The more unprocessed a food is, the more energy the body needs to digest it. A person could increase their energy expenditure quite substantially (say 10-25%) by switching from a diet of processed food to unprocessed (e.g. eating Kelloggs crappy cereal to eating boiled vegetables). Broccoli contains more calories than is used to digest it. Peanuts (and nuts in general) are interesting because the body cannot harvest all the energy that is contained within them. About 9% of the stated caloric value for peanuts isn't used, other nuts have different numbers. https://www.ncbi.nlm.nih.gov/pubmed/17912269 edit: A whopping 32% for almonds! https://www.ncbi.nlm.nih.gov/pubmed/22760558