The whole point of Spector's work is not to invalidate this as a basic principle, but it is clear that (a) different foods of the same calories as measured release different amounts of calories when eaten and (b) different people respond differently to the same foods. Calories are measured by burning dry food and that's not how we gain calories from food, otherwise we could eat coal. You might need to be more than five to understand this, but it's not hard.