Coeliac disease is a permanent intolerance to gluten, which is found in the seeds of cereals such as wheat, barley, oats, rye and others.

Lactose intolerance is the inability to digest the sugar lactose due to a lack of the enzyme lactase, which can lead to diarrhoea and abdominal cramps.

Two very different complications that are, however, closely related. Many coeliacs are also lactose intolerant, although the incidence of lactose intolerance is much higher than that of coeliac disease, reaching 30% of the Spanish population, compared to 1% of diagnosed coeliacs in Spain.

A person with coeliac disease who is not treating the condition with a gluten-free diet (because he/she is not diagnosed) is more likely to develop a lactase deficiency and become lactose intolerant. This is because lactase is produced in the mucosa of the small intestine, the part of the intestine that is damaged in a person with untreated coeliac condition. The two conditions can also produce similar external symptoms, such as diarrhoea, bloating and stomach cramps.