IBS or Food Intolerance?

personal stories,IBS

9 September 2026

Written by

kirsten Jackson

Estimated reading time:

11 minutes

IBS or Food Intolerance? How to Tell the Difference and When Digestive Enzymes May Help

Bloating after a bowl of pasta. Cramping after eating out. An urgent trip to the toilet after ice cream.

When digestive symptoms appear after eating, it is understandable to assume you have a food intolerance. However, symptoms after food do not always mean that you are intolerant to a particular ingredient.

Irritable bowel syndrome (IBS) and food intolerances can cause very similar symptoms, including bloating, abdominal pain, excess wind, diarrhoea and changes in bowel habits. They can also occur together.[1,2]

Understanding the difference is important. It can help you avoid unnecessarily restricting your diet and determine whether a targeted digestive enzyme could be useful.

What is IBS?

IBS is a condition involving recurrent abdominal pain alongside a change in bowel frequency or stool appearance.[1,2]

People with IBS may experience:

Constipation
Diarrhoea
A mixture of constipation and diarrhoea
Bloating or abdominal distension
Excess wind
Abdominal pain or cramping
A feeling that they have not fully emptied their bowels

IBS is described as a disorder of gut-brain interaction. This means that changes in communication between the digestive system and the brain can affect gut sensitivity, movement and the way the bowel responds to food.

IBS symptoms are real. However, they are not always caused by one specific food.

Stress, sleep, hormones, medications, constipation, altered gut motility and the overall sensitivity of the digestive system can all affect symptoms.

UK guidance supports making a positive diagnosis of IBS when the symptom pattern fits and appropriate investigations have excluded other likely conditions.[1,2]

Coeliac disease, inflammatory bowel disease and other medical conditions may need to be considered before assuming that symptoms are caused by IBS.

Kirsten’s dietitian tip: Rather than immediately asking, “Which food should I remove?”, start by asking, “What pattern do my symptoms follow, and what else was happening at the time?” Food is only one part of the IBS picture.

What is a food intolerance?

A food intolerance is a reproducible adverse response to a particular food or food component.

Unlike a food allergy, a food intolerance does not involve the same immune response and is not normally life-threatening.

Lactose intolerance is a useful example.

Lactose is the sugar naturally found in milk and some dairy products. It is normally broken down by lactase, an enzyme produced in the lining of the small intestine.

If your body does not produce enough lactase for the amount of lactose you have eaten, some lactose continues into the large bowel. It is then fermented by gut microbes and may also draw water into the bowel.

This can cause:

Bloating
Excess wind
Abdominal discomfort
Loose stools
Diarrhoea

The amount of lactose eaten matters. Many people with lactose intolerance can tolerate a small amount, particularly as part of a mixed meal, without experiencing symptoms.

Can you have IBS and a food intolerance?

Yes. It is possible to have IBS and a food intolerance at the same time.

Having IBS does not protect you from lactose malabsorption, fructose malabsorption or difficulty tolerating another fermentable carbohydrate.

Equally, reacting after eating one particular meal does not prove that you have a food intolerance.

People with IBS can have increased visceral sensitivity. This means that normal stretching, fluid or gas within the bowel may feel more uncomfortable.

A fermentable carbohydrate may therefore cause stronger symptoms in someone with IBS, even though fermentation by gut microbes is a normal digestive process.

This can also explain why you may tolerate a food on one day but experience symptoms after eating it on another.

Your response may be affected by:

The portion eaten
The other foods in the meal
Your existing level of constipation
Stress
Sleep
Your menstrual cycle
How quickly you ate
Your overall symptom threshold that day

Kirsten’s dietitian tip: Look for repeatability rather than blaming the last food you ate. I would usually want to see a similar reaction on more than one occasion before considering something a likely food trigger.

IBS or food intolerance: how can you tell the difference?

There is no single symptom that reliably distinguishes IBS from a food intolerance.

However, the pattern can provide useful clues.

