Millions of Britons have 'imaginary' food intolerances after self-diagnosis over internet

Up to 12million claim to be intolerant to foods from milk to mustard - but less than a quarter have had their condition medically diagnosed.

While it is likely that many of the remaining nine million are intolerant to one or more foods, it is estimated that up to three million are simply fussy eaters.

Many have made major changes to their diet after carrying out self-diagnosis with help from the internet.

One in 50 of the 1,500 men and women polled in a survey on food intolerances decided they suffered from an intolerance on hearing a friend's diagnosis.

Self-diagnosis is likely to be flawed, leading to them unnecessarily cutting foods, or entire food groups, from their diets.

Those who change their eating habits drastically also run the risk of suffering vitamin or mineral deficiencies, which can cause health problems.

Olympic gold medalist Denise Lewis mistakenly tried self-diagnosis as she attempted to find the cause of the stomach problems that had plagued her for years.

"I've suffered from irritable bowel syndrome-related symptoms for 13 years and these have affected my performance on and off the track," she said.

"I was often guessing what could be wrong with me and eliminating a range of foods I thought could be the problem."

However, she discovered what the problem was after taking a food intolerance test.

"I found out I was intolerant to cow's milk, egg yolk and garlic.

"Since reducing these from my diet, I've not suffered my usual bloating and stomach cramps, have more energy and feel brighter and lighter.

"My stomach has healed itself and I can even tolerate a little bit of those 'forbidden foods' in my diet once again."

The survey, by food intolerance testing firm YorkTest, follows other studies suggesting celebrity food fads are to blame for many wrongly diagnosing themselves with food intolerances.

Research by Norwich Union Healthcare found that 19 per cent believe they have a gluten intolerance, such as that suffered by TV presenter Carol Vorderman, while 18 per cent claim a lactose intolerance like that of Rod Stewart's ex-wife Rachel Hunter.

However, while some intolerances are in the mind, many are real and are behind symptoms from digestive problems to migraines and skin complaints.

Culprits range from milk, wheat and food colourings to more exotic offenders such as sushi and grapefruit.

Unlike food allergies, which are caused by an over-reaction of the immune system, intolerances are not life-threatening. They occur when the body finds it hard to digest a particular type of food.