Introduction
Scientific Overview
Stress and Stress Tolerance
HPA Axis
Circadian Rhythms
Immune System
Placebo Effect
Burnout
Chronic Fatigue Syndrome
Chronic Pain
Psychiatric vs Organic Debate
Irritable Bowel Syndrome
Chronic Lyme Disease
Recovery
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Irritable Bowel Syndrome

IBS is very misunderstood, and most explanations for the condition are very simplistic—simply putting the symptoms down to stress or a neurotic personality. While stress will certainly make digestive symptoms worse, many if not most IBS patients are not under particularly great stress, and most are not neurotic.

Research shows that the HPA axis— the body's energy regulation and stress tolerance system—has a large infleunce over colon motility and absorption, and IBS patients show altered HPA axis function, which is likely to be the cause of the symptoms.

CRH, the hormone which initiates HPA axis activation in the hypothalamus, increases the motility of the colon. During any kind of stressful situation, this release of CRH results in increased colon movement. Experiments have shown that this increased gut motility from CRH happens to everyone (as well as many animals), but the effect is more pronounced in IBS patients.

Cortisol, the end-product of HPA axis activation, causes increased absorption of water and sodium by the colon and rectum (i.e. it removes water and sodium from the colon and rectum). Too much CRH or too little cortisol will therefore result in diarrhea, while too little CRH or too much cortisol will result in constipation.

Studies show that patients suffering from diarrhea-predominant IBS tend to have a greater circadian rhythm of cortisol—higher in the morning and lower at night than controls—as well as having higher levels of cortisol after meals and during stress. This points to a greater HPA axis activation, or a greater stress tolerance, rather than being simply due to too much stress.

There is a large overlap between CFS and IBS, with many CFS patients suffering from IBS symptoms, and many IBS patients suffering from symptoms such as fatigue, depression and anxiety. In both cases it is likely that the HPA axis is the cause of the symptoms, and that this HPA axis imbalance is ultimately caused by similar factors.

Many IBS patients follow a pattern of alternating constipation and diarrhea, which suggests abnormal HPA axis activity. In many cases this pattern follows the patient's lifestyle—for example, diarrhea during the week or during periods of high activity, and constipation at weekends or when relaxing. Rather than simply being due to stress, it is more likely that IBS patients simply have a greater variation in HPA axis activity. Many IBS (as well as CFS) patients have what could be described as a over-achiever/burnout-prone personality—they are able to achieve high levels of activity or workload (probably due to being able to sustain higher-than-normal HPA axis activation), but they suffer from "burnout" after these periods of high workload or when they lose motivation.

Gut flora

The colon is home to a variety of bacteria which are beneficial to digestion. These "good bacteria" break down undigested food and fibre without causing unpleasant smelling gas or irritating the colon. The action of these bacteria is also important in generating vitamins as a by-product of the breakdown of indigestible fibre.

Although the immune system tries to keep a balance of good bacteria in the gut, sometimes other, more harmful types of bacteria can take up residence, giving rise to symptoms such as diarrhea, bloating and flatulence. Some factors which are known to upset the balance of bacteria in the gut include the use of broad-spectrum antibiotics, excessive alcohol consumption, stress and poor diet.

An upset balance in gut bacteria—sometimes called "small intentinal bacterial overgrowth" (SIBO)—is sometimes postulated as a cause of IBS-D. However, recent research has shown that the lactulose hydrogen breath test does not actually measure SIBO, and that SIBO is not likely a cause of IBS.

It is more likely that any bacterial imbalance is caused by the underlying HPA axis abnormality. This will result in an excessively short or long transit time of food through the gut and colon, either causing the bacteria to be flushed out of the colon too quickly or else letting them build up to excessively high levels. In addition, if undigested food is pushed too quickly into the colon, this can promote the growth of undesirable bacteria which thrive on undigested protein and fat. These bacteria tend to cause problems such as diarrhea and foul smelling gas when they become too prolific.

Interaction of Factors

Most IBS patients find that their symptoms are exacerbated both by lifestyle (or psychological) factors, as well as by diet. It is likely that certain foods cause problems due to them either being more difficult to digest, or because they are more likely to cause the "bad" bacteria to proliferate in the gut when they are not fully digested. It may be the combination of these foods with an abnormal HPA axis rhythm which then causes the symptoms of IBS.

Treatments/therapies for IBS

Most drug treatments for IBS simply reduce the symptoms—pain, constipation or diarrhea—without dealing with the underlying cause. A more effective treatment plan involves managing lifestyle to avoid excessive stress, and balance HPA axis activation, as well as avoiding foods that exacerbate symptoms.

References

Spiller, R; Aziz, Q; Creed, F; Emmanuel, A; Houghton, L; Hungin, P; Jones, R; Kumar, D; Rubin, G; Trudgill, N; Whorwell, P (1 December 2007). "Guidelines on the irritable bowel syndrome: mechanisms and practical management". Gut 56 (12): 1770-1798.

Fukudo, Shin (19 January 2007). "Role of corticotropin-releasing hormone in irritable bowel syndrome and intestinal inflammation". Journal of Gastroenterology 42 (S17): 48-51

Physiologic and Pharmacologic Effects of Corticosteroids. 2003.

Brennan M.R. Spiegel, "Questioning the Bacterial Overgrowth Hypothesis of Irritable Bowel Syndrome: An Epidemiologic and Evolutionary Perspective", Clinical Gastroenterology and Hepatology, 9(6), 461-469.

Elsenbruch S, Orr WC, "Diarrhea- and constipation-predominant IBS patients differ in postprandial autonomic and cortisol responses", Am J Gastroenterol 2001 Feb;96(2):460-6

Patacchioli FR, Angelucci L, Dellerba G, Monnazzi P, Leri O, "Actual stress, psychopathology and salivary cortisol levels in the irritable bowel syndrome (IBS)", J Endocrinol Invest 2001 Mar;24(3): 173-7

Chang, L., et al. "Dysregulation of the hypothalamic.pituitary.adrenal (HPA) axis in irritable bowel syndrome." Neurogastroenterology & Motility 21.2 (2009): 149-159.

Stratakis, Constantine A., and George P. Chrousos. "Neuroendocrinology and pathophysiology of the stress system." Annals of the New York Academy of Sciences 771.1 (1995): 1-18.

Majzoub, J. A. (2006). Corticotropin-releasing hormone physiology. European Journal of Endocrinology, 155(suppl 1), S71-S76.



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