The stomach has stretch sensors which detect how bulky and satisfying a meal is, which send a message to the brain to stop eating when full. But refined food, such as chocolate and ice cream, is often not bulky and the message - which takes about 20 minutes to get through - arrives after eating past the point of comfort. It's little wonder eating large amounts of this type of food leaves you feeling bloated and sick.

Then there is the disastrous effect on blood sugar levels. Refined carbohydrates give the body an instant sugar 'hit' which sends blood sugar and insulin levels rocketing - and then plummeting again, as the body desperately tries to clear the overload.

This causes the paradoxical situation where you can feel very hungry immediately after sugary or starchy food. It also explains why some people get ravenous after Chinese food. Not only is a lot of white rice consumed, but monosodium glutamate stimulates insulin production. Drinkers will find booze, which is another kind of sugar, gives them the 'munchies'. Alcohol stimulates insulin, the hunger hormone, and the tendency to overeat is compounded by low blood sugar and weakened resolve.

On the other hand, unrefined whole foods such as meat, fish, wholemeal bread, brown rice, vegetables and fruit take much longer to digest. Unprocessed carbohydrates are wearing nature's jackets, in the form of fibre, which gives the body much more work to do. Even fruit, though containing fructose, takes a diversion through the liver during digestion which slows down the rate of sugar absorption.

So how do you know when enough is enough? People who have never dieted and those who eat unprocessed food would say they just know. Their body tells them. For those who have lost touch with these sensations, here is how to regain appetite control.

In their book Heart Of The Mind: Engaging Your Inner Power To Change With Neuro-Linguistic Programming, Connirae and Steve Andreas give a simple strategy.

First, start at the point where a food stimulus occurs. This could be seeing food, lunchtime or someone talking about food. Next, check how your stomach feels. Ask yourself, 'What would feel good in my stomach?'

Visualise different food, for example a bowl of soup or chicken salad. Now imagine eating the dishes, one at a time. Consider how it will taste, then feel the food slipping into your stomach and get the feeling of how this amount will feel in your stomach over time if eaten now.

If this feeling is better than the thought of eating no food at all, keep this food item as one possibility. If not, discard it. Next, visualise another possible choice. Imagine tasting this second item, and experience how it would feel going into your stomach, and staying there for some hours.

Is this feeling better than your best choice so far?

Now run through in your mind all the available options, comparing them and always thinking how your stomach will feel after eating each.

When satisfied that enough options have been considered, eat the food that makes you feel best over time. A healthy meal takes several hours to digest, after all.

Reading this, any naturally slim and healthy eater would say: 'Of course, how else would anyone decide what to eat?' But if you have a weight problem or eat the wrong kind of food, you've probably been making food decisions differently.

So what stops this person from gorging on rubbish? Nothing. But if you imagine eating a whole basket of greasy fries which sit like a lump in your stomach all afternoon, and then consider how you'll feel, they don't seem so appealing, do they? By contrast, imagine how differently you'll feel a few hours after a nice big bowl of vegetable soup. For those diehard calorie counters who still clamour for amounts, imagine how much food you can hold in your cupped hand as a rough meal guide. Then start learning to listen to your body. Eat slowly, savour every mouthful and give the full message time to reach your brain.

The writer is a specialist counsellor for eating disorders and obesity