Travelling in Thailand and Vietnam last month I started eating five meals a day. Greedy, yes, but it was also good manners. East Asians like to eat every three or so hours. And that's not snacking: a typical on-the-road lunch was a salad of green papaya, cashews and dried shrimp; some greens stewed in garlic and oyster sauce; a fish boiled whole at the table in a stew of herbs, onion and bitter gourd. All with rice, of course.

As ever in Asia, everything arrived from the kitchen when it was ready, straight into the middle of the table for our group to dig in. It was relaxed and friendly. All that starter, entrée, your order, my order palaver when Westerners dine out seems so stiff by comparison. And, although they seem to eat an awful lot, there's no question that the South-East Asian way is healthier. Well, you don't see many fat Thais.

The other key ingredient that they use is fish sauce. Most Brits view it rather as our grandparents did garlic - foreign and smelly. How we miss out. Fish sauce is unbeatable for giving depth of flavour to so much that's otherwise bland. If you're poor in Asia, “fish water” and chilli may be the only way of adding some excitement to the rice or cassava you depend on for your nutrition. It's pretty good on chips too.

The essence of fermented fish may be the world's most ancient condiment. The Romans knew it as garum, and the poet Martial writes of how delicious it is if made from the blood of still-living mackerel. He also cautions against kissing girls just after some fish sauce has been eaten. The nearest British equivalent is Lea & Perrins Worcestershire sauce. You need to take a magnifying glass to the label to find out that its key ingredient is anchovy. In any case, it's too horrid to use for anything except Bloody Marys.

One of the problems is that the imported fish sauce in our shops was never very good. Pseudo-Oriental labels have been pumping out bland, sweet and madly overpriced fish sauces for years: few cooks bother unless the recipe demands it. There are better products around now: the Thai Squid Brand (though that's not what it's made from) is a pretty good basic.

But we still use fish sauce a bit like a cook who thinks that all cheese is cheddar. In fact, a range of different fish and “oyster” sauces are incredibly useful in the kitchen for producing stir fries and marinades for chicken or beef in spicy Asian salads - simple food that makes your friends sit up and go “Cor!”

Vietnamese Phu Quoc nuoc mam is celebrated for its deep, oaky colour and smoky smell. I like using it for the most basic of Asian fish sauce-driven dishes: salad. A chemical miracle happens when you put fish sauce and lime juice together - mixed at a ratio of 1:5, with a little sugar and some finely chopped chilli you get a tangy, eyebrow-raising dressing. It works with a standard British salad too. In Thailand you would use it for the great Siamese som tam salad, whose key ingredient is crisp, green papaya. That is not easy to find in Britain, but I've made som tam in this country as Thai restaurants do, using a mix of shredded white cabbage, carrot, shallot, tomato, mint and cucumber. It works, but you need really fresh and organic ingredients: standard supermarket carrots and cabbage don't have the taste.

You can put in a handful of dried shrimp or some chopped left-over chicken. Radish and raw green beans work well too. But the key to som tam is that all the ingredients need to be pounded together with the dressing - you can do it in a heavy bowl or saucepan with a bottle or the end of the rolling pin. East Asians use a large pestle and mortar.

When you're done, sprinkle some chopped peanuts on top, and serve with rice - best of all is the steamed “sticky” type, loved by small children.

I would advise not telling people the key to the dressing is the juices of long-rotted fish - wait till they've finished eating.

alex.renton@thetimes.co.uk

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