We've all seen the impact of low-carbohydrate diets over the last 10 years; and whether you like the idea, think it works for you, or just don't care either way, one thing "low-carb" has done is alert us to the fact that there is a limit on the quality and perhaps quantity of carbohydrate that's useful in healthy eating practices.
The more active you are, the more carbohydrate you need. For example, elite marathon runners or Tour de France cyclists might eat the equivalent of up to 50 slices of bread a day. This is calculated at around 4 to 5 grams of carbohydrate for each pound of bodyweight each day, such is the demand of these endurance sports. Carbs are the main fuel for most exercise activities, although fat plays an important role as well.
Naturally, if you don't do much exercise, don't have a physically active job or just can't do anything physically active, then your carb requirements are much less, perhaps only 1 to 2 grams per pound bodyweight each day.
Fitness practitioners doing weight training, aerobics classes at gym, jogging, cycling or equivalent for 4 or 5 times each week will fall in between in their requirements. One important point to remember is that unless you're an elite athlete doing several hours of training each day at high intensity, you mostly want to stick to high-fiber, low-GI types of carbohydrate in fruits, vegetables and whole grains. Eating lots of refined carbs and sugars is one of the reasons that people on low-fat diets have failed to lose weight or improve health over the years. Athletes have a little more choice because of the rapid metabolism of these refined foods in fueling their activity.
So don't be afraid of carbohydrates, they provide valuable antioxidants and fiber and vitamins and minerals: Just make sure you get a good balance of whole foods and refined foods in the right quantities for your activity.