Measuring human digestive efficiency vs. a flame

today on applied science we're going to talk about calories in food you know these nutrition labels are everywhere and in times past the way they figured out how many calories a piece of food had to take a sample of it and load it into a sealed chamber filled with pressurized oxygen and burned the food and see how much heat was released this is called bomb calorimetry in this case the term bomb is kind of an archaic use of it in this case we really don't want the chamber to blow up but it's still a sealed vessel with pressure inside which is why it's called a bomb my bomb calorimeter actually has a couple of cool features though it has glass windows so we can actually see the thing burning and i've got some high speed video and also a high speed pressure gauge connected to the chamber so we can have kind of a time synchronized pressure profile with the video going which i think is pretty original but anyway i mentioned this only is how they did this technique of measuring calories in food in times past by now we've basically characterized every possible ingredient and so all of the nutrition labels that you find now are basically assembled mathematically like the the manufacturer knows how much weight of each ingredient they used and they just add up all the stuff so we really don't use calorimetry anymore for for food labels but it is still used in metabolic studies which we'll get to as i was making this video a lot of interesting questions came up like for example you could load paper and mineral oil into this chamber and burn it and it would burn very well but you couldn't survive on paper and mineral oil and if you tried to you probably wish you weren't alive anymore but the question remains if you see a calorie label and it says 190 calories does that mean flammable calories or digestible calories or both basically does it include the whole thing and then it gets even more interesting for example in a recent video sally lepage said that 20 of all the calories that a ruminant consumes like a cow go into just feeding its gut microbiota so those 20 of calories aren't even available for the energy for for the animal to survive so then i started wondering well how efficient is the human gut right i mean like if you ate the calories there's all these ways that you can lose it like some calories are flammable but not digestible some of the calories are consumed by the two or three pounds of bacteria that are living in your body right now and some of the calories your body just misses i mean no system is 100 efficient so i i went on a journey to try to discover how efficient the human gut is and what i did was i ate nothing but soylent for an entire week so that i had a very consistent calorie intake and then i collected the output from this week experiment and we're going to do some calorimetry on the input and the output and try to come up with a bound for how efficient the human gut can be so a lot of interesting things to talk about in this video so let's get started let's talk about the design and build of this pressure chamber the most difficult thing about this design was finding out what pressure it really needed to contain go ahead try to find out what the maximum pressure in a food type calorimeter like this is on the internet i couldn't find anything so we had to estimate we know that when we put the food in here we charge it with oxygen up to maybe about 30 atmospheres and i think it's likely that we're not going to get above 300 atmospheres that would mean that the entire thing is filled with flame and the flame is 10 times higher in terms of absolute temperature so if we're at 300 kelvin now if the entire flame was 3000 kelvin then that would mean the temperature or the pressure is also up 10x so 300 atmospheres i think that's a fair upper bound for where this should be but you never know so starting off with small samples is a good idea and of course standing clear is also a good idea so how did i build this thing i started with schedule 160 steel pipe and this pipe has a working pressure of 6000 and a burst pressure of fifteen thousand so way you know of course we're drilling holes in the side so that kind of goes out the window but this is definitely meant to not be the failure point of the design i knew i wanted to have clear windows nice big clear windows on the front and the back so that we could look all the way through it and i settled on this idea of using the lathe to cut a ledge on the inside of the pipe and then putting an o-ring on that ledge and then putting a window on the o-ring like this and then the top part also has a nice smooth turned ledge on there that will come down this way and press down on the window and you can actually just tighten it by hand it doesn't even require tools to make a good seal initially i thought i would want to use solid thick glass windows and i found this is actually a solid chunk of glass that i got from mcmaster and it's not quite thick enough designing pressure windows in glass is kind of an iffy business already because glass fails one suddenly it cracks and flies apart which is not so good but two it also doesn't really have a strength of material like a ductile material would glass is a brittle material and it fails statistically so you have to settle on a probability like a one in a million chance that if you take it up to this pressure it's going to break and none of this is sounding that great so i actually decided instead to use a composite window so i have a relatively thin piece of glass facing the burn side of course you can't have plastic facing anything inside the chamber because there's going to be pressure and pressurized oxygen and super high temperature flames in there so absolutely nothing flammable can face the chamber side as we'll see this ended up coming back to bite me with these o-rings but anyway so it's glass-faced to get good uh flame resistance and then i backed it up with some acrylic