Glucose is the body's preferred source and it is also the main source of fuel for your brain. Therefore one reason you might have feelings of a foggy brain is when you don't have enough glucose in your blood. (Another reason could be toxins.) Glucose is readily found in carbohydrates. If you need quick energy one healthful option you can choose is fruit which is a simple carbohydrate and quickly digested. It's actually the juices of the fruit that quickly enter into your bloodstream and provide you with quick energy. (See energy drink recipes.) But choose complex carbohydrates of whole foods such as baked potatoes with skins, brown rice, quinoa and colorful vegetables for longer lasting blood sugar (glucose) levels.