Cortisol is a behavioral influencer (well, just about every hormone is in a way...I think  it's the nuerochem counter agent to adrenalin) but it doesn't have a direct physiological role in fat gain compared to say insulin...which is released by sugar...and more of it is released when the blood sugar concentration occurs sharply in the case of eating refined sugar than say, brown rice).  There  is some...barely tenuous physiological grounding to the fatlogic but it's been horribly mangled like a burger carton set upon by two legged wilderbeast: http://www.ncbi.nlm.nih.gov/pubmed/12972680  "Carbohydrate overfeeding increased basal and postglucose energy expenditure and net carbohydrate oxidation." In English, eat more carbs, your body raises BMR to compensate, thermogenesis (increase in body temp) is an indicator of this. The rest of the results essientially say "Eat tonnes of carbs your body will push dietary fat into fat stores because it's not going to waste a fuel substrate". To what degree does it compensate? Not enough that you can get away mainlining large Starbeetus cream and coffee. Which is essentially what fatties are doing all the time, gorging on huge amounts of carbs which the body uses to function in the first instance and your body is then like "Hmm, this cola is great for all the CHO I can use right away, but the pancreas is telling me to push all this ranch dressing out the blood too, better tell the fat real estate management to build a new suburb on the ass so they've got somewhere to store it"