Why don't crash diets work?
If you listen to good advice, it is clear that losing weight gradually is much more effective than crash dieting. It is also safer. Eating very little means your body does not get enough of the nutrients, minerals and vitamins that you need, and you will end up so listless you may well feel faint from time to time. Eating just one or two different foods is not a good idea either, as this is likely to lead to a vicious cycle of starving and bingeing. Whichever way you attempt to crash diet you will certainly have no energy for keeping yourself occupied in any meaningful way that will keep your mind off food!
Any weight loss your scales register during a crash diet will come from loss of essential water, or from muscle wastage, rather than fat loss. The rate at which your body breaks down food (your metabolic rate) will also drop, meaning losing weight gets even harder.
If you aim for a weight loss of about 1kg a week, and stick to a good low-calorie diet with a well-balanced variety of foodstuffs, and combine this with a regime of regular exercise, you are far more likely to achieve a long term lifestyle change that will leave you feeling fitter, happier and the right size for you!