When you read a food packet you get a breakdown of what is in the food. There is a line giving calories for 100 grams of the packet or the equivalent.
I may be wrong but I think laboratories get this figure with a bomb calorimeter. Basically they burn the food and measure the heat put out.
If this is how it is done the lab burns any roughage in a way that the body cannot. Therefore the body sees things like muesli as less energy dense than the packet shows.
Any views?

It's been my experience that for the basic nutritional information label, the lab experimentally determines the moisture content, fatty acids, cholesterol, simple sugars, complex carbohydrates, fiber, protein, and basic vitamins values of the sample. Caloric content is not determined directly, but is calculated with basic addition using the 9-4-4 method for digestible fat,carbs, and protein.

Without knowing if the assays to get a nutritional label are standardized, I can't say what the calorie value would mean on any label other than the ones I was looking to use. My guess would be, if the label lists the fiber, the lab went through the trouble to measure it in order to provide a more accurate calorie count in the context of human nutrition.

They wouldn't be able to give values for carbohydrates, proteins, fats and fiber if all they did was bomb calorimetry. Total calories are calculated after having determined the amounts of carbohydrate, fat and protein etc in a set of, presumably, randomly obtained samples.

thanks for that,I am reassured