Is your daily fizzy drink making you depressed? German study links half a can a day to low mood

A German study published in JAMA suggests that consuming as little as 200 milliliters of carbonated soft drinks per day, roughly half a can of cola or lemonade, is associated with higher depressive symptoms among adults diagnosed with major depressive disorder. The researchers say the link appears stronger in women and did not show the same pattern in men.

To explore a possible mechanism, the team looked at gut microbiota, focusing on two bacteria previously linked with mood disorders: Eggerthella and Hungatella. They collected stool samples from 405 patients aged 18 to 65 with a depression diagnosis, 68 percent of whom were female, and compared them with 527 controls who did not have major depressive disorder. Participants kept diaries of fizzy drink intake and mood, using a standard mood scale to rate symptoms, and they completed a validated German 101 item food frequency questionnaire to estimate usual intake of carbonated beverages over the prior year. For lemonade and Coke, the researchers assessed the frequency of a 200 ml portion on a scale from never to 11 times per day.

Results showed that higher soft drink consumption correlated with more severe depressive symptoms among women and with greater abundance of Eggerthella in the gut. Higher intake did not show the same pattern in men. Lead author Sharmili Edwin Thanarajah said sex differences in the gut microbiome could help explain why women in the study appeared more affected by soft drink consumption, even though men reported higher overall consumption.

Based on the findings, the researchers concluded that soft drink intake may contribute to major depressive disorder through alterations in the gut microbiota, particularly involving Eggerthella. They described soft drinks as a widely distributed but avoidable risk factor and urged clinicians to advise patients to reduce soft drink consumption as part of a balanced diet.

Contextual notes about mood disorders and health trends accompany the study. Depression is described by the NHS as a persistent low mood that can last or recur. Mental health organizations, including MIND, estimate that a substantial share of adults in the United Kingdom will be diagnosed with depression at some point, with millions affected in the United States as well. The new study adds to a growing body of research examining how diet and the gut microbiome may influence mental health.

In related work published earlier this month, Brazilian researchers reported that drinking just one daily diet fizzy drink could rapidly raise the risk of brain decline. In the broader literature, some artificial sweeteners used in diet beverages have been examined for potential associations with various health issues, underscoring the complexity of how beverage choices may affect long‑term health. The study under discussion is observational and cannot establish causation, and its authors acknowledge that self-reported intake and mood assessments may introduce biases. Further research is needed to determine whether reducing fizzy drink consumption could improve mood in people with depression and to clarify the role of specific gut bacteria in these associations.

Overall, the findings contribute to the ongoing conversation about how everyday dietary choices may intersect with gut health and mental well-being, potentially informing clinical guidance on beverage consumption as part of holistic approaches to managing depression.