Q: Why doesn't the sum of the % calories from protein, fat, carbohydrate, and alcohol equal 100%?
Calorie content of individual foods in the NCC Food and Nutrient Database is based mostly on USDA values that have been calculated using the specific Atwater energy factors. These factors are specific to individual foods or groups of foods and take into account energy losses that occur during digestion and metabolism. Therefore, the factors used to determine the caloric content of a food may be somewhat different than the general Atwater factors (4 kcal/g protein, 4 kcal/g carbohydrate, 9 kcal/g fat, and 7 kcal/g alcohol).In calculating the percent of calorie intake from each of the energy nutrients in a daily diet, the NDS-R program used the general Atwater factors. The use of the two sets of calorie factors may cause the percent of calories per day from each of the energy nutrients to total more or less than 100%. The following example illustrates the calculation used for the percent of calories from each nutrient and provides examples of specific Atwater energy factors for some foods.
% kcal from a specific nutrient in a daily diet = kcal from the nutrient (A) x 100 / total kcal (B)
"A is calculated using the general Atwater factors:
"B" is calculated by summing the calories for all the foods in the daily intake. The calories for each food have been derived from the Atwater energy factors that are more specific by food type.
- 9 kcal x g of fat in daily intake
- 4 kcal x g of protein in daily intake
- 4 kcal x g of carbohydrate in daily intake
- 7 kcal x g of alcohol in daily intake
Q: Why doesn't the sum of the sugars, dietary fiber and starch equal the value for total carbohydrate in NDS-R?
The values for the three components of the carbohydrate are often taken from a variety of sources, mainly food analyses appearing in the scientific literature. Generally, for a single food entry, the fiber value is from one data source, the sugar values from another, and the starch value from a third. The total carbohydrate value is usually from the USDA database. Since the data were obtained from a variety of sources, and therefore a variety of food samples, the individual carbohydrate fractions do not necessarily equal the total carbohydrate.Even if the carbohydrate values are all taken from the same source, there may be a difference between the total carbohydrate and the sum of the fractions. This is because the total carbohydrate for 100 grams of food is derived by subtracting the amount of fat, protein, ash, and water from 100 grams. Therefore, the resulting total carbohydrate may include compounds other than sugars, dietary fiber, and starch.
Additionally, the NCC Food and Nutrient Database contains fields for sucrose, glucose, fructose, lactose, maltose, and galactose. There are many other sugars in foods that are not yet included in the database due to inadequate data.
Q: Why doesn't the sum of the fatty acids equal the value for total fat in NDS-R?
The total fat in a food includes phospholipids, sterols, and the glycerol portion of the triglyceride as well as the fatty acids. Therefore, the sum of the fatty acids will always be less than the value for total fat. The magnitude of the difference depends on the amount of phospholipids and sterols in the food.
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