fatchance:
I think the theory is that some of the fat from the cream stores in the liver and gets stored as fat over a few days.
I certainly noticed that the gain from cream did not start right away and continued for days after I stopped.
becomingoverweight:
That would just be a transfer of mass from the liver to adipose tissue though. The body wouldn't get heavier.
My experience is that there is a delay in the fat getting to the adipose tissue and I'm not sure if the fat is stored in the liver or possibly the lymph system until that happens. I have experienced the weight gain after finishing a few weeks of daily cream on more than one occasion and I suppose changes in water content in the body must cause this (as I'm a great believer in the law of conservation of mass).