Black coffee, without any sweeteners or creamers or other additives, contains about one to two calories per eight ounces. While black coffee is low in calories, from a nutritional perspective it is also a negligible source of energy, even though it also contains very small amounts of natural fats, sugars, and proteins. And, as everyone knows, coffee contains caffeine which is considered a stimulant.
Just one cup of coffee has enough caffeine to temporarily increase your physical and mental energy levels. Other short-term side effects may also be experienced from just one cup of coffee, depending on your sensitivity to caffeine, which is determined by your genetic makeup.