I eat fast food all the time in "stretches." Maybe get it 12-15 times in a month or two then won't eat it for 3 months. Will I put weight (bad weight) on if I'm not working out while doing so for a couple of months? Absolutely. Will I not put weight on if I'm working at during that stretch? Absolutely (and I'm not a crazy cardio person). Oh and my vessels are 100% clear. No buildup whatsoever (and I'm not exactly 35 anymore...cough, cough). Been doing this my entire adult life because, sometimes, I just enjoy it (and it's easy...especially when you can walk from your office to a few of them OR have it delivered now...).
All about genetics IMHO. Same guy my size/weight could do the same thing for 5 years and be done.
(Yes, LOVE it at the moment, HATE it 5-minutes later, lol....)