Soft drinks linked to depression through gut microbial changes

Soft drinks may contribute to an increased risk of major depressive disorder (MDD) through alterations in the abundance of certain bacteria species in the gut, according to a study.

In an analysis of cross-sectional data from the Marburg-Münster Affective Cohort in Germany, soft drink consumption was a significant predictor of an MDD diagnosis (odds ratio [OR], 1.081, 95 percent confidence interval [CI], 1.008–1.159; p=0.03) and depressive symptom severity as measured using the Beck Depression Inventory (partial η2 [ηp2], 0.012, 95 percent CI, 0.004–0.035; p<0.001). These associations were pronounced for female participants (MDD diagnosis: OR, 1.167, 95 percent CI, 1.054–1.292; p=0.003; symptom severity: ηp², 0.036, 95 percent CI, 0.011–0.062; p<0.001) but not among male participants. [JAMA Psychiatry 2025;82:1095-1102]

Additionally, soft drink consumption showed a significant association with increased Eggerthella abundance (ηp2, 0.017, 95 percent CI, 0.0002–0.068; p=0.007), but not with Hungatella abundance (p=0.57), among female participants.

Mediation analysis indicated that the changes in Eggerthella abundance accounted for 3.82 percent and 5 percent of the total effect of soft drink consumption on MDD diagnosis (p=0.01) and depressive symptom severity (p=0.005), respectively, among female participants.

The analysis included 405 patients with MDD (mean age 36.37 years, 67.9 percent female) and 527 healthy controls (mean age 35.33 years, 65.5 percent female). Compared with controls, MDD patients had higher BMI (26.04 vs 24.08 kg/m²; p<0.001) and fewer years of education (13.45 vs 14.10 years; p<0.001).

Sugars and Eggerthella growth

“Soft drinks—ultra-processed, calorie-dense, and rich in simple sugars like glucose and fructose—can overwhelm the small intestine’s absorptive capacity and promote the growth of specific bacterial genera,” the study authors said. [Eur J Nutr 2021;60:2087-2097]

Earlier research provides strong evidence that certain gut microbiota—specifically Eggerthella and Hungatella—play a direct causal role in the development of MDD. [Brain Behav 2021;11:e02177; Transl Psychiatry 2023;doi:10.1038/s41398-023-02670-5; medRxiv 2024;doi:10.1101/2024.12.05.24318549]

“We identified Eggerthella abundance as a potential mediator in the association between soft drink consumption, MDD diagnosis, and depression severity. Excessive simple sugars in soft drinks disrupt the gut microbiome by fostering proinflammatory bacteria, weakening gut barrier integrity, and impairing mucosal immunity,” the authors explained. [Nutrients 2020;12:1348]

“Eggerthella species are Gram-positive, anaerobic bacteria typically present at low levels in the healthy gut microbiome of adults and adolescents. High-sugar diets may indirectly promote Eggerthella growth by altering microbial competition. Future studies using shotgun or metatranscriptomic sequencing are needed to confirm these functional shifts observed via 16S rRNA sequencing,” they added. [medRxiv 2024;doi:10.1101/2024.12.05.24318549]

Policy changes

The authors noted that while soft drinks have small effect sizes on MDD diagnosis and symptom severity, the clinical and public health implications are still important because soft drinks represent a population-wide exposure that can be completely eliminated through changes in dietary behaviour.

“Dietary assessments and consultations should be integrated into prevention guidelines, as well as routine evaluations for patients with depressive symptoms. Nutritional counselling and interventions to reduce soft drink intake should complement depression treatments. Moreover, [the study] findings support policies limiting soft drink availability and marketing, such as taxing sugar-sweetened beverages, restricting school sales, and regulating advertising to youth,” they said. [Nat Rev Endocrinol 2022;18:205-218]