Fiber, fats, proteins, organic acids, polyols, and ethanol all release energy during respiration — this is often called 'food energy'. When the food (providing fuel) reacts with oxygen in the cells of living things energy is released. A small amount of energy is available through anaerobic respiration. Nutritionists usually talk about the number of calories in a gram of a nutrient, but this implies that the food actually 'contains' energy. It's better to say that each gram of food (fuel) is associated with a particular amount of energy (released when the food is respired). Fats and ethanol have the greatest amount of food energy per mass, 9 and 7 kcal/g (38 and 30 kJ/g) respectively. Proteins and most carbohydrates have about 4 kcal/g (17 kJ/g). Carbohydrates that are not easily absorbed, such as fiber or lactose in lactose-intolerant individuals, contribute less food energy. Polyols (including sugar alcohols) and organic acids have less than 4 kcal/g.