I am fairly certain you are just seeing the fiber that is concentrated in the feces. It has about the same heating value per unit mass as the original, but indigestible. Most all the sugars, starches and lighter fats are likely to be used for energy – converted to energy, CO2 and water with not much left over. Sugars (I read the nutrition label on a bag of sugar) have about 30 KCal for 8 grams. That is 30,000*4.184/8 = 15,690 Joules/gram. Fats (reading a nutrition label for vegetable oil) are about 120 KCal for 14 grams. That is 120,000*4.184/14 = 36.863 Joules/gram. If you only ate sugar for your 2000 KCal/day requirements, that is about 2000 KCal*(8 grams/30 KCal) = 533.3 grams sugar. About 1.18 pounds. To get 2000 from vegetable oil, if that is possible for the body to process, it would be 2000 KCal*(14 grams/120 KCal) = 233.3 grams oil. And I cannot remember the density of cooking oil to give you fluid measure. Check me, it has been another long day.
Rice is pretty much starch. That bag says 45 grams gives 160 calories of which “carbohydrate” is 36 grams and zero dietary fiber. The rest, I presume is water. I think there is a category of fiber in rice that is not “dietary” but still indigestible. Or maybe it depends on how much and how long you chew. If rice is only carbohydrate, and there were no feces, then the body would be converting 36 grams per 45 gram serving, and you would need 2000*(45/160) = 562.5 grams per day of rice (of which 9/45ths is “something not carbohydrate”).
I am happy to see a calorimeter built and used. But, if I were going to do it, I would use the chemical structure of the foods, measure them non-destructively with a variety of NMR or ESR/EPR spectroscopy, or IR or microwave spectroscopy – then do the same for the resulting feces, and keep track of water. It is not an easy problem, but worth doing. We still need that Star Trek gadget the “doctor” uses to scan the interior of the human body, any object or place and give a complete analysis and its implications. We could use it in the transporter to separate covid and other bad viruses. I think it could transport just the viruses out of the body. Too long ago to remember clearly. By the way, I did look. There ARE researchers trying to image and zap viruses – with electric and magnetic fields, lasers and ultrasound. Generally, if I can think of something, there are almost always 10,000 people and groups in the world who have been working on it for decades. It is when there are tens of millions working on something, all re-creating the same basic information, never getting off first base – that bothers me.
Thanks again. I just wish you would not only rely on your own skills, but produce videos where there is a team to help you get it right, exactly right – with resources, tools and links to more tools and materials for those who want to try things on their own.