The lemon diet is a popular cleansing routine that rids the body of toxins. People definitely drop weight, but it is a reduction of water retention rather than fat loss.
A lemon diet is probably not a good idea. There are other fruit diets however which may be more healthy and still keep your weight under control. Fruits in general are 90% water, so it is very hard to over eat fruits.
I've heard of lemon playing a role in several 'crash' diets and cleanses. I believe the Master Cleanse uses lemon juice or lemon water a lot. It's low in calories.
