Food: Lose weight now, ask the Japanese how

rom time to time, I do this curious diet where I eat nothing but protein and citrus fruit. It works for me, this tedious mix, because as a professional cook, I feel challenged to make it as interesting as possible. Having said that, I find myself marvelling at the delicious taste of a simple steamed breast of chicken (from a fine bird, naturally) cooked in a covered dish with just salt, pepper and lemon juice. Its succulence and unadulterated flavour is a revelation.

If I want to eat out, I make a beeline for a Japanese or Chinese restaurant. Japanese will be my first choice, as I can gorge myself on protein-rich sashimi. I have always preferred this to sushi (I like sushi, but I like the raw fish more than the rice). And for preference, the neat wooden board upon which the fish is displayed will contain a higher ratio of toro (the gloriously rich and fat belly part of the tuna) to other specimens that are good that day. Mind you, in the best Japanese establishments, all the fish will be better than in any other kind of restaurant in the world, on that day. And every day.

I do not like cooked tuna, never have, be it from a tin, a rare-grilled slice with modishly piquant salsa or a freshly cooked piece used in salad Nicoise. As sashimi, though, with a dish of finest shoyu and a generous smear of pale green wasabi, I think it one of the greatest dishes it is possible to eat. But beware, toro is also one of the most expensive pieces of fish it is possible to buy.

It is prized so highly, first, because of its melting, fatty tenderness. When you press a cold, firm slice against the roof of your mouth for the very first time, it performs palate pleasures of such extraordinary delicacy, you immediately know that it is like no other taste or texture you have ever previously experienced; a piece of toro literally melts in the mouth. The second reason it is so prized - and priced - is that the belly cut of the tuna makes up only a fraction of the weight of a whole fish. Some of the best I have yet to eat in Britain is at the sushi counter of the restaurant Wakaba (122a Finchley Road, London NW3, 0171-586 7960). Wakaba is family-run in the most charming way and was designed by John Pawson in his serenely minimalist fashion.

I sometimes wonder why we chefs play around - and that is surely what it amounts to - with the finer points of Japanese cooking. It is, after all, a culture far removed from ours and the way we think about food and cookery. If we once stopped to think, before we tried to mimic, surely we would see this point? We don't use square or rectangular china and wood surfaces; we don't use chopsticks (a pair of sticks look as silly in a European restaurant as would a knife and fork at a sushi bar); we don't have the right kitchen knives (some chefs do, but I wonder if they are used quite as much as they are proudly brandished - a good one costs a small fortune); and, much more than anything else at all, we go to a Japanese restaurant to enjoy sashimi and they come to us to eat a nice veal escalope in a cream sauce with mushrooms and white wine.

Another thing which the Japanese do better than us is the simple orange. There used to be a time when you could easily request, as dessert, a freshly peeled orange (the diet pudding). Claridges or The Savoy may still do it under sufferance (the Grill Room of the latter can't even be bothered to peel an out-of-season new potato - I did it myself last time I was there), but I suspect that the breakfast chef's larder will be the corner of the kitchen to be raided for this mundane request. This was certainly the case when I ordered fresh orange segments at The Connaught; "fridgey" to say the least, wet and soaking in long-exuded juice. Demand an orange at any Japanese restaurant, however, and it's a different story. In one particular place, seven perfect pithless segments appeared in an arrangement which looked like the Sydney Opera House. Each segment remained attached to the peel by a whisker for decorative purposes, but also, therefore, was detached with ease by the teeth. Because I am an anally retentive eater (I find myself impelled to push each discarded double mussel shell into the last, so as to make a semi-circle of blue/black shells around the edge of the bowl, as I wade through a dish of moules marinieres), I then tried to re-form the de-nuded skins into the sculpted curves of the Bilbao Guggenheim.

It is, of course, important not to be too easily tempted by the pleasures of alcohol while doing this diet. So it is green tea for the Japanese places and a pot of jasmine in Queensway, London W2, at The Mandarin Kitchen (0171-727 9012). Some of the finest shellfish protein to be had in the capital is cooked here. Scottish lobsters are specified on the menu as being the best there is, and are a seasonal speciality. It is typical that it takes a Chinese restaurant to do justice to our native British crustacea, when, for instance, they are serving unseasonal Canadian critters at Glyndebourne. How very Tepid Britannia.

With chilli and garlic, steamed and served with matchsticks of ginger in vinegar for dipping, or with spring onions, a lobster at The Mandarin is so accurately cooked that its flesh is almost crunchy. I reckon that the secret is in its dispatch, deftly chopped into almost bite-size pieces, but still in its shell. Then it is flung into a hot wok with oil and flavourings for about one minute, stirred, tossed and seasoned all in one go. This really is "Meals in Minutes". Or less than that. Crabs are given a similar treatment, too, and are wonderfully messy to eat. But these may just be a bit too messy to cook, even for viewers at home ... "Hello? Is that Pizza Hut?"