With rising cases of Covid19, the news full of ever-changing restrictions, it’s not difficult to see why people are feeling increasingly stressed. With predictions that at least half a million people in the UK may well experience mental health concerns as a result of the SARS-nCov2 pandemic, this is a challenging time.

It is becoming clearer who are greatest risk of higher mortality and morbidity from Covid19; these include people with diabetes, obesity, cardiovascular disease, deprivation, male sex, age and black, Asian and minority ethnicities. Central to the majority of these chronic diseases is nutrition. This article explores the two-way relationship between stress and nutrition and how practical tips to support your health.

It’s not unsurprising you might be feeling stressed and found your eating patterns have changed. Food and emotions are interconnected on so many levels, food really isn’t just simple nutrients to be consumed like tablets, instead there is a profound connection between mood and diet.

What is Stress?

Although there is no consensus as to which symptoms or biomarkers define stress, some common signs that are widely accepted include clinical and hormonal indicators, fatigue, weight loss, decreased performance, insomnia, change in appetite, mood disturbances such as irritability and anxiousness, inflammation and immunosuppression.

How Are Eating and Stress Linked?

So many factors influence our eating patterns including stress, tiredness, medications, boredom, and even our gut micro-organisms. Stress has both a psychological and physiological effect on appetite. With emerging evidence about the two-way connection between our gut and our brain, (gut-brain-axis), there is evidence that not only does stress affect nutrition, but nutrition also affects stress.

Stress appears to change overall food intake in one of two ways, resulting in either over or undereating. Interesting this can be determined by severity of the stressor. Chronic life stress is associated with a greater preference for energy and nutrient dense foods, such as high in sugar and fat foods. In men, studies have suggested that chronic life stress may be linked to weight gain. Chronic stress is thought to affect up to 25% of the population. For society, chronic stress is a considerable health concern, associated with various disease states, including an increased risk for neuropsychiatric disorders such as anxiety and depression.

The Cortisol Stress Response

A gland situated above the kidneys, produces steroid hormones. Corticosteroids are a class of steroid hormone that are divided into two different types: glucocorticoids have an important role in regulation of the immune system and carbohydrate metabolism and mineralocorticoids that help to control salt and water balance.

At times of stress glucocorticoid hormones are secreted. They are hormones that regulate multiple aspects of the control of blood glucose levels. In the liver, they act to promote synthesis of new glucose (gluconeogenesis), whereas in muscles and fat, they reduce glucose up-take. Together with opposing the effect of insulin, glucocorticoids lead to a rise in blood glucose. This is to provide the brain with more glucose during times of stress, and to promote maximal brain function.

From an evolutionary perspective, glucocorticoids have played a vital role in the fight or flight response, providing a rapid increase of blood glucose, enabling quick decision making at a time of intense stress. However, in modern society feelings of helplessness, and repeatedly concentrating on and thinking about the stressful events, may intensify the secretion of glucocorticoid hormones. This can become a prolonged and exaggerated stress response. To help future avoidance of danger, and survival, glucocorticoids may even have a role in consolidating fear-based memories. While stress may be unavoidable in live, coping with the stress, confrontation of the stressors, and refection may all help to reduce the secretion of cortisol.

Numerous inflammatory and autoimmune diseases such as asthma, allergy, inflammatory bowel disease, multiple sclerosis, leukaemia, and lymphoma, are routinely treated with glucocorticoids (or steroids for short). Recently two steroids hydrocortisone and dexamethasone have been found to improve the survival of critically ill patients with Covid19. The use of therapeutic steroids is limited by the adverse side effects that are associated with high doses, such as abdominal obesity, diabetes, high blood pressure to name just a few.

Corticosterone and Appetite

Hyperphagia is the abnormally strong sense of hunger, leading to overeating. Both exogenous, in the form of steroid medications, and endogenous, which are steroids manufactured in the body, are associated with hyperphagia.

Higher doses seen with steroid medications, mean that this effect is more pronounced with exogenous steroids. It does however demonstrate that that the effects of stress on appetite are also physiological not just psychological.

Cortisol (the main glucocorticoid hormone), in mice has been shown to have the opposite effect to the hormone leptin, which inhibits hunger. Mice who had higher levels of cortisol continued to eat and subsequently gained weight.

Stress-induced eating may be one factor contributing to the development of obesity. Research has found chronically raised levels of steroid hormones are seen more frequently in people classified as obese. This has led to the hypothesis that in individuals who are more sensitive to glucocorticoids, stress may play a major role in the development and maintenance of obesity.

