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The theory
Juice and vegetable fasts help you lose weight, increase energy, and detoxify the body from the harmful effects of indigestion and environmental toxins.

The plan
Most juice fasts last from one to five days. 100 per cent fruit and vegetable juices - occasionally diluted with filtered water - are the only foods allowed during the fast. Organic, freshly squeezed juices are preferred, and all juices should be salt, sugar and additive-free.

Pros

• This plan is simple to follow, since the choices are so limited. You'll lose weight quickly because of the very low calorie intake, although weight loss is not usually the goal of fasting. Many people believe that juice fasts allow the body to cleanse, rejuvenate and heal itself.

Cons

• This is an extremely low-calorie diet, combined with zero protein, complex carbohydrates and fat, which can make you feel weak and disorientated.
• You may get headaches from caffeine withdrawal. It is usual to get a furry tongue and you may find your body odour gets worse for a few days.
• Your metabolism will slow down with so few calories to burn. This can make the situation worse for yo-yo dieters who are constantly setting their metabolism downwards.
• Some people should not even consider a fast, including diabetics, those with any diagnosed illness, or those with eating disorders.

Duration
One to three days ? more than this could be dangerous.

Tips
Don't plan on participating in any vigorous activity or expect your brain to be at peak mental function. Do not carry on with a fast for too long - three days should be a maximum without professional supervision. Drink plenty of water and avoid caffeine. After the fast, ease slowly back into solid foods such as porridge, cottage cheese or yoghurt.

Checklist
Restaurants: Juice bars are your only option.
Alcohol: No.
Caffeine: No.
Need to buy special foods: You'll either need a juicer to make your own juice with organic produce, or you'll need to purchase organic juices from a health food store.
OK for vegetarians: Yes.

The pros say
Although fruits and vegetables are recommended as a major part of any diet plan, juice fasting takes a good idea too far. Many experts believe there is no proven benefits of fasting as your liver is capable of eliminating all bodily toxins on its own. While there may be a case for re-balancing and re-educating the body ? after all periodic fasts are a traditional part of many cultures and religions ? for most people this can be dealt with by less stringent methods.