IBS and diet: the latest evidence


Although certain foods may exacerbate Irritable Bowel Syndrome (IBS) symptoms, foods do not cause the symptoms in most patients. Diet can however be used to treat IBS symptoms, says registered dietician Kim Hoffmann.

Irritable bowel syndrome is a chronic, relapsing and often lifelong disorder characterised by a collection of symptoms including abdominal pain and discomfort, bloating, and changes in bowel habits. The diagnosis of IBS depends on symptoms as there is no abnormality in the individuals radiological, endoscopic or laboratory tests. 

Most individuals with IBS mistakenly believe that diet plays a significant role in their symptoms and that avoiding specific foods will reduce their symptoms. Although certain foods may exacerbate the symptoms of IBS, foods do not cause the IBS symptoms in most IBS patients. Diet can however sometimes be used to treat the symptoms of IBS. 

Certain Facts about IBS

  • 7-20% of people worldwide suffer from IBS, with females being more prone to IBS than males. The most prevalent age group is 20-30 years. It is also more prevalent in the lower socio economic groups, in individuals who lack employment and those who are single
  • The cause is unknown and possibly multi-factorial and genetic
  • It is considered to be a psychological disorder
  • Events such as antibiotics, abdominal surgery, GI infections, diet, stress and sleep deprivation are considered to be triggers
  • What is certain is that the impaired health related to IBS decreases the quality of life of the individual


  • Genetic factors
  • Chronic stress, anxiety, or depression (these stress hormones cause the release of inflammatory chemicals)
  • Intestinal flora imbalance and small intestine bacterial overgrowth (78% have bacterial overgrowth)
  • Poor diet and food intolerance
  • Infections in the digestive tract such as viruses, bacteria, or parasites; inflammation in the digestive tract such as in inflammatory bowel disease or celiac disease; or surgical procedures on the digestive tract
  • Hormone fluctuations

From a diet perspective, foods that worsen the inflammation include allergens in food, chemicals that enhance the release of inflammatory mediators (e.g. benzoates), raw foods and fibre, alcohol and caffeine.


Fibre supplementation is the most widely studied dietary treatment for IBS. However, increasing the amount of insoluble fibre in the diet, especially in patients without constipation, may worsen IBS symptoms. For some patients with IBS, especially those with constipation, increasing the intake of soluble fibre by 10-20g/day in the form of supplements such as ispaghula, psyllium, and foods high in soluble fibre can improve their IBS.


Lactose is a disaccharide that is not well digested and absorbed by some adults. Individuals with or without IBS may report increased symptoms, including bloating, flatulence, abdominal discomfort, nausea and loose stools following the intake of lactose containing foods. This is attributed to low levels of the enzyme lactase. Lactose malabsorption does not appear to be a cause of IBS or to be more prevalent in individuals with IBS than in the general population.

Other poorly absorbed carbohydrates

Poorly absorbed carbohydrates include fructose, fructose-containing compounds, sorbitol and other sugar-alcohols.  These can increase the load or weight in the gut and provide a substance for bacteria to grow on, which can result in gas production, a change in bacterial populations, and change in movement of the waste.

Fructose is naturally found in honey, fruits, fruit juices and table sugar. Because of high-fructose corn syrup which it is added to many foods such as cool-drinks, breakfast cereals, baked goods, candies, jams, and many packaged convenience foods the amount of fructose in our diets has increased substantially in the past 20 years, quantities that could be responsible for gastrointestinal symptoms in healthy individuals as well as in individuals with IBS. Fructose is absorbed better when it is ingested with glucose.  In fruits such as bananas and strawberries glucose is present in equal or greater amounts, whereas in products such as honey, dates and oranges there is more fructose than glucose.  In other fruits such as cherries, apples and pears there is more fructose and sorbiol.  A mixture of fructose and sorbitol is absorbed more poorly and causes more symptoms than sugar alone in both normal and IBS individuals.

