I'm sure that this question has been asked before, but I've been unable to find the correct wording to give useful search results.
Nutritional information assumes the following energy values: 4kcal/g carbohydrates), 9kcal/g fat etc.
How much variation is there between individuals in the energy that is absorbed from food. I'm looking for quantitative data (e.g. with st. dev and error bars), such as good PubMed studies.