Is There a Connection Between Soft Drinks and Depression?

Summary: Yes, there is a connection between soft drinks and depression. This is not a new concept, but previous research has been inconclusive, and lacked the scientific rigor required to draw evidence-based conclusions on the topic.

Key Points:

• Research shows a connection between high sugar diets and diagnosis of major depressive disorder.
• A new study examines the impact of drinking soft drinks on diagnosis of depression and the severity of depressive symptoms.
• Researchers also examined whether sugar-induced changes in the gut microbiome affect diagnosis of depression and symptom severity.
• In a surprising result, the connection between soft drinks and depression appeared in one gender only, rather than in both males and females.

Soft Drinks and Depression? Really?

Yes, really. We know, we know. The world changes quickly. When researchers discover new scientific and medical information and supply evidence to support their findings, we need to pay attention. The proof, as the saying goes, is in the math.

And with regards to whether there’s a connection between soft drinks and depression, the scientists have the math. Or, as we may say in a different context, they brought the receipts.

About the Study: The Connection Between Soft Drinks and Depression

A group of researchers in Germany designed a study called “Soft Drink Consumption and Depression Mediated by Gut Microbiome Alterations” to answer two questions:

1. Is soft drink consumption related to depression diagnosis and severity?
2. Is this association mediated by gut microbiome alteration?

Here’s how they conducted the study:

First, the research team collected data from 405 patients with major depressive disorder (MDD) and 527 healthy control patients in the Marburg-Münster Affective Cohort, all between the ages of 18 and 65.

Second, to assess severity of depressive symptoms, researchers analyzed results from the Beck Depression Inventory (BDI-I).

Third, to assess soft drink consumption, they administered the German 101-item food frequency questionnaire (FFQ2). For soft drinks, respondents reported the frequency of consumption of 200mL – 6 oz – servings of soft drinks on any given day. The FFQ2 test presented 11 possible answers, ranging from never to several times a day, with energy intake estimated in kilocalories.

Fourth, to assess levels of microbiota in the gut, they analyzed the RNA content of stool samples using standardized collection protocols verified effective in detecting two species of microbiota, Eggerthella and Hungatella. Prior research identifies a causal connection with major depressive disorder (MDD).

Finally, to ensure accuracy of results, researcher applied the MacKinnon permutation test, as well as controlling for body mass index (BMI).

Let’s take a look at the results.

Outcomes: Does Consuming Soft Drink Increase Depression Risk?

We’ll start by evaluating the first research question:

Is soft drink consumption related to depression diagnosis and severity?

Here’s what they found:

1. Soft drink consumption and clinical diagnosis of MDD, i.e. the connection between soft drinks and depression:
   • Higher soft drink consumption was associated with an 8.1% increased risk of clinical diagnosis of depression
   • Researchers observed this effect in women, but not in men.
2. Soft drink consumption and depressive symptom severity, i.e. the connection between soft drinks and depression symptoms:
   • Higher soft drink consumption was associated with higher levels of symptom severity
   • Researchers observed this effect in women, but not in men.
3. Soft drink consumption and abundance of Eggerthella and Hungatella species of microbiota (both species previously associated with increased risk of MDD):
   • Higher soft drink consumption was associated with greater abundance of Eggerthella
   • Higher soft drink consumption was not associated with greater abundance of Hungatella
   • High soft drink consumption was associated with lower overall diversity of all microbiota in the gut, i.e. the microbiome
   • Researchers observed these effects in women, but not in men.

Those results answer the first question posed by the research team:

Is soft drink consumption related to depression diagnosis and severity?

The answer is a clear yes, soft drink consumption is associated with depression diagnosis and severity. That data also supports the answer to the question we pose in title: yes, there’s a connection between soft drinks and depression.

Outcomes: Does our Microbiome Affect the Impact of Soft Drinks Depression Risk?

We’ll continue by evaluating the second research question:

Is [the] association [between soft drink consumption and depression] mediated by gut microbiome alteration?

Based on the data related to the first question, researchers limited their analysis to the impact of Eggerthella on diagnosis of major depressive disorder (MDD) and depressive symptom severity among women.

Here’s what they found.

1. Abundance of Eggerthella mediated association between soft drinks and MDD:
   • The effect was significant and accounted for close to 4% of the effect of soft drink consumption on MDD diagnosis.
2. Abundance of Eggerthella mediated association between soft drinks and depression symptom severity:
   • The effect was significant and accounted for close to 5% of the effect of soft drink consumption on depression symptom severity.

Those results answer the second question posed by the research team:

Is this association mediated by gut microbiome alteration?

The answer is another clear yes, the impact of soft drink consumption on depression symptom severity is mediated by changes in the gut microbiome.

Drawing on previous research, the study authors theorize that the large amount of sugar in soft drinks has a negative effect on the gut microbiome by increasing the production of inflammatory bacteria, which affects the integrity of the gut wall, which in turn has a negative effect on immunity in mucosal tissue. In addition, a high sugar diet decreases diversity in the gut microbiome. Previous research indicates negative downstream effects of this phenomenon on mental health symptoms in the rodent model. Therefore, the researchers propose, excess sugar intake may “indirectly promote Eggerthella growth by altering microbial competition.”

We’ll elaborate on these outcomes below.

Soft Drinks and Depression: What This Study Can Tell Us

This study identifies a small but consistent effect of soft drink consumption on depression diagnosis and severity. However, the effect appeared only in males. Therefore, more research is needed to understand why. According to the research team:

• Biological sex influences the microbiome
• Diet affects the microbiome
• Biological sex impacts the effect of dietary interventions on the microbiome
• Women are more vulnerable to the negative effects of a high sugar diet om the microbiome, compared to men

Here’s how the research team describes these outcomes:

“Despite small effect sizes, the link between soft drink consumption, Eggerthella abundance, and depression may have clinical and public health implications. Given the complex interaction between diet and mental health, it is not surprising that the effect of soft drinks on MDD diagnosis and depressive symptoms is rather small. However, it is important to highlight that this is a widely distributed but fully avoidable risk factor.”

What this research can tell us – and teach us – appears in that last sentence. Drinking soft drinks is one hundred percent avoidable. That means that for all our female patients with depressive disorders, reducing soft drink consumption has a significant chance of reducing the severity of depressive symptoms. And for people at risk of developing depression – specifically women, for now – we can safely say that decreasing soft drink consumption can reduce risk of developing major depressive disorder (MDD), which is a significant, new, and actionable piece of information.