Week 3: Patience

Forget what the crackpot diet plans say. If you're really going to lose more than a kilo a week, you need to reduce your portion sizes by at least 40%. That's a reduction of 800 calories per day on your needs - starvation, in other words.

If you manage to stick to such a fad diet, you'll certainly lose weight quickly...but you'll also be completely shattered, you'll have dull hair, teeth and skin, and you could even find your periods stop. You starve yourself, and when you start eating normally again your body will be so confused it will react by piling all the weight back on. It's not worth it. 

For effective, long-term weight loss, you need to give your body several weeks, if not months, to get used to gradual change. Be patient and you'll get the results you want.