Leon, London W1

A friend once remarked that my cooking could be pared down to two instructions: "pour over cream" and "bake". But I'm trying to change. So I was thrilled to hear about Leon, a London restaurant with a menu that monitors carbs, sugars and fats for you. Of course, the best way to diet is to eat naked in front of a mirror - restaurants will almost always throw you out before you can eat too much. Leon happen to have a mirror. I couldn't fail, I was bound to lose a few pounds.

A friend once remarked that my cooking could be pared down to two instructions: "pour over cream" and "bake". But I'm trying to change. So I was thrilled to hear about Leon, a London restaurant with a menu that monitors carbs, sugars and fats for you. Of course, the best way to diet is to eat naked in front of a mirror - restaurants will almost always throw you out before you can eat too much. Leon happen to have a mirror. I couldn't fail, I was bound to lose a few pounds.

Leon is in a busy pedestrianised area in Soho, behind Liberty. It's a pleasant enough place to set down a few tables. Not like hardcore Soho, where diners are never more than, say, three feet away from a car exhaust. Apart from the proximity of the Great Marlborough Street public conveniences, this would be a charming place to sit out with a glass of wine on one of the last nice evenings before winter really hits.

At Leon, they serve food fast. As in "food that is fast", not "fast food". Although you could be forgiven for thinking otherwise. Behind the counter was a multi-channelled chute, just like McDonald's. I gave the waitress my order and she turned round to get it, just like McDonald's. But at Leon the chicken is free range, the coffee is fair trade, and - if you sing at the counter - you get a free sticker. Which isn't like McDonald's at all.

I sat indoors. The food came in little pots, with no plates, but there was warm pitta to mop up any accidents. The glorious Moroccan meatballs (£2.80) tasted sweetly lamby, and the taramasalata (£3) had a clean tang of lemon. The magic beans (£2.50) were, well, magic. They showed what could be done with just green beans, lemon, rosemary and chilli. And gluten-free/lactose-free/meat-free to boot!

From the two forks the South African waitress gave me, she clearly thought I was expecting company. But I wasn't. I was just doing my job. When I ordered two more main courses, she smiled and said, "What you've eaten already tonight would feed a family of five for three days where I come from." She clearly thought I had an eating disorder. I pointed out that I wasn't finishing every dish I ordered, but she was off serving someone else.

The crunch-coated fish, wrapped in a Lebanese flatbread (£3.90) tasted like a fast-food fish burger. And I mean that as a compliment. The taste of some fast food is chemically enhanced, and has more to do with men in lab coats than anyone in chef's whites. But the Leon fish burger was cooked in olive oil and slathered in a tartar sauce, rich with capers. The fact that the fish came from sustainable sources was of secondary importance. This was a really happy meal.

I must confess, the name of Nash's mineral water (£2) was new to me. I used to drink tap water as a matter of course but, recently, I've started buying bottled. But you know what Nash's offered me? Wetness. If I'm going to pay for water, I want something with real, discernible flavour, not just something in a nice bottle. So I forgot the Nash's, and sprang for a carafe of decent house white.

My idea of eating less by sitting next to the mirror wasn't working. It didn't even make any difference having a walking, talking conscience waiting tables. So I decided to head home for the night, after I had tested the vanilla rice pudding (£2.30). I think this is one dish that needs to be done unhealthily if it's to end up with a satisfyingly thick skin. It was the only disappointment of the evening, and the only dish I won't be supersizing when I return.

Leon is run by the former chef Henry Dimbleby (son of cookery writer Josceline), business consultant John Vincent, and the chef Allegra McEvedy. The entrepreneurial threesome have spotted a real gap in the market and are planning to open more. "We want to make it possible to get away from empty, sugary foods that make you fall asleep in the afternoon and wake up fat," says Vincent. For some of us it's too late. But for the rest? There's finally a place where you can have your cake and eat it.

Leon, 35 Great Marlborough Street, London W1, 020-7437 5280

Food
Ambience
Service

Meal for two, with wine, about £30

SIDE ORDERS: FAST FOOD, BUT NOT AS YOU KNOW IT

By Caroline Stacey

Glo

Thai curry with African couscous and apple crumble for afters at this new joint. Take a cardboard tray and pick-and-mix nicely cooked dishes from around the world for around a fiver.

9 Shaftesbury Avenue, London W1 (020-7930 7826)

Square Pie Company

Pie and mash, London's fast food, gets a makeover. Steak and Guinness or jerk chicken and sweet potato pies for £4.25, a quid for mash, and mushy peas for 45p. All in a cute cardboard box.

Old Spitalfields Market, London E1 (020-7377 1114)

Tiffinbites

Excellent Indian takeaways served in stacking tiffin boxes (plastic rather than the real Bombay metal McCoy). A complete vertical meal of three different dishes costs around £6; a kebab wrap costs half that.

Bull ring, Birmingham (0800 5053 060)

V1

Baseball-cap-wearing staff and fries with everything. It's fast food but it's all vegetarian - vegan if you have the organic mushroom burger with tortilla chips, not the cheese salad.

Hounds Gate, Nottingham (0115 9415121)