The most energy-rich nutrient is fat, according to the GoodLife Kids Foundation. Fat has nine calories per gram, while carbohydrates and proteins have only four calories per gram, as per McKinley Health Center. The calorie is a unit of energy.
The human body needs fat to survive, but it is important to eat the right amount of fat each day. It is also important to eat the right types of fats. In fact, experts from the Harvard School of Public Health say the percentage of calories someone gets from fat does not matter as much as the type of fat consumed. They recommend avoiding trans fats, limiting the intake of saturating fats and choosing foods with monounsaturated and polyunsaturated fats.