Scientists reveal how your favorite soft drink can silently affect your mood

Even one or two soft drinks a day can disrupt your gut health enough to affect your mood, a new study shows.

Researchers in Germany studied more than 900 adults — about half with clinical depression and half without — and found that those who drank more soda were, on average, 8% more likely to be diagnosed with major depression and experience more severe symptoms, according to findings published this week in JAMA Psychiatry.

The association was especially pronounced among women who regularly drank soft drinks, although no distinction was made between which types. Their risk of major depression increased by about 16%, while there was no significant association between 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 were really able to show that soda consumption was associated with the diagnosis of depression, but also with the severity of symptoms,” said Dr. Sharmili Edwin Thanarajah of the University Hospital Frankfurt in a JAMA Psychiatry podcast interview.

The link appeared to be partly explained by higher levels of a gut bacteria called Eggerthella, a bacterium previously linked to inflammation and found in higher amounts in 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 the immune system,” says Trista Best, a Georgia-based registered dietitian and consultant with Balance One Supplements.

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“The high sugar and acid content can also irritate the intestinal lining, which can lead to inflammation and bloating over time,” Best, who was not involved in the study, told Fox News Digital.

When too much sugar from soft drinks reaches the intestines, it feeds bacteria such as Eggerthella, that can multiply and throw the intestinal ecosystem out of balance. That imbalance promotes inflammation that doesn’t just stay in the stomach, News Medically reported — it can also spread throughout the body and even affect the brain, affecting mood and mental health. It can also disrupt the production of serotonin, the neurotransmitter that helps regulate mood.

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In mice, Eggerthella has been found to reduce key compounds that support gut and brain health, including tryptophan, which the body uses to produce serotonin.

The new findings suggest a possible link between soda, gut microbes and depression, especially in women. (iStock)

‘Good’ gut bacteria, on the other hand, thrive on fiber-rich foods and help produce compounds that reduce inflammation and protect the intestinal lining.

Probiotic supplements can also help improve and stabilize mood, Best said.

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Soft drinks have long been linked to obesity, diabetes and heart disease, but their impact on mental health is only beginning to be understood, the researchers wrote in their paper. However, previous studies have shown that high sugar intake can cause inflammation that affects brain chemistry.

Experts recommend limiting intake of sugary drinks to support gut and brain health. (iStock)

Experts caution that while the study does not prove that soda directly causes depression, it adds to a growing body of evidence suggesting that the gut microbiome plays a key role in mental health. The sex-specific differences indicate the need for tailored prevention and intervention strategies, she added.

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“We can see that there is a link between soft drink consumption and depression,” Thanarajah said. “It could go either way. It could be depression causing soft drink consumption, or the other way around.”

Either way, she said reducing soda intake is a safe bet. “It has major implications for metabolic health, but certainly also for mental health,” she said.

The researchers said that even moderate consumption – about one or two sugary drinks per day – can contribute to poorer mental health over time. They called for public education and policy changes to reduce soda consumption, especially among children and teens.

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“Education, prevention strategies, and policies aimed at reducing soft drink consumption are urgently needed to reduce depressive symptoms,” the authors wrote.

Even one or two soft drinks a day can affect intestinal balance, researchers warn. (iStock)

Thanarajah noted that soft drinks are still a significant source of added sugars worldwide.

‘They contain almost nothing else [but] sugar, and the prevalence is extremely high,” she said, adding: “What is really considered harmful is daily consumption, and we think that about 10% of children and adolescents consume soft drinks every day, which is clearly associated with weight gain, obesity and diabetes [and] fatty liver.”

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Future studies will focus on determining the clinical implications of the link, according to JAMA Psychiatry.

Fox News Digital has contacted the researchers and the American Beverage Association for comment.