A college couple approached me at the walking track to ask me for the time a few weeks ago. The guy was pretty muscular and had what looked like about a 28 or 29 inch waist - no body fat at all.
I asked him what his diet was like and he said all he ate were egg whites, tuna, Greek yogurt, and protein shakes. I looked at his girlfriend and she shook her head 'yes' so I guess it was true.
Sounds horrible but it sure works for him.