Last week’s government announcement that free fruit will be handed out to more than 80,000 four to six-year-olds each day was welcome news.

Studies show that one in four children - compared with one in five adults - is obese. Yet diet and exercise for children receive much less media attention than the latest dieting and fitness regimes for adults. And this is despite the fact that eating patterns established in childhood are known to set trends for life.

Fat is not only about food, of course. Many other factors are involved, including genetic determination of metabolic rate, early feeding patterns, diet selection and, in some cases, emotional problems that influence eating habits.

However, food is also strongly linked to social context and this is one area where parents and teachers can exert an influence. Meal times matter. It takes 20 minutes for the hypothalamus (an area of the brain involved in the perception of hunger, sexual behaviour and temperature control) to register that enough food has been eaten. The body’s normal response to food is for blood sugar (glucose) and insulin levels to rise. Glucose enters the cells, any excess is stored as fat, and appetite decreases.

Fast foods are exactly what they say they are: instantly available, eaten fast, often “on the hoof”, and they generally have a high fatsugar and refined carbohydrate content. When food is eaten at speed, the brain does not have time to recognise that the body has had enough, and respond by switching off the hunger signals before more food has been eaten.

High sugarfatcarbohydrate content foods cause an immediate and rapid rise in blood glucose and insulin levels. If too much insulin is produced, the blood glucose falls too low, which results in a craving for more sugar. It is at this stage that a child will demand a “quick fix” snack such as a packet of crisps, candy bar or fizzy drink (one fizzy drink contains the equivalent of seven teaspoons of sugar). This will temporarily relieve hunger but a similar pattern will recur within two to three hours. Sugar-craving cycles increase the likelihood of obesity.

There is evidence that obese individuals secrete above-average amounts of insulin in response to food and are therefore more sensitive to sensations of hunger. Rapidly-changing blood sugar levels can also deplete the body’s ability to produce insulin in the long term, which may be one reason why children of 10 to 12 are now developing the type of diabetes that used to be found only in the middle-aged.

But, of course, it is not only thetype of food children eat that has changed over the past generation. The manner in which we eat is also very different.

Sitting down to a formal meal with set courses involves taking time over the food - usually longer than the 20 minutes that the hypothalamus needs. It also enables children to learn the value of regularly-spaced, balanced meals. If slow-glucose-releasing foods (such as wholemeal bread, protein, fruit, vegetables and unsweetened fruit juices) are taken at regular intervals, energy is used up rather than stored as fat.

Cafeteria-style feeding puts the onus of choice upon the child. Children tend to select items they either know or that taste good - too often foods with a high refined carbohydrate and fat content. Canteen meals also require the child to select the entire meal in advance, as opposed to deciding after the first course whether a second course is necessary.

An increasing number of families do not have sit-down meals. Many children start the school day without breakfast with low level of blood glucose.

The body’s natural reaction to low blood sugar is to compensate by increasing adrenaline output. Such a biochemical combination can affect attention, concentration and impulse control. In the long term, sharp swings in blood sugar levels increase irritability, fatigue and bouts of hyperactivity.

Food, after all, is fuel for the brain as well as the body. Today’s increase in obesity among the young is a social concern as well as a personal problem and potential health risk. Expectant mothers are encouraged to eat well for their unborn child. Children also need continued guidance in selecting and regulating food for life.

Sally Goddard Blythe is based at the Institute for Neuro-Physiological Psychology, 4 Stanley Place, Chester CH1 2LU TelFax 01244 311414. email: inpp@virtual-chester.com

HOW SCHOOLS CAN HELP

Ensure that lunch and break times allow sufficient time for every child to sit down to eat.

* Do not allow more than two to three hours to elapse between lunch and break times (particularly for younger children).

* Emphasise the importance of breakfast, and point out - particularly to teenage girls - that small, regularly spaced meals do not cause excessive weight gain. l Instigate discussion sessions about the type of foods that help maintain well-being and teach children how body chemistry can affect the functioning of the mind as well as the body.

* Encourage children to see mealtimes as social events.

* Help children to experiment with “new” tastes and types of food by guiding selection.

* Allow sufficient time within the school day for daily physical exercise.