From Mouth to Muscle: How Your Body Absorbs Protein

one of my favorite things to show students is how we get this protein all the way to something like this a skeletal muscle that we may want to strengthen and enlarge and I actually don't think we give our digestive system enough credit for all the steps that are necessary to break down the protein absorb it into the bloodstream and get it to the actual muscle So today we're going to go on a little journey through the digestive tract to show what it really takes to get that protein from mouth to muscle which will then help

us to understand if it even matters what type of protein we ingest do we have any control of where that protein actually goes in our body and even get into some recommendations on when to eat or ingest that protein as well as the overall amount so let's do this as we start our story with protein I want you to keep a couple of things in mind two words actually digestion versus absorption with digestion we are talking about the breaking down of the food into smaller molecules then those smaller molecules can later be absorbed and with

absorption we're talking about those smaller molecules actually being absorbed into the bloodstream and what we're going to see is that certain segments of the digestive tract are primarily going to be dealing with digestion and other segments are primarily going to be dealing with absorption this concept doesn't completely exist in a vacuum for example digestion begins here in the oral cavity that you can see I'm tracing with the probe this is done mechanically chemically with chewing and even chemically with enzymes that are released from salivary glands but there is some ability to absorb a few smaller

simpler substances in the mouth such as sublingual medications sublingual glucose but again digestion is primarily going to be taking place here in the oral cavity or the mouth through chewing in saliva now in the case of say like a protein shake there's not much chewing going on there because we usually just drink that down however if you are eating something with protein in it like chicken or steak or some other food you're obviously going to be doing more chewing or mechanical digestion in that case but in either example when we take that food from the

oral cavity and swallow it down it will move down the food tube or the esophagus and into the stomach now this is a really cool dissection that we've removed from another body but the stomach is actually in the left upper quadrant which you can see in this other cadav dissection but we've removed it over here so you can see it a little bit better and what's really cool with comparing this stomach stomach we haven't cut into but if I show you this one look how cool this stomach dissection is I can actually turn it inside

out to show you what the inside lining looks like and this inside lining is very cool looking obviously but it's called the tuna mucosa and you can see these awesome folds called gastric rugie which allows the stomach to stretch when you fill it up with a whole bunch of food or protein in today's story but also this tuna mucosa has various cells that secrete mucus to protect the stomach other cells called parietal cells will secrete hydrochloric acid and the hydrochloric acid will kill pathogens and also denature proteins which is part of this process of digesting

that protein we just ingested that hydrochloric acid also converts something called pepsinogen into pepsin this is important because other cells in the tunuk mucosa of the stomach called Chief cells secrete the pepsinogen and once the pepsinogen comes in contact with the hydrochloric acid it gets converted into its active form pepsin and pepsin is an enzyme that also breaks down the proteins that we just ingested So based on this the hydrochloric acid and the pepsin denaturing and breaking down the proteins we can see that the stomach is still also primarily going to be participating in digestion

chemically through the use of acid and enzymes and mechanically digesting by churning and mixing that food all together and once that food gets mixed together with the stomach juices we call it Kim now again like the mouth some things can be absorbed ABS through the stomach such as certain medications even a little alcohol and fluids but primarily we're dealing with digestion here and the protein still needs to move further Downstream before it can be absorbed and at the end of the stomach there's this really important sphincter that you can see I'm pinching here you can

see it's a little bit more thick in the wall of the stomach here and this is called the pyloric sphincter the pyloric sphincter will regulate how much food can move out of the stomach and into the small intestine and how long it takes for the food to move from the stomach and and into the small intestine through this pyloric sphincter is dependent on the amount and type of food that you've ingested in general really fatty foods will take longer to break down in the stomach and therefore take longer to pass into the small intestine whereas

a very simple protein powder like o protein especially if that's all that you ingested or maybe even if you ingested it with a few simple carbohydrates that can all be mixed together and go through this initial process of digestion fairly quickly and we'll move from the stomach and into that small intestine in a shorter amount of time now once we're in the small intestine we're going to find that it's broken down into three different segments the duodenum dunum and the ilium the first segment the duodenum actually means 12 because it's about the width of 12

