REVIEW OF: Edwin Thanarajah S et al, JAMA Psychiatry 2025;82(11):1095–1102

STUDY TYPE: Cross-sectional cohort study

Soft drinks are already tied to obesity and diabetes, but their impact on mental health is less clear. This German cohort examined whether soft drink consumption is associated with major depressive disorder (MDD) and whether the gut microbiome helps explain the link.

The study analyzed 932 adults (405 with MDD, 527 healthy controls) aged 18–65 from the Marburg-Münster Affective Cohort. Researchers compared daily soft drink intake with MDD diagnosis and symptom severity and analyzed stool samples to assess gut bacterial composition, focusing on Eggerthella and Hungatella species. Importantly, the study could not reliably distinguish sugar-sweetened from artificially sweetened soft drinks, so the findings apply to soft drink intake overall rather than to sugar alone.

Higher soft drink intake was associated with both an MDD diagnosis and greater depression severity. The effect was strongest in women, who also showed higher gut levels of Eggerthella, a proinflammatory bacterium previously tied to depression. Mediation modeling suggested that Eggerthella explained about 4%–5% of the soft drink–depression relationship. These findings persisted after adjusting for BMI, education, and total calorie intake. No link appeared in men or with Hungatella.

CARLAT TAKE
We’ve long known soft drinks are bad for the body; it’s possible they are bad for the mind too. While this study can’t prove cause and effect, it strengthens the idea that diet, gut microbes, and mood are intertwined, especially for women. For patients with depression, a quick dietary screen and advice to cut back on soft drinks may be as worthwhile as any lifestyle recommendation. As microbiome research evolves, targeting gut health could become a novel adjunct to depression care.