Breakfast/Lunch/Dinner near Atlanta Aquarium
I second the recommendation for Star Provisions - delicious, high quality sandwiches, pastries, and fun food items. The website is www.starprovisions.com. Downtown, there is also Spoon...which is a Thai place. Very good and open for lunch most days I believe. Their website is spoonatlanta.com. There is also a nice upscale "sports bar" type place that serves a wide variety of types of food. It's called Stats (the restaurant group has a website at www.concentricsrestaurants.com). I havent been yet...but the initial review of the food is fairly good.
Star Provision's in front of Baccanalia will provide you with a great lunch.
There is a Ted's Montana Grill near the aquarium and McKormick and Schmidt's (I know I butchered the spelling) in CNN Center. There is a Ray's in the City, for another seafood option close by.
Hope you have a great time. Good luck on the healthy part!