When you eat 2000 calories in a day, do you absorb all 2000?
What if you always ate 2000 carlories a day, but then one day you ate 10000? or once a month ate 10000 (pig out day)? Would the body absorb all 10000? only 2000? or somewhere in between?
A corollary is, would your excrement have the missing caloric value?
The amount you take in is not tied to the amount you absorb.
You might enjoy reading The Hackers Diet. It is an engineering approach to dieting, very heavy on caloric intake, how much you use and the difference. It will clarify a lot of this.
Or, a short answer, based on what I have learned in the past 6 months about nutrition:
Your body burns an average (very broad average) of 10 calories per pound per day just from normal life activities (not including added exercise). If you weigh 200 pounds and consume 2000 calories, you should come out about even and store none of it. If you consume 10,000 calories in a day, you would presumably store about 8,000 of them. It is possible to even out over time if you have an occasional pig-out day, by added exercise or reduced calorie intake on a lot of other days.
It takes 3500 extra (i.e. not burned off, but stored) calories to produce one pound of stored fat to your body.
Calories are not the same thing as food, so the question as stands can’t be answered.
Food is digested by the body through a series of complex processes that start in the mouth and stomach, but mostly take place in the small intestine, which gets flooded by half a million enzymes when food enters it through the pyloric valve.
To absorb food, the proteins have to be broken down into amino acids, the carbohydrates into simple sugars, and the fats into fatty acids. That’s the job of the enzymes. (Most of what happens earlier is physical breakdown into smaller pieces, not a chemical breakdown.)
Those 10,000 calories in the OP would all be broken down and absorbed if your body had enough time to process them. Food moves very slowly through the intestines, taking hours to get to the end of the small intestine, to give your system a better chance to do all the necessary processing. If the timing is right, then all 10,000 calories in the food will be absorbed into the body.
If the timing is off, then the food leaves the body unprocessed. There are two routes: up, meaning vomiting, and down, meaning diarrhea. Vomited food obviously is not chemically broken down and absorbed. That’s actually the more likely route if you devour too much food in too little time.
If you can keep the food down but overwhelm the system, then undigested food will leave the small intestine and move on to the large intestine, the colon. Fiber, which is normally indigestible, does this as a matter of course. Too much fiber in the diet can lead to gas and diarrhea because it is hydrophilic: it retains water rather than allowing the water to be absorbed as it normally is. Too much undigested food will likely have the same effect.
What percent of the calories will this be? Again, this is unanswerable, because it depends completely on what foods you eat over how long a time and what the state of your intestines are.
But the body is marvelously efficient. If you give it time to digest food, it will do so to a very high percentage of the original calories. Otherwise, the food and its caloric content is rejected, one way or another.
I don’t understand what EM is trying to say enough to refute it, but to make it simple, no you won’t absorb all 2000 calories.
The caloric value assumes that every single chemical bond in the item is broken leaving only elemental dust, heat, and gas. This does not happen in your body. You know this if you have ever looked at poo and seen corn hulls.
Excrement has a caloric value, but will probably not be of much use to your body since it already didn’t intake it once. Again, you know this since desert nomads burn camel poo.
So, if your real question is “I ate 10,000 calories on Thanksgiving, do I need to cut 8,000 calories out of my diet this week?” the answer is no, you don’t need to cut all 8000 to break even.
If your real question if “I wanna eat 5,000 calories a day, but I know my body only uses 2,000 calories a day, can I use poo calories to balance the equation?” the answer, again, is no. 2000 calories isn’t derived by direct imperial science (like calculating calorie conversion to ATP to cell motility, metabolism, etc) but by observation (like people who eat 1200 calories lose weight and people who eat 3000 gain weight)