One serving a day is plenty.. you want to eat a variety of foods on this plan to get a variety of nutrients. One mini bag of popcorn a day is plenty or else one portion from a larger bag. And of course this means without butter. The book says air popped corn, but personally I haven;t been able to do that. Find popcorn with the least calories per serving. I like American's Best brand . It's 90 calories a serving. If you find one up to 120 calories a serving, you should be okay.