Irritable bowel syndrome (IBS) is a chronic digestive condition which is associated with cramping stomach pains, bloating of the stomach, and alternating diarrhea and constipation. This condition is thought to affect up to one in five people at some point in their life, and it usually first develops when a person is between 20 and 30 years of age.
Different people have different symptoms, of varying severity. Even in the same person, symptoms wax and wane, lasting for a few days or months. Flare-ups occur during periods of stress, or in response to specific trigger foods.
The prevalence of IBS is about 20%, overall. Typically, it starts between the age of 20 and 30 years, and is twice as common in women as in men. Though it lasts a long time, significant remission may occur as time goes on.
IBS is due to some unknown pathology which causes the digestive tract mucosa to become hypersensitive to ordinary food. The resulting mucosal changes lead to indigestion and bacterial proliferation, with the production of several toxins which further aggravate the symptoms.
The pathophysiology of IBS includes:
- Slowing of gut movements and an increase in mucosal permeability. This allows toxins to cross the mucosa, affecting gut integrity.
- Changes in the gut flora accompany altered interactions between the gut and the brain.
- Food triggers are increasingly being identified, with 84% of patients finding that symptoms start or become worse after a meal.
- Bloating due to bacterial fermentation of undigested food produces pain. Delayed or rapid passage of food through the gut may also occur, depending on the exact processes that are occurring. Stress also plays a role in altering normal gut metabolism.
It is observed that some foods may worsen the symptoms of IBS.
These may include:
- Fatty foods which produce bloating, nausea and pain: patients with IBS have a lower pain threshold in the intestine for normal stretching in response to food. Fat molecules may slow bowel transit, leading to the accumulation of gas which accounts for the symptoms.
- Again, the motility of the colon is stimulated by the gastrocolic reflex which is more active in these patients, causing diarrhea after each meal. IBS patients are primarily either constipated or diarrheal, and the same lipid meal can cause different reactions, of rectal pain and rectal urgency respectively.
- Lactose-containing foods, possibly because of lactase deficiency. The sugar then passes unabsorbed into the large bowel, and is fermented to produce gas and short-chain fatty acids, which cause further symptoms as discussed above.
- Alcoholic or caffeinated beverages which can irritate the gut mucosa, worsening diarrhea.
- Artificial sweeteners in significant amounts.
- Foods which ferment readily such as cabbage or beans.
How to identify food triggers
People with IBS can try to pinpoint which foods cause their symptoms by keeping a food diary. This will contain:
- What foods are eaten at what time
- What symptoms are experienced, and the time
After a few days, these entries can be discussed with the health care provider to help formulate a list of foods which should be avoided.
IBS dietary guidelines
People with IBS may consider going on a diet which greatly reduces or avoids foods such as starches and other carbohydrates that cannot be easily digested. This is called a low FODMAP diet, the letters standing for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. This describes the types of sugars found in the following foods, which are not quickly digested and absorbed.
As a result, bacteria in the gut feed on them, releasing gases which cause bloating and cramping. These foods are avoided over the first 1.5 to 2 months. They are then carefully reintroduced one at the time, to test how they are tolerated.
During this period, developing a food plan is important to avoid deficiency diseases. Some foods that should not be eaten include:
- Fruits or fruit juice, including apples, apricots, mangos, watermelons, as well as canned fruit which contain a lot of natural fruit juice
- Vegetables such as artichokes, asparagus, broccoli, cabbage, cauliflower, garlic-containing spices, onions, mushrooms, lentils and other legumes
- Milk and milk products
- Foods containing wheat and rye which contain little absorbed, short-chain carbohydrates that are ideal for bacterial fermentation; these not only hold water but also produce gas, leading to stretching of the gut which is interpreted as pain because of the known hypersensitivity of the gut in these patients
- Sweeteners such as honey or high-fructose corn syrup, as well as products containing sweeteners such as sorbitol, mannitol, or xylitol
Reviewed by Dr Tomislav Meštrović, MD, PhD