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Mithu Storoni MD, Ph.D.


Stress and Your Diet: Can Certain Foods Affect Your Mood?

A specific type of food may trigger negative emotions in certain settings.

Source: iStock

That feeling of needing to rush to the bathroom to empty the stomach’s contents – in either direction – at times of intense stress is a striking example of the close connection between the mind and the gut, which most of us will have experienced at some point in our lives. What you eat affects your gut’s well-being. Your “gut feeling”, in turn, influences your mind.

A gut can be stressed too.

To understand the relationship between food, stress and the brain, we need to zoom into a disorder that was long dismissed as a functional diagnosis of exclusion (it is diagnosed when every known disease is “excluded”), irritable bowel syndrome or IBS.

IBS is emerging as a key link in the chain connecting diet and the brain, in the setting of chronic stress. Chronic stress, including chronic psychosocial stress, induces IBS in laboratory animals. Combat training can bring on IBS symptoms and people with IBS report significantly higher levels of perceived stress and emotional suppression, compared to healthy controls.

IBS can include a wide spectrum of symptoms, from heartburn to bloating, to abdominal cramps, to constipation and diarrhoea. Symptoms may be mild or severe, chronic or fleeting. Many people with IBS may not be aware they have it.

Its “functional” label is fading fast: there is emerging evidence that IBS results in both localized and systemic low-grade inflammation, at least in a subset of sufferers.

A brief history of IBS.

One of the earliest descriptions of IBS was in a German academic paper in 1901. In the paper, the authors called IBS by a different name, “Gährungsdyspepsie” or “Fermentation dyspepsia” because their data suggested IBS was the result of excessive fermentation taking place in the intestines. This theory followed on from Louis Pasteur’s work on fermentation at the end of the previous century.

Later, this idea of excessive fermentation was pushed aside when the “fiber hypothesis” of the 1970s was all the rage. IBS was instead attributed to insufficient fiber in the diet.

Well over a century later, we have returned to square one.


A series of recent randomized controlled trials show that restricting one particular food group known by the acronym “FODMAPs,” which stands for Fermentable Oligo-, Di-, Mono-saccharides And Polyols, removes the symptoms of IBS.

FODMAPs are short chain carbohydrates, which our small intestines don’t absorb very well. As a result, they are fermented within the digestive tract by gut bacteria.

Fermentation of FODMAPs produces compounds that include short chain fatty acids (SCFAs). While doing a great deal of good at moderate doses, at excessive doses and in the wrong zones of the intestines, SCFAs may promote inflammation, disrupt motility and increase intestinal permeability.

In line with the 1901 hypothesis of Schmidt and Strasburger, emerging evidence points to people with IBS having a bacterial landscape that promotes excessive and disordered fermentation of FODMAPs.

As a result, reputedly "healthy" foods such as onions, garlic, beans and lentils can cause gastrointestinal distress in IBS sufferers.

Chronic stress shifts the gut's microbial landscape.

Both animal and human studies have shown that chronic stress shifts the bacterial landscape in the gut.

If this shift causes certain bacterial species that ferment FODMAPs to multiply excessively and in the wrong zones of the intestines at the expense of other benign bacteria, this can result in symptoms of IBS.Reversing this shift can normalise IBS.

For instance, going through stress can lead to a decline in Bifidobacterial species, and there is evidence of reduced populations of Bifidobacteria in IBS. Probiotics that contain Bifidobacteria can help with IBS symptoms and also increase stress resilience.

FODMAPs and mood.

FODMAPs can increase feelings of anger and sadness in IBS sufferers shortly after a meal, even if they have no idea they have just eaten FODMAPs as shown in one recent randomized, double-blind, controlled study.

In the study, a group of patients with IBS and a matched group of healthy volunteers were each given a range of foods directly into their stomach through a gastric infusion tube.

Fructans are a type of FODMAP. Examples of foods that contain Fructans are wheat, onions and garlic.

Infusing Fructans increased feelings of anger to some degree in both healthy controls and IBS patients, but feelings of anger, sadness and tension were especially elevated in the IBS group following Fructan infusion.

This effect was seen in as short a time as 30 minutes after the infusion.

This implies that a meal containing onions, garlic or other Fructans can rapidly incite anger or sadness to some degree, in vulnerable individuals.

FODMAP restriction during stress can protect the intestinal lining (animal studies).

Source: iStock

If we put rats through the chronic stress of being restrained, they develop intestinal inflammation and a “leaky gut”. Feeding the rats a low FODMAP diet mitigates this and can help to normalise their gut bacteria.

The idea of using a low FODMAP diet at times of heightened stress is being explored in the sphere of sport science, following a case report of an athlete whose exercise-induced gastrointestinal symptoms and perceptual well-being were improved when daily FODMAP intake was reduced from 81g/day to 7g/day during the training period.

Managing FODMAPs in IBS.

It is exciting to think that a certain food type might trigger anger or frustration and that another may calm anxiety. As research progresses, we might one day be able to tailor a meal perfectly to our exact psychological needs at any one time.

If you have any semblance of gastrointestinal symptoms, be sure to get these checked out by your physician. If your physician attributes these to IBS, then it is worth considering the effect of FODMAPs on your mood and general well-being and investigating a FODMAP elimination diet.

An individual with IBS will not be intolerant to all FODMAPs, so a short FODMAP elimination period is followed by a gradual reintroduction of FODMAPs, to identify the culprit FODMAP in each individual case. This is a carefully managed strategy that should be implemented under the guidance of a medical professional.

Once an offending FODMAP has been identified, keeping its levels low may bring noticeable benefits to your mental and physical well-being, especially on high stress days. Your medical professional may also suggest a course of probiotics to support your gut’s microbial population during a restrictive diet.

Other actors in stress reactivity.

FODMAPs are one piece of the gut’s jigsaw. Another major piece is the gut’s microbial population. Several randomized controlled studies now show that a course of probiotic therapy can improve anxiety, stress reactivity and mood, both in people with IBS as well as in healthy controls.

Eating a variety of fermented food at every opportunity and taking probiotic-containing fermented products with Lactobacillus and Bifidobacterial species, may help reduce anxiety and stress reactivity even in the absence of IBS.

Other contributors to chronic stress, such as disordered circadian rhythms, may influence symptoms of IBS, and melatonin is currently being explored as an adjunct therapy for IBS. It also plays a stress-buffering role independent of its intestinal effects.

Taking action.

The gut’s microbes and dietary FODMAPs are two key areas to think about in the setting of chronic stress. Research in both areas is still ongoing and many gaps remain unfilled.

Beyond these, the standard rules of a healthy diet apply – eat a whole-food, varied, unprocessed diet, without preservatives, emulsifiers, or other additives. Always eat in accordance with your circadian rhythm and never, ever, overeat.

Please note: this piece is for discussion only and should not be used as medical advice. Please check with your physician before making any changes to your diet or medications.


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About the Author

Mithu Storoni, MD, Ph.D. is a physician, researcher, and the author of Stress-Proof: The Scientific Solution to Building a Resilient Brain and Life.