Alcohol and the Microbiota

The alcohol we consume is partially absorbed in the stomach, the rest passes further into the intestine, where it is not only absorbed but also interacts with our microbiota. And here it acts partially as an antibiotic, because it has antimicrobial activity. This causes disruption of the microbial balance and a dysbiotic state. Some microorganisms die, while those that prove more resistant begin to grow rapidly. Therefore, alcohol consumption is one of the factors of excessive bacterial growth in the small intestine. In this context the number of Bacteroides decreases, while pro- bacteria, including various opportunistic pathogens among them, increases.

In addition to the direct risks associated with cultivating and selecting potentially pathogenic strains in one’s own gut, the excessive growth of Gram-negative biota leads to an increase in lipopolysaccharides. Given that alcohol itself and its metabolic products further increase intestinal permeability, such a combination of circumstances leads to the development of a state of chronic inflammation and is a factor in the development of obesity and type 2 diabetes.

But the main “betrayal” does not even start here.

How is alcohol metabolized?

Part of the consumed ethanol is indeed metabolized in the liver to acetaldehyde, and then it is distributed throughout the body and further processed into acetic acid. It then enters the Krebs cycle and, in the end, we get carbon dioxide and water. That is all fine. If it weren’t for the fact that practically all intermediate products and the alcohol itself are capable of interacting with many important biological molecules and not only simply damaging them, but also forming metabolites with carcinogenic properties. They can disrupt the stability of DNA molecules, create crosslinks, and trigger the formation of free radicals.

The intestine is one of the first to bear the brunt of alcohol’s toxic effects. There accumulates acetaldehyde , ... which is produced from ethanol by the microbes that survived. Yes, not only our liver is able to process ethanol to acetaldehyde with the help of alcohol dehydrogenase — microbial enzymes (catalases) also perform these simple activities for them. The problem is that the next step (conversion of acetaldehyde to acetic acid) occurs somewhat more slowly and acetaldehyde (which is carcinogenic) actively accumulates when alcohol continues to enter.

The local action of such aggressive compounds is predictable: with alcohol consumption there is a significant risk (about 60% increase) of developing colorectal cancer. Admittedly, such figures are relevant for daily alcohol use and were calculated for "heavy drinkers" who consumed 50 ml or more of alcohol daily. However, if there is already a family history of gastrointestinal tumors, even 30 ml of alcohol per day will significantly increase this probability. Moreover, "light" consumption of alcoholic beverages once a week for 6 months, in tandem with a body mass index above 30, will increase the chances of developing colorectal cancer several times.

Photo by Vincenzo Malagoli on Unsplash