A food intolerance may be more likely when:

Symptoms consistently follow the same food or carbohydrate
The response changes according to the portion eaten
Reducing that specific food component improves symptoms
The food can be tolerated when the problematic carbohydrate is removed or broken down
A targeted digestive enzyme improves tolerance

IBS may be more likely to be playing a broader role when:

Symptoms feel unpredictable
Many unrelated foods appear to cause the same reaction
Symptoms continue even when suspected trigger foods are removed
Bowel habits, stress, sleep or hormones strongly influence symptoms
Abdominal pain is associated with a change in bowel frequency or stool appearance
Symptoms occur without a consistent connection to a particular food

For many people, the answer is not simply one or the other. A particular carbohydrate may trigger symptoms within an already sensitive digestive system.

What are digestive enzymes?

Digestive enzymes break food components into smaller units that can be absorbed or processed more easily.

Our bodies naturally make many digestive enzymes. However, some people do not produce enough of a particular enzyme, while there are other enzymes that humans do not naturally produce at all.

Supplemental digestive enzymes may help by breaking down a particular food component before it reaches the large bowel, where it could otherwise be fermented by gut microbes.

However, enzymes are highly specific.

Lactase acts on lactose. It will not help someone whose symptoms are being triggered by fructose.

This means that the useful question is not simply, “Do digestive enzymes work?”

It is:

“Which food component am I struggling with, and does this enzyme act on it?”

Which digestive enzymes may help?

Lactase for lactose

If your small intestine does not produce enough lactase, taking a lactase enzyme with a lactose-containing meal can work like an enzyme “top-up”.

The supplemental lactase helps break lactose into smaller sugars that can be absorbed more easily.[3]

This may provide more flexibility around foods such as:

Milk
Ice cream
Cream
Some yoghurts
Some soft cheeses
Foods made with milk

Lactase should normally be taken immediately before eating or with the first bite, according to the product instructions.

It is important to remember that lactase only helps with lactose. It will not prevent symptoms caused by milk protein allergy, a high-fat meal or another ingredient in the food.

Kirsten’s dietitian tip: Test lactase with a straightforward lactose-containing food that has caused repeatable symptoms. Testing it during a complicated restaurant meal with multiple possible triggers will make the result much harder to interpret.

Alpha-galactosidase for fructans and galactans

Fructans and galactans are fermentable carbohydrates within the FODMAP group.

Fructans are found in many everyday foods including:

Garlic
Onion
Leeks
Wheat and wheat-based products
Some vegetables
Some nuts

Galactans, which include galacto-oligosaccharides or GOS, are particularly common in foods such as:

Beans
Chickpeas
Lentils
Other pulses
Soy products
Some nuts

These complex carbohydrates are not fully digested in the small intestine and can therefore reach the large bowel, where they are fermented by gut microbes.

Alpha-galactosidase is a digestive enzyme that can help with the digestion of complex carbohydrates including fructans and galactans.

This may give some people greater flexibility around foods such as garlic, onion, wheat, beans, pulses, soy and nuts.

Clinical research has particularly investigated alpha-galactosidase for GOS. In a randomised, double-blind, placebo-controlled crossover study involving people with IBS, taking alpha-galactosidase alongside a diet high in GOS significantly reduced overall gastrointestinal symptoms and bloating in participants who were sensitive to GOS.[4]

As with other digestive enzymes, this does not mean it will prevent symptoms from every fructan- or galactan-containing food. The response can depend on the food, portion, enzyme dose and the individual.

Kirsten’s dietitian tip: Garlic, onion, wheat, beans and pulses contain several different components that can influence digestive symptoms. Look for a repeatable pattern rather than assuming every reaction to these foods is caused by the same carbohydrate.

Xylose isomerase for excess fructose

Fructose is a sugar found naturally in fruit, honey, some vegetables and many processed foods.

Fructose can be less efficiently absorbed when a food contains more fructose than glucose. This is often referred to as excess fructose.

Foods that may contain excess fructose include:

Honey
Apples
Pears
Mango
Dried fruit
Certain fruit juices
Products containing high amounts of fructose or agave syrup

Xylose isomerase converts some free fructose into glucose, potentially making it easier to absorb in the small intestine.

A double-blind, placebo-controlled study involving people with fructose malabsorption found that xylose isomerase reduced breath hydrogen and improved some gastrointestinal symptoms following a fructose challenge.[5]

However, the research remains relatively limited. A positive result during a controlled fructose challenge does not guarantee that the enzyme will resolve symptoms after every mixed meal.

