We may think we know what constitutes a wholesome diet for children, Ann Treneman says, but a doctor who treats young anorexics condemns parents who see raw carrots and a bit of fruit as a healthy snack.

Dr Dee Dawson is a mother of five and an expert on eating disorders who believes that grown-ups do not have a clue about what children should be eating. She says this as often, and as loudly, as possible in the hope that we adults come to our senses. Five minutes into our interview, she had attacked the Government, schools and the medical profession. But then she gets personal and turns to the vexed subject of her children's lunchboxes.

"The rules at my children's school are stupid. They are not allowed to bring Jaffa cakes because they have a bit of chocolate on them," she says. "I send them anyway. They aren't supposed to bring crisps. Why?" Perhaps, I say, because crisps are meant to be bad for you. "No they're not! They're a wonderful form of nutrition. They give energy. The headmistress suggested that they might bring carrots, celery and fruit. I said if my kid wants a break, she wants to eat. If I send carrots and celery, I might as well give her a cardboard box to chew on."

This sounds like a joke but Dr Dawson, the 50-year-old medical director of Rhodes Farm Clinic for anorexic children in North London, does not laugh. But surely, I say, children can only benefit from fresh vegetables? "Of course children have to have salad and fruit and fresh vegetables," she says, "but they have no calories and no nutritional use except for the vitamins. They don't contribute to the child's growth and energy. This is what a child is all about - growing, strong bones, strong teeth, healthy muscles. Kids need so much energy and none of those foods provide any of that. You give a child a carrot stick at break and you may as well give them nothing."

Dee Dawson specialises in making such challenges. Why shouldn't children eat between meals if they are hungry? Why should children worry about fatty foods? Why don't we teach our children that fat is essential to our diets and that some fats are good for you? What is wrong with vending machines in schools? Dr Dawson believes that the answer to each of these questions is obvious if we would just rediscover the common sense that we have lost in our fat-phobic age. And the woman who, before qualifying as a doctor, founded a company devoted to making clothes for those size 16 and over is on a campaign to put things right.

"Parents are confused. Doctors are confused. The Government is confused. Schools are confused," she says. Last month she attacked the Government in a speech to the Girls' Schools Association, criticising advice that children should eat low-fat foods, and a report that suggested tuck shops should close. Her views ended up on the front page. "I was delighted," she says.

Since then the Department of Health has distanced itself from the leaked report that was submitted in the run-up to next year's green paper on public health. "It has no status other than as a document requested," said a spokeswoman who confirmed that there are no nutrition guidelines for children. The Health Education Authority touches on the subject briefly in its booklet "Balance of Good Health" which is full of advice on how to eat less fat. Nor does the Department of Education provide much help. In June it was announced that nutritional standards were to be set for school lunches but there is no progress yet. A spokeswoman said they hadn't yet begun drafting the Healthy Eating Initiative.

The Department of Health added that it was always keen to hear other opinions and urged Dr Dawson to feel free to contribute. Somehow, I don't think she will need much encouragement. "I would like to see the Government prepare a proper resource kit for schools which talks about healthy eating, healthy exercise, about laxative abuse, anorexia and the long term effects of eating disorders," she says. "Schools are interfering in aspects of nutrition that they don't really understand. If they had a pack, then we could all agree to not tell children they should be on a low-fat diet. Lots of teachers think that's a good idea! But it's not for children."

The core of Dr Dawson's philosophy is that most children, left to themselves, do not have eating problems. "Adults eat for comfort and when they are not hungry because they like food. Children tend not to do that. I personally wouldn't restrict my child's calories. I would allow them to find their own level." As long as her children eat three meals a day, she is not worried about snacks. Children become anxious about food because their parents are and she points to the boom-and-bust Christmas and New Year period as evidence. "Dieting has become a national pastime. It's not often that you find someone who says they eat what they like, when they like, and aren't worried."

Many parents, under the impression that all fat is bad and all carrot sticks good, end up depriving their children though Dr Dawson uses a harsher word. "What happens when you starve kids is they become dull and less outgoing. They've lost their joie de vivre. This happens before you see any weight loss. The whole metabolism will drop. A lot of parents are doing that. If their children were eating more they would be living life on a different plane with energy to burn."

No child should be on a diet unless under the care of a doctor, she says, and only 4 per cent of children are considered to be overweight anyway. But 1 to 2 per cent of all school children have anorexia and the two groups are not unrelated. "Some children are hampered by being truly fat and they could do with a bit of help. But it needs to be done carefully, because something like a third of the children at my clinic have been overweight, have gone on diets and just not stopped."

The clinic is in a large house and takes 32 children at a time. When you walk up the drive, you can see into the dining room. It is a sad sign of our times to see so many shrunken children gathered together to learn how to eat. So far 400 children have come here over the years and all arrive weighing 80 per cent of their normal body weight or less (48 per cent was the lowest). Dee shows me a picture of a boy near the lower end of the scale - it is like looking at a victim of famine. "He was absolutely terrified of fat," she says. Her youngest patient was six years old. "She thought that she had fat thighs and her tummy wasn't flat."

But children do not become anorexic just because their mums won't let them eat chips. Anorexia is a disease that strikes a certain type of child (a perfectionist and an obsessive) at a particularly stressful time. The child's life feels out of control and so she controls the one thing she can: her body. (Only 10 per cent of anorexics are boys.) Dee Dawson is saying that we are raising a nation of children who are confused about food and that grown-ups are only making it worse. "Do parents know whether we are supposed to be giving kids skimmed milk or semi-skimmed, butter, chips or crisps? What about chocolate?

So, I ask, it's crisps and chocolate bars all round then? "Not every day," she says. "You've got to be sensible." And for once she sounds just like any other mum.