Zachary Levi was perfect casting to play the child in a man's body that is the superhero Shazam. However, Levi didn't necessarily have the body of a superhero when he was cast in the role. The actor has spoken a lot about what he had to go through to be believable as a superhero. It required a lot of work on his part, but a large amount of that work was actually eating.
While Zachary Levi spent a lot of time at the gym, as you would expect, that gym work was designed to convert calories into muscle, and so he had to consume a massive amount of calories in addition to his workouts. According to Levi...
I got the job and I was in the gym 5-6 days a week. When I was trying to build mass, you’ve got to eat a lot of calories, 3,500-3,700 calories a day. And they have to be really clean calories, they can’t just be Häagen-Dazs!
A fairly standard adult diet would be something around 2,000 calories a day, which means that Zachary Levi was eating nearly double that along with working out nearly every day of the week. On the one hand, working out that much is going to require a pretty impressive calorie intake to keep you from feeling perpetually starved, but that's still a crazy amount of food.
If you could eat anything you wanted then eating that much might not be all that bad, but as Zachary Levi tells People, it's not like he just sat around and ate ice cream. I mean, it's dairy so there's some protein in ice cream, but there was probably a lot more meat and other more serious protein sources included. Levi has said his diet was basically meat and vegetables five times a day, and considering the calorie count, these were probably pretty close to full meals five times a day. Even with the hunger that you get from working out, I can imagine around meal number five eating more food is not what you'd want to spend your time doing, but it's just as necessary as the exercise.
Being a movie star may be largely as glamorous as it appears to be, but sometimes there is some pretty serious work to be done. Levi says it was a dream come true to play the lead in a superhero movie but the guy had to work to make that dream a reality. While looking like a superhero can be done with padded suits and CGI, to feel like a superhero, you've got to still do a lot of the real work.
On the plus side, if you do throw in some ice cream, you probably burn it off pretty quickly based on how much you're working out.