Measuring human digestive efficiency vs. a flame

"200 Calories" on a nutrition label doesn't describe the total flammable caloric content. I explore the differences between digestible and flammable calories using a homemade calorimeter with glass windows.

Pressure sensor:

Schedule 160 pipe on McMaster:

32 ga nichrome wire:

Power supply (used for ignition wire):

Keithley 6.5 digit multimeter:

Tek MSO 4 series oscilloscope:

Soylent:

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[pulseworks]

He has parmesan goldfish crackers, not the standard, I like the idea that he's a goldfish cracker connoisseur

[sauercrowder]

Thanks, this video convinced me. Finally going to replace my digestive tract with a flame

[qfytidw]

"I did a sloppy job doing the lamination" he says holding something that looks optically perfect.

[aeroscience]

Really interesting video! I think it’s important to note though that 1g of soylent doesn’t go to 1g of poop. A lot of the mass is gonna be breathed out at co2. So even though the energy density of the poop may be almost as large as the food, that cannot be translated into an efficiency directly.

[wojciechmilczarek]

Really cool video! One theory I have why the efficiency is so low is if the digestive system is taking calories out of the food, it's also reducing it's mass. So in other words, the fecal matter is more concentrated than the input was. So for example, let's say you eat 100g and your body takes out 30%, the mass of the poop you'd have to burn would be 70g and not 100g. And in that case, with some foods that have a lot of flammable but not digestible calories, if the same mass is burned, I think it might be possible to have the poo contain more calories than the food, because it becomes more concentrated.

[Afrotechmods]

This is one time I don't mind our Patreon dollars going to waste 😎

[HuygensOptics]

A week of Soylent... the sacrifices you make for science are beyond incredible.

[Nighthawkinlight]

Boy does this ever bring me back to what was probably my first science class. My school book was entirely unsatisfying in telling me how this process could be done in my basement. I really like your high pressure window making method. I'll have to file that one away.

Super interesting result also.

[BjornV]

15:05 Try a U shape groove (not too deep) for holding the silicon seal in place.
Ideal is when the glass is pressed firmly down and barely touching the metal holder, that way the gap of exposed silicon seal to the burning environment is almost zero and the seal will last much longer.
This technique is used in small (50a70cc) 2 stroke watercooled bike engines (pocketbike etc...)

[kmacdough]

"The process is basically making astronaut ice cream. It's exactly the same." I no longer like astronaut ice cream.

[thethoughtemporium]

The "eua du toilet" bit had me laughing pretty hard.
EDIT: damn it I wrote out a whole thing on how to improve this and it got deleted. One sec lemme re write
EDIT 2 - electric poop-a-loo:

Ok so some things that are important to keep in mine. First poop is about 30% bacteria, 30% fiber, 15-20% fats/protein/cell debris, and the rest insoluble minerals. The minerals explain the residue you saw. But the important thing is that poop is like a filter, its the concentrated waste resulting from lots of eating. Also the cell debris is important. Your body uses the calories and those get turned into biomass. But then the cells die and get yeeted out with the rest of it, so some of the input calories end up in the output as "spent" calories. So you need to calibrate the actual mass in vs mass out to account for all this.

To do that there's some things you'd need to do. The easiest, though also the least pleasant would be to take a ton of laxatives to clear yourself totally out, then fast for 1 day. After that eat 1 days food, then fast again for another day That would suck, no question about it. But that way you know the only thing you collect would be the result of a single day of eating. A less painful way to do that would be to add some sort of insoluble non toxic fluorescent marker to the soylent and then when you eventually pass it, only collect the part of the sample that's glowing. Then weigh it and compare that to the mass of input soylent during that meal. Then perform the test on that sample. Should give a much cleaner result.

Frankly this is way more playing with shit than I'd be comofrotable with but, would clean the data up a lot and resolve some of the myster

[nvg]

Thank you for doing this! This has bugged me ever since we had to do calorimetry in high school science. I asked about the difference between flammable caloric content and what your body can use, and basically got told to shut up and burn my peanut so we could get on with it.

[alfredoespinozapelayo]

I love how it could´ve been a clickbait thumbnail but was not, thank you

[myronv]

Been watching your channel for years and never commented. Just wanted to say thank you. The amount of time you spend on a 30min video must be insane. And its highly appreciated. Thank you.

[arunpcet]

You are a gem. Your Patience and dedication towards scientific experiments is admirable. Love you. Keep going 👍👍

[enquiryplay]

"How many calories are in a turd?" This is the type of question that keeps me up at night.

[drdca]

So you measured the flammable-calories per gram of each, but, if evaluating efficiency, wouldn't you have to also factor in how the amount that went in corresponds to the amount that went out?

[Timestamp_Guy]

The calories per gram is probably much less relevant than total grams input vs total grams output. You should be excreting a significant amount of mass as H2O and CO2, so for every 100 grams you consume, you likely only get half of that out in waste (totally made that fraction up. Anything between 30% and 80% seems plausible). Also, ion content (Na, K, some Mg and Ca as well) will be eliminated mostly through urine, and should be relatively low amounts in stool. Chemically, you would still expect stool to be largely the same as the food input in terms of carbon, hydrogen, nitrogen content, and comparable ratios of the assorted chemical bonds common to most organic compounds. Really not at all surprising that it's so close.

[KomradZX]

I TRUELY LOVE YOUR VIDEOS!!! Speaking as a person who uses a wheelchair and has a severe physical disability that keeps me from being able to use things like lathes and many other things I see you using all the time, your amazing videos keep me from going crazy thinking of all the things I wish I could do but cannot with my disability. The world really needs more people like you in it!!!

[brandonberchtold]

Really cool video! Though I was under the impression that a large amount of the carbon we excrete is via respiration (2.3 lbs per day if I recall correctly). So factoring that in would probably be pretty important.