sheets that i laminated together cut on the laser and then turned on the lathe and i did a little bit of a sloppy job kind of laminating them here but it gets the idea across so i like this and this is actually a similar construction to what i used for the high pressure supercritical co2 chamber that i built i really like this idea of using a relatively thin piece of glass for chemical resistance and backing it up with a ton of plastic so if we put the o-ring in and then put this in with the glass window down another benefit is that it's the plastic surface that is up here so when we screw this steel cap down it's going to put a fair bit of force around the edge here and if this edge were glass if there were like a tiny little you know particle of sand or something in there when you crank down on this there's a very good chance you could cause a stress concentration and crack the glass so it's nice to be able to work with a plastic window on this side another benefit is that if this does fail probably what's going to happen is the glass will crack first and allow the vessel to leak hopefully leak fast enough so that the pressure goes down before the plastic windows fail so it has kind of an inherent leak before burst property to it i mentioned that these o-rings came back to bite me yeah as it turns out i i started off using just buna and you know nitrile o-rings and these burn in pure oxygen of course like a lot of things do and i had a trouble with with these actually lighting on fire and not extinguishing so then it was late one night and i didn't want to wait around to buy silicone o-rings so if you ever need to make really fine very detailed thin silicone parts that are around what you can do is double stick tape a piece of flat silicone rubber to a piece on a lathe and then use an exacto blade in the tool holder and just slice out a really thin really high quality seal so putting this in and then the glass and then the top and that's it we're ready to go the pressure fill port is a bicycle gate of a schrader valve and this worked kind of okay one challenge is that we're filling this to about 30 atmospheres of oxygen so the amount of force that it takes to push the schrader valve open is pretty high you have to it takes it's about as high as you really want to go by hand it just takes too much force to force the valve open and i'm of course you know way overdoing it i i just you know i just got a cheap schrader valve thing and this thing is way over its rated pressure but these are all metal pieces and you know 30 atmospheres isn't too crazy there the copper tube is fine this is rated to take a lot of pressure and i also tried like a higher quality schrader valve and i i was having trouble finding ones that had a valve on both sides and i found some that you needed an on off valve but anyway this is the easiest quickest way for sure the pressure gauge actually came from digikey and this one is neat because it has a an analog output that's very high frequency it claims like a one millisecond response time which is neat and this thing goes all the way up to 10 000 psi so we're not going to have any troubles with the pressure gauge and then finally the electrical pass-throughs so we need a way to ignite what's inside there and we do this by using a thin piece of nichrome ignition wire and we need to get you know a handful of amps through the outside here and there aren't really any commercial off-the-shelf pass-throughs that would work super well in this case what i need is to have a pretty stout screw terminal inside there i can't really use out there's not enough room for alligator clips or terminal blocks or anything like that so what i came up with is a use a piece of steel welding rod and braze on the little terminal block the little screw terminal at the end there it's just a piece of threaded standoff and then also braze on a collar and then put this whole thing together into a barbed tube fitting using an insulator so there's a piece of plastic as a centering and an insulating element between the welding rod and the pipe fitting and then i filled it up with my favorite hysol 1c epoxy and the little collar that i braised on there provided like a positive lock so if there's a huge amount of pressure applied to this side the force will go through that collar through the epoxy and into the body of the thing and it can't fail catastrophically unless it rips the metal apart so even if the epoxy fails the little the metal piece won't come flying out of here unless it's able to rip that braised collar off which i don't think it's going to all right so let's burn something here i'm going to use this 32 gauge nichrome wire as the ignition wire and what we're going to do is cut a little bit off and i'm going to form a loop like this and put it down into the chamber so that the loop is low because i'm going to put the piece of food we're going to burn on the bottom here so i'm just going to go in there and screw this use the screw terminals to attach this little piece of nichrome next what we need to do is attach something that's flammable directly to the ignition wire like this pure cotton string and this is actually a huge amount so i'm actually just going to take one of the little strands from this string and the idea here is that we need a um a slightly bigger match to get our piece of food going if the thing that we're burning is not super flammable by itself then we need something that's already got a pretty good flame going from that ignition wire so what will happen is we'll tie this piece of cotton string to the ignition wire and then put the piece of food near that and then the flame from the cotton will get the piece of food going as it happens my oxygen cylinder in my oxy acetylene welding set is a little low right now in fact it's pretty much perfect right at about 30 atmospheres so i took the regulator off entirely and just connected that copper tube right to the output because it's pretty much the pressure