Fructans are long chains of fructose with glucose ends. They are poorly digested and can cause abdominal symptoms in normal individuals. They are found particularly in wheat-based products as well as onions. The shorter chains of fructose (10 units of less) are well tolerated (fructo-oligosaccharides).

Sugar alcohols, including sorbitol, mannitol, xylitol, and isomalt are digested and absorbed poorly in the upper gut – these may cause abdominal discomfort in healthy individuals. 

A diet low in all of the above mentioned fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs) has been suggested for individuals with IBS.  Some studies have shown sustained improvement on the low FODMAP diet although more controlled trials are needed for confirmation.

Gas forming foods

The foods that have been reported to form a large amounts of gas (due to their fermentation in the colon) include beans, Brussels sprouts, onions, celery, carrots, raisins, bananas, prune juice, apricots, wheat germ and bagels.  There is no clear evidence that IBS patients generate more gas than normal individuals, but they may be more bothered by intestinal gas because of greater sensitivity or abnormal handling of the gas.


IBS patients seem to have increased intestinal sensitivity to fat, although no controlled studies of a low-fat diet for treatment of IBS has been done.


Coffee, with or without caffeine, stimulates gastrointestinal motility and can cause diarrhoea in normal individuals. Studies with IBS patients have shown an improvement when caffeine was excluded and recurrence of the symptoms when caffeine was reintroduced.  Up to 26% of individuals with IBS report limiting or avoiding use of coffee due to adverse reactions.


Up to 21% of individuals with IBS report intolerance to various alcoholic beverages and up to 12% limit or avoid them.

Several Strategies if you do have IBS

(don’t try all at once; preferable ask a dietician for help to make sure you are still eating in balanced fashion)

  • Avoid large meals
  • Reduce lactose (eliminate milk, ice cream and yogurt)
  • Reduce fat
  • Reduce sorbitol, mannitol and xylitol (read labels)
  • Reduce fructose in all forms, including high-fructose corn syrup (read labels), honey, and high-fructose fruits (e.g. dates, oranges, cherries, apples, and pears)
  • Reduce gas-producing foods (e.g. beans, peas, broccoli, cabbage, and bran); also gassy cool-drinks
  • Eliminate all wheat and wheat-containing products
  • A diet low in fermentable oligo-, di-, and monosaccharides and polyols
  • Eliminate wheat, banana, corn, potato, milk, eggs, peas, and coffee
  • Avoid caffeine containing beverages (tea, coffee, coke)

Some Basic Principles to Remember

  • Routine
  • Small meals and snacks (don’t skip meals!)
  • Avoid caffeine and alcohol in sensitive periods
  • Ensure adequate water intake
  • Sit down to eat and chew food well
  • Take time to relax (stress management)
  • Don’t smoke, especially on an empty stomach
  • Don’t self medicate
  • Exercise at least 3x weekly for a minimum of 30 minutes
  • Sleep


There is evidence that undesirable reactions to food cause the symptoms in some individuals with IBS, especially those with diarrhoea, but evidence suggests that dietary restrictions will help only about a quarter of IBS patients. Also important to remember is that the diet that improves the IBS symptoms is different for each person, and there are currently no reliable laboratory tests or other simple, clinically applicable methods to determine what dietary restrictions will be helpful for a particular person.

A careful history is needed and it is best to keep a diary of foods eaten and symptoms experienced. Take note of foods that seem to be followed by increased symptoms within 1 to 3 days, paying particular attention to milk, lactose, fructose, sorbitol, gas-forming foods, wheat, fat, and coffee. Elimination of these foods should be done with the guidance of a dietician as you need to be careful to maintain a nutritionally adequate diet.

(Written by registered dietician Kim Hoffmann of The Lean Aubergine Dietetic Services. Sign up for her monthly newsletter by sending an email to kimh.rd@mweb.co.za)

Read more:

Irritated by Irritable Bowel Syndrome?
Stress and anxiety lead to IBS
The real reason for IBS
10 foods that cause bloating

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