Intoleran’s Fructase contains xylose isomerase. Despite the product name, Fructase is the name of the product rather than the active enzyme itself.

What about DAO and histamine?

Diamine oxidase, or DAO, helps break down histamine, including histamine from food.

Histamine can be found in aged cheeses, fermented foods, cured meats, wine and other foods.

DAO is different from the carbohydrate-digesting enzymes discussed above. Histamine is not a FODMAP.

Symptoms attributed to dietary histamine are wide-ranging and can overlap with IBS, allergies and several other conditions. There is currently no single, well-validated diagnostic test for histamine intolerance, and the evidence for DAO supplementation is still developing.[6]

Persistent or systemic reactions should therefore be assessed by an appropriate healthcare professional rather than managed through long-term dietary restriction alone.

Can digestive enzymes help IBS?

Digestive enzymes do not treat IBS as a whole.

Instead, the correct enzyme may help with one specific food-related contributor to symptoms.

A digestive enzyme may be worth considering when:

You experience a consistent reaction to a particular food or carbohydrate
The enzyme clearly matches that carbohydrate
The reaction changes according to the portion eaten
You want greater flexibility around a known trigger
The enzyme can be tested in a structured way

Digestive enzymes are less likely to resolve symptoms caused mainly by:

Constipation
Altered gut motility
Pelvic floor dysfunction
Medication side effects
Coeliac disease
Inflammation
Stress-related gut sensitivity
A food allergy
Another underlying medical condition

They should be viewed as a targeted tool rather than a cure for IBS.

How to try a digestive enzyme without guessing

If you decide to try a digestive enzyme, use a structured approach.

1. Identify one repeatable trigger

Choose a food that has caused similar symptoms on more than one occasion.

2. Match the enzyme to the carbohydrate

For example:

Lactase for lactose
Alpha-galactosidase for fructans and galactans
Xylose isomerase for excess fructose

3. Use a realistic portion

Do not deliberately eat an unusually large portion to “test” the enzyme. A very high dose of the carbohydrate may overwhelm even a helpful enzyme.

4. Take it at the correct time

Most targeted digestive enzymes need to be present when the food enters the digestive system.

Follow the product instructions. This will usually mean taking the enzyme immediately before eating or with the first bite.

5. Keep the rest of the meal simple

Avoid testing the enzyme with a meal containing several other suspected triggers.

6. Repeat the test

One good or bad day is not enough to establish a reliable result. Symptoms naturally fluctuate, particularly in IBS.

7. Review whether the difference is meaningful

Did the enzyme allow you to tolerate more of the food with noticeably fewer symptoms?

If nothing changed after a structured trial, increasing the dose indefinitely or adding several more supplements is unlikely to provide a clearer answer.

Kirsten’s dietitian tip: Change one variable at a time. If you start an enzyme, remove several foods and add another supplement during the same week, you will not know what made the difference.

When should you seek medical advice?

Digestive enzymes should not be used to mask symptoms that require assessment.

Speak to your GP or another qualified healthcare professional if your symptoms are new, persistent, worsening or accompanied by:

Unintentional weight loss
Blood in your stools or rectal bleeding
Anaemia
A persistent change in bowel habits
Symptoms that regularly wake you during the night
A family history of bowel or ovarian cancer
Fever
Significant or worsening pain

Symptoms such as swelling, wheezing, throat tightness or difficulty breathing may indicate an allergic reaction and require urgent medical attention.

Food allergy is different from food intolerance. Digestive enzymes cannot prevent an allergic reaction.

The bottom line

IBS and food intolerance are not the same, although they can occur together and cause similar symptoms.

IBS involves a broader interaction between gut sensitivity, bowel movement, the gut-brain connection and other individual factors. A food intolerance involves difficulty tolerating or processing a particular food component.

Digestive enzymes are not a cure for IBS. However, the correct enzyme may improve tolerance when lactose, fructans, galactans, excess fructose or another specific food component is contributing to symptoms.

The useful question is not simply:

“Do digestive enzymes work?”