People who sell food have found ways to trick you into thinking that their product has fewer calories than there actually are. We call this negative caloric illusion. The theory behind this was carefully postulated by Alexander Chernev a psychologist at Northwestern University.
He did a series of experiments involving hamburgers. The results showed that if you ask people to estimate the calories in a hamburger, they will usually estimate more calories for a hamburger by itself than for a hamburger with celery or carrot salad on the side. His conclusion was that it is as if we believe that a piece of fruit or some vegetables will bring the total calories down.
If you pay attention to this concept you will begin to see it everywhere. It might be an add showing some broccoli on a squeeze bottle of cheese or some fresh fruit on a bowl of sugary cereal. This negative calorie illusion works because we are stuck on the notion that we must eat more good foods. Of course this is true, but we need to remember that eating a little good food will not cancel the negative effect of all the bad food we shovel down.