It is quite easy to get confused when you rely on all the information available online. There are several online articles about proteins that pretty much contradict. Therefore, to help you understand this important nutrient, we saw it wise to explore it further. In this work, we will look at the process of protein absorption and digestion. We will explore how big protein blocks from the food we eat are broken down and processed into amino acids so that your cells can make new proteins.
As a head start, the gut breaks down the proteins we eat into individual amino acids, which are later absorbed into the blood to be used by the cells for various functions. Before focusing on the absorption part (which is what this article focuses on), we will have to explore the process of digestion of this nutrient from the onset.
Digestion of proteins
A 2-hour session in a biology class will inform you that digestion starts in the mouth where food is chewed into smaller particles that can be easily broken down further and absorbed into the bloodstream. Chewing also eases swallowing. While in the mouth, proteins are broken down and then swallowed with the help of saliva, which is produced by the salivary glands. Once this gets to the stomach, the stomach walls secrete gastric juice, which comes with a fair supply of hydrochloric acid and pepsin.
It is the pepsin that commences the process of protein breakdown in the stomach. It breaks down the protein chains into smaller and relatively easy to absorb particles. The process of churning then takes place. Churning is the contraction of the stomach walls, which mixes food with the digestive enzymes.
Keep in mind that digesting proteins is relatively longer than that of carbohydrates because of the complicated chains. Therefore, if you decide to eat a high-protein food, be sure that it will take longer to digest in the stomach. This is the reason why you will feel full for long when you take a high protein meal.
The second phase of protein digestion takes part in the small intestines. This is after the emptying of the chyme into these intestines. Immediately after, the pancreas secretes digestive juice with enzymes charged with the role of breaking down the proteins further. These are the chymotrypsin and trypsin.
Also, the cells in the walls of the intestines secrete more enzymes that finish the role. They break down the remaining small proteins into amino acids required by the body. The muscle contraction in the small intestines then comes in handy in mixing and pushing the digested proteins to the absorption sites. The whole process of protein digestion breaks down proteins into dipeptides and amino acids to aid absorption.
Transportation of the amino acids
The amino acids are transported to the lower parts of the small intestines, where they further move from the intestinal lumen through the intestinal cells and finally to the blood. I know that this seems like a long process but isn’t as complicated as it sounds. This movement requires special transport proteins and ATP, which is the main source of energy for the cells. From the blood, these amino acids move to the liver. The liver facilitates the further breakdown of the amino acids and acts as a point of distribution.
Keep in mind that further breakdown of amino acids will release nitrogen-containing ammonia since this component has quite a bit of ammonia. The liver, therefore, transforms the ammonia into urea to prevent your body from the toxic effects. The urea then makes its way to the kidneys, which facilitate the process of excretion through urine. Remember, your body relies on amino acids if it needs to synthesize other proteins, and therefore, around ninety percent of your protein you eat will not be broken down further.
Unless you are eating too many proteins, you won’t find any sight of them in the large intestines. This may be a good chance to explain why too many proteins produce smelly gas. When you take in a lot of proteins, a good number find themselves in the colon and broken down by the gut microbes producing smelly gas.
This brings us to our main topic of discussion. We had to explore the process of protein digestion to help you have a quick idea of what happens before it gets there. It is worth knowing that almost all the proteins are absorbed as tripeptides, dipeptides, or amino acids in adults. The absorption of proteins takes part in the duodenum, otherwise known as the small intestines’ proximal jejunum. This happens when the amino acids pass through the interstitial brush border through facilitative diffusion, famously known as active transport. I am pretty sure that you must have learned a thing or two about this.
This process requires energy, which is supplied by ATP and sodium, which the body also provides. These two are required for the molecules to make it through the membranes. There is no specific transporter, and it is upon the R group to decide the one that will be sued to facilitate this process. Once the amino acids have made their way through the membrane, they are released into the intestinal bloodstream and then transported to the liver thanks to the hepatic portal veins in a process called enterohepatic circulation.
Just like we mentioned, not all the proteins ingested in the body are further broken down. Therefore, once these amino acids get into the liver, roughly 60 will be used to synthesize a range of components. These include protein and nitrogen compounds. Do not also forget that the amino acids will also be used to form purine bases.
In rare cases, you will find these amino acids or dipeptides converted into energy, which the body needs to stay afloat. It is worth noting that it is the liver’s role to regulate the amount of amino acid found in the blood. The resultant amino acids will then pass through the liver from where they are transported to the rest of the body. From here, they will be used by the different cells in the body.
Where does the nitrogen go?
One of the main reasons why we chose to discuss this topic is to have their discussion. One thing that makes amino acids distinctive is the fact that they contain nitrogen. We might have mentioned that this nitrogen becomes ammonia, after which is it is excreted in the form of urine but didn’t mention that several other things can also happen.
One, this nitrogen does not have to be broken down, as we said. It can remain in its molecular form to be included in whatever the cell is making. The nitrogen can also be transaminated to form new amino acids. This happens when the amine group transfers to another carbon skeleton. The process of the removal of this amine group is known as deamination. It is also responsible for removing nitrogen in the body, which can be toxic on accumulation. In case you are wondering what happens to the carbon skeleton after this process, it is used in energy production provided that there is an abundant supply of Vitamin B6.
Back to our first point, this nitrogen from the amino acid can be done way in several ways. It can be excreted in the form of urea, just like we mentioned. In fact, urination is one of the most popular ways of dealing with excess ammonia. You can also get rid of nitrogen in your feces, skin, hair, and even nails. The last two are mostly made of proteins, and therefore, the nitrogen will be bound to the surface of the protein.
Can amino acids be recycled?
Yes. The body finds a way of recycling amino acids. They are reused to make new proteins that play important roles all over the body. Keep in mind that for cells to function properly, they need proteins that break down as they build new ones. This process is known as protein turnover. The amount of proteins disintegrated in a day is similar to the amount built. How are these proteins formed? Simple. The amino acids from the foods we eat and in the destroyed proteins are pooled. Therefore, the body will draw amino acids from the pool if the need arises.
Remember, amino acids have a bigger role than only building proteins. They are also used in the production of relatively essential biological molecules that have nitrogen in them. This is why you are always encouraged to eat foods with high-quality proteins such as quinoa. If you don’t eat such foods, your body will always be forced to recycle amino acids, which encourages the breakdown of muscles. You don’t want to look all wasted, frail, and thin.
The digestion and absorption of proteins is quite an interesting discussion. Even after absorption, a large percentage of this nutrient is pooled to be used when needed. Therefore, you should always strive to eat meals full of proteins.
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