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Fat has a food energy content of 38 kilojoules per gram (9 kilocalories per gram) proteins and carbohydrates 17 kJ/g (4 kcal/g). [ 2 ] Water makes up a large proportion of the total mass ingested as part of a normal diet but it does not provide any nutritional value.
A moderate energy density would be 1.6 to 3 calories per gram (7–13 kJ/g); salmon, lean meat, and bread would fall in this category. Foods with high energy density have more than three calories per gram (>13 kJ/g) and include crackers, cheese, chocolate, nuts, [10] and fried foods like potato or tortilla chips.
Energy; system unit code (alternative) symbol or abbrev. notes sample default conversion combinations SI: yottajoule: YJ YJ 1.0 YJ (2.8 × 10 17 kWh) zettajoule: ZJ ZJ 1.0 ZJ (2.8 × 10 14 kWh)
The conversion procedure for some units (for example, the Mach unit of speed) are built into Module:Convert as they are too complex to be specified in a table. That is indicated by entering a code (which must be the same as used in the module) in the Extra column.
Based on the work of Atwater, it became common practice to calculate energy content of foods using 4 kcal/g for carbohydrates and proteins and 9 kcal/g for lipids. [2] The system was later improved by Annabel Merrill and Bernice Watt of the USDA, who derived a system whereby specific calorie conversion factors for different foods were proposed. [3]
The unit is most commonly used to express food energy, namely the specific energy (energy per mass) of metabolizing different types of food. For example, fat (triglyceride lipids) contains 9 kilocalories per gram (kcal/g), while carbohydrates (sugar and starch) and protein contain approximately 4 kcal/g. [29] Alcohol in food contains 7 kcal/g. [30]
Proteins and most carbohydrates have about 17 kJ/g (4 kcal/g), though there are differences between different kinds. For example, the values for glucose, sucrose, and starch are 15.57, 16.48 and 17.48 kilojoules per gram (3.72, 3.94 and 4.18 kcal/g) respectively.
The physiological caloric value of glucose, depending on the source, is 16.2 kilojoules per gram [106] or 15.7 kJ/g (3.74 kcal/g). [107] The high availability of carbohydrates from plant biomass has led to a variety of methods during evolution, especially in microorganisms, to utilize glucose for energy and carbon storage.