Is it bad to have fast food all weekend long?

Well it certainly isn't good for health, or if you are trying to lose weight. It's fine as a treat here or there, but moderation is what is important.

You do not want to starve yourself and eat just salad, but you also do not want to eat fast food multiple days a week- even once a week is more than what I allow my kids. But fast food is a quick way to gain back those four pounds.

I want to say again- do not try to combat those fast food meals with just eating salad. Continue to eat a relatively healthy diet in moderation. Fruits, veggies, protein, dairy, grains- there are lots of aspects to a healthy diet, and it should be accompanied with exercise at least three days a week (again- in moderation) for ideal results. It is all about balance, and lacking the basic food groups are just as bad as gorging on junk food. Worse, even. But in both aspects, self control is important. Limit your junk food intake, and that certainly includes fast food. But do not do so by eating next to nothing, or missing out on the basic elements needed for a healthy diet.