Irritable bowel syndrome is a chronic functional disorder in the digestive system that can affect any part of the intestines. There is a wide range of symptoms, including abdominal pain, bloating, gas, diarrhea, constipation, or a combination of these, along with discomfort in the upper abdomen. This syndrome is highly prevalent across various age groups and populations, and in many cases, it can impact quality of life and daily functioning. While most cases do not pose short or long-term dangers, a proper medical assessment is required for diagnosis and to rule out other conditions. This document focuses solely on nutritional intervention and does not provide a comprehensive overview of the various therapeutic options for this syndrome.
The exact causes of the syndrome are not fully understood, but in most cases, it's not attributed to a single cause. Nutritional changes, however, can significantly improve symptoms in many cases. When we eat, we also consume our intestinal cells and a diverse population of bacteria in the gut, collectively known as the microbiome. A balanced diet can potentially alter the natural intestinal composition and restore balance between the intestines and the microbiome.
In many cases, the syndrome is also associated with stress and anxiety, which can exacerbate the symptoms. The intuitive belief (largely accurate) that dietary changes might lead to improvement can sometimes create confusion due to the placebo effect (a perceived improvement in response to a dummy treatment). People might avoid different foods, making it difficult to attribute improvements to a specific food component. Furthermore, just like with inflammatory bowel diseases and even more so, not everything that works for one individual will work for another. Some might improve by eliminating simple sugars, while others might benefit from a gluten-free diet, lactose-free diet, or avoiding fermentable foods that cause gas. Some individuals experience improvement due to the direct influence of food on intestinal cells, while for others, the improvement results from avoiding a dietary component that cannot be digested due to genetic changes (as seen in lactose malabsorption or sucrose malabsorption).
There are several conditions that lead to clinical symptoms resembling irritable bowel syndrome but can be easily overcome by avoiding specific foods. Here are three common conditions that might not fall under the classification of irritable bowel syndrome but can present similar symptoms:
Lactose Intolerance (Lactase Enzyme Insufficiency)
A very common condition that requires special attention. Lactose is a disaccharide found in large amounts in milk and its products. It needs to be broken down in the intestines into monosaccharides (glucose and galactose) for absorption. This condition exists in about 80% of adults because lactase enzyme activity, responsible for breaking down lactose, decreases over time. Lactose that remains undigested reaches the large intestine, where the microbiome ferments it, producing gas and water. The gas causes abdominal pain and bloating, and the water leads to loose stools. Sometimes there might not be any complaints (since lactose intake in adults is generally lower than in children), while other times, there can be abdominal pain, gas, or loose stools, similar to irritable bowel syndrome.
This disorder can cause discomfort but is not dangerous and does not lead to complications. When someone with lactose intolerance consumes foods containing lactose, they might experience symptoms, but there are usually no long-term implications. Lactose intolerance can be checked using a simple breath test, but it's also easy to test by avoiding dairy and its products for a week or two while keeping a symptoms diary. Improvement is often dramatic and immediate. If lactose intolerance is diagnosed, consulting a dietitian is recommended to ensure proper calcium intake, as avoiding dairy might lead to deficiencies. After improvement, gradually reintroducing dairy products can help identify an individual's personal tolerance threshold (which might change over time).
Different individuals are sensitive to varying amounts of lactose, and the amount of lactose varies among different dairy products. Therefore, even if lactose intolerance exists, there are dairy products that can still be consumed. Products like yogurt and hard cheeses contain less lactose than fresh cheese or regular milk, for example. It's important to note that after gastrointestinal infections, there might be a temporary decrease in enzyme activity that breaks down lactose. In such cases, it's possible and recommended to gradually reintroduce dairy. Enzyme supplements can also be added artificially before lactose consumption, which might slightly improve lactose tolerance in certain cases. Lactose intolerance is entirely distinct from milk protein allergy. Milk allergy, which has significant clinical implications and requires medical supervision, mainly occurs in infants and young children (where lactose intolerance is rare).
Sucrose Intolerance (Sucrase-Isomaltase Enzyme Insufficiency)
This disorder, similar to lactose intolerance, occurs in people who are born with a congenital deficiency in an enzyme responsible for breaking down sucrose, a disaccharide present in table sugar and various natural foods like fruits. The breakdown into monosaccharides (glucose and fructose) does not occur, and sucrose is not absorbed. As a result, sucrose serves as a food source for gut bacteria, producing gas and water. This can lead to complaints that range from severe diarrhea in infants to symptoms identical to irritable bowel syndrome or lactose intolerance.
Lack of gluten tolerance
Another disturbance that might manifest similarly to irritable bowel syndrome is gluten sensitivity or non-celiac gluten intolerance. However, this is not diagnosed as celiac disease. The mechanism here is not yet entirely clear, but it is not an autoimmune attack on the intestinal system as in celiac disease. Unlike celiac disease, the symptoms of non-celiac gluten intolerance are mostly not dangerous and do not necessarily require treatment unless the symptoms become too disruptive. Unlike celiac disease, blood tests and intestinal biopsies are usually normal, so the only way to diagnose non-celiac gluten intolerance is through a trial period of about three weeks without gluten while maintaining a symptom diary. It's essential to emphasize that one should not start a gluten-free diet before ruling out celiac disease (usually a blood test is sufficient), as overlapping symptoms might occur, and a gluten-free diet could hinder the ability to diagnose celiac disease in the future.
