Two tablespoons of peanut butter provide more than 8 grams of protein and 2 grams of fiber, 208 milligrams potassium, over half a gram iron, 24 micrograms of folate, 188 calories, and just 3 grams of sugar. All this makes peanut butter a perfect nutritional supplement for those who enjoy lifting weights. All you need to do is make sure you carry a jar of peanut butter on hand to give your body an instant boost of protein following your workout. Brushing the apple slices clean is an excellent option.