Frances Beg can now offer her students chocolate biscuits without feeling tempted to have one herself. It’s a significant achievement for the 49-year-old modern languages tutor. “For about 25 years, I would eat up to 30 bars of chocolate a day,” she confesses. Now she feels like a recovered alcoholic. “When I pass round a plate of chocolate biscuits I’m not in the least bit interested.”

Her problem with chocolate began at the age of 17, when she was studying modern languages in Germany. “I was lonely and started to eat for comfort. But during the next couple of years it grew out of control.

“Some weeks I would eat nothing but chocolate. I’d have it for breakfast, lunch and tea,” she says. Other weeks, chocolate would supplement an otherwise healthy diet and exercise. “Some months I’d have a break from it in an attempt to break the habit. Then I’d revert to my old pattern. It was as though I became chemically dependent on chocolate. But because I wasn’t 20 stone and hooked on illegal drugs, I wasn’t really taken seriously.”

Chocolate is a so-called mood food, believed to affect our temperament by stimulating our body’s production of feel-good chemicals known as endorphins. Psychological and emotional conditioning may make us crave it and other foods as we associate them with past happy events and experiences.

Amanda Geary, a former science teacher, and member of the British Association of Nutritional Therapists who runs “food and mood” workshops, believes cravings can develop into an addiction. “Chocolate, sugar, wheat, yeast and dairy food stimulate endorphins and the production of opiate-like chemicals,” she says. “And some people get hooked on them.”

But she adds: “Most of us have cravings for certain foods, which is not always a bad thing. It is a sign the body is deficient in certain minerals.” For instance, she says menstruating women often crave dark chocolate. It contains iron and magnesium, which their bodies need.

Amanda Geary says the key to keeping cravings in check is to establish healthy eating patterns in early childhood. “Too often children reach for sweets in their school breaks. I’ve had calls from teachers who say the children seem more unruly after a break. But then teachers often skip breakfast, which is essential for giving them a good start to the day, balancing their energy level.”

Although fashionable, the idea that food influences our mood is not new. Medieval medical textbooks noted the aphrodisiac qualities of eggs, peacock, beef and pomegranates. Quince, dates and elderberries have been used as mood enhancers; lettuce and chicory as tranquillisers.

Mood food protagonists argue certain foods contain compounds that affect the brain. Chocolate, for example, is said to contain theobromine, which stimulates the central nervous system, and phenylethylamine - also found in cheddar cheese and some cold meats - said to improve mood in depressed patients.

Scientists at the Neurosciences Institute in San Diego, California, in 1996 found that dark chocolate contained substances that mimicked the effects of cannabis, producing “a transient feeling of well-being”. Other foods contain tryptophan, which the brain converts into serotonin, a chemical that controls appetite, body temperature, libido and mood, and plays an important role in alleviating some forms of depression. Tryptophan-rich foods include clams, oysters, octopus, squid, bananas, pineapples, plums, nuts, milk, and turkey.

Other foods are blamed for inducing negative effects such as lethargy, depression and anxiety. Popular culprits include caffeine, sugar, wheat and milk. Sugar is rapidly absorbed into the bloodstream and boosts the brain’s serotonin levels. But the sudden rise in blood sugar stimulates a rapid increase in the production of insulin, a hormone that transfers sugar from the blood to other cells where it is used to generate energy. As a result, the blood sugar level slumps, along with endorphin and mood levels, so sugar-eaters start to feel sluggish. But the brain will try to regulate this by tempting them to have more of the same, creating a craving.

Maria Griffiths, nutrition consultant and education co-ordinator at the Institute for Optimum Nutrition in London, believes food addictions - particularly with caffeine, sugar, wheat and dairy produce - are often caused by food intolerances. “If you keep overloading the body with a particular food that it cannot cope with, it will react with a variety of symptoms. You might put on weight, develop a skin complaint or suffer water retention,” she says.

Professor Jane Wardle, of the health behaviour unit at University College London, accepts that foods may influence moods, but says there’s no sound scientific evidence to support the concept of food as a chemical addiction.

“The studies have not been of a very good quality,” she says. “While it’s plausible that food nutrients might affect mood, it’s difficult to specify the precise effects. The intolerance and craving theory is completely outside the boundaries of normal science. It’s fringe medicine - and one I have no time for.

“As for food addiction, it depends how you define addiction. There are all sorts of psychological motives that have no basis in biology and therefore do not conform to the definition of addiction. Someone can wash their hands 100 times a day, but they have a compulsion not an addiction. The same can be said for food.”

Swimming teacher Kathy Morris, 40, a mother of four from Brighton, used to suffer pronounced sugar cravings for two weeks every month, which she linked to pre-menstrual tension.

“It kicked in after the birth of my third child in 1990,” she explains. “I’d buy some ingredients with the intention of baking a cake and end up eating the lot - glace cherries, slabs of fondant icing and marzipan. I’d pinch the cake my kids brought home from other children’s birthday parties and I developed a penchant for custard creams, sometimes eating a couple of packets in one go.

“My moods see-sawed at the same time I’d crave these sugars, just before menstruation. I felt totally out of control. The other two weeks of the month I felt fine.

“My GP prescribed a mild antidepressant. I found it frightening - the assumption that my head was affecting my body rather than vice versa. But I was desperate. Then a hospital consultant suggested I have a hysterectomy. I was 33. I was so cross, I started looking for an alternative and in September 1999 consulted the Women’s Nutritional Advisory Service.

“They advised that I cut down on caffeine. I also cut back on sugar and gluten - because they said wheat can hinder the absorption of vitamins - and salt. I also took some vitamin supplements including zinc, cod liver oil and the herb St John’s wort.

“Within six weeks I started to feel an improvement. I had more energy. The pre-menstrual feelings were still there but the downs were not half as desperate. After three months I felt like a human being again. I’ve hit the custard creams a couple of times, but I’m off that horrible roller coaster.”

Frances Beg found salvation in complementary medicine after a specialist in a London psychiatric unit told her there was nothing wrong. “I tried acupuncture, homeopathy, iridology and nutritional therapy. Nothing worked for very long.

“Then a friend told me about kinesiology. It is a complementary therapy that uses muscle testing to pinpoint vitamin deficiencies and weaknesses in internal organs.

“I was put on six or seven supplements. I was prepared to try anything. Gradually, after six months, my liking for chocolate waned. Now I don’t feel the urge at all.”

Women’s Nutritional Advisory Service: 01273 487366. British Association of Nutritional Therapists: 0870 6061284. Institute for Optimum Nutrition: 020 8877 9993. For information on Food and Mood Workshops or the Food and Mood Workbook (pound;4.95), contact: Amanda Geary, PO Box 2737, Lewes, East Sussex BN7 2GN