Mark did an excellent post a long time ago that doesn't directly answer your question:
17 Reasons You’re Not Losing Weight | Mark's Daily Apple
He explains common reasons for weight gain even when eating within the Primal Blueprint guidlines, but does not explicity state what happens on a cellular level.
I am not sure he would advise very low carb across the board based on more recent writings. I know he still would in certain situations such as when the person is "metabolically broken" (diabetes, etc.) and has a lot of weight to use. But the hypothesis that insulin is THE driver of fat gain is no longer seen as truth. You can most certainly gain fat weight on a no-carb diet. This post from Kurt Harris comes a little closer to what you are asking I think:
Archevore - Archevore Blog - Insulin is a doorman at the fat cell nightclub, not a lock on the*door