fingers now most names in anatomy make a lot of sense but this is one of those names where I just kind of wonder how the anatomist of old came up with it I just imagine this group of anatomists circled around a Cav trying to decide what to name this part of the small intestine and one of those anatomists just randomly walks up and is like hm 4 8 12 duodenum it's a great name I know I digress a little bit here but the important thing for us to note is that the duodenum connects with the

common bile duct and this common bile duct receives bile from the liver and the gallbladder as well as secretions from the pancreas which includes bicarbonate as well as pancreatic enzymes the bile from the liver and the gallbladder is used to break down fats which we aren't quite as focused on on in this story because we're mostly focusing on protein and the bicarbonate from the pancreas is also a little bit of an FYI as this helps to neutralize the acidic mixtures that are coming from the stomach but the pancreas releases several enzymes that will further break

down and digest proteins so in the first part of the small intestine this duodenum we are still breaking down and digesting the protein but after these final steps of digestion in the duodenum we can now finally start to absorb how however we do need to take a second to talk about something very important when it comes to the absorption of digested proteins and getting those to our muscles and this is the important distinction between proteins peptides and amino acids now if you've spent much time thinking about protein in building muscle you may have also thought

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so back to this important distinction between proteins peptides and amino acids amino acids are the building blocks you Bond or string together some amino acids and you create a peptide you could create a dipeptide which is two amino acids strung together or a tripeptide which would be three amino acids strung together all the way up to many amino acids strung together creating large peptides called polypeptides and then these polypeptides get folded and oriented in a specific shape and you can build a full protein so pretty much you go from amino acid to peptide to protein

but why would I take the time to explain this well based on what we've talked about so far you may have already got the idea that you cannot absorb a full protein or even a polypeptide it first must be broken down into smaller peptides and amino acids before it can even come close to getting absorbed through the small intestine and eventually into the bloodstream but what we can absorb are very small peptides like dipeptides and tripeptides and obviously in individual amino acids and this is going to be very important in just a second when we

talk about if the type of protein you eat even matters and if you have any control on where these proteins can be distributed throughout your body but let me actually finish up getting these small peptides and amino acids absorbed the small intestine is the longest part of the digestive tract and can be over 20 ft long and with this particular dissection we're only showing a portion of that small intestine but the reason why it's so long is because it is the main area of absorption and longer means we have more time and length to absorb

nutrients not only does a small intestine have length but it also has increased surface area due to the tunic mucosa having folds called circular folds and you can see these folds that I'm tracing with the probe right here now if we were to zoom in to these circular folds we would also see that on top of the folds they would have microvilli which would further increase the surface area for absorption and I've got to show you another structure on another Cav dissection that is super cool in relates to absorption as I'm holding up this portion

of the small intestin you can see this yellowy tissue called mesentary but if you look closely you can see a ton of blood vessels in there that are going to be absorbing all these nutrients and in this case those nutrients are the amino acids that we've been talking about and here's how this would work the amino acids and the dipeptides and tripeptides will move from the Lumen which is just the hollow space inside the intestine and they will move from this Lumen and into the cells that are a part of the tunic mucosa and here's

something that's interesting any dipeptides or tripeptides that are now in these mucosal cells will get broken down further into amino acids so now all the protein that we initially ingested has been broken down into amino acids and some of those amino acids won't even leave the mucosal cells because those mucosal cells will use some of those amino acids to construct cellular proteins that they may need for themselves but the majority of the amino acids that are not incorporated into those cellular proteins will then move from the mucosal cells and into the bloodstream and then go

directly to the liver the liver has a huge role in monitoring the supply of amino acids and dictating which amino acids will be transported to the tissues and after a protein containing meal over 50% of the amino acids absorbed will be found in and utilized by the liver and then the rest will be released as free amino acids into the systemic circulation and become available for the body tissues and some of those body tissues are the the skeletal muscles that you may have just worked out so now that we know how this all works does

