I'm not claiming special knowledge here but I think the hypothesis is that there is a complex relationship between caloric intake/composition and metabolism. S

I'm not claiming special knowledge here but I think the hypothesis is that there is a complex relationship between caloric intake/composition and metabolism. So if you reduce your caloric intake but your body reacts with a reduction in basic metabolism or more aggressive storage of fat, then total weight may not go down. In addition this response mechanism is different for different people.