3500 really isn't very much when you're trying to put on weight. Soylent in the morning and three after work (400/each) is ~half that, plus protein shake after the gym (350) and full breakfast/lunch at the office (~600/each) come out to roughly 3500. Plus I'll snack on stuff, maybe have some grapes or string cheese or whatever treats people bring in.

I'm not super strict about it, so it ends up between 3000 and 3750 most days. The Soylent makes it a lot easier because you're not constantly eating. Even something as simple as using half and half instead of skim milk in your coffee adds up.

Edit: but yes, I work out quite a bit.