Stress destroys your gut flora and makes you sick

This column is written by Stig Bengmark – professor emeritus, researcher, lecturer and author. Read more of Stig’s columns here.

It is a well documented fact that our brain and immune system are constantly exchanging information to make us feel as good as possible, both when we are healthy and sick. It is especially important when we are exposed to acute or chronic stress. Chronic stress is likely the most dangerous of all known causes of disease – maybe even more dangerous than a poor diet. Stress releases an array of hormones, neuropeptides and other “neurochemical products”, which have devastating effects on the important functions of the immune system. Almost all of the cells in our body are sensitive to these substances, but stress-related neurohormones such as adrenaline and norepinephrine are especially damaging to our immune cells and gut bacteria. All of the lymphatic organs – such as our bone marrow, thymus, spleen and lymph nodes – are packed with nerve fibres that carry messages from the brain, but ultimately, it is all about our gut.

Fig. 1 The body’s network of organs communicate in a number of ways – but this communication is primarily controlled by the brain. When you are under stress, the large intestine plays the main role, along with the brain and adrenal glands. The large intestine is special because it largely “programmes” and controls the immune system and is also home to 1-2 kg of our gut bacteria. The brain and intestines are constantly engaged in intimate two-way communication, but this increases dramatically when we are under stress, both in terms of fibre (nerve)-bound communications but also wireless long-distance communications (endocrine – with hormones) or short-distance communication (from cell-to-cell – paracrine signalling – and if in the brain – neurocrine signalling).


The brain influences the gut and its bacteria via 500 million nerve fibres

It has been reported that our gut contains at least 500 million nerve fibres that directly connect the gut to the brain (1). Both physical and mental stress cause our gut bacteria to be “showered” with “stress hormones” such as adrenaline, norepinephrine and dopamine, which radically change the pattern of our gut bacteria and causes the beneficial bacteria to largely vanish and the malicious bacteria to more or less take over. It has been reported in the medical literature that “stress hormones” – both natural hormones such as adrenaline, norepinephrine and dopamine, but also synthetically produced drugs such as dobutamine and isoprenaline (known for treating asthma, for example) – increase both the growth of malicious bacteria and their severity (virulence) by 100,000 times (2).

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Prenatal and infantile stress lay the foundation for poor health later in life

Stress is something that often haunts a person from the time we are in our mother’s womb up until our last breath. Stress has disastrous effects on the establishment of a well-functioning immune system, a process that has already started in the last few months of pregnancy and continues through early infancy. In much the same way, the establishment of well-functioning gut flora during our first few months/year of life is crucial for our health later in life. A voluminous, highly-diversified gut flora, as well as a well-functioning immune system, impacts our ability to withstand stress and illness well into old age and actually affects everything from the onset of allergies and ADHD in early life to Alzheimer’s and metabolic syndrome later in life.

Babies born through caesarean sections have weaker immune systems

There is an extensive body of research which shows that children born via caesarean section show an approximate 20% increase in the occurrence of asthma later in life (3). Caesarean section, especially if it is an unplanned, emergency caesarean section, results in an enormous increase in stress in the mother and large amounts of stress hormones are transferred to the fetus, even at the time preparations are made for the operation, and these hormones continue to be transferred in the next few days after the operation via the breast milk. The negative effects of the operation are mitigated to some extent through successful breastfeeding and a plentiful supply of breast milk rich in lactobacilli and important types of fibre, such as oligosaccharides. Unfortunately, this is not always possible due to an insufficient supply of breast milk.

Closeness between mother and baby relieves the effects of stress

Under these circumstances, it has been shown that it is especially important that the newborn be allowed to stay with his or her mother as this contact dramatically reduces stress levels in the newborn. Separation from the mother during the first week of life has been shown to lead to a significant increase in stress levels and highly impaired development of the gut flora in the newborn (4), which is believed to have negative health effects much later in life. Recently published animal studies show that newborns who are separated from their mother for more than 3 hours a day during the days leading up to the 12th day of life, develop gut flora that is permanently inferior to that of other people.(5).

