Lactose is the naturally-occurring sugar found in milk and other dairy products. It’s broken down by an enzyme, called lactase, in order to be properly digested.
But, some people don’t produce enough lactase – or any at all – so the sugar can’t be properly digested.
This is known as lactose intolerance, and can cause abdominal discomfort, and other gastrointestinal problems.
About five per cent of the UK suffer from the condition.
Food intolerance expert Dr Janet Aylott told Express.co.uk: “Lactose intolerance usually causes gastrointestinal discomfort including bloating, abdominal pain and cramping, excess wind, diarrhoea and in some cases vomiting.
“These tend to be persistent symptoms that occur following consumption of milk or dairy foods.
“Unfortunately because the symptoms are quite generic, it’s important to keep a record of any symptoms and the foods that have been eaten, to discuss with your GP.”
If it remains undiagnosed, lactose intolerance can lead to nutritional deficiencies, as patients avoid certain foods to avoid symptoms.
Patients with lactose intolerance must find ways to maintain a balanced, nutrient rich diet, Aylott said.
“For someone with lactose intolerance, where all lactose is causing an issue, choosing lactose-free alternatives is important,” she said.
“Lactose-free milk and dairy foods such as cheese and yogurts are available from most major supermarkets, and these tend to still contain the important nutrients, such as calcium, that are required.”
Maintaining a balanced, healthy diet was key to preventing the condition, as well as plenty of exercise, she added.
Lactose intolerance can develop at any age, but most cases develop between the the ages of 20 and 40.
In the UK, the condition is more common in people of Asian or African-Caribbean descent, according to the NHS.
Forty per cent of the UK experiences digestive discomfort at any one time, according to dairy products maker Rachel’s.
The company launched a new lactose-free yogurt this autumn, for those suffering lactose intolerance, and those looking to cut the amount of lactose in their diet.