It doesn't take money to eat healthy. It's not that fast food restaurants are the only choice is you don't have money. You can go to a grocery store and eat extremely healthy if you want to.
Those who eat at fast food restaurants all the time are more uneducated than poor (although both things might go hand-in-hand), and might not know how many calories are in a burger or more importantly sodas (I've seen people drinking liters every day).
You can buy an apple instead of a can of coke and save you both a few hundred calories and a few pennies. Nothing to do with money.