The Snackwell effect is a term used to describe what happens when people think that because something is labelled as "low-fat" or "fat-free" they can eat as much of it as they want without gaining weight. It's like when you go to a grocery store and you see a box of Snackwell cookies and it's labelled "low-fat" so you think, "Hey, I can eat as many of these as I want and I won't get fat!". This can be a problem because eating too much of anything, even if it is low-fat, it can still add up and cause you to gain weight. So it's important to remember that just because something is labelled low-fat or fat-free, it doesn't mean you should eat too much of it.