Among the panel of speakers at "Defusing the diet time bomb" will be Dr Susan Jebb, head of nutrition and health research at the Medical Research Council. Here she answers some of the most pressing concerns among parents about obesity in children.

Who do you think is most to blame for children's poor diets and rising levels of childhood obesity - advertisers, the food industry or parents?

Obesity is a complicated problem and no one factor explains the weight gain in ech individual.. Without doubt, most children are less active than previous generations and so they need less energy. But there are more opportunities to eat than ever before, and a wider range of tasty food and drink to choose from, often in extra large portions, so it is perhaps not surprising that it is all too easy to eat more than needed. A child does not become obese overnight, the problem creeps up.

It’s rare to have a day when we don’t eat sufficient energy, so the few additional calories we don't use become stored as body fat. As the days go by and these extra stores are not called upon, they build up. The process is continual.

Blaming one single group for obesity in children is probably counter-productive - we need to look at the cumulative effect and, more importantly, find ways to stem the rising number of obese children.

The recent "Leaner Fitter Future" initiative by the Medical Research Council and Association for the Study of Obesity looked at options for action to prevent childhood obesity and found that all the interested groups - in food, advertising, sports, health and consumption - were committed to taking action. There is now a real sense of urgency and we need to capitalise on that and press for change.

Why are "bad" foods so much tastier to children than "good" foods?

The foods we choose to eat are the result both of biological factors and learned preferences. Research shows that even young babies prefer sweet flavours, and many foods are more palatable because the fat content has an attractive texture and mouth feel. On the other hand, foods such as cruciferous vegetables may seem bitter, especially to young children. Salt is an acquired taste and repeated consumption of salty foods tends to reinforce a preference for this flavour.

However, children rapidly learn to associate certain foods with particular experiences and the end result is that certain foods are perceived to be tastier than others. Serving crisps, chocolate and fizzy drinks at parties quickly gives them the appeal of special, highly desirable food and, hence, tastier.

There is increasing concern that the use of bright, colourful images and popular cartoon characters to promote fatty, sugary or salty foods can reinforce the appeal of these products to children, making them appear "tastier" than other, less heavily promoted foods.

Many parents feel they are losing the battle against advertising and peer pressure to persuade their children to eat the "right" foods. How can they fight back?

I suggest tackling the problem from two sides. First, limiting availability at home is a great place to start. While children are young, parents should impose control - even though it can be hard to exercise it - and should work out a clear strategy about foods so that the "rules" are applied consistently.

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