Even when there's no specific problem with a particular food, most people with irritable bowel syndrome learn to avoid certain foods. Undoubtedly, dietary and lifestyle changes are crucial for managing the syndrome. However, limiting certain foods can also lead to nutritional deficiencies unnecessarily. Therefore, it's crucial to undergo a comprehensive nutritional assessment and conduct a trial-and-error process over time to identify the connection between food consumption and symptom occurrence, understanding that what works for one person might not work for another. This approach can improve symptoms and prevent nutritional deficiencies.
Numerous diets have been proposed for irritable bowel syndrome, but the most prominent and researched is the FODMAP diet, which has been clinically shown to notably improve symptoms (especially gas) in a significant percentage of those with irritable bowel syndrome, particularly the subtype characterized by diarrhea and bloating. The name is an acronym for the problematic foods. Essentially, it involves avoiding foods rich in poorly absorbed components that can undergo fermentation by gut microbes, leading to intestinal gas and discomfort, abdominal pain, and diarrhea (see the food table below). These sugars include, among others, lactose (dairy products), fructose (found in honey and fruits), polyols (such as sorbitol, mannitol, xylitol, maltitol, and pitted fruits), and some poorly absorbed dietary fibers like fructans (found in wheat, onions, and garlic), and galactans (found in legumes).
In cases where symptoms significantly disrupt daily life, a personal trial of this diet might be reasonable. Given the difficulty in adhering strictly to the diet, it's advisable to try it only after a three-week trial without the specific foods associated with the individual's issues mentioned above (3 weeks without lactose; if there's no improvement, 3 weeks without gluten; if there's no improvement, 3 weeks without sucrose). Then, if there's a positive response, gradually reintroduce the suspected foods into the diet (a new food every 4-5 days at a small portion size while keeping a symptom diary). It's necessary to retry the suspect foods to confirm their problematic nature. This method requires patience and perseverance but allows for the identification of problematic foods. However, it's important to note that sometimes the cause of the syndrome might involve a combination of different foods, making it harder to identify the problematic components.
Food Table for Irritable Bowel Syndrome According to FODMAP Diet Recommendations
We have divided the problematic foods into two groups in the table: foods containing low amounts of sugars that can be reintegrated into the menu in small quantities (and gradually increased if improvement is achieved), and foods containing high amounts of sugars that should be avoided initially.
Low-Sugar Content Foods (possible in small amounts) High-Sugar Content Foods (should be avoided)
Fruits and Juices Banana, strawberries, pineapple, grapes, melon, kiwi, orange, raspberry, blueberry, cranberry, lemon, orange, passion fruit, papaya, lychee, plum, watermelon, peach, fig, cantaloupe, loquat. Apple, apricot, cherries, mango, pear, nectarine, peach, plum, papaya, passion fruit, papaya, persimmon, lychee, jujube, fig.
Vegetables Carrot, celery, parsnip, eggplant, lettuce, tomato, the green part of spring onion, green beans, asparagus, broccoli, bell pepper, cucumber, eggplant, ginger, olives, mushrooms, artichoke, chives, endive, taro, pumpkin, zucchini. Cabbage, artichoke, leek, garlic, onion, shallot, cruciferous vegetables, turnip, radish, celeriac, beet, fennel, Jerusalem artichoke, dandelion, rutabaga, kohlrabi.
Grains White rice, tapioca, quinoa, millet, cornmeal, oats. Wheat, rye, barley, wheat bran, bulgur.
Legumes Chickpeas, lentils, soybeans, mung beans, adzuki beans, kidney beans. Lentils, chickpeas, soybeans, black beans, baked beans.
Nuts and Seeds Pistachios. Almonds, pecans, cashews, walnuts, hazelnuts, pine nuts, pumpkin seeds, sesame seeds.
Dairy and Dairy Alternatives Lactose-free milk, almond milk, coconut milk, rice milk. Dairy milk and products, including sheep's milk, goat's milk, and soy milk.
Sweeteners Sucrose (including white sugar), maple syrup, aspartame, fructose, barley malt syrup, honey, agave, artificial sweeteners based on alcohols (sorbitol, mannitol, xylitol, maltitol, erythritol), saccharin.
Note on the table: Allowed foods without restriction include poultry, meat, fish, eggs, and oils.
It's highly recommended to consult with a clinical dietitian before starting the diet to avoid nutritional deficiencies. For those interested in following this diet, it's advisable to do so under the guidance and supervision of a qualified dietitian. To assess the impact, one should avoid consuming all foods listed in the table for six weeks while maintaining a symptom diary. In the second stage, if the response is positive, gradually reintroduce the foods into the menu (trying a new food every 4-5 days at a small portion size while keeping a symptom diary). It's important to retry suspicious foods to confirm their problematic nature. This approach requires patience and persistence but enables the identification of problematic foods. However, it should be remembered that sometimes the cause of the syndrome might involve a combination of different foods, making it harder to identify the problematic components.