The body uses carbohydrate to produce energy and convert other nutrients, such as fat, to energy, thus the body has a much larger need for carbohydrates than protein, since protein’s primary function is maintaining tissues that already exist. In addition, some sources of carbohydrate provide vitamins, minerals, fiber and other substances (e.g., bioflavonoids and phytochemicals) that can have a positive impact on overall health.
Carbohydrates are also considered “protein sparing,” as they can be used for energy, reserving protein for tissue repair and building, especially during training/exercise. Finally, the brain and central nervous system run best on a fuel of glucose supplied by carbohydrate and the brain and other organs use more calories per pound than any other body parts. Lowered glucose levels resulting from inadequate carbohydrate levels or long periods between eating can leave people feeling “spacey.”
Carbohydrates are pure-energy foods that you continually use to keep your body alive and in motion. As mentioned, protein is used primarily to maintain existing structures like muscles and therefore very little is needed. A 150LB person doesn't need any more than ~100gms of protein unless they are in heavy training and/or dieting, at which point they may need to go as high as 1gm of protein per pound of body weight. As an example, 150gms of protein is ~1/3LB and no one can put on that much new muscle every day (that would be almost 2lbs/wk for the rest of your life) but an active 150LB person will use 400-500gms of carbohydrates daily to support normal energy needs.