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I am interested to know if a human body can store protein.

Absolutely for the bodybuilders, does it really matter if they divide their protein consumption during the day or eat all of it in one meal at anytime they want?

Is there any constrain on protein absorption per hour?
What will happen for the extra protein we eat?

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The human body can not store Proteins (technically).

BACKGROUND :

PROTEIN is a very broad term and there are hundreds and thousands of proteins.[1] Proteins are heteropolymers consisting of amino acids held by peptide bonds.

Amino acids :

There are 9 amino acids which we need to intake.

Phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.

Amino acids our bodies can produce:

These five are alanine, aspartic acid, asparagine, glutamic acid and serine.

These amino acids combine in different arrangements to give those thousands of Proteins. This process is carried out by Ribosomes (cook) and mRNA (recipe) inside every* cell.

Protein metabolism in humans :

During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and proteaseactions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body. Trypsin and Chymotrypsin as Trypsin and Chymotrypsinogen are the enzymes necessary.

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MAIN ANSWER :

The excess Amino Acids are broken down into Glucose ( carbohydrate like stuff ) and the Nitrogen moiety is converted into Urea / Uric acids. This is then excreted by kidneys.

Amino acids can be broken down into precursors for glycolysis or the Krebs cycle. 

Amino acids can also be used as a source of energy, especially in times of starvation. Because the processing of amino acids results in the creation of metabolic intermediates, including pyruvate, acetyl CoA, acetoacyl CoA and so on; amino acids can serve as a source of energy production through the Krebs cycle.

Therefore excess protein is simply used to make energy like carbs and the Nitrogen part is excreted. Now the excretion process can strain the kidneys due to increased work load, and prolonged stress can lead to malfunctions.

Also,

Our body is very concerned with conserving nitrogen levels, since our body can't fix nitrogen gas (N2) into ammonia (NH3). but, we can't just store huge amounts of ammonia because it's toxic. sugars and fats aren't toxic, so we can store them. because of this, our body either quickly utilizes excess ammonia to make nitrogenous compounds like amino acids and nucleotides, or it excretes it via Urea in our urine.

Problem with Protein storage :

If our bodies had to store proteins, it would need several sophisticated mechanisms and specialised storage cells.( Like we have adipose tissues short fats and lipids storage ).

if you examine the structure of amino acids, they are very similar to many of the carbon-hydrogen-oxygen metabolic intermediates. for example, alanine is an amidated pyruvate, glutamine is an amidated alpha-ketoglutarate, etc. many are easy to make, and most don't cost much to do so, so the body would rather use these intermediates to either:

  1. Create acetyl-CoA, NADH, FADH2, and ATP for energy. this would happen during exercise or starvation.

  2. Create glycogen, fatty acids, nucleotides, NADPH, and other metabolic compounds. this would occur after a big meal, during sleep, and when energy is not needed in high amounts. these compounds are very expensive ATP-wise.

So there's no need to store whole Amino Acids because they can be immediately used for whatever the body needs and then remade when necessary.

We do not store amino acids because we don't need to.

Right dose of Proteins :

Research shows:

A total of 80 g of whey protein was ingested in one of the following three conditions: 8 servings of 10 g every 1.5 h; 4 servings of 20 g every 3 h; or 2 servings of 40 g every 6 h. Results showed that MPS was greatest in those who consumed 4 servings of 20 g of protein, suggesting no additional benefit, and actually a lower rise in MPS when consuming the higher dosage (40 g) under the conditions imposed in the study. 

Check here for the interesting results ( this is very relevant to your second question )

Therefore distributed intake of right amount of protein is important!

Scientific literatures :

Proteins: https://en.wikipedia.org/wiki/Protein_(nutrient) https://en.wikipedia.org/wiki/Amino_acid

Protein Metabolism: https://opentextbc.ca/anatomyandphysiology/chapter/24-4-protein-metabolism/

Protein intake and storage: https://newsnetwork.mayoclinic.org/discussion/are-you-getting-too-much-protein/ https://www.self.com/story/what-protein-does-in-your-body

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  • $\begingroup$ I have written a long answer, do take time to read and understand 😅 $\endgroup$ – Navoneel Karmakar Mar 5 '20 at 11:45
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I'll add a more straightforward answer than the previous answerer (who was certainly more in-depth and informative than I will be), for the purposes of clarity. I think protein is stored in the body very much functionally, just not in reservoirs of reserve chemical energy such as adipose tissues do with fat.

I am interested to know if a human body can store protein.

The body cannot store dietary protein; it breaks it down into amino acids, which are absorbed and then turned into protein. One cannot repurpose dietary protein without breaking it down into its constituent monomers, the amino acids.

Amino acids are then used in a plethora of ways, the primary of course being protein synthesis (a kind of anabolism, or 'body-building' if you will). Amino acids are strung together to form newly made proteins for the body's needs, and this is a constant process of (re)building in the body. This is why protein intake is essential for survival, given that it's an essential macronutrient.

Does the body store protein in any meaningful way?

Certainly one could argue that you can store protein by making proteins which are long-lived and later available for catabolism, such as those that make up muscles. The muscle tissue can then be used up at a later time if there is need for energy. This is seen with muscle wasting in the elderly or those that are starved. Proteins are a source of gluconeogenic substrates (see this wiki about gluconeogenesis), and thus can be used as a held store of energy. However, please keep in mind that this phenomenon is rather minimal for dietary protein.

(As an aside: notice I am not talking about proteins that are unavailable for breakdown; many proteins are indeed long-lived, such as collagen, but these escape the ability to be re-used. I wouldn't consider this storage, since their function cannot be said to be one of storage.)

Is there any constrain on protein absorption per hour?

Yes, there is a constraint on amino acid (digested protein) absorption per hour by the GI tract. Most dietary amino acids (and some small peptides) are absorbed in the small intestine, though there is evidence the large intestine can also perform this task in humans.

What will happen for the extra protein we eat?

Remaining protein that is not broken down and subsequently absorbed by the intestinal epithelium, will pass through the digestive track and gets pooped out. Along with anything else that the body was unable to digest, such as fibre (like cellulose which makes up much of plant tissue). Not much more to it. Simple!

Additional interesting readings and protein turnover?

A suggested item if you like.


Does it really matter if [people who wish to be bodybuilders] divide their protein consumption during the day or eat all of it in one meal at anytime they want?

It is certainly possible to live on both regimes. This question is unfortunately off-topic for this SE. There are many different philosophies of body-building.

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