The Psychological Impact of Stress

Reward pathways in the brain that are associated with pleasurable experiences, are stimulated by high-fat and high sugar foods. Withdrawal of these foods often results in increased cravings for them. Stress is an important factor in the development of addiction and relapse. Stress may be linked with addiction to the neurochemical rewards of these high-fat and high sugar foods, increasing the risk of obesity and diabetes. Chronic, uncontrollable stress changes eating patterns, and with the consumption of these hyperpalatable foods, there is concern that this could lead to alterations of neurobiological pathways that promote compulsive behaviour. Increased sensitisation of dopamine rewards follows with further seeking of hyperpalatable food, coupled with the physiological changes of increased blood sugar, and insulin resistance, to promote increased body fat and weight. With the possible opposing action of glucocorticoids on leptin, as seen in mice, there is less opposing regulation of satiety, leading to overeating and chronic weight gain.

Gut Health and Stress

The trillions of bacteria, fungi, parasites, and viruses that happily live inside us, termed the gut microbiota, can influence many processes such as development, metabolism and immune function. The gut microbiota is now well recognised to play a role in susceptibly to many diseases.

While the human microbiota colonisation probably begins at birth, if not before, it isn’t until aged 2 years that a stable, adult-like, community is established. The adult microbiota is relatively stable, but they are shaped by a number of factors including mode of delivery (vaginal or caesarean section), breastfeeding or bottle-feeding, diet, some medications such as antibiotics, exposure to infections, stress and other factors like smoking. 

In studies of special germ-free mice, who have no organisms living on or inside them, they found that faecal transplant from obese humans, was associated with a greater weight gain than mice that received microbes from healthy weight humans. This suggests that the gut microbiota in mice has a critical role in weight determination.

Incredibly, our behaviours such as social activity, stress and anxiety related responses can be modulated by our microbiota. However, the methods by which this influence occurs remains poorly understood. Studies on mice have identified that manipulation of the microbiota can lead to changes in specific types of behaviour, such that those animals with reduced or absent microbiota were less likely to forget fearful stimuli (reduced fear extinction learning). Additionally, in germ-free mice who have no microbiota, four metabolites were found at significantly decreased levels; these metabolites are reported to be related to neuropsychiatric disorders in both humans and mice. This suggests that compounds produced by the microbiota may directly affect brain function and behaviour.

Chronic stress is associated with an increased risk of gastrointestinal disorders such as irritable bowel syndrome (IBS). Research has suggested that depression even promotes the onset of IBS, possibly by different microbiota profiles. Both chronic and psychological stress, can affect the intestinal barrier of the gut wall, leading to increased gut permeability. Most of us have probably experienced ourselves, that psychological stress can cause bowel dysfunction such as nausea, vomiting, abdominal pain and alteration in bowel habits.

The gut brain axis describes the two-directional signalling between the gut microbiota and the brain. Communication occurs through three different pathways; via nerves such as the Vagus nerve; endocrine, via hormones like glucocorticoids, such as cortisol; and immunological pathways, through the modulation of inflammatory cytokine messengers.

Studies have shown that alterations in the composition of the microbiota, and also the production of different neuroactive metabolites formed by the gut microbiota can have direct effects on the brain. In a large population study, the presence of different microorganisms was correlated with quality of life and the incidence of depression. 

Can Probiotics Help?

Probiotics have been found in animal studies to maintain gut permeability under stressful conditions, and decrease glucocorticoid induced inflammatory cytokine responses, which have been associated with reduced depression and anxiety. Similarly, small scale clinical trials have found that probiotics are associated with decreased self-reported mood. Other studies have found decreased hypersecretion of cortisol in response to the stress of an academic examination, associated with probiotic use, but more research is needed.

How to Reduce the Impact of Stress

While stress may be unavoidable in life, coping with the stress, confrontation of the stressors, and refection may all help to minimise your stress response. Try regular exercise to improve your mental health and find techniques such as mindfulness, journaling and being thankful to help you get through challenging times. Aim to optimise and support your microbiota, eat fermented food such as kefir, steer clear of the high-fat, high sugar foods where possible, and instead choose a healthy balanced diet of whole-grains, fruit, vegetables and healthy fats.

Follow Dr Harriet Holme at @healthyeatingdr or find more science backed nutrition information on her website www.healthyeatingdr.com











Follow Dr Harriet Holme at @healthyeatingdr or find more science backed nutrition information on her website www.healthyeatingdr.com