Irritable bowel syndrome (IBS) is a functional gastrointestinal disease with a high prevalence in the population. This disorder can be debilitating, uncomfortable, and affect the patient’s quality of life.
Treatments include medication, nutrition, and psychotherapy. In particular, nutrition plays an important role in reducing the severity and recurrence of the disease.

1. Overview of IBS
a. Definition of IBS:
Irritable bowel syndrome (IBS) is a functional bowel disorder (it is not associated with structural or biochemical abnormalities detectable with today’s conventional diagnostic tools) characterized by symptoms of abdominal pain or discomfort, abnormal stools, and bloating.
b. Classification of IBS:
There are 4 main models of irritable bowel syndrome classified according to Rome IV criteria (2016):
- IBS-C: IBS with constipation
- IBS- D: IBS with diarrhea
- IBS-M: Mixed IBS with both constipation and diarrhea
- IBS- U: IBS unclassified/specified
c. Symptoms of IBS:
Irritable bowel syndrome is characterized by:
- Stomach bloating, flatulence
- Abdominal cramps and can vary in intensity and location, defecation relieves pain
- Irregular bowel movements – loose stools, sometimes constipation
- Faeces without blood
d. Diagnosis of IBS
Common in all diagnostic criteria are: abdominal pain and/or discomfort associated with abnormal bowel habits: diarrhea (loose and frequent stools) or constipation (hard and few stools) or alternating constipation and diarrhea.
All of these symptoms require a certain duration and frequency to meet the Rome IV diagnostic criteria for irritable bowel syndrome; that is, the symptoms must be chronic and relapsing.
Thus, the clinical diagnostic criteria for irritable bowel syndrome are practically related to the history: a combination of symptoms occurring ≥1 day/week for 3 months, with symptom onset ≥6 months before diagnosis.
2. IBS diet
In addition to ensuring adequate nutrition and adequate calories, it is also important to contribute with medication to reduce bloating, gas and diarrhea. The general rule is:
– Add soluble fiber
– Do not eat foods that cause gas in the intestines, causing bloating and gas, such as eggs, milk, fried spring rolls, fatty meat, black beans, raw onions, grapes, plums, red wine, beer, coffee, carbonated water, canned lemonade.
– The FODMAPs diet.
– Limit drinking beverages containing stimulants such as coffee, alcohol, dry tea, etc. You can use drinks and soups with sedative effects such as leaf soup, lotus heart tea.
3. How to supplement fiber?
Fiber can improve constipation in irritable bowel syndrome because fiber:
- Makes stools softer and easier to pass.
- Improves diarrhea, cleanses the intestines, reduces bowel movements, and relieves pain.
- Is a substrate for beneficial intestinal bacteria to use to grow and form beneficial compounds in the body.
There are two types of fiber:
- Soluble fiber, found in bean products, fruit, and oats.
- Insoluble fiber, found in whole grain products and vegetables.
Research shows that soluble fiber is more helpful in relieving irritable bowel syndrome symptoms
However, adding too much soluble fiber at once can produce a lot of gas due to gut bacteria fermentation and increase disease symptoms. Adding fiber slowly about 2 to 3 grams to your diet each day can help prevent gas and bloating.
4. What is the FODMAPs diet?
FODMAPs (short for Fermentable Oligo-, Di-, Mono-saccharides, And Polyols) are a group of small indigestible carbohydrates containing only 1-10 glucose monomers poorly absorbed in the small intestine that can be fermented by intestinal microorganisms.
FODMAPs include fructans found in wheat, rye, onions and chicory; galactan in legumes, disaccharides (lactose milk sugar found in milk and dairy products), monosaccharides (fructose found in artificial sweeteners, fruit) and polyols (sugar alcohols found in apples, pears, nuts, cauliflower, mushrooms, and sweeteners).

Effects of FODMAPs on the gut:
- Increase water content in the small intestine
- Increase gas production: FODMAP fermentation leads to more gas production like hydrogen, methane and carbon dioxide.
- Overproduce short-chain fatty acids (SCFAs): SCFAs, including propionate, butyrate, and acetate, are products of bacterial dietary fiber metabolism and have many beneficial effects.
However, butyrate may increase intestinal sensitivity. SCFAs can be epithelial toxic if present at high concentrations by stimulating the release of 5-hydroxytryptamine (5HT) from the intestinal mucosa, facilitating the initiation of high-amplitude diffuse colonic contractions, thereby accelerating intestinal transit.
These effects, in the context of intestinal hypersensitivity typical of patients with irritable bowel syndrome, can cause abdominal pain, distention, flatulence, and altered bowel habits. Therefore, a diet that restricts foods containing FODMAPs may improve irritable bowel syndrome symptoms.
References:
[1] P. Enck et al., “Irritable Bowel Syndrome”, Nat Rev Dis Primers, vol 2, p. 16014, March 2016, doi: 10.1038/nrdp.2016.14. [2] G. Barbara et al., “The Immune System in Irritable Bowel Syndrome”, J Neurogastroenterol Motil, vol. 17, p.h. 4, pp. 349–359, October 2011, doi: 10.5056/jnm.2011.17. 4,349. [3] “Diet and Nutrition for Irritable Bowel Syndrome | NIDDK”, National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/eating-diet-nutrition (accessed December 13, 2022).4] “What Is New in Rome IV – PMC”. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5383110/ (accessed December 13, 2022).
[5] B. Radovanovic-Dinic, S. Tesic-Rajkovic, S. Grgov, G. Petrovic, and V. Zivkovic, “Irritable bowel syndrome – from etiopathogenesis to therapy”, Biomedical Papers, vol. 162, no. 1, p. 1–9, March 2018, doi: 10.5507/bp.2017.057.Article source: Nutrition Research and Development Institute
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