"The problem with this," says the health and nutrition consultant Dr Gina Shaw, "is that when this defence mechanism is happening three or more times a day, the rest of the body is left undefended and the immune system is put under considerable strain."

But is there any positive evidence that raw food is good for us? Raw followers report everything from increased energy levels and resistance to colds and flu, to clearer skin and healthier, glossier hair. And, they say, this is largely due to the fact that the food they are eating remains nutrient-rich, as vitamins and minerals haven't been destroyed in the cooking process. What's more, raw plant foods contain compounds such as carotenoids, flavonoids and pycnogenols, which research has repeatedly highlighted as having health-enhancing properties.

Another healthful aspect of the raw-food diet is enzyme preservation. "Enzymes help you digest food, and they act as catalysts for every metabolic reaction in the body. Without them, there can be no cell division, energy production or brain activity. In addition, no vitamins or hormones can do their work, nor can the immune system," says the raw-food chef and co-author of Raw, Roxanne Klein.

We know, however, that cooking food above 48ºC (118ºF) destroys natural enzymes, forcing our bodies to generate enough for digestion. According to Klein, this causes problems: "The body cannot produce enzymes in perfect combinations to metabolise foods as completely as those created by nature. This results in partially digested fats, proteins and starches that can clog the body's intestinal tract and arteries."

But, for many, the very idea of eating nothing but uncooked food leaves them cold. Another concern is that we simply don't have access to an abundance of good quality, fresh fruits and vegetables in this country, and what we do have is often picked when it's young and under-ripe. Then there's the social aspect. Dining out with friends, where food is predominantly cooked, can become tedious - or impossible. But the raw-food diet may have other, more tangible pitfalls as far as health is concerned.

"Eating only raw food can limit the variety of foods you consume, which could lead to an imbalance of nutrients. For example, starchy carbohydrates such as rice, pasta, bread and potatoes provide insoluble fibre, as opposed to the soluble fibre provided by fruit and vegetables; plus, B vitamins, such as the thiamine and riboflavin needed for metabolic pathways, may be lacking," says Dr. Sarah Schenker of the British Nutrition Foundation. And while followers of the diet believe that cooking destroys nutrients, Dr. Schenker refers to a recent study from the Institute of Food Research in Norwich, which says that "cooking carrots actually releases more of the antioxidant carotenoids that are present, so they are better absorbed by the body when eaten."

"It's also unlikely that raw-food dieters get sufficient protein, as they avoid meat and fish, and probably avoid beans or pulses that require cooking," warns Dr Schenker. While you might feel great for a while, with insufficient protein the body could start to use up its reserves - and then your health would inevitably begin to deteriorate.

According to its advocates, though, a raw-food diet can incorporate "superfoods" such as sprouts and wheatgrass, which can make up for these nutritional shortfalls. "Sprouts are baby plants in their prime," says the sprout and wheatgrass expert Steve Meyerowitz. "At this stage of their growth, they have a greater concentration of proteins, vitamins and minerals, RNA and DNA enzymes, bioflavonoids and so on than at any other point, and all these nutrients exist in elemental form, thus making them easily digestible."

Meanwhile, a shot of fresh wheatgrass is like a single complete supplement. As well as enzymes and amino acids, it has all the B-group vitamins plus vitamins A, C, E and K, and contains calcium, magnesium, manganese, phosphorus, potassium, zinc and selenium. "Wheatgrass also has up to 40 per cent protein by dry matter content, mostly as polypeptides. Indeed, wheatgrass gives our bodies all the raw materials to manufacture what it needs and balances its own chemistry," says Meyerowitz. There is, however, a missing link in the raw-food diet: vitamin B12 (found in meat, fish, eggs and milk), which is needed for the formation of red blood cells and healthy nervous and cardiovascular systems. "Up until recently, many of us have felt that additional supplementation with sea vegetables or probiotic formulas was sufficient for protection against B12 deficiency, but this does not seem to be the case," warns the nutritionist Gabriel Cousins. In order to be a successful raw fooder, supplementation with either an injection or a high dose oral administration is advised.

There is also a chance that raw fooders will develop essential fatty acid (EFA) deficiencies. Without linoleic acid - which the body does not produce itself and must obtain from diet - the body cannot produce such important fatty acids as Gamma Linolenic Acid (GLA), which is important for reducing cholesterol, boosting the immune system and preventing skin problems such as eczema.

To add insult to injury, many people - even healthy raw fooders - also eat too many sugary foods, which inhibits the conversion of linoleic acid to GLA. Also, while most raw foods - especially green plant foods - are full of fibre, as well as enzyme-rich and nutrient-dense, raw fooders should be aware that sugar from fruit can negate these properties by upsetting blood-sugar levels. Moreover, many people like to juice their fruits and vegetables; this removes the fibre that slows down the release of sugars into the bloodstream. It is best, therefore, to drink green juices, which aren't as high in natural sugars. Green juice also supports a slightly alkaline pH within the body, which, according to Dr Robert Young, author of The pH Miracle, is the single most important thing when it comes to health.

The reality today, however, is that many people are highly acidic. As a consequence, bodily functions from the beating of the heart to the neural firing of the brain are interrupted; if this process is left unchecked, body tissues begin to decompose. According to Dr Young, the way to counteract this breakdown in health is to eat the right balance of alkaline- and acid-forming foods. This means that 80 per cent of our diet should be alkalising foods, such as green vegetables, leaving a much smaller portion of acid-forming foods, such as meat and grains, on our plates.

Raw fooders, of course, have a head start here. "Those who eat a raw-food diet, which is high in green plant food, have very clear blood with a slightly alkaline pH and a low amount of fermentation," says the nutritional microscopist Catherine Daly. But not all raw fooders necessarily have healthy blood. Indeed, continues Daly, "those who eat a lot of fruit often have high levels of candida in the blood, while those who eat a lot of nuts often have high mould content. Certainly, some people on a raw-food diet can be considered to be unhealthy. It's important to know what you're doing."

"It's not advisable for people to eat nothing but raw foods for long periods," adds the author and raw-food revolutionary Leslie Kenton in her latest book, The Powerhouse Diet, "but an all-raw diet can be a wonderful tool for short periods, especially if you are healing something like cancer, AIDS or depression."

It's certainly true that raw foods are used in health institutes and clinics all over the world to aid healing, and when it comes to everyday life, there's little doubt that incorporating at least some raw food into your diet is beneficial. So what better time to give it a go than now, when local produce is starting to flood the farmers' markets and it's too hot to turn on the oven?

Raw For a Day - What You'll Be Eating

If you want to try it, there are a few things you need to know. Choose a mix of carbohydrates and proteins, and foods with sufficient energy content to meet your needs. Opt for local, seasonal, organic produce where possible.

Here are some recipe examples:

Fresh fruit salad:
Mixed fruit topped with chopped almonds, wheatgerm, pumpkin seeds and coconut cream.

Mixed salad:
Various green leaves, peppers, tomatoes, red onions, cauliflower florets and parsley, topped with sprouted lentils and alfalfa.

Thai Lemon Coconut Soup:
1 to 2 large squash, juiced milk of 1 coconut, 1 to 4 lemons - juiced to taste, 5 mushrooms - chopped, 2 carrots - sliced.
Mix all ingredients together in a large bowl.

Water, fruit and vegetable juices and smoothies are suitable drinks, while good snacks include vegetable sticks, fresh fruit, soaked dried fruit and nuts.

You can also make almond flax crackers, sunflower-seed cheese, hummus, tahini milk, pine nut and herb pâté, and nut and seed butter. All you need is a blender.

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