A question I've had that I never really looked into or found an answer to: How does calories in vs calories out work regarding the energy left in food that is

A question I've had that I never really looked into or found an answer to: How does calories in vs calories out work regarding the energy left in food that is not extracted (i.e. the caloric value of poop basically). Is digestion / energy extraction pretty consistent throughout the population or do the specifics of people's digestive systems play a role in how many calories are actually available to the body? Basically, would a constipated person's digestive tract pull more energy out of the food since it is in the intestines longer?