Energy density

The amount of energy stored in a given food per unit volume or mass. Fat stores 9 kilocalories/gram (gm), alcohol stores 7 kilocalories/gm, carbohydrate and protein each store 4 kilocalories/gm, fiber stores 1.5 to 2.5 kilocalories/gm, and water has no calories. Foods that are almost entirely composed of fat with minimal water (e.g., butter) are more energy dense than foods that consist largely of water, fiber, and carbohydrates (e.g., fruits and vegetables).