Would purging for 2 days on healthy food and then eating marshmallows, chocolate and pizza the third day cause weight loss or gain?

Not recommended: Why not eat healthy food every day? Healthy food every day, at a rate of calorie stores appropriate for you, would be best. There is not much value in marshmallows, chocolate or pizza, in that order.

A cheat day: Here and there is ok but every 3rd day is a bad idea. Not only that but remember when you have a cheat day make sure you are not too out of control in terms of what/how much you eat. As too much caloric intake, even a single day, can really derail an overall healthy eating week, when it comes to weight loss.