Could Fiber Intake Reduce Depression Risk?

Gut-brain interactions may help explain inverse link between dietary fiber and mental health

Illustration showing the link between the stomach and brain

With Yunsun Kim MD, Stephanie Faubion MD and Olivia Swann 

Dietary fiber is beneficial for many reasons, including weight management and reduction of risk of diabetes, heart disease and some cancers.

Now, new research suggests it may also be linked with a reduced risk of depression, at least in premenopausal women. The study, from Korea, echoes other recent research that has found an association between fiber and mood in other age groups as well.

“We think the most important finding of our study is that dietary fiber intake was inversely associated with depression in pre-menopausal but not post-menopausal women,” says study author Yunsun Kim MD, a researcher in the department of family medicine at Chung-ang University Hospital in Seoul.

Why the link? “The inverse relationship between dietary fiber intake and depression could be explained by the gut-brain interactions: changes in the gut microbiota composition may affect neurotransmission and various neuropsychiatric phenomena in the brain,” Dr. Kim says.

And why not in post-menopausal women? Dr. Kim says there might be an interaction between estrogen and gut microbiota, and because postmenopausal women have estrogen depletion, the decreased interaction between estrogen and the gut may explain the insignificant association they found between fiber intake and depression in older women.

Study Details

Kim’s team used data from the Korea National Health and Nutritional Examination Survey for 2014, 2016 and 2018.They used 24-hour dietary recall to assess fiber intake and the Patient Health Questionnaire-9  (PHQ-9)  scores, a commonly used measure, to assess depression. A score of 10 or higher was termed depression.

Of the 5,807 women, 2,949 were pre-menopausal and 2,858 were post-menopausal.

Average age was 36 years for the pre-menopausal women and 62 years for the post-menopausal women. Overall, the BMI’s were normal weight, with an average of 23. Among all participants, the estimated mean fiber intakes were significantly higher in the non-depressed group than the depressed group (14.07 grams per 1,000 kcal/day versus 12.67 g/1,000 kcal/day, p =0.003.)

When they looked just at premenopausal women, the link remained significant, 12.45 versus 10.30, p<0/001. However, in postmenopausal women, it was not significant, with 16.43 g versus 15.33g, for a p value of 0.13.

In the odds ratio values for depression according to daily dietary fiber intake with a scale of 1g/1,000 kcal, increased intake was linked with a decreased prevalence of depression in the total population (OR, 0.962, p=0.009) and in premenopausal women (OR, 0.914, p<0.001). The link did not remain significant in postmenopausal women in the unadjusted model or the adjusted models that took into account such factors as age, BMI, smoking and alcohol status. The study is published online ahead of print in Menopause.

Earlier Research on Fiber and Depression

Researchers from the University of Tasmania in Australia found a similar link between a high-fiber diet, depression and inflammation. In one of their recent studies, they looked at more than 1,900  adolescents, ages 14 and 17, says study author Olivia Swann, a PHD student and researcher at the university.

The evaluated dietary fiber intake, depressive symptoms and inflammatory data that was available for a sub-sample. The odds of depressive symptoms were lower in the highest quartile of overall fiber intake (OR, 0.273) compared with the lowest, after taking into account sex, age, adiposity, family and lifestyle factors. However, after further adjustment for dietary patterns, the results were attenuated. The researchers conclude that the association between a high dietary fiber intake and lower odds of depressive symptoms may reflect a high-fiber diet, with all its accompanying nutrients, rather than an independent effect of fiber alone.

“There is a growing body of evidence to suggest that there are cross-sectional associations between dietary fiber and depression in various age groups,” Swann says, citing another report by her team that reviewed some of the studies and potential mechanisms.

As for inflammation, Swann’s team suggested that it may mediate the relationship between dietary fiber intake and depression. “A high-fiber diet potentially lowers inflammation by modifying both the pH and the permeability of the gut,” her team writes. “The resultant reduction in inflammatory compounds may alter neurotransmitter concentrations to reduce symptoms of depression.”

However, as Swann says, “Cause and effect is very difficult to establish in population-based research like this.”  Even so, she says, the recent research studies ‘’provide valuable evidence of a link which can be explored in further research to determine causality.”

More Expert Perspectives

The odds ratio observed between fiber intake and depression in the fully adjusted model in the Korean study was small, points out Stephanie  Faubion MD, director of the Mayo Clinic Center for Women’s Health and medical director of the North American Menopause Society (NAMS), which publishes the journal Menopause. 

The odds ratio was 0.949, so those with higher fiber intake are just 5% less likely to be depressed, she says. As others point out, the link is an association, not cause and effect. “The direction could be the other way, that mood dictates what you are eating. Do those with a better mood to begin with eat a better diet? Or do those with depression sit on the couch and eat Cheetos?”

However, she adds that: “I think it’s biologically plausible that a high fiber diet does change your gut microflora.”  And, she adds, fiber intake over time might then in turn change neurotransmitters.

While Dr. Faubion supports exploring this link further, she cautions, ‘’Real depression needs cognitive behavior therapy and medications. We need to go with things that are proven to work.”

Take-Home Points

According to Dr. Kim, women should have fiber-rich diets regardless of their menopausal status. As the fiber intake of the post-menopausal women was relatively high, she says this might have confounded the effort to demonstrate the link found in younger, pre-menopausal women.

It’s too early to recommend fiber for depression, Swann says, as a causal relationship has yet to be proven. It’s also difficult to separate out the impact of fiber from the impact of other nutrients found in high-fiber foods such as whole grains and vegetables. The impact of fiber on mood might actually be due to those other nutrients, she says.

"Even so, doctors can advise patients to meet the meet the dietary guidelines for fiber in their country, to get all the proven benefits," says Swann. In the US, the Dietary Guidelines for Americans recommend adult men get about 34 grams of fiber a day from food, and women about 25.

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