T Nation

Looking for Protein Studies

Not looking to start any arguments here.
I wanted to see if anyone can direct me to primary source studies on protein intake. I don’t like making uninformed arguments, not looking for bro-science. I want to know what peer-reviewed research actually says about how much protein can be absorbed in a sitting.

I’m curious to see if I can find the studies behind the “you can only digest 20-30g protein in one sitting” theory. It seems like such a generalized, counter-intuitive theory, but the fact is I don’t have any evidence against it.

I’d also be interested in knowing how much protein can be absorbed in one sitting. I usually drink about 40g - 60g in one shake, so it’d be nice to know if I should be splitting them up more.

Not a study here, but our own Dr Lonnie Lowery posted this in a past article:

“Everyone wants to know what the optimal dose of protein is,” said Lowery. “How much can you digest at once? Well, most people will say about 30 grams. But that’s usually based on a plausibility argument based around how much protein you should eat in a day broken down over six meals. Now we may know the actual answer to that question based on a new study.”

This year, Tarnopolsky’s lab did a study (2) to examine the effect of how different dosages of egg protein powder affected protein synthesis rates. Researchers had healthy men who had previous weight training experience perform intense resistance exercise and consume an egg protein drink that contained either 5, 10, 20, or 40 grams of protein.

Basically, Lowery explained that researchers found that increasing protein intake stimulated protein synthesis in a dose dependent manner up to 20 grams of protein, after which there was no further increase in protein synthesis. In other words, forty grams didn’t stimulate protein synthesis greater than 20 grams.

Researchers speculated that consuming 20 grams of protein five or six times daily would be the optimal measure to increase anabolism and muscle mass.

“Now,” says Lowery, “You may still want to eat more than that for volume purposes since you’ve got to eat something, but the answer to the question is 20 grams… at least with egg protein. And I bet we see different proteins tested over the next year.”

I asked Dr. Lowery how this new info is causing him to alter his own protein intake.

“I’ve actually cut back on the amount of protein I eat at any given time. I just make sure I spike it with leucine. I usually put a scoop and a half, about 7 or 8 grams, of leucine in just 20 grams of protein. But I’ve stopped sucking down 50 or 60 grams of protein at a time. I just don’t do that anymore; I don’t think it has that much benefit. Plus this prevents me from becoming a protein oxidizer or burner.”

I asked if this changed his total protein intake per day.

“For me, not that much really. Twenty to thirty grams every few hours, spiked with leucine. I’m getting between 180 and 210 grams per day.”

“Which brings me to another point,” continued the Doc. "There may be benefits to separating protein/leucine boluses.

Lowery was referring to the “protein pulse” approach that Biotest has been studying for some time now.

“There were a few French researchers ? the name I remember is El-Khoury ? who found about a 15% improvement in anabolism by taking a ‘pulse feeding’ approach to protein intake.”

Essentially, while traditional dogma has urged lifters to keep a steady-state flow of amino acids in the blood stream, the new thinking indicates that it might be best to let amino acid levels fall and then introduce a protein bolus.

Bilsborough S, Mann N. A review of issues of dietary protein intake in humans. Int J Sport Nutr Exerc Metab. 2006 Apr;16(2):129-52.

Moore DR, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr. 2009 Jan;89(1):161-8.

Campbell B, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2007 Sep 26;4:8.

Tipton KD, Wolfe RR. Protein and amino acids for athletes. J Sports Sci. 2004 Jan;22(1):65-79

Symons TB, et al. A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects. J Am Diet Assoc. 2009 Sep;109(9):1582-6.

Note: Research compiled by Alan Aragorn for web article published Feb 22, 2010.

Sort of related question:

For someone who trains seriously and is consuming a ton of calories (i.e. 4k or so), what is a BUN level that would be concerning?

[quote]BlueCollarTr8n wrote:

[/quote]

Ooh! That’s the one I really wanted, BCT!

Thanks!

This 20 grams per sitting seems extremely low. I eat 7x per day. each of my protein shakes has about 50 grams of protein in it. If i cut back to 20, that will drastically reduce my overall total levels. What about that saying, you must take at least 1 - 1.5 grams of protein per lb of bodyweight. What about pros that eat 400 grams per day. and by cutting out the protein, that also reduces the total calories. how do you make up for that loss? I don’t want to add carbs. I have read other contrary articles on this site that say the opposite.

I recently read an article on this site a very short time ago, that said, cause protein takes time to digest, theres really no limit to how much can be absorbed in one sitting, even 75 grams per sitting wouldn’t be to much.

Even if protein synthesis doesn’t increase after 20 grams, if it remains the same, thats great. if you have 45 grams per sitting, thats 25 grams more protein, whether or not its the same protein synthesis level, your getting in more protein, more protein to build more muscle and more calories.

