What is the difference between complex and simple carbohydrates?

Complex carbohydrates are starches in their natural, unrefined forms - potatoes, pasta, rice, beans, whole wheat bread, apples, and so on. Complex carbohydrates are low in calories, high in fiber, and they are bulky, so they fill you up before you eat too much. Besides filling you up, they biochemically signal your brain that you have had enough to eat. When you eat fat, on the other hand, it’s very easy to consume too many calories before you feel full. In one study, for example, adding complex carbohydrates to food caused people to eat less (because the starches caused them to feel full), but adding fat to food did not cause them to eat less.

In contrast, simple carbohydrates - table sugar, alcohol, honey, molasses, corn syrup - do not fill you up. They have no fiber and are not at all bulky. When sugar is “refined,” the fiber and warning signals that tell your brain you’ve had enough to eat are removed. Because of this, it becomes very easy to consume virtually unlimited amounts of it and thus a large number of calories without feeling full. Sugar is less important than fat, but you would be wise to limit how much of it you eat.