The 12 week thing is something I was confused about so did dome research- it is to do with 'starvation mode' it takes about 3/4 months for your body to go into starvation mode if your body has less than half the calories it needs. So saying 12 weeks means you wont get to that stage. Obv the point at which you go into starvation mode varies amongst individuals and depends on how much less than half you are getting but you get the point.