Even one or two sodas a day could be disrupting your gut health enough to affect your mood, a new study has found.
Researchers in Germany examined more than 900 adults - about half with clinical depression and half without - and found that those who drank more soft drinks were, on average, 8% more likely to be diagnosed with major depression and to have more severe symptoms, according to findings published this week in JAMA Psychiatry.
The link was especially pronounced among women who consumed soft drinks regularly, though it did not differentiate what kinds. Their risk of major depression rose by about 16%, while there was no significant association among men. Participants self-reported their mental health symptoms and soda intake, and researchers analyzed stool samples to assess their gut bacteria.
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"We could really show that soft drink consumption was associated with the diagnosis of depression, but also of symptom severity," said Dr. Sharmili Edwin Thanarajah of University Hospital Frankfurt in a JAMA Psychiatry podcast interview.
The connection appeared to be partly explained by higher levels of a gut bacterium called Eggerthella, a bacterium previously linked to inflammation and found in greater abundance among people with depression.
"Soda can disrupt gut health by feeding harmful bacteria and reducing the diversity of beneficial microbes, which are essential for digestion and immune balance," said Trista Best, a Georgia-based registered dietitian and consultant at Balance One Supplements.
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"Its high sugar and acid content can also irritate the gut lining, leading to inflammation and bloating over time," Best, who was not involved with the study, told Fox News Digital.
When too much sugar from soft drinks reaches the gut, it feeds bacteria like Eggerthella, which can multiply and throw the gut ecosystem out of balance. That imbalance promotes inflammation that doesn't just stay in the stomach, News Medical reported - it can also spread throughout the body and even affect the brain, influencing mood and mental health. It can also interfere with serotonin production, the neurotransmitter that helps regulate mood.
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In mice, Eggerthella has been found to lower key compounds that support gut and brain health, including tryptophan, which the body uses to produce serotonin.
"Good" gut bacteria, on the other hand, thrive on fiber-rich foods and help produce compounds that reduce inflammation and protect the gut lining.
Probiotic supplements may also help improve and stabilize mood, Best said.
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Soft drinks have long been associated with obesity, diabetes and heart disease, but their impact on mental health is only beginning to be understood, the researchers wrote in their paper. Previous studies, however, have indicated that high sugar intake can trigger inflammation that affects brain chemistry.
Experts caution that while the study doesn't prove soda directly causes depression, it adds to a growing body of evidence suggesting the gut microbiome plays a key role in mental health. The sex-specific differences suggest the need for tailored prevention and intervention strategies, they added.
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"We can see that there is a correlation between soft drink consumption and depression," Thanarajah said. "It could be either way. It could be depression causing soft drinks consumption or the other way around."
Either way, she said reducing soft drink intake is a safe bet. "It has large impact on metabolic health but also mental health - for sure," she said.
The researchers said even moderate consumption - about one or two sugary drinks a day - may contribute to poorer mental health over time. They called for public education and policy changes to reduce soft drink consumption, particularly among children and teens.
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"Education, prevention strategies, and policies aiming to reduce soft drink consumption are urgently required to mitigate depressive symptoms," the authors wrote.
Thanarajah noted that soft drinks remain a major source of added sugar worldwide.
"They contain almost nothing else [but] sugar, and the prevalence is extremely high," she said, adding, "What is really considered as harmful is a daily consumption, and we think that around 10% of children and adolescents consume soft drinks every day, which is clearly associated with weight gain, obesity, diabetes [and] fatty liver disease."
Future studies will aim to determine the clinical implications of the connection, according to JAMA Psychiatry.
Fox News Digital has reached out to the researchers and the American Beverage Association for comment.
