The pursuit of self interest is not a license to do anything one wants. It is not in your self interest to become a glutton. Self interest is the energy that drives you, your values are the beacons that give you direction, your reason is the faculty that shows you the way, and your will is the force that keeps you from straying. To take away self interest would be to take the engine out of a car, but to live without conscious values is to drive the car in random directions, not only without a care for a destination, but also without a care for any obstacles that may be in your way.
To say that food is good for the human body is not to say that one should gorge on as much of it as possible until one becomes sick, merely to say that it is a necessity of life. To say that one should pursue self interest in life is to say that one should eat to stay alive. To say that one should eat healthily, however, is not to say that one should avoid food, but rather, that one should pick what one eats, how one prepares it, and how much of it is consumed.