Anyway, often all that is just association. Here is a study which seems to offer some mechanism of why sitting around makes you fatter....
Static Mechanical Stretching Accelerates Lipid Production in 3T3-L1 Adipocytes by Activating the MEK Signaling Pathway
Sustained stretching brings new fat cells into existence.
Eureka have a commentary:
inactivity actually encourages the body to create new fat in fat cells, says Prof. Amit Gefen of TAU's Department of Biomedical Engineering. Along with his Ph.D. student Naama Shoham, Prof. Gefen has shown that preadipocyte cells — the precursors to fat cells — turn into fat cells faster and produce even more fat when subject to prolonged periods of "mechanical stretching loads" — the kind of weight we put on our body tissues when we sit or lie down.
All very interesting.
Of course I know it is just mice....