that we need okay so we're going to burn a goldfish cracker which weighs about half a gram which is i think a good weight for this size chamber and i'm going to put this guy here near the front so we can get a good look at it okay we got the kronos on we got the chamber sealed it's time to add some oxygen and let's see if we can get this without disturbing the whole thing as you can see on the oscilloscope here we've got some pressure in there and you can read it off here it's at about 480 psi so there's our 30 something atmospheres or 30 atmospheres about and let's see we're almost ready for ignition i was having a ton of problems with the force of the oxygen blowing into the chamber blowing a little cracker around in there so what i ended up doing is just using a a tiny bit of uv cure adhesive and i just glued the cracker to that steel cup there so that it'll hold it in place let's try that okay chronos running face shield down ignition on ah so it looks like there might be some o-ring carnage here so let's uh take a look at what we've got try to vent this slowly by the way the chamber is warm it's it's not hot or anything but it's definitely warmer than it is out in the garage today which is pretty cold yeah so let's take a look at that you can see my idea of using a silicone o-ring because it wouldn't burn uh didn't work out quite perfectly everything burns in pure oxygen while a lot of things burn in pure oxygen and what's interesting here is that um the part that was exposed to the flame burned but the part that was pinched tightly between the glass and the metal uh was able to stay okay i mean the thing still kept a seal and everything it was able to sink heat away fast enough where it couldn't catch fire but i guess there was a part of the o-ring that was exposed enough to the flame front where it did catch fire and left quite a bit of quite a bit of ash and everything in here so this will of course affect our readings by the way the the cracker appears to be completely gone there's you know a little bit of ash and stuff in there a lot of it's from the o-ring but that that goldfish cracker is is gone so we also verified that the peak pressure only got up to about 1600 psi in that experiment and it took a whole three or four seconds to get up there so when i first started this i thought you know bomb calorimeter maybe it goes bang or something but no it actually burns relatively slowly i mean if you have a solid piece of food in there it does take a while for the flame front to move through that solid piece of material so yeah it burns quickly but but not instantly i probably wouldn't recommend maybe like atomizing gasoline or anything inside there that sounds like it might burn a little too fast in pressurized pure oxygen so this whole setup is really meant for doing food samples things that burn but are not super super highly flammable i wouldn't put any sort of liquid fuel in there okay so let's take some measurements with this thing let's find out really answer that age-old question how many calories are in a turd so what i'm going to do is remove the pressure gauge and put a plug in here so that i can dip it into that tank of water and then we'll be able to measure the temperature change that results from the heat that's released from what we're burning in here and i'm going to have to orient it vertically so i'm kind of worried about the o-ring again being in the more of the path of the flames and so i'll see if i can maybe come up with like a teflon seal or something in this configuration in order to make a numerical measurement with this setup we need to know how much the temperature is going to change for a given heat input so if we burn something inside this calorimeter there has to be some way to translate the temperature change that we're going to measure into a heat output so we could do this just by trying to add up all the different materials we could say well we've got you know a kilo of water we've got a half a kilo of steel there's you know a few grams for the thermometer itself there's another 20 30 grams for the stir but that is extremely unreliable and difficult to do so a better way to calibrate this system is to just use a known quantity of fuel and benzoic acid is always the one they use for reasons that i'll tell you in a second and put a certain you know carefully measured quantity of that in there burn that and then just check what the temperature changes and say okay well it's a black box we don't know what all the materials are but we do know that it changes this much temperature when we burn this much known fuel and the reason benzoic acid is always picked is because it's a solid at room temperature it can be easily crystallized it burns slow but not too slow it's non-toxic it's easy to get it's cheap you really could use a lot of different things but this just has physical properties that make it you know a nice choice okay so we've got our benzoic acid measured out into this metal crucible here and i added a little mesh tray inside there so we can put use this thing vertically i've got the pressure gauge removed and replaced with a plug and so i'm going to do is put that crucible down in there and then drape the ignition wire and the cotton wire down into the crucible and i decided to just go with the same silicone seal it's still going to be just fine for the top here well it might burn up actually but we will try something but i did chicken out on the window instead of having the glass up here i was worried that the flames are going to roll up and hit right on the glass there so instead i turned an aluminum window and this will go in here and screw this on top and the fact that we're changing materials doesn't matter yet because we haven't calibrated anything so this will be the first run with calibration okay some of you are probably realizing uh yeah it doesn't work to just have full pressure behind the straighter valve because what ends up happening is it just blows the thing