All through my teens and twenties, I could eat whatever I wanted and not put on weight. I think at times I showed it off by eating a lot, and it irked my boyfriend no end sin ce he had to spend all of his time at the gym. He said I worried it off. But time and medication has seen to that.
MacDonalds is one of those things that I'll occasionally get cravings for but will make me feel toxic if I actually eat. And my tastes have changed to the point where I find eating say too much fat really unpleasant.
Chocolate raises serotonin levels (and lowers your blood pressure). But too much of it will give me a migraine. All things in moderation. Including moderation.