The most common causes of IBS

If I had five people in front of me with a diagnosis of Irritable Bowel Syndrome, both adults and children, it is highly likely they will all have different causes, and therefore require varied treatments.

Here are the most common causes of IBS:


1. Lactose intolerance

This means that your body isn't able to digest lactose, a sugar found naturally in milk. It is a common cause of IBS symptoms such as bloating, flatulence, nausea, diarrhoea or constipation. The bacteria in your gut feast on the undigested lactose, making for a very uncomfortable digestive system. Lactose intolerance may be genetically determined or may be secondary to other intestinal issues such as leaky gut, infections or coeliac disease.

A simple breath test can assess your ability to digest lactose and a saliva test can test your genetic predisposition.

What can I do?

Eliminate lactose-containing dairy products from your diet for up to four weeks, and re-introduce them one by one to see if your symptoms re-appear. A nutritionist can often make a potentially complicated strategy easy for clients with an elimination programme.

2. Fructose malabsorption

Fructose is a natural sugar found in fruits and some vegetables. Like lactose, it is digested in the small intestinal lining. Any fructose that is not digested and unable to be absorbed may cause symptoms such as bloating, change in bowel habits, fatigue, headaches and brain fog. It's believed 30% of us have the gene.

A simple breath test is available for diagnosis.

What can I do?  

Eliminate any fruits and vegetables containing high levels of fructose or try a low FODMAP diet (fermentable oligo-, di-, mono-saccharides and polyols) for four to eight weeks only, remember this is not a long-term diet. The latter is best done under the guidance of a qualified nutritional therapist as it involves re-introductions to ascertain the groups that may be contributing to your symptoms.

3. Dysbiosis

This is a state of imbalance between your good and bad bacteria in your intestines, most commonly the large intestine. When the bad bacteria dominates, this can be associated with digestive problems such as an overgrowth of bacteria, yeasts or parasites. As well as digestive symptoms such as pain, bloating and flatulence, it can also lead to non-digestive symptoms such as anxiety, depression, diabetes, heart disease, cancer, weight gain and autoimmune diseases. The most common culprit causing dysbiosis is antibiotic usage. The more courses you have taken over your life, the higher your risk of developing dysbiosis.

A stool test can identify your bacterial balance plus further intestinal markers can guide your nutritional therapist to the root cause of your IBS.

What can I do?

This is highly individual. Generally, the aim is to eliminate bad bacteria, yeasts or parasites with natural anti-microbials and reinoculate the intestines with good bacteria to restore the balance. This is best done under the guidance of a qualified nutritional therapist. A stool test often takes the guesswork out of finding your root cause.

FODMAP foods

4. Yeast overgrowth

A yeast overgrowth can transpire when dysbiosis has occurred, usually due to antibiotic usage and a diet containing sugar and refined foods which feed the yeast. Intestinal pain, bloating and flatulence are common symptoms, with some people suffering non-digestive symptoms such as brain fog, mood swings and fatigue. Yeasts release strong chemicals that can make many people feel unwell.

Urine and stool tests can indicate if yeast infection is present.

What can I do?

Conventional medication or natural anti-fungals combined with a reduced-sugar diet can support the immune system and help fight the yeast. This is best done under the guidance of a qualified nutritional therapist; too many people try Google-aided diets such as the ‘anti-candida diet’, these are not recommended and may lead to nutrient deficiencies and the eventual recurrence of yeast.

5. SIBO (small intestinal bacterial overgrowth)

This is an overgrowth of bacteria in the small intestine, as opposed to the large intestine, where most of your resident bacteria are found. A smaller surface area in the small intestine can lead to an overcrowded space - often bacteria is back-flowing from the large intestine - giving rise to symptoms of belching, bloating and intestinal pain. It is believed that 50% of people with IBS have SIBO.  SIBO may occur as a result of low stomach acid, constipation and stress. It is also common alongside food intolerances.

A breath test can detect SIBO from your output of methane and hydrogen.

What can I do?

SIBO is a difficult problem to address as you need to understand and change the cause, otherwise it may keep re-occurring. A multi-stage protocol is required to support digestion, avoid sugars and hard-to-digest foods, ensuring good bowel motility (managing constipation) and treatment to eliminate the bacterial overgrowth. This may take many months to restore your bacterial population, address any leaky gut or maldigestion occurring and is best undertaken with the guidance of a nutritional therapist.

Nutritionist Resource is not responsible for the articles published by members. The views expressed are those of the member who wrote the article.

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Guildford, Surrey, GU4 8JW
Written by Jane Barrett, DipION, mBANT, CNHC
Guildford, Surrey, GU4 8JW

Jane Barrett DipION, mBANT, CNHC is a registered nutritional therapist specialising in optimising digestion and managing food intolerances, in both adults and children. Having turned her own health around with nutrition, she now helps others to do the same in a practical & supportive way through one to one consultations and workshops.

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