completely to you know disarray in there and so now all the powders in the bottom so i'm going to clean all this out and then i will shut off the oxygen at the tank connect the valve up and open the valve slowly to try to you know not disturb the powder in there okay back in a sec okay so we're ready to put all this together here we've got our sealed chamber full of pressurized oxygen and the half gram about of benzoic acid and what i'm going to do is put it inside this tall paint can inside the styrofoam and inside here we've got a platinum 100 very sensitive thermometer well the thermometer itself is not sensitive but the thing that's reading it certainly is you ever seen that many digits behind a temperature reading very very accurate and very very sensitive to change and so just putting my hand in there is just air in there right now will actually cause the graft to change a little bit so what i'm going to do is put this inside and then tip the camera over so you can see the setup looking down into that paint can you can see we've got our calorimeter set up there and the stirrer going we're going to add some water to it and the amount of water again is not critical as long as it's controlled and not changed between the calibration run and the actual sample run so let's pour in enough water to cover that thing up okay so now we can run the whole experiment from here when the temperature has stabilized to whatever degree of satisfaction that we want that the temperature is in fact stable we'll hit the ignition there and then we'll see the temperature change and again we can wait until we decide it's stable there's also some other interesting mathematical ways of determining what the total change is based on you know the slope and the change and all this stuff but let's uh wait for this to stabilize and then we'll collect a run i just cleared the buffer here and the graph auto scales and so it looks like the thing is still changing a lot but we're talking about you know thousandths of a degree c so let's just go for it i'm gonna wait face shield on okay let's hit the ignition of course you don't really hear anything because we noticed it didn't even make that much noise even in the even with the glass windows on but here we got a big temperature change going on now okay so the o-ring looks good uh it's still there i mean it's that's a good sign and the benzoic acid is gone and there's this red kind of exhaust material there but otherwise i think that's a good burn so i think that was a good calibration okay so now i'm going to measure out about half a gram of the soylent into our little metal crucible and again the exact amount doesn't matter as long as it's you know kind of close to half a gram just so we know we're not going to burn too much or too little fuel but as long as you record the number the exact amount is not that important but i do have to get it in the crucible and not onto the platter of the scale there okay here it goes soylent wait face shield okay so i went [Music] so now we come to the finale input on the left output on the right this is kind of life in a nutshell here is turning brown powder into other brown powder you know dust to dust but anyway the scientific name for what's on the right would be lyfolyzed fecal matter but i'm just going to say yeah it's a freeze-dried ground-up turd and i made that in my freeze dryer it took about 10 hours and the process is basically making astronaut ice cream it's it's exactly the same and when we're done uh by the way this thing has almost no smell it doesn't smell like anything and that's because all the volatiles including the water and everything else that was in there ended up in the trap in the freeze dryer and uh believe you me if anything should be called you know uh it's it's this stuff because this is like concentrated distilled essence of poop so the smell is gone along with the water and that's actually interesting for our experiments too because some of those volatiles might have been slightly flammable like would contribute calories but again this is not a publication quality thing we're just kind of screwing around here so let's uh weigh out about a half a gram of that powder and see how much see how much fuel is in there okay bombs away this is interesting after that last sample there's quite a bit of residue in there and i haven't seen that with anything else we've burned that could be minerals or something that are more concentrated in that last sample don't know but that's an unusual observation so i've crunched the numbers and have some surprising results but first if you haven't heard of soylent what is this stuff it's basically just ensure you know that milkshake for retired folks but it's in dry powder form and it's marketed towards younger people and it has this ridiculous name it's not soylent green it's soylent brown but you know i like this stuff there's nothing wrong with it the only reason i chose this for my experiment is because it's dry and it's very consistent like i can eat this all day every day and kind of know exactly i'm getting the same macronutrient breakdown so for the for the test here i just needed to know that i wasn't going to have something inconsistent going on so after eating this for a week i would be sure that my output was you know aligned to whatever the input was but as we'll see this this gets a lot more complicated by the way i would recommend trying this crazy diet if you just want something interesting to do eating this only this for a week i had black coffee water and soylent and that was it for seven days and it was quite a um quite an interesting experience like i say i would recommend it at the end of the week food tastes so good that it's worth it just to introduce a little bit more dynamics into your life it's just it's just kind of an interesting thing to do but anyway let's take a look at the numbers because this is actually pretty interesting as well so first the calibration i did another run where i