Scientists have discovered an unexpected link between the consumption of non-alcoholic carbonated beverages and the risk of depression — even moderate soda intake may alter gut bacteria in ways that increase the likelihood of depressive symptoms, especially in women. The findings were published in JAMA Psychiatry.

Soda contains large amounts of simple sugars (glucose and fructose), which are not fully absorbed in the intestines. The unabsorbed portion promotes the growth of certain bacteria, weakening the intestinal mucosal barrier, increasing inflammation, and allowing bacteria or their metabolic products to “leak” into surrounding tissues. This process is closely associated with neuroinflammation and mood disturbances.

The study included 405 people with clinically confirmed major depressive disorder (MDD) and 527 healthy participants from the Marburg-Münster Affective Cohort. The researchers analyzed the relationship between soda consumption, depression severity, and changes in gut microbiota composition — particularly bacteria of the Eggerthella and Hungatella genera.

Results showed that with each additional serving of soda, the odds of having a depression diagnosis increased by about 8%. The effect was especially pronounced in women: their risk rose by approximately 17%. Women who consumed more soda also had higher levels of Eggerthella, which partially mediated the link between soda intake and depression (accounting for about 4–5% of the effect).

Interestingly, the association between soda consumption and depression was not statistically significant in men, and reduced microbiota diversity was observed only among women.