What if your gut microbiota is the one ordering the drinks?

Studies show that alcohol influences the composition of our gut microbiota, which in turn influences our behavior. But does the gut microbiota influence our behavior towards alcohol? Spanish researchers have explored this hypothesis by comparing the weekly alcohol consumption and gut microbiota composition of 507 students. They first noted that the “heavier drinkers” had harder stools typical of constipation. This came as a surprise since alcohol was thought to cause diarrhea. They then found that the main difference in gut flora composition between the students who drank the most alcohol and those who did not drink was that the former had significantly higher levels of Actinobacteria (sidenote: Actinobacteria Actinobacteria are one of the gut microbiota’s four major bacterial groups (phyla), together with Bacteroidetes, Firmicutes, and Proteobacteria. Notable among Actinobacteria are Bifidobacteria, the most common Actinobacteria in the gut flora. Binda C, Lopetuso LR, Rizzatti G, et al. Actinobacteria: a relevant minority for the maintenance of gut homeostasis. Digestive and Liver Disease. 2018 May 1;50(5):421-8. ) .

Rats receiving the microbiota of alcoholic conspecifics develop a taste for alcohol

The scientists continued their research on rats by making them dependent on alcohol and transplanting their fecal microbiota into “sober” rats. Two weeks after the procedure, when given a choice between water containing alcohol and pure water, the formerly sober rats were more likely to prefer the water containing alcohol than “control” rats. According to the researchers, the time-lapse suggests that the new gut microbiota composition is the cause, rather than a consequence, of increased alcohol consumption. In the recipient rats, the gut microbiota of the alcoholic rats is a predisposing factor in an increased desire to consume alcohol, which in turn favors the abundance of certain “alcohol-loving” bacteria. Through the “gut-brain axis“, the gut microbiota may also affect the so-called “reward” neuronal circuits, which are involved in the development of addictions.

The scientists thus believe that the gut microbiota modifies our behavior towards alcohol. A recent study, this time on humans, seems to confirm this, but with a more positive outcome: alcoholics saw their cravings for alcohol strongly reduced after a fecal microbiota transplant from non-alcoholics.

Probiotics, a solution to alcoholism? 

A gut microbiota analysis in the alcoholic donor and recipient rats suggests that the bacterial genus Porphyromonas, which was less abundant in these animals than in controls, may be associated with the increased urge to consume alcohol. The researchers did not find any bacterial genus with increased content, but noted that in other studies, Actinobacteria were more abundant in alcoholic mice, just like they are in humans. However, they believe that treating the human gut microbiota with, for example, probiotics and/or prebiotics, may help manage alcohol use disorder. The relevant genera and species have yet to be determined.