Atwater factors 20

The caloric contents of diets are usually calculated by the use of Atwater caloric conversion factors which were derived for the mixed diets consumed by Americans around the turn of the century. These factors are based upon the assumptions that each gram of carbohydrate, fat, and protein in the diet will yield 4, 9, and 4 Calories (kcal), respectively. However, the Atwater factors were not intended to be used for single foods or for mixed diets that differed markedly in composition from those for which they were derived. Today, there are a wide variety of diets that have been drastically modified from the average American dietary pattern. Therefore, it is important that dietary planners understand the basic principles of food calorimetry. 

J. Saltiel and B. W. Atwater, Spin-statistical factors in diffusion-controlled reactions, Adv. Photochem. 14, 1-90 (1988). 

Diffusion-Controlled Reactions, Spin-Satistical Factors in (Saltiel and Atwater). 

Along with the development of food chemistry from the point of view of analytical chemistry came the development of interest in food chemistry from the nutritional point of view with Rubner, Voit, Atwater, and Lusk stressing the need for proteins, fats, and carbohydrates as essential food components. It was in relatively recent times that the requirements of vitamins, minerals, and other essential food factors were recognized. 

Saltiel, J., Atwater, B. W., Spin statistical Factors in Diffusion controlled Reactions, Advances in Photochemistry, Vol. 14, John Wiley Sons, Inc., New York, 1988, pp. 1 90. 

The traditional factor used in calcnlating the amount of energy of dietary lipid is 9 kcal/g (32.7 kJ/g), compared to 4 kcal/g (16.7 kJ/g) for carbohydrate and protein. These values were introduced by Atwater, and are based on the amount of energy released when these macronutrients are metabolically oxidized, allowing for incomplete intestinal absorption. Other correction factors are inappropriate for the dietary oils and fats commonly consumed the 9 factor for converting grams of dietary lipid to energy is more suitable and offers consistency. 

The Atwater procedure, in brief, was to adjust the heats of combustion (gross calories) of the fat, protein, and carbohydrate in a food to allow for the losses in digestion and metabolism found for human subjects, and to apply the adjusted caloric factors to the amounts of protein, fat, and carbohydrate in the food. The contents of protein and fat were determined by chemical analysis, and the percentage of carbohydrate was obtained by difference that is, it was taken as the remainder after the sum of the fat, protein, ash, and moisture had been deducted from 100. This so-called total carbohydrate, therefore, included fiber (an all-inclusive term for carbohydrates that are not digested by people) as well as any noncarbohydrate residue present... 

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