Within hours of Victoria Beckham being photographed in Los Angeles clasping a copy of Skinny Bitch , the diet book by Rory Freedman and the former model Kim Barnouin, sales rocketed. Now it has landed on our shores. While Americans are better known for exporting their fat-laden burgers and calorie-bulging shakes, this diet, based on firmly vegan principles, could not be more different.

Though veganism boasts devotees such as Richard Gere, a relatively small percentage of the population follows this style of eating (vegans eat no meat, poultry, fish or animal products including eggs, milk or even honey).

Such abstinence is not to be undertaken lightly. Women of childbearing age, those who are pregnant or have an infant, need to take particular care. It is hard to get all the omega3 essential fats from nonanimal sources and these are needed both by the growing foetus and for breast milk. This was illustrated in the recent tragic death of a six-week-old boy from Atlanta who weighed just 3½lb after his vegan parents fed him only soya milk and apple juice.

A sudden switch to veganism can also result in a lack of minerals, such as iron, needed for energy and concentration. This is because your digestive system takes a while to adjust to absorbing iron from plant sources. You can therefore be tucking in to iron-rich aduki and soya beans but not be able to extract as much as you need. A multivitamin and mineral supplement for the first few months helps.

Since vitamin B12 is available only from animal foods, it is crucial to take a daily supplement or to eat foods such as breakfast cereals and yeast extract fortified with it, since a lack, over time, causes irreversible nerve damage.

Much more common is the switch that an increasing number of people are making from meat-eating to vegetarianism, which still allows you to eat dairy products and eggs. While the main pitfalls involve not getting enough nutrients, one of the less publicised consequences of vegetarianism is the potential for its adherents to gain weight.

Vegans tend to be a slim bunch. This is not always the case for vegetarians, who often rely heavily on cheese and vegetarian versions of dishes such as lasagne, moussaka and risotto, as well as high-fat pies, rissoles and bakes (along with an overload of nuts).

With careful planning this does not need to be the case. While a vegetarian lasagne has 410 calories and 20g of fat in each 350g serving, the same size pasta dish with tomato sauce has just 224 calories and 1.4g of fat. A vegetarian pie from the ready-meal section of a supermarket can pack in 400 calories and 21g of fat, compared to a more carefully thought-out purchase of a quorn cottage pie with just 147 calories and 3.5g of fat.

The key is to become label savvy. You will soon realise that it is well worth trading in macaroni cheese, with 486 calories and 30g of fat, for spinach and ricotta cannelloni (ricotta cheese is much lighter in fat and calories than cheddar) with 275 calories and 9g of fat.

Healthy-sounding dishes such as lentil nut-roast can be anything but when you get to the nitty-gritty of calories (at least 450 in each portion) while opting for a spicy bean burger will gobble up 505 calories, and a garlic mushroom bake a staggering 841. A simple baked potato with cottage cheese has just 250 calories, a tofu stir-fry 350 and baked beans on toast a mere 300.

You also have to watch your nuts and seeds. Yes, they are a fantastically good source of protein and minerals. A couple of Brazil nuts a day offer heart-protecting selenium, vital for male fertility. Almonds are especially good for bone-building calcium with 100g giving us about a third of our daily needs, and cashews are known for their zinc, essential for a healthy immune system. Many nuts are vital sources of omega3.

But 100g of nuts has 612-688 calories. Seeds are equally nutritious but equally calorie-laden. Sesame seeds are great for calcium, as are products like tahini and hoummos, while flax seeds also give us omega3.

The key to being a healthy vegetarian minus a weight problem requires you to follow the same rules as the rest of us. Read the labels, prepare simple, home-cooked meals and eat fat in moderation.

www.amandaursell.com

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