DIETARY FIBRE, DEPRESSION AND ANXIETY

A recent systematic review and meta-analysis by Australian researchers published in 2024 suggests a possible role for dietary fibre in anxiety and depression.

A growing body of evidence suggests a link between the gut microbiome (i.e., bacteria, yeasts, fungi, viruses, archaea, and protozoa) and mental health issues like depression and anxiety. Dietary fibre is a key dietary component which can influence our gut microbiome, so the researchers wanted to look at existing research on dietary fibre and depression and anxiety.

There were two main parts to their review:

1. Investigation of the association between fibre intake and depressive and anxiety outcomes observational studies.
2. Investigation of the effect of fibre intervention on depressive and anxiety symptoms compared with placebo in randomised controlled trials.

Observational study evidence

There were 23 observational studies, including more than 180,000 participants. This included 16 cross-sectional studies, 3 longitudinal studies, and 4 case-control studies. Cross-sectional studies measure both the exposure (fibre intake) and the outcome (symptoms of depression or anxiety) at a single point in time for each participant. Longitudinal studies measure exposure (fibre intake) at the start of the study, then follow participants over a period of time, assessing outcomes (e.g symptoms of depression or anxiety) at later points. Case-control studies compare individuals who have a specific outcome (e.g. individuals with depression) with individuals who do not have the outcome (controls) and look back in time to see if there were differences in exposure (fibre intake) between the two groups.

In cross-sectional studies, a small but significant inverse association was observed between total fibre intake and depressive outcomes. This means that higher fibre intake was associated with lower levels of depressive symptoms. A significant inverse association was also found between total fibre intake and anxiety, although this analysis included only 3 studies.

• In longitudinal studies, with follow-up periods ranging from 3 to 17 years, a small but significant inverse association was found between total fibre intake and depressive outcomes.
• In case-control studies, there was no statistically significant difference overall in total fibre intake between individuals with and without depression. However, the researchers noted that individual studies often reported lower total fibre intake among participants with depression.

Overall, observational studies suggest a potential benefit for higher fibre intake and symptoms of depression and anxiety. However, the observed effects were small, and observational studies have limitations, including potential confounding factors, such as overall diet quality, that were not always adjusted for.

Randomised controlled trial evidence

The 10 randomised controlled trials included 740 participants. All the studies used fibre supplements rather than dietary changes. Most evaluated fermentable fibres, such as galacto-oligosaccharides (GOS) and fructans. The meta-analysis of these RCTs found no significant difference between fibre supplementation and placebo for overall depressive and anxiety outcomes. The dose of fibre didn’t change this finding. A subgroup analysis looking at different types of fibre supplements suggested that GOS supplementation might lead to improved anxiety symptoms, although this mainly came from the findings from one study.

The authors conclude that evidence from current randomised controlled trials does not support the use of fibre supplements for improving depressive or anxiety outcomes. However, they note several limitations of the findings including the small number of studies, the use of fibre supplements rather than whole diet modifications, short study durations (2-8 weeks) and the fact that only one study included participants with a clinical diagnosis of depression and most didn’t include depressive or anxiety outcomes as primary end points.

Overall conclusions

Combining all the findings, the researchers conclude that, while observational studies suggest a potential link between increased dietary fibre intake and a lower risk of anxiety or depression, the findings of randomised controlled trials don’t support the use of fibre supplementation for improving these outcomes. They suggest that more research is needed including adequately powered randomised controlled trials with a good study design in participants with depression and/or anxiety and using a broader range of fibres, including whole-diet interventions, where participants obtain dietary fibre from whole foods.

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