When your energy is low, you might reach for a cup of coffee or a handful of candy to provide a quick boost.Too much caffeine can deliver the opposite of a jolt. And quickly digesting carbohydrates, such as sweet beverages, white bagels, pretzels, and candy will cause your blood sugar to spike and give you a short-lived high that ends in a crash. . . . Protein in particular increases the production of a brain chemical that regulates concentration. Protein improves focus, making you feel alert and on top of your game. When the mid-afternoon energy slump strikes, a well-timed, protein-packed snack can provide an instant pick-me-up and keep you satisfied for hours. . . . Foods like nuts, plain yogurt, and whole grains will keep your snacks low in calories and high in satisfying fuel.