We usually eat out once a week to once every 2 weeks. Usually it is to socialize with our church friends. Any more eating out than that and my digestive system turns on me. It probably also helps that we often split meals and don't go whole hog on anything.  A slim person could eat out 5 times a week and have it be fast food and not gain weight. It comes down to total calories consumed vs used. But that slim person isn't going to feel as well as someone who makes healthier choices regularly.