Rock-n-java has many healthy options on the menu for breakfast, lunch & dinner. even whole grain items.
In fact, you can eat quite healthy in Cozumel. I know I eat much more healthy when I'm on the island than I do when I'm home...sad, but true.
Fresh veggies and fruit are everywhere. I don't think I've ever been to any restaurant for breakfast where I couldn't get a fresh fruit plate & yogurt (usually with granola, but you could skip that to avoid the carbs, it's usually served on the side)
Mexican food you get in Coz is NOT the Mexican food you get at home...It's not Tex/Mex with a lot of heavy chili sauce on it. Because of it's location on the Caribbean, the food from the Yucatan is heavily influenced by Caribbean fare and is not as heavy as it is in Central or Northern Mexico. There are MANY Mexican dishes that don't have tortillas involved at all & can be found on most restaurants around town.
You can get fresh fish grilled, mojo de ajo style (garlic fish), with grilled veggies, skip the rice if you are that hung up on carbs, or substitute it for beans. This dish is very traditional to the region and available almost everywhere on the island.
grilled chicken can be found everywhere as well, for another low fat meat choice. I pretty much try to avoid beef on the island, I've just not had much luck in that department.
I'm not a huge seafood eater & usually only eat it when on vacation for the most part, I generally live off of chicken dishes when on the island.
When I first started coming to Cozumel, black beans where on almost every dish, usually frijoles (refried), but black beans just the same. It seems like most places now serve pintos. not sure why the change came about.
I always figured black beans were the staple here because if it's location & I assume that it is an "Amiericanization" thing that has made folks move to pintos...just because that is what most people from the U.S. are used to...I prefer black beans.
Habaneros used to be the standard for pico de galio in the island as well, because the Scotch Bonnet is the traditional chili of the Caribbean.