I'm not sure if Subway is THE healthiest fast food restaurant, but it does have some very good healthy choices. I work there, and trust me a lot of the subs are not healthy. It all depends on how you eat there. If you get a Spicy BMT with mayo you might as well just go to McDonalds. But you can choose a 6 in on wheat or honey oat bread, turkey, ham, or chicken sandwich. And a 6 in typically gets two slices of cheese, to lower the amount of fat just ask for one. Then pile on the veggies. Go for spinach, bell peppers, cucumbers, olives and carrots (if they have them) For the sauce stay away from the mayo and those types of dressings. Try getting regular mustard or sweet onion sauce. And just ask for one line of it (they usually do three across the sandwich) You'll get just as much flavor with less calories. Also NEVER put oil on it. I don't understand why we have it. But you can try some red vinegar, it does have health benefits. And try not putting salt, pepper I'm sure isn't bad, but the salt is just way to load on the sodium. And you'll be asked if you want chips and a drink most likely, skip on the soda and ask for a water cup. And then if you do want a side get apples or a yogurt.
Things you should never get at Subway:
Anything with bacon (Subway melt, BLT, Chicken Bacon Ranch) and don't ever add bacon to anything.
Spicy Italians and Spicy BMTs (horrible horrible for you)
Seafood Sensation and Tuna Salad (These wouldn't be so bad, but it meat is mixed with regular mayo, not light)
The Feat and Philly Cheesesteak, or any double stacked subs