Many diseases that develop later in life are rooted in stress

The far-reaching, negative effects of mental stress are well known and often lead to significant digestive and intestinal problems. This is the case for perhaps the most common disease of all – IBS (irritable bowel syndrome) – which is strongly associated with psychological stress and poor quality gut flora. Extensive studies have been done on astronauts, who are considered to be living under more or less permanent stress, which showed evidence of extensive and severe deterioration of the gut flora and, not least, a steep decline in the number of probiotic bacteria (mainly lactobacilli and bifidobacterium) along with a catastrophic increase in the number of malicious bacteria (such as enterobacteria and clostridia).

Studies have also been carried out that looked at the gut flora of university students during exam periods as well as athletes who are engaged in very strenuous sports. Results showed that both of these groups actually lost a large percentage of their gut flora and their immune function during particularly stressful periods, periods when they often got sick and were susceptible to severe infections. It is my hope and belief that the intensive reconditioning of the gut via synbiotics – i.e. supplementation with a combination of prebiotic fibre (food for the bacteria) and good bacteria – should be able to reduce this risk.

Stress is especially dangerous for overweight people (and especially for those who have a potbelly)

Stress is extra dangerous if you are overweight, especially if you have a lot of abdominal fat – aka a potbelly. In this case, stress exponentially increases the risk of getting acute cardiovascular disease, such as stroke. Typically, you should have no more than about 25 ml of abdominal fat – this is the amount our ancestors are believed to have had. Recent studies have found people who have up to an unimaginable six litres of fat in their abdomen.

Stress causes the body to accumulate large amounts of fat and to release large quantities of what are called proinflammatory cytokines (such as IL-6 in combination with a factor called PAI-1 – plasminogen activator inhibitor-1, which is known to strongly control blood coagulation, among other effects). It is widely recognised that the stress-induced increase in proinflammatory and pro-coagulative factors in the blood, in extreme situations, can be in the range of a 1000-fold increase, which then induces an enormous accumulation of fat in the liver, creates insulin resistance and contributes to a number of diseases that are summarised in the attached image: cardiovascular disease, abnormal amount of lipids in the blood (dyslipidemia), high blood pressure (hypertension) (6), impotence (erectile dysfunction), multiple ovarian cysts (polycystic ovary syndrome), dementia (cognitive decline), bone decalcification (osteoporosis), excess fat in the liver (NASH – non-alcoholic fatty liver disease) as well as general obesity, sleep apnoea, loss of muscle (sarcopenia) and type 2 diabetes.

Fig 2. Metabolic syndrome (see my column on Inflammation ) is often associated with increased abdominal fat and is in many ways the “mother” of a series of diseases that plague modern humans. In addition, it is common for those affected by one of these diseases to develop multimorbidities – i.e. to have multiple illnesses. Long-term mental and physical stress are major contributing factors to this condition.


How can you counteract the negative effects of stress and restore the gut flora? Super Synbiotics has written an article on the subject that you can find here.


(1) Furness, J.B. (2006) The Enteric Nervous System, Blackwell Publishing Oxford OX4 2DQ, UK, 2006
(2) Freestone PP, Haigh RD, Williams PH, Lyte M. Stimulation of bacterial growth by heat-stable, norepinephrine-induced autoinducers. FEMS Microbiol Lett. 1999;172:53-60.
(3) Thavagnanam S, Fleming J, Bromley A, Shields MD, Cardwell CR. A meta-analysis of the association between Caesarean section and childhood asthma. Clin Exp Allergy. 2008;38, :629-633.
(4) O’Mahony L, McCarthy J, Kelly P, Hurley G, Luo F, Chen K, O’Sullivan GC, Kiely B, Collins JK, Shanahan F, Quigley EM. Lactobacillus and bifidobacterium in irritable bowel syndrome: symptom responses and relationship to cytokine profiles. Gastroenterology. 2005;128:541-551.
(5) O’Mahony SM, Marchesi JR, Scully P, Codling C, Ceolho AM, Quigley EM, Cryan JF, Dinan TG. (2009) Early life stress alters behavior, immunity, and microbiota in rats: implications for irritable bowel syndrome and psychiatric illnesses. Biol Psychiatr. 2009;65:263-267.
(6) Item F, Konrad D. Visceral fat and metabolic inflammation: the portal theory revisited. Obes Rev. 2012;3, (Suppl 2):30-39. 


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