The benefit of eating starches, and especially fiber, rather than sugars is that they can help you feel fuller for a longer time because they are either broken down slowly or aren’t broken down at all. And the idea is, if you’re feeling full, you’ll eat less. Of course, keep in mind that complex carbs aren’t a free pass to eat as much as you like — extra calories consumed will still be stored as fat.
Compared with fat, carbohydrates are less calorie-dense: 1 gram of carbohydrates contains 4 calories, whereas a gram of fat contains 9 calories. However, because carbohydrates are broken down and absorbed quickly, they can lead to a quicker burst of sugar into the bloodstream than fat does. Therefore, carbs may raise blood sugar levels more than fat does (when compared in equal amounts).