacteria in people with fatty liver produce enough ethanol to be worth taking seriously as a contributor.

Source: Microbiome-derived ethanol in nonalcoholic fatty liver disease

What feeds the alcohol producers

The practical question is what encourages these strains, and the answer points at diet.

Alcohol-producing bacteria thrive on simple sugars and refined carbohydrate reaching the gut in quantity. Fructose in particular gives them abundant raw material. It's also processed by the liver in ways that promote fat storage directly.

Fibre-fermenting bacteria compete with these strains for space and resources. The compounds they produce also help keep the gut barrier tight, which limits how much of anything crosses into the blood.

So the same dietary pattern works on both ends of the problem. It gives the alcohol producers less to work with and supports the bacteria that hold the barrier together.

What this means for you

Fatty liver needs proper assessment from a doctor, since it can progress to inflammation and scarring. Weight loss where appropriate remains the treatment with the strongest evidence. In addition, the research above found gut bacteria producing enough alcohol internally to drive the disease in animals, and removing a single strain was enough to prevent it. A varied, plant-rich diet supports the same gut bacteria this research ties to a tighter gut barrier and less internally produced alcohol. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.