I teach consumers about how to calculate calories from a Nutrition Facts using the 4-4-9 method. We get 150 calories in a serving of cheese sauce, but the label shows 140. How can I explain the difference?
The difference is likely due to rounding. Per FDA's rounding rules, a derived value of 144 would be reported as 140 while a derived value of 145 would be reported as 150. Also consider that the Nutrition Facts displays rounded values for carbohydrate, protein and fat. As an example, a label value of 10g fat per serving could be based on an unrounded value ranging anywhere from 9.50g to 10.49g, which would then contribute anywhere between 86 and 94 calories.
It is also possible to get different calorie values depending upon which of five allowable methods the manufacturer used.
While the 4-4-9 method is allowable and generally used with laboratory analysis, it is the least accurate of the allowable methods because it uses "average" factors. The 4-4-9 method assumes that carbohydrate and protein each contribute 4 calories per gram and fat contributes 9 calories per gram. These "average" factors sometimes overstate calories because specific ingredients often contain fewer calories than the average factor would indicate. For example, dextrose (a carbohydrate) contains 3.4 calories per gram, not 4 calories per gram as the 4-4-9 method would indicate.
The five methods FDA allows for determining calories are:
(1) a straight 4-4-9 calculation
(2) an adjusted 4-4-9 calculation where all fibers are subtracted from the carbohydrate total before multiplying by 4, then polydextrose is multiplied by 1 calorie/gram and added back in, other soluble fibers are multiplied by 2 calories/gram and also added back in; insoluble fibers are not counted as they do not contribute calories
(3) specific Atwater factors
(4) other specific food factors approved by FDA
(5) bomb calorimetry