Bloating, constipation and gut symptoms: could food be a trigger?

Start by understanding the cause

Bloating, wind, constipation, diarrhoea and abdominal pain can have several causes. Food intolerance, irritable bowel syndrome (IBS), digestive enzyme deficiencies, coeliac disease and Crohn’s disease can produce overlapping symptoms. Symptoms alone cannot reliably distinguish between them.

Constipation can also relate to inadequate fibre or fluid, medicines, slow movement through the bowel or difficulty coordinating the muscles used to pass a bowel motion. Removing more foods may reduce fibre intake and make constipation worse. A doctor can assess the possible causes, while a dietitian reviews how your eating pattern may contribute.

IBS: when the gut is more sensitive

IBS is a disorder of gut–brain interaction, affecting gut sensitivity and bowel function. It commonly involves recurrent abdominal pain with constipation, diarrhoea or both. Bloating and wind are also common. Food, stress and changes in routine can influence symptoms. IBS does not cause the intestinal damage associated with Crohn’s or coeliac disease.

How is it diagnosed? A doctor assesses your symptom pattern, medical history and examination. Blood or stool tests may be used to check for other conditions, including coeliac disease or bowel inflammation. There is no single test that confirms IBS, and a colonoscopy is not routinely needed for everyone. Constipation or bloating alone does not establish an IBS diagnosis.

Which foods might trigger symptoms?

Some people with IBS are sensitive to FODMAPs: carbohydrates that may be poorly absorbed, draw water into the bowel and ferment to produce gas. Examples of potential triggers include:

• Onion, garlic and some wheat products, which contain fructans.
• Some beans and lentils, which contain fermentable carbohydrates.
• Apples, pears and some other fruits, which contain excess fructose and/or polyols.
• Milk and ice cream containing lactose, when lactose is poorly digested.
• Sugar-free sweets or chewing gum containing polyols such as sorbitol.

These foods can be nutritious, and tolerance depends on the person, portion and combination of foods eaten. This is a list of possibilities, not a list to avoid. Reacting to wheat does not automatically mean you react to gluten: fructans may be involved.

Disaccharidase deficiency: difficulty digesting certain sugars

Sometimes called “disaccharide deficiency”, the more accurate term is disaccharidase deficiency: a shortage of enzymes that break down sugars in the small intestine. Lactase digests lactose in milk; sucrase-isomaltase helps digest sucrose (table sugar) and products of starch digestion.

When these carbohydrates are not fully digested, they can cause wind, bloating, cramps and diarrhoea. Constipation is less characteristic and deserves assessment for other causes. Enzyme deficiencies may be inherited or develop with damage to the intestinal lining, including from coeliac or Crohn’s disease.

A dietitian can tailor carbohydrate amounts to the enzyme affected and your tolerance. Lactose-free milk may help preserve calcium intake, for example. A standard low-FODMAP diet does not specifically restrict sucrose or starch, so it may not address sucrase-isomaltase deficiency. Some people need ongoing adjustments or clinician-recommended enzyme replacement; secondary deficiencies may improve when the underlying disease is treated.

How is it diagnosed? Depending on the suspected enzyme, a clinician may arrange a breath test, commonly for lactose malabsorption, or specialised enzyme testing on small-intestinal biopsies taken during gastroscopy. Sucrose breath testing is available in some settings. Tests have limitations and need interpretation alongside symptoms; a positive malabsorption test does not necessarily mean that food causes symptoms. A dietary response alone does not confirm an enzyme deficiency.

How a short-term elimination diet can help

After appropriate medical assessment, a dietitian can help decide whether a targeted food trial is useful. Sometimes adjusting meal patterns, fibre and fluids is enough. Sometimes a lactose trial or a structured low-FODMAP approach is appropriate. Removing multiple food groups at once is rarely a helpful starting point.

