Anxiety and Gut Health

Anxiety disorders, as a family of conditions, represent the most prevalent mental health disorders globally.

As a dietitian, I’m inevitably curious about what role food and nutrition might play in reducing anxiety severity in those who suffer from it – whether clinically or otherwise.

Which brings us to the topic of today’s post.

The connection between anxiety and gut health.

Given the emerging science around the gut-brain axis, mental health researchers have become increasingly intrigued by how manipulating one’s gut health may interact with their mental health.

There is a bi-directional relationship between the human brain and the gut microbiome and, as such, dysbiosis and inflammation within the digestive tract have been identified as potential drivers of both anxiety and depression.

But is there enough evidence to suggest that intervening in these issues can actually improve the severity of someone’s anxiety?

Let’s take a closer look.

Anxiety & Probiotics

These days any discussion around improving gut health will inevitably pass through a discussion of probiotic supplementation but an honest assessment of the literature in this area reveals mixed results.

In October 2021 Clinical Nutrition ESPEN published the results of their systematic review & meta-analysis looking at the best available studies on probiotic use in anxiety and depression.

The review looked at a total of 16 eligible experimental studies with over 1,000 participants and found that while probiotic supplementation improved measures of anxiety and depression as measured by certain symptom tests, others showed no statistically meaningful effect. 

They concluded that probiotic supplementation may improve symptoms of depression and anxiety in clinically diagnosed cases, which echoed the sentiment of a 2019 paper out of Neuroscience & Behavioural Reviews which determined probiotics to have a small but statistically significant effect on both anxiety and depression.

My assessment of these and other similar studies resulted in a few important conclusions:

1. Although evidence suggests a potential benefit for both depression and anxiety, it seems that the effect is stronger and more consistent in depression. My overall sense is that the evidence for the success of dietary intervention on mental health is generally stronger for depression.

2. The benefit of probiotics on both depression and anxiety symptoms was largely reserved for clinical cases, meaning probiotics may offer little to no symptom reduction in those who are otherwise healthy with no clinically diagnosed disorder.

In the vast majority of studies, either single or multi-strain probiotic supplements using various members of the Lactobacillus or Bifidobacterium family were used, but the variation between studies makes it nearly impossible to suggest a specific strain or product, although it does appear multi-strain supplements may generally be more effective.

Interestingly, there is also some evidence to suggest that in otherwise healthy individuals probiotic supplementation may reduce perceived stress levels over time.

Prebiotics, Fermented Foods & Anxiety 

Obviously, probiotic supplementation is not the only way to manipulate our gut microbiome, and having written previously both on prebiotics & fermented foods , I was thrilled to see emerging research on their use as potential tools for anxiety management.

A 2021 study out of Scientific Reports found that a 4-week prebiotic intervention (using galacto-oligosaccharides GOS) in young women (aged 18-25) led to an increase in healthy Bifidobacterium populations and demonstrated some anti-anxiety potential in this otherwise healthy population.

From the dietary perspective, legumes such as lentils & chickpeas are among the highest sources of the prebiotic fiber GOS.

An observational 2015 study out of Psychiatry Research found that higher fermented food intake may protect certain predisposed individuals against symptoms of social anxiety.

Fermented foods include probiotic yogurts, kefir, kimchi, kombucha, and related foods.

The evidence in these areas is limited at best, and while encouraging dietary variety around some of these food items is generally a low-risk, high-reward endeavor, there is certainly insufficient evidence to make strong claims that they can meaningfully improve anxiety symptoms in those who suffer from it.

A Note On Anti-Inflammatory Supplements

I mentioned at the outset of today’s article that inflammation of the GI tract was considered one of the potential drivers of worsening mental health, and so it unsurprisingly follows that traditional “anti-inflammatory” type supplements including omega-3 fatty acids ( ~ 2g/day) and curcumin (~ 1g/day) have been studied in a limited capacity to demonstrate some potential anti-anxiety effect.

It should be noted that the long-chain omega-3s DHA/EPA, used in the study cited above, are found essentially exclusively in fatty fish such as salmon, trout, and sardines.

Interestingly enough, these foods also represent a near-exclusive dietary source of Vitamin D – another compound of interest in anxiety symptom management.

Final Thoughts 

Despite being the most prevalent mental health disorder globally, there is only very limited evidence available relating to the role dietary manipulation could play in making meaningful improvements to anxiety symptoms.

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