Why does food intolerance cause diarrhoea?

Diarrhoea is a common presentation of Food Intolerance. After a trigger food, the gut may hold extra water and move contents along before the bowel can reabsorb it. Stools can become loose or urgent, and bloating, wind or cramping may occur at the same time. The pattern may be clearer after particular ingredients, portions or drinks, rather than after every meal.

An intolerance is different from a food allergy. Allergy symptoms can include swelling, hives, wheezing or breathing difficulty and need urgent assessment.

Keep drinking small, frequent amounts of water or an oral rehydration drink. Choose simple foods if you feel able to eat, and avoid the food you suspect until you can discuss a sensible plan with a clinician or dietitian. A food-and-symptom diary can record what you ate, the timing of symptoms and any medicines or supplements taken. Do not remove several major food groups for a long time without advice, because this can make it harder to maintain a balanced diet.

Seek urgent medical care for blood or black stools, severe or worsening abdominal pain, fainting, confusion, signs of dehydration such as very little urine, or swelling or breathing problems after eating. Arrange a medical review if diarrhoea persists, keeps returning, wakes you from sleep, or is accompanied by unplanned weight loss. A clinician can consider other digestive causes and advise whether testing or a supervised dietary change is appropriate.

Ask which foods are reasonable to avoid while symptoms are assessed, whether a symptom diary would be useful, and what warning signs should prompt urgent care. Mention recent travel, antibiotic use, sick contacts and any family history of bowel disease, as these details can affect the assessment.