Here's how the gut impacts vulnerability to addiction

Research of Andrew Day, a molecular microbiologist at Tufts University, suggests that gut imbalances can make one more prone to addiction behaviors. Here's a Nature summary:

• Gut health, in particular bacterial population and gut permeability can set the stage for addiction behaviors. 
• Mechanism via leaky gut: When food particles and bacteria leave the gut and enter the bloodstream via a damaged intestinal wall, immune cells secrete proteins called cytokines. Cytokines travel to the brain, where they can trigger inflammation. This in turn results in reduced serotonin production (a key hormone for mood regulation), activating several parts of the brain involved in threat perception, reward anticipation, inhibitory control and compulsive behavior. Lower serotonin levels can make us subjectively feel less happy, pushing us to seek pleasure in substances such as sugar, alcohol or drugs, while disturbing our objective perception of pleasure and impulse control.
• Mechanism via bacteria: Gut microbes like the bacteria Lactobacillus, Enterococcus and Bacillus produce molecules that could modulate addiction behaviors. An imbalance in the gut could impact these molecules and increase a person's susceptibility to addiction compared to someone with a healthy gut.

Sources:

Nature 2024