Are you feeling stressed and find that this affects your eating patterns? Or maybe eating healthily makes you feel stressed? 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, decreased performance, insomnia, change in appetite, weight loss, mood disturbances such as irritability and anxiousness, inflammation and immunosuppression.
How are eating and stress linked?
Our eating patterns are influenced by so many factors including tiredness, boredom, medications, our gut microbiota and stress. Stress has not only a psychological effect on eating but also a physiological one too. With emerging evidence about the bi-directional connection between our gut and our brain, (gut-brain-axis), there is evidence that not only does stress affect nutrition, but nutrition affects stress.
Stress appears to change overall food intake in one of two ways, resulting in either under or overeating. Evidence supports that the severity of the stressor can affect this. A greater preference for energy and nutrient dense foods, namely those high in sugar and fat, is associated with chronic life stress. Longitudinal studies have suggested that chronic life stress may be linked to weight gain, especially in men. Chronic stress is a considerable health concern for society, associated with various disease states, including an increased risk for neuropsychiatric disorders such as depression and anxiety. Some suggest that up 25% of the population are affected by chronic stress.
The cortisol stress response
Cortiosteroids are a class of steroid hormone produced by the adrenal cortex 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.
Glucocorticoid hormones are type of hormone that are secreted at times of stress. They are hormones that regulate multiple aspects of the control of blood glucose levels. They promote synthesis of new glucose (gluconeogenesis) in the liver, whereas they reduce glucose up-take in fat and muscle. 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, it’s clear to see that 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, rumination and magnification of the stressor may intensify the glucocorticoid secretion and become a prolonged and exaggerated stress response. Glucocorticoids may even have a role in consolidating fear-based memories to help future survival and avoidance of danger. While stress may be unavoidable in live, coping with the stress, confrontation of the stressors, and refection may all help to minimise cortisol secretion.
Glucocorticoids (or steroids for short) are widely used across the world for treating numerous inflammatory and autoimmune diseases such as asthma, allergy, inflammatory bowel disease, multiple sclerosis, leukaemia, lymphoma, and have recently hit the headlines for improving the survival of critically ill patients with Covid19. Unfortunately, their use is limited by the adverse side effects that are associated with high doses, such as diabetes, abdominal obesity, high blood pressure to name just a few.
Corticosterone and appetite
Both exogenous (in the form of steroid medications) and endogenous (manufactured in the body) steroids are associated with hyperphagia (abnormally strong sense of hunger leading to overeating). This is more pronounced with exogenous steroid medications (as these are at higher doses), but demonstrates that the effects of stress on appetite are physiological not just psychological.
In mice, cortisol (the main glucocorticoid hormone) has been shown to have the opposite effect to the hormone leptin, which inhibits hunger. This means that mice who have higher levels of cortisol continue eating and gain weight.
Stress-induced eating may be one factor contributing to the development of obesity. Research on people defined as obese have found some to have chronically raised levels of steroid hormones. This has led to the hypothesis that stress may play a major role in the development and maintenance of obesity in individuals who are more sensitive to glucocorticoids.
Psychological impact of stress
High-fat and high sugar foods stimulate the reward pathways in the brain, and withdrawal of these foods often results in increased cravings for them. Stress is an important factor in the development of addiction and relapse. It maybe that stress is also 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. This leads to increased sensitisation of dopamine rewards, further seeking of hyperpalatable food, coupled with the physiological changes of increased blood sugar, and insulin resistance, to promote increased body fat and weight.
Gut health and stress
Our gut microbiota, the trillions of bacteria, fungi, parasites, and viruses that live inside us, can influence many processes such as development, metabolism and immune function, and are associated with 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. For more information on the breastmilk and the microbiota see here. While adult microbiota are relatively stable, they are shaped by a number of factors including mode of delivery (vaginal or caesarean section), breastfeeding or bottle-feeding, diet, some medication such as antibiotics, exposure to infections, stress and other factors like smoking.
Incredibly, alterations in the microbiota, can also modulate our behaviours such as social activity, stress and anxiety related responses. 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 via different microbiota profiles that have been observed. The intestinal barrier of the gut wall, can be affected by both chronic and psychological stress, 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.
It is now established that there is bidirectional signalling between the gut microbiota and the brain, called the gut brain axis. Communication occurs through three different pathways; neural, mainly via the Vagus nerve and enteric nervous system; endocrine, via glucocorticoids, such as cortisol; and immunological pathways, through the modulation of cytokines.
Studies have shown that the gut microbiota can modulate this axis via a number of mechanisms including alterations in the composition of the microbiota, and also the production of different neuroactive metabolites. In a large population study, the presence of different microorganisms was correlated with quality of life and the incidence of depression.
Can Probiotics Help?
Animal studies have found that probiotics can 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, and in other studies decreased hypersecretion of cortisol in response to the stress of an academic examination, but more research is needed.
How to Reduce the Impact of Stress
Optimise and support your microbiota, steer clear of the high-fat, high sugar foods where possible, instead choosing a healthy balanced diet of wholegrains, fruit, vegetables and healthy fats, and try regular exercise to improve your mental health. While stress may be unavoidable in live, coping with the stress, confrontation of the stressors, and refection may all help to minimise the stress response.
This post was written by Dr Harriet Holme who studied medicine at the University of Cambridge and has over a decade of experience as a paediatric doctor. Harriet also has a PhD in genetics from University College London. Harriet now uses her skills for the benefit of her clients and students, exclusively consulting as a Registered Nutritionist with the Association of Nutrition and lecturing in culinary science and nutrition. You can find Harriet @healthyeatingdr and on her website Healthy Eating Dr.
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