Like digit posted it's all about how you eat and train. Of course genetics play a HUGE role as well. Flex Wheeler would diet for the Olympia and drink cokes, eat pizza etc! Dexter can do this too.
I was an extreme ecto when I started. I was 144.5lbs exactly (I'll never forget weighing myself the first day I started lifting, lol). At a height of a little over 6'4 that's super thin. I can eat anything I want and still not get fat. I am now 264lbs or so (244 in my avi right before I started my last 500mg test cycle and Amp stack.) and even though I drink shakes with 7 tablespoons of olive oil before bed, I still wake up starving 4 hours later and need to eat some eggs or a can of tuna with some natural pb on the side. But if my friend Bill did this, he would have a double chin within 2 weeks.
So, genetics, diet and training all play a role. But as a general rule of thumb it's always easier to go on all out bulks to gain massive amounts of muscle than it is to bulk and get cut at the same time.
Post up some stats, age, cycle history, training, nutrition habits, genetic structure, etc and I think we will all be able to help you better. It's one thing for us to give you our personal experiences but if you want more personal, clear cut answer, we will need more info.
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