Adrian Mourby has been discovering why fiction makes him fat
Earlier this year I had three months in which to write a book, and I found that it wasn't too difficult, providing I was at my word processor by nine every morning with a packet of biscuits at the ready.

The biscuits were essential. At the time, I didn't understand why but I do know quite a lot of people who write for a living and the biscuit, or the cigarette, is an essential tool.

Three months later, the book was finished and I went happily back to my normal routine of producing programmes and writing articles - except that I returned one novel and three-quarters of a stone heavier. Next year, I'm scheduled to write another book and, unable to face the prospect of putting on yet more weight, I consulted Ruth, a dietician friend of mine, last weekend about losing some pounds beforehand. She looked at me gravely.

"It's not a diet you want. You've got Mouth Hunger."

At first I thought it was a joke. It does sound a touch tautological - who, after all, is going to have Nose or Ear Hunger? - but my friend referred me to the Manual of Dietetic Practice. "It is important to help the patient regain the knowledge of true hunger, showing them the difference between stomach and mouth hunger."

In my case, what clinched the diagnosis is that when working on any other kind of project I could get through the day with a cup of coffee and lashings of adrenaline, but faced with an empty screen and 110,000 words to think up, I reached for the digestives. I didn't even like them after a while but I had to keep shovelling them in.

And this is odd. On location or travelling round between interviews, I seem to lose all sense of wanting to eat, but give me the challenge of pure fiction and my hand goes to my mouth with immediate and monotonous regularity.

According to Ruth, Mouth Hunger is a reaction to stress, and this is something that affects everyone, not just first-time novelists. When children fall over we give them sweets, when we have a shock we drink tea or reach for the whisky. Sticking something nice in the collective mouth is associated with comfort from an early age. Ruth thinks that from childhood we believe that certain foods can overcome pain and illness: "Maybe we come to believe that food can also help with the psychological pain of stress."

But what is the solution? Smoking is, of course, one answer. It certainly answers the oral need and actually keeps the weight down. But it also kills you. Besides which, smoking or chewing pencils or sucking your thumb is only treating the symptoms and not the problem. Ruth recommends a bit of self-analysis to start off with.

If, like me, you find yourself suddenly eating too much for no good reason, write down what's going on and what's going in. Pretty soon a pattern of what is bothering you should emerge: sales conference = chocolate biscuits, deadline = Liquorice Allsorts, etc.

The second thing is not to diet. Dieting is stressful, and adding stress to stress may result in binge eating, guilt and low self-esteem. Make sure you have regular, substantial meals. It's better to start stressed on a full stomach (as long as you don't throw up).

I'm also advised to establish a regular pattern of breakfast, lunch and evening meal. Also to stop work, yes, really stop work, when breaking for a meal. I must admit my tendency to glory in the narcissistic pleasure of rereading what I've written. But if I want my body to get food back in proportion, it seems I've got to concentrate on the pure munchiness of what's going into my mouth, rather than absent-mindedly dropping it between the keys.

It's also important to try to be hungry, says Ruth. Reassert the primacy of stomach hunger. Finding time for exercise followed by a good square meal is sensible advice for anyone to follow, but we mouth merchants need it more than most.

Next January, I shall be stocking the house with food and sitting down slightly later at my laptop after a hearty breakfast of porridge, toast and marmalade. Providing I don't fall asleep, I hope to get up again three months and 110,000 words later, roughly the same shape.