the protein we ingest even matter and do we have any control over where the ingested protein ends up within our body well let's answer that second question first do we have any control where the ingested protein ends up and the answer is no not so much let's say we ingest some whey protein or maybe even a collagen supplement as collagen is a protein we know that we can't absorb either one of those until it gets broken down or digested into the amino acids and it's not like before we ingest that whey or that collagen that

we can have this moment of silence and internally tell our body hey the amino acids that make up this way are earmarked for my biceps that's the only place they can go or the amino acids that make up this collagen are earmarked for the skin of my face that's the only place they can go no our body doesn't care where we want those amino acids to go we even saw that when amino acids are absorbed into the mucosal cells of the small intestine some of those get taken and utilized by those cells and then all

the rest first go to the liver and then the liver utilizes over 50% of those amino acids to create plasma proteins and other proteins that are important to the functioning of the human body and may even use some of those for energy and then the rest can be utilized for the other tissues like muscle skin tendons ligaments Etc so you can see we don't really have much of a say of whatever protein we ingest it's going to get distributed where the body wants it so what this means is that the most important thing that you

can do first if you're concerned with muscle growth and protein synthesis is to eat enough protein so that there's enough amino acids available to circulate and be utilized by your muscles and other tissues and this is where you can get into something that's known as nitrogen balance nitrogen balance is the difference between total nitrogen intake and total nitrogen loss nitrogen intake comes from protein intake and nitrogen loss comes from the breakdown of proteins throughout the body so when intake is equal to loss a state of nitrogen balance exists when intake is greater than loss a

person is in positive nitrogen balance but when loss is greater than intake this would result in a negative nitrogen balance and nitrogen balance is fluctuating throughout the day exercise and feeding obviously play a role in this but again overall you would want to try to be in a POS positive nitrogen balance in order to consistently build muscle and finally does the type of protein you eat even matter well that depends on a few variables often you hear about whey and caseine as some of the main protein powders that are available for supplementation and these are

derived from milk which means these are animal proteins animal proteins are termed complete proteins because they contain all the indispensable amino acids in the proper amounts and proportions which would prevent amino acid deficiencies by comparison plant proteins May lack one or more of the indispensable amino acids or the proper concentrations and are therefore sometimes referred to as incomplete proteins now this doesn't mean that someone that is vegan or vegetarian can't get all the indispensable amino acids they need they just may have to get a little bit more creative and get them from multiple sources and

as an FYI indispensable amino acids are amino acids that must be provided by the diet because the body can't synthesize them on its own and these used to be commonly referred to as essential amino acids and something else to consider about the type of protein that you ingest is how fast it can be digested and absorbed whey protein for example is known to be broken down and absorbed quickly so wouldn't this also mean that the type of protein you ingest is important well in certain situations yes but let me go back to something I said

earlier first the most important thing you can do is ingest enough protein get in positive nitrogen balance it is more important to get enough protein in a 24-hour period than it is to worry about the exact timing the rate of absorption and making sure you get that whey protein shake right after you exercise now how much protein depends on various factors and can range anywhere from 1.2 to 2 gram of protein per kilogram of body weight depending on your goals but we do have a video where we get into the amount of protein needed in

great detail so I will link that to this video but once we get to that op optimal amount of protein during a 24-hour period then yeah if you're concerned about recovering as quickly as possible let's start looking at optimizing the timing of protein ingestion and might as well get the potential benefits of ingesting the fast absorbing protein right after a workout to help start reversing the catabolic state of those recently exercised muscles and may as well also start replenishing your glycogen stores while you're at it by mixing some of that protein with some carbohydrates which

we should probably talk about how those carbohydrates are also broken down and absorbed but in a different video so hopefully you learned some cool information about how our bodies digest absorb and utilize proteins and like I mentioned earlier if you're interested in learning more about how much protein you need we'll link that video here and if you want to check out Ivor store we've got that information in the description below and if you want to move a little bit further I'll meet you down in the comments