Justine Picardie meets a small-waisted nutritionist with a message that is sweet, sweet, sweet
Debra Waterhouse has an important message for the world, which is that women need chocolate. Many of us already know this to be true, but Ms Waterhouse has another, even more important message, which is that chocolate is good for you. Not only that, chocolate makes you thin! Yes! It says so in her exciting new book, Why Women Need Chocolate (Vermillion).

Before you scoff, it should be pointed out that Debra Waterhouse (MPH, RD) is an expert, a well-respected American nutritionist. She knows all about things like brain chemicals and biological phenomena (for example, explains Ms Waterhouse, chocolate boosts serotonin and endorphin levels in the brain, which have a calming and uplifting effect). Plus, she says, chocolate contains phenylethylamine (a chemical allegedly released in the brain when we fall in love); theobromine (another chemical, which increases "alertness, concentration and cognitive functioning"); and magnesium ("a mineral involved in manufacturing serotonin and stabilising mood").

The bad news is that you don't need very much chocolate to gain all these incredible benefits: one little square will do, says Debra. The good news is that you need regular doses: denying chocolate cravings will lead to bingeing; saying yes to chocolate, or indeed any other food craving, in moderation, keeps you happy and in control of your own body (and therefore you own destiny).

"Women are wonderfully unique, ever-changing, compassionate beings," says Debra. "We have mood swings. We have food cravings. We have special food needs. We did 1,000 years ago, 100 years ago, and we do today. Each of these physical and emotional traits is an integral part of being a woman - and their balance is vital to woman's mind and body." We must learn to take responsibility for what we eat, says Debra, and the rest will follow. Chocolate is a feminist issue. Sort of.

Debra Waterhouse has come to London on a flying visit from Californiato preach her message to the British. She's got a hectic schedule: all the big daytime telly shows, and talk radio, and me. I get to meet her for tea at Brown's Hotel, which has the best cakes in London. Strangely, Debra is not eating anything: no chocolate eclairs, no frosted fudge brownies, nothing. She's just sipping a cup of weak tea, looking very trim in a short black skirt and a MaxMara jacket nipped in at her neat little waist.

I get suspicious, and ask her what she's eaten today. She looks at me with her wide blue eyes, and adjusts her discreetly highlighted shiny blonde hair, and goes through the list. "On the plane at 7 o'clock this morning, I had cereal - a type of granola. I also had pineapple, strawberries and some kind of berry yoghurt. At about a quarter to eleven, when I got to the hotel, I had some rolls. Then I had lunch - wonderful grilled swordfish, and broccoli. For dessert I had a pot of chocolate - a very intense, bitter-sweet dark chocolate. And after half an hour, I'm going to need something else."

I decide she's OK after her detailed description of the chocolate pudding, and tell her that right now, my body is telling me I need something more than a cup of tea. She is solicitous, and asks the waiter to bring cake, and then delves into her handbag and gives me a handful of little bars of chocolate wrapped in gold foil. They have WHY WOMEN NEED CHOCOLATE inscribed on the front. "Aren't they wonderful," she says, with enormous enthusiasm.

By the sound of things, Debra's life has always revolved around food. "I've had my own distorted body image and struggles with weight," she confesses. "I had anorexia in high school. I went down to 98lbs - and I was 5ft 6in. I'd look in the mirror and I'd think I was still fat, and that was why I didn't get asked out on dates or get to be in the popular group at school.

"Then I went to college to study nutrition, and I became a compulsive over-eater, in secret - pizza, crisps, and chocolate - because I thought I'd be labelled a bad nutritionist if people saw me eating them. My metabolism was very low after the anorexia, so I went up to 148lbs. That was 50lbs worth of fat. At 24, I said to myself I have to get healthy." She's now 35, and she says she never weighs herself. "I practise what I preach. It's allowed me to be at peace with food, and at peace with myself."

You can see why she has already written one best-seller (Outsmarting the Female Fat Cell), and why she has a thriving private practice as a dietician. She tells her anxious clients and readers that there's no such thing as good food or bad food. "You can eat anything you want as long as you don't overeat," she says, which is a simple yet also sensible piece of advice.

Whether this will stop women tormenting themselves with guilt over what they eat remains to be seen. Still, I feel liberated as I leave the hotel. I'm listening to my body, just like Debra tells us to do. My body says it wants chocolate. I unwrap one of the dinky little bars she gave me, and eat it. It tastes great. I eat another one, and think of all those wonderful chemicals that are being released in my brain. I'm trusting my body, and it's trusting me to keep the chocolate coming. I remind myself that I am a wonderfully unique, ever-changing, compassionate being, and then I tell my body to shut up, it doesn't need any more chocolate. Not yet anyway.