First, let’s address the notion that has thrown everyone off: the idea that carbs are always “bad” for you, or just plain unhealthy. I think this fad came about because somebody got pissed off at his friend for being so thick skulled about not wanting to think critically. He finally just had it and told his friend to stop eating carbs if he wanted to lose weight. Why did he do this? Because his buddy thought there was no difference between eating Grandma’s Chocolate Chip Cookies and eating an apple. Most people can intuitively make the distinction between cookies and broccoli, but people generally don’t know why. We’ve only been taught binaries of “healthy” or “unhealthy” with no real way to understand those categories. Because that was addressed earlier, I won’t go into the distinctions here. The point is, people are generally not to eat carbs because that eliminates candy. Unfortunately, it also eliminates a lot of extremely helpful carbs (and creates a poor relationship with food in general).
The simple difference is that complex carbs take longer for your body to break down and digest than simple carbs. This is because simple carbs generally lack fiber, and pretty much any real nutritional value. But last time I checked, I didn’t see anyone buying a Kit-Kat for the purpose of getting their daily vitamins.
In short, simple carbs will break down very quickly and provide very quick energy. White rice is a great example of a simple, non-candy, carb. White rice is fantastic if you’re a competitive athlete who is in constant need of replenishing his glucose stores. White rice is not so helpful if you work a desk job and your longest walk throughout the day is to your car. Once again, food is for the purpose of achieving a nutritional goal. If you aren’t an athlete, you will have little use for simple carbs. However, everyone will do well to eat complex carbs. For a simple run down of what’s what, check here. Note: I do not know nor care what else the website supports. I am only linking them for the sake of their simple vs. complex carb page, as it is fairly helpful.
A quick aside: in order for your body to store carbohydrates as glycogen, they must be bound with a minimum of 3 grams of water per gram of carbohydrate. This is why people “lose weight,” not fat, quickly following a low carb diet. Any diet can work, so long as it is in a caloric deficit.