1. Establish a baseline. Review your usual food intake, symptoms, bowel pattern, medicines and nutritional needs. A brief food and symptom diary can help identify patterns without assuming every symptom has a food cause.
2. Trial a temporary reduction. For a low-FODMAP trial, higher-FODMAP foods are usually swapped for suitable alternatives for two to six weeks. Other targeted trials may use a different timeframe.
3. Reintroduce systematically. If symptoms improve, challenge individual carbohydrate groups in planned portions to explore which types and amounts you tolerate.
4. Personalise your everyday diet. Bring tolerated foods back and limit only what is needed. If the initial trial does not help, review the approach with your dietitian and doctor instead of extending restriction.

The aim is a varied, adequate diet with manageable symptoms. The strict low-FODMAP phase is temporary; reintroduction is part of treatment.

If you already eat a very limited diet or have a history of disordered eating, tell your dietitian. A gentler approach may be more suitable. Food challenges for suspected intolerance are different from allergy testing and should not be used to test a suspected food allergy at home.

Coeliac disease: lifelong gluten avoidance after diagnosis

Coeliac disease is an autoimmune condition in which gluten triggers damage to the small intestine. It can cause bloating, diarrhoea, constipation, fatigue or nutrient deficiencies, and some people have few digestive symptoms.

How is it diagnosed? Testing usually starts with coeliac antibody blood tests, commonly tissue transglutaminase IgA together with total IgA. A gastroenterologist usually confirms the diagnosis with small-bowel biopsies during gastroscopy. Selected children may qualify for a specialist-led pathway without biopsy. Genetic testing can help exclude coeliac disease in some situations, but cannot confirm it alone.

Once diagnosed, coeliac disease requires a strict lifelong gluten-free diet, even when gluten causes no noticeable symptoms. A dietitian helps with food labels, avoiding gluten cross-contact, eating out and meeting fibre, iron and calcium needs. Gluten is not reintroduced as a symptom challenge after diagnosis.

Crohn’s disease: nutrition as part of lifelong medical care

Crohn’s disease is a form of inflammatory bowel disease (IBD) that causes inflammation in the digestive tract. It is different from IBS and can cause ongoing diarrhoea, abdominal pain, fatigue and weight loss.

How is it diagnosed? A gastroenterologist brings together your history, examination, blood and stool tests, usually colonoscopy with biopsies, and imaging such as MRI or CT when needed. Stool tests can look for inflammation and infection. No single symptom or food elimination trial can diagnose Crohn’s disease.

Crohn’s disease requires lifelong medical follow-up. Treatment may include medicines, specialist nutrition therapy and sometimes surgery. There is no universal lifelong list of foods that everyone with Crohn’s must avoid. A food may worsen discomfort without causing inflammation, and feeling better does not always mean inflammation is controlled.

A dietitian works with your IBD team to prevent or treat malnutrition, address deficiencies and adapt intake during flares, recovery or bowel narrowing. Some people benefit from prescribed liquid nutrition or a structured Crohn’s disease exclusion diet under specialist supervision. These treatments differ from an IBS food-trigger trial and require monitoring by the treating team.

When to seek medical advice

Arrange a medical review for persistent or changing bowel symptoms, especially with blood in the stool, unexplained weight loss, anaemia, fever, diarrhoea waking you at night or a family history of bowel disease. Seek urgent care for severe abdominal pain, persistent vomiting, or a swollen abdomen with inability to pass stool or wind.

How a dietitian can help you move forward

Finding relief from gut symptoms can feel overwhelming, especially when you are unsure what to eat or have already cut out several foods. A dietitian can help you understand your food and symptom patterns and develop a practical plan that suits your diagnosis, preferences and everyday life.

This starts with reviewing your usual meals, bowel habits, symptoms and nutritional needs. Where appropriate, your dietitian can guide you through a short-term elimination trial, suggest nourishing alternatives and help you reintroduce foods step by step. Follow-up appointments provide an opportunity to interpret your response, adjust the plan and build confidence in the foods you can enjoy.

If you have coeliac disease, Crohn’s disease or a diagnosed digestive enzyme deficiency, a dietitian can translate your treatment requirements into everyday food choices. Working alongside your GP or gastroenterologist, they can help you meet your nutritional needs, manage dietary restrictions and adapt your eating as your needs change. The aim is to support your health while keeping food as varied, enjoyable and manageable as possible.