the atwater general factor for dietary carbohydrate is
Atwater system 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] This takes cognizance of the fact that first the gross energy values of the protein, fats and carbohydrates from different food sources are different, and second, that the apparent digestibility of the components of different foods is different.
Carbohydrate digestion Carbohydrates not digested in the small intestine, including resistant starch foods such as potato, bean, oat, wheat flour, and several monosaccharide oligosaccharides and starch, are digested in a variable when they reach the large intestine. The bacterial flora metabolize these compounds anaerobically in the absence of oxygen. This produces gases (hydrogen, carbon dioxide and methane) and short-chain fatty acids (acetate, propionate, butyrate). The gases are absorbed and excreted by breathing or through the anus (flatulence). Fatty acids are rapidly metabolized. Butyrate is used mainly by cells in the colon and acetate is absorbed into the blood and taken up by the liver, muscle and other tissue. Propionate is an important precursor of glucose in some animals, but not humans.