At the fundamental level, obesity is nothing more than a dramatic increase in the size of the lipid droplets in the adipocyte, see here for a diagram . ( Damn why the fuck is that study behind a paywall ? :(
Obesity is also an increase in the total number of adipocytes you have but thats another story....
But anyway, the point is this, if obesity was "causative" of diabetes and insulin resistance, then what you are essentially saying is that an increase the average size of the lipid droplets in adipocytes is straight up causative.
Is that true?
This clever study says NO!
Increased fatty acid re-esterification by PEPCK overexpression in adipose tissue leads to obesity without insulin resistance.
Overexpression of PEPCK in adipose tissue leads to increased glyceroneogenesis and thus an increase in average lipid droplet size ( i.e. obesity ), but there is no accompanying insulin resistance or T2DM.
Thats a VERY big strike for the theory that obesity is "causative" of insulin resistance and T2DM. NO baby, whats more likely is that obesity is an unfortunate side affect of the same "thing" that is promoting T2DM, i.e. a red herring, its the smoke that tells you there's possibly a fire nearby. But the smoke absolutely does not CAUSE the fire, if there is indeed a fire at all.