Hard to stomach?

Gillian Anderson blames sugar for her mood swings and Billy Bob Thornton used to have migraines before he cut out wheat, dairy and shellfish. Adverse reactions to certain foods have become de rigeur, with one in five people claiming to be 'allergic' to wheat, dairy, soya or yeast.

While it's unlikely you have a food allergy - sufferers have an immunological response so severe that it can kill - it is possible you lack the enzymes needed to break down a specific food, making you intolerant.

The discomfort can hamper your quality of life with a host of symptoms such as bloating, skin complaints, lethargy or frequent headaches. The culprit is the modern Western diet, where the focus is not on wholegrains, pulses, fruit or vegetables and overeating certain food groups, against which the body eventually rebels.

So, is your sensitivity to food an overblown celebrity cachet or a genuine aversion? Here's a round-up of the latest tests by three volunteers who all believe they have a food intolerance.

1. Food scan test

Foodscan Food Intolerance Indicator, £20. Tel: 0800 074 6185, www.yorktest.com

Jocelyn Marchington, 25, a TV production assistant from London, has suffered with irritable bowels for the last year since coming back from a year abroad. He tried out this DIY test, measuring the raised IgG antibodies levels which indicate food intolerance.

His verdict: 'The test requires a small blood sample taken using a pin-prick wand, though I had trouble getting enough blood to cover it. When I got the results from the lab it confirmed that I did have an intolerance but no indication to what food.'

2. Alcat blood test

Price: £280. Tel: 024 7632 0333, www.alcat.co.uk,

Sarah Mollitt, 26, a student from Leeds, thinks she's intolerant to dairy and recently became a vegan. She had blood taken for the Alcat test, which is carried out by a nutritional expert. Mixtures of blood and test foods are incubated in simulated body condition and a computer picks up immune system changes.

Her verdict: 'This was fantastic. It tests for the 100 commonest foods and additives and results come back in a few days showing what you react to and how intolerant you are to certain foods. It turned out I don't have any problems with dairy but I am intolerant to sugar which poses me a problem as a chocolate lover. They clearly pointed out what foods I shouldn't eat, what's fine and what I should try to limit in my diet. It's only been a week and I'm already feeling healthier.'

3. Bio Resonance testing

Price: £75, Tel: 020 7627 8890, www.claphamcommonclinic. co.uk

Tracy Black, 29, a teacher from South London, has had severe irritable bowel syndrome which she puts down to being wheat intolerant. Her holistic treatment uses a machine to scan the energy of the body's own bio-electrical system, looking for substance sensitivities. The practitioner then identifies the supplements and homeopathic remedies required.

Her verdict: 'The consultation began with my practitioner Claudia asking me various questions about my diet, lifestyle, stress levels and past illnesses. All this was then entered into the computer and my bio-resonance measured using sensors placed on my body. The results showed that I am highly intolerant to chocolate, dairy and wheat mould. Apparently my bacteria levels are also in a bit of a mess and I've been recommended to supplement them.

'I felt confident in Claudia, who has a traditional medical background as well as being a homeopath, and I'll definitely be following her advice and trying out some natural remedies.'

Other options include self-diagnosis, where you exclude suspected foods from your diet. Keeping a food diary, you reintroduce a food every other week and record the results. Ideally this should be done under the guidance of a nutritionist. Ultimately, eating a wide range of different foods is advisable to keep your digestion tip-top.

For more information on intolerances and allergies, call 020 8303 8525 or visit www.allergyfoundation.com