Complex carbohydrates are starches and take more effort to break down than simple carbohydrates (a.k.a. sugars), stabilizing your blood sugar. Whole grains help keep your blood sugar more stable than refined carbohydrates. Athletes consume carbohydrates for energy; they call it “carb loading.” Carbohydrates are the body’s principal source of energy, but if you choose to follow a low-carbohydrate diet, fats and proteins can also be used for energy.