Stress and the gut microbiome

The following blog was written by Olivia Rogers, a Human Nutrition MSc student joining us for work experience. Olivia is working toward associate nutritionist (AfN) qualifications at Oxford Brookes University. Upon completion of her Postgraduate Masters degree, Olivia is aiming to work in Public Health, helping others eat better with science-based nutrition.

Stress is inevitable - something that everyone experiences at some point throughout their day to day lives. Current research looks at how stress can affect the gastrointestinal (GI) tract of the human body, and in turn, how this effects the physiological processes. The gut microbiome, the ecosystem of microorganisms in the gut, includes bacteria, fungi and viruses. The gut microbiome plays a significant role in maintaining not just gut health, but the overall health and functioning of the human body1. The gut microbiome supports homeostasis of body functions by enabling the healthy gut microbes to assist and maintain a healthy immune system1.

The scientific community is aware that a more diverse human gut microbiome, both in genetics and composition, is more beneficial for human health2. Alongside medications, lifestyle factors such as diet, physical activity, stress and sleep can affect the composition of the gut microbiome.

The connections between stress and the gut

In recent years, the role of mental health - specifically stress - on nutrition and gut health has become a popular talking point. Although clinical studies are still limited, many pre-clinical trials show extensive evidence for the role stress can play on the diversity and structure of the gut microbiome3. Psychological stress has been shown to induce myriad physiological effects that could influence the gut microbiome. Additional effects could include altered cognition and behaviour in response to gut microbiome signaling. It is increasingly evident that there is not only a relationship between the gut and the brain, but that this relationship is bidirectional. The connection is known as the ‘gut-brain axis'2.

Stress is the body’s natural response to danger, both real and perceived4. Stress is necessary from an evolutionary perspective as it provides protection from harm. Studies have shown this response can become abnormal when stress is frequent, excessive and long lasting. Stress often indirectly affects physical health - for example, it can impact the motor activity of the colon, resulting in a reduction in potentially beneficial microbiota such as Lactobacillusand reducing the diversity5.Research has shown that those suffering with heartburn acid reflux in the GI tract, associated with digestive disruption, found stress reduction helped decrease incidence of heartburn4.

Effects of psychological stress on the gut

Psychological stress, such as anxiety and worry, is often the result of life events causing alterations in neurohumoral communication between the gut and the brain. This causes altered signaling to the nervous system, resulting in negative effects on the GI tract such as inflammation, intestinal damage and increased permeability2. Pre-clinical studies have shown anxiety-like behaviour, such as social avoidance and pro-inflammatory states found in mice, mimic the aspects of post-traumatic stress disorders in humans, known as the social defeat model2. A lower abundance of Lactobacilluswas found in the gut of the mice after being exposed to unpredictable yet mild stress for 3-5 weeks. Lactobacillus is one of the beneficial bacteria that resides in the gut. This probiotic bacteria aids digestion, supports regular immune functioning and positively modulates gut physiology2.

Physical stress and sleep deprivation

Physical stress in athletes has been the subject of studies, which find a high correlation between physical or emotional stress during exercise and changes in gut microbiome composition. Gut conditions of athletes can be linked to the health of the gut microbiome6. As well as the challenges of physical stress, sleep deprivation also puts a strain on the body and can increase gastrointestinal permeability, which can result in an altered immune response that is associated with IBS2.

Stress and the diet

It is understood that stress can alter the gut microbiome, but what about the effects of stress on our food choices? Could they inadvertently alter gut diversity? Research shows students who had higher perceived stress levels consumed more sugary, caffeinated and high fat foods as well as energy dense and fizzy drinks7. These types of foods do not aid in the production of different types of gut bacteria, which are important for a diverse gut. In contrast, carbohydrates such as fibre-rich wholegrains, legumes and vegetables containing prebiotic fibre, can increase the level of good bacteria in the gut, but are shown to be consumed less often during times of stress4.

Diet-first strategies

It is known that food choices can influence our gut health but how can we manage stress or the effects of stress in order to improve gut health? Gut sensitivity seems to increase in relation to stress, and there is a reduction of gut issues when relaxation techniques are used. Those who suffer with functional gastrointestinal symptoms present greater physiological response and exacerbated symptoms when faced with greater psychosocial stress, therefore lifestyle management to reduce stress may be beneficial5.

Alternatively, targeting the health of the gut microbiome could be an intervention approach in the future, based on the research on the gut-brain axis. A food-first approach is encouraged to support the gut microbiome, but supplementation such as prebiotic supplements can be helpful, especially during times of high stress. Studies have found that supplementing the diet with prebiotics helps to support gut microbiome diversity, and in turn, can help lower stress response. A lowered stress response was reported after supplementation of Bimuno GOS and results showed a suppression of endocrine stress response, along with an increase in positive attentional vigilance8.

Stress may reduce the diversity of the gut microbiome and increase symptoms of IBS and gut related problems, therefore there is reason to consider gut health when managing stress. Inadequate numbers of good gut bacteria can negatively impact psychological stress symptoms and psychological functioning, suggesting that targeting the gut microbiome could be beneficial for the stress response. Dietary strategies and adequate sleep are recommended for groups at greater exposure to physical stress, such as athletes. Stress management, a varied diet, and possible supplementation can all be beneficial in improving stress levels, and improving gut health.

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