I LOVE Twinkies!! They're an all time classic. I could eat a whole box in one setting. But yes, it can make you fat if taken in large quantities. Eat it sparingly, you're good.
If you balance what you eat with how much you exercise you should be fine. Think of it this way, for each Twinky you eat, you have to run 500 meters. You can eat as much as you like of whatever you like, but be sure to burn off all the calories.