burned just the cotton thread in the ignition wire and the temperature of the water bath changed by a very small amount 0.0176 degrees so i'll subtract this from all the other ones later on and you know that's how i'm going to get rid of the cotton and the ignition wire and assume it was the same throughout okay so then we did the run with the benzoic acid in there about a half gram of benzoic acid and we're using this value from the internet 26 000 joules per gram as the heat of combustion for benzoic acid so this is what we're using to calibrate the entire system and you know we run through the numbers and multiply it by the weight and we get this calorimeter constant of 16 642 joules per degree so if the water bath changes by one degree c then we know that 16 642 joules have been released easy enough as long as we don't change anything same amount of water same amount of steel and the thermometer and everything else are the same then this constant will stay correct okay so then we did the soylent and found something interesting if we go through the numbers we know how much heat was released because we know the temperature change and we know the constant and then we divide by the amount of mass of soylent that we put in there we get a value of 20 368 joules per gram for the soylent now if we go to the label a serving is 60 grams and has 270 calories remember a dietary calorie is actually a thousand calorie calories so 270 000 divided by 60 and then multiply by 4.184 to get joules would give us 18 828 joules per gram so it's a little bit off but something very interesting happens here if we subtract out the dietary fiber from the from the mass then it starts working out almost exactly correct so i can't tell i can't tell it says dietary fiber and soluble fiber and it's kind of under the ledger so i don't know if the four includes the two or if they're in addition so i tried it both ways and if we include both of them then the the real mass is only 54 grams and if we divide this all out we get a number of 20 920 which is pretty darn close to our measured value and if we you know assume that the fiber is the other way around we end up with 20 173 so now we're getting really close to our measured value so this is great i mean it's always nice when you you know come up with a crazy setup like this and it's actually coming in within you know what five ten percent or something that's that's pretty nice so i think the system is working and the food leaf and the food label seems accurate so now here's the surprising bit there's a lot of calories in fecal matter right so i this the the fecal matter actually ended up with 16 thousand joules per gram and remember the soylent was only twenty thousand so is that possible the output actually has like what seventy five percent or more the calories per gram than the sweat than the input does so this is a surprise and i'm glad it was so far off because if i did all this and it ended up feeling like there was 20 remaining then i'd say okay well maybe the human body is 80 percent efficient right you eat the calories and 20 of them come out because your body wasn't able to utilize them but the fact that we're so far off here is good because now we can tell that we're missing a piece of information so clearly what's happening here is there's flammable calories in the fecal matter but they aren't usable for dietary purposes anymore at least not by a normal mammal digestive system it's composed of the fiber so we just realized that this stuff doesn't count towards the calorie budget this is already interesting so that when you see the number of calories on a label like this it does not include the flammable calories that are in the dietary fiber i mean that makes sense but that's that's kind of an interesting thing to note and if you're using a oxygen bomb calorimeter like we're doing then you have to take that into account because if you burn it you burn everything and that doesn't represent what you would get dietarily from it you know so you know this is kind of uncovering more questions than answers which is okay and then i think a really good follow-up is going to be how to get these macronutrient breakdowns out of it so how do we actually know how much fat uh protein and carbohydrates are in a sample because then we could go through this all again with all the samples and try to figure out what really happened and it's really the macronutrients that we care about so i think that's what's going to be for next time or or the time after or something but i find all this dietary science stuff pretty interesting because there's such a lack of it on the internet if you want to look for dietary science you know where you go there's these livestock information sources farmers have been very very carefully characterizing exactly how many calories to feed their livestock to maximize you know their profits basically so that's been studied to the nth degree but in humans it's just not studied as well partially because maybe it's hard to convince people to eat soylent every day all day for a week or something that i i don't know it does seem like there's a lot to be learned here and if we did come up with an actual efficiency number for the human gut maybe that explains why some people can eat a lot more calories than others and it seems like they don't you know gain as much weight from it or something but a lot of interesting stuff to look at in here so i'm looking forward to coming back to this topic sometime soon all right well i hope you found that interesting see you next time bye you

Channel: Applied Science

Views: 181,621

Rating: 4.9690323 out of 5

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Id: 9wZ0wTqJIxY

Length: 32min 31sec (1951 seconds)

Published: Mon Feb 22 2021

Reddit Comments

[u/Roofofcar]

Applied Science is one of the very best channels on YouTube, and I encourage everyone to watch at least a few of his videos.

Ben is brilliant.

[u/NoCalorieWater]

RemindMe! 5 hours