IBS Fact : Evidence-based management of irritable bowel syndrome

What causes irritable bowel syndrome?

For a better understanding of IBS, one first needs to understand the many tasks performed by the digestive system. Because digestion is not a conscious or voluntary process, we are mostly unaware of its complex nature. Naturally, we take this process for granted. At a closer look, however, one can appreciate the many challenges faced by the digestive system and the ingenious solutions to these challenges evolution has provided over the course of millions of years. At first glance, the task seems simple: absorb all useful nutrients and excrete the waste. Yet, the first challenge is presented by the physical form of our food, which is usually a mixture of semi-solid particles. These need to be broken down into smaller pieces in order to allow any kind of efficient extraction of nutrients. The second challenge is how to chemically separate and extract these nutrients from the various indigestible components present in our food. Fruits and vegetables, for instance, require a different extraction process than meat, as they contain a large amount of indigestible material which we cannot break down. In addition, major nutrients such as sugars, fats and proteins have very distinct chemical structures and physical properties. Thus, a targeted processing is required for each. As omnivores, we are able feed on a large variety of foodstuffs, which is often ingested as a mixture of various products. Thus, digestion of chemically and physically very distinct materials must take place simultaneously and within the same compartment, which is another challenge. Consequently, for any kind of efficient digestion to occur, our bowels need to monitor this processing and select the various types of chemical and mechanical programs required at each step. Although we are largely not aware of it, our intestinal tract can sense both the physical and the chemical properties of food and decide which type of mechanical and chemical program is required in terms of mixing, separating, incubating with different digestive enzymes, extracting, and transporting to the next processing stage. This is not a trivial task and requires a sophisticated system that can receive and process large amounts of information and return instructions how to efficiently coordinate the entire operation. It has been assumed for a long time that such a complex task can only be managed by our brain. This idea was further supported by the large number of nerve fibers between our bowels and brain. However, striking evidence against this view was the observation that the intestinal tract can in fact perform all of its normal tasks without much trouble even after all the connections to the brain have been severed. Further studies showed that this is only possible because the bowel contains its own independent nervous system consisting of nearly 100 million neurons interspersed over the entire length of our bowels. Because of its large size and autonomy, this neuronal network is also called the “little brain”. As we will see later, the proper functioning of the “little brain” is central to the development and treatment of IBS.

Another challenge faced by our digestive system is that the ingested food is a potential source of pathogens such as parasites, fungi, bacteria and viruses. Thus, besides absorbing as much nutrients as possible from a large number of foodstuffs, our body needs fight off these intruders. This requires not only a detection system but also knowing the difference between friend and foe. The recognition, destruction and elimination of harmful intruders are performed by the immune system which employs a vast array of specialized cells. These also communicate with each other chemically via so called pro- and anti-inflammatory mediators. Given the large surface area of the gastrointestinal tract – between 30 and 40 square meters, or as large as a studio apartment –  it is not surprising that the major part of our immune system is located in the bowels. But it gets even more complicated: humans, and most animals for that matter, employ “friendly” bacteria and yeasts to help with the digestion of foodstuffs and breakdown of toxic by-products. So, in addition to the food we process, our bowels also house billions of bacteria and yeasts of various species. This microbial community is an ecosystem on itself and contains more individual organisms than the number of cells our bodies are made of.  So, by number of cells, we are more bacteria than we are human. Why do we need all these microbes? Why did we not evolve the necessary tools to deal with digestion by ourselves? Evolution, it seems, strives for the most cost effective solution, and collaboration can be an efficient way to get things done. Once you have an effective collaboration going on, there is no further need (or evolutionary pressure) to design an entire new way for solving the same problem.  It seems nature prefers to combine what is available rather than invent things from scratch.

We have now discussed the machinery for processing of food, which is under the control of our “little brain” and communicates with our “big brain” while the immune system wards off any pathogens that may enter along with our food. In addition, an entire ecosystem of bacteria and yeasts inhabits our bowels.

This system works beautifully if you consider how efficient it is in processing the various foods, extracting nutrients, excreting waste, and maintaining a barrier against harmful agents. Even more, it is adaptive, meaning it responds to changes in the environment, such as availability of certain foods, to maintain its efficiency. But as for any complex system, it is can be very difficult to trace back any type of defect or malfunction. Because this system is so interconnected, it may be even difficult to determine whether a dysfunction is the cause or the consequence of a certain defect. Another interesting observation is that despite its complexity, dysfunction of the digestive tract manifests itself predominantly by just two symptoms: pain and altered bowel habits. Certainly, other complaints, ranging from fatigue to decreased psychological well-being, can also manifest, but these are much more difficult to relate directly to the digestive processes. This leaves us with a very limited number of symptoms that can be used to differentiate between IBS and any other similar pathology, such as food intolerance, allergy or infection. Precise diagnosis of IBS is therefore not always easy, or is much more difficult than that of other diseases with characteristic symptoms. As a consequence, IBS patients can remain undiagnosed for a long period of time; and because a patient population cannot be clearly delineated, any medical or pharmacological treatment is also much more difficult to study.

The complexity of the digestive process is also one of the main reasons for the lack of an effective treatment for IBS. Although scientists have made an impressive progress over the last 100 years, there are still vast gaps in our understanding of the physiology of the intestinal tract. Thus, in the context of IBS, medical science intends to correct or treat a pathology without proper understanding of the normal function in the first place. Obviously, this is a severe handicap to work with.

To circumvent such apparent paradox, medical treatment of IBS is often limited to improving the main symptoms such as abdominal pain, diarrhoea or constipation. Although this certainly improves the quality of life of IBS patients, it does not provide a long term solution or cure by eliminating the actual cause of the disease. Fortunately, a large number of factors that contribute to IBS can be identified and eliminated; examples include nutrition, drugs, pollution and allergens, stress and mental attitude. Likewise, various treatment options are available and effective in certain IBS patients. This makes IBS special in the way that behavioral changes and new habits can be used to improve or cure the condition. Indeed, a majority of IBS patients manages their symptoms by adjusting their lifestyle. This is a major difference when compared to other disease such as for instance cancer or epilepsy, in which behavioral changes less effective.

Trial and error is a strategy used by many IBS patients to eliminate factors that worsen their IBS or to evaluate therapies, but such approach is time consuming and not specific. Fortunately, the modern information age allows direct access to a vastly growing amount of data on IBS research worldwide.

The number of options for IBS treatment is growing every day and includes medical products, food supplements, diets, probiotic treatments, elimination of allergens and toxic agents, life style changes, such as stress reduction and physical exercise, coping strategies and psychological approaches.

The effectivity of each treatment or combination of treatments depends on the cause of IBS, personal predispositions, genetic makeup, and lifestyle and most likely several other unknown factors. However, proper knowledge of pathophysiological mechanisms and therapeutic options and methods for their assessment significantly improves chances for cure or management of IBS and is therefore a valuable tool for IBS patients and therapists likewise.

Next article: What are the symptoms of IBS

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