I think its suggested that its better to take 60 grams across 2 servings instead of 1, but I think 20 is a bit low personally, I may cut my 60g shakes down to 30 and just drink them more often

[quote]roguevampire wrote:
This 20 grams per sitting seems extremely low. I eat 7x per day. each of my protein shakes has about 50 grams of protein in it. If i cut back to 20, that will drastically reduce my overall total levels. What about that saying, you must take at least 1 - 1.5 grams of protein per lb of bodyweight. What about pros that eat 400 grams per day. and by cutting out the protein, that also reduces the total calories. how do you make up for that loss? I don’t want to add carbs. I have read other contrary articles on this site that say the opposite.

I recently read an article on this site a very short time ago, that said, cause protein takes time to digest, theres really no limit to how much can be absorbed in one sitting, even 75 grams per sitting wouldn’t be to much. [/quote]

I agree that 20 grams seems very low even with frequent feedings. But to use pro bodybuilders as an example of how much to take in is not applicable to most of us. Genetics aside, there is also the issue of PEDs which can enhance the amount of protein utilised towards muscle growth.


Study on elderly women showing that feeding them 80% of daily protein in one meal improved protein retention over an equal amount of protein spread over four meals.


Further work by the same author, this time with young women, feeding them either their daily protein in one meal or spread over four meals. There was no significant difference in protein retention.


Intermittent fasting study, with an average protein consumption of 101g in a four hour period with 20h fast, no difference in muscle protein and lean mass.

These findings seem to show that the body can certainly digest more than the 20-30g ‘ceiling’ theory

[quote]Gl;itch.e wrote:
I agree that 20 grams seems very low even with frequent feedings. But to use pro bodybuilders as an example of how much to take in is not applicable to most of us. Genetics aside, there is also the issue of PEDs which can enhance the amount of protein utilised towards muscle growth.[/quote]

It isn’t an issue of how much protein can be utilized, it’s an issue of how much protein (or, rather, amino acids) can be absorbed by the small intestine. Taking steroids or training intensely won’t allow for greater amino acid uptake. There are only so many amino acid transporters in the digestive system. If those transporters are constantly saturated, the extra amino acids will be excreted as feces.

http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_aacids.html

It would be interesting to see if subQ administration of amino acids and fluids further increases protein synthesis in a person who eats 20 grams of protein 6 times per day.

Also, the study didn’t distinguish if the group who received 20 grams of egg protein had higher protein synthesis rates because there were more amino acids in the blood, or just because the people who received the 20g egg protein ate more calories.

Even a pro bodybuilder may only need 100 grams of amino acids per day. Of course pro BBers need to eat tons of food, but that could be because of a calorie requirement and not an amino acid requirement.

[quote]roon12 wrote:


Intermittent fasting study, with an average protein consumption of 101g in a four hour period with 20h fast, no difference in muscle protein and lean mass.

These findings seem to show that the body can certainly digest more than the 20-30g ‘ceiling’ theory[/quote]

Amino acids are absorbed by the small intestine. Things like beef can take 12+ hours to digest completely, especially if large amounts are eaten at once.

[quote]anime wrote:
Amino acids are absorbed by the small intestine. Things like beef can take 12+ hours to digest completely, especially if large amounts are eaten at once.[/quote]

I would seem like the variables that affect digestion rates would be endless.

IMHO, it seems many guys are overeating their protein requirements.
Isn’t the goal to feed the LEAN mass the recommended 1 - 1.5 g per lb of protein? Why take into account additional body fat when making that calculation?

[quote]anime wrote:

[quote]Gl;itch.e wrote:
I agree that 20 grams seems very low even with frequent feedings. But to use pro bodybuilders as an example of how much to take in is not applicable to most of us. Genetics aside, there is also the issue of PEDs which can enhance the amount of protein utilised towards muscle growth.[/quote]

It isn’t an issue of how much protein can be utilized, it’s an issue of how much protein (or, rather, amino acids) can be absorbed by the small intestine. Taking steroids or training intensely won’t allow for greater amino acid uptake. There are only so many amino acid transporters in the digestive system. If those transporters are constantly saturated, the extra amino acids will be excreted as feces.

http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_aacids.html

It would be interesting to see if subQ administration of amino acids and fluids further increases protein synthesis in a person who eats 20 grams of protein 6 times per day.

Also, the study didn’t distinguish if the group who received 20 grams of egg protein had higher protein synthesis rates because there were more amino acids in the blood, or just because the people who received the 20g egg protein ate more calories.

Even a pro bodybuilder may only need 100 grams of amino acids per day. Of course pro BBers need to eat tons of food, but that could be because of a calorie requirement and not an amino acid requirement.

[quote]roon12 wrote:


Intermittent fasting study, with an average protein consumption of 101g in a four hour period with 20h fast, no difference in muscle protein and lean mass.

These findings seem to show that the body can certainly digest more than the 20-30g ‘ceiling’ theory[/quote]

Amino acids are absorbed by the small intestine. Things like beef can take 12+ hours to digest completely, especially if large amounts are eaten at once.[/quote]

I don’t think the part about there being only so many amino acid transporter’s in the digestive system is correct. AA’s will travel through the blood stream in their digested form without a transporter. The only time a transporter is needed is for them to cross through a cell membrane.

So basically it is not how much protein you can digest in one sitting. You will digest it all eventually(barring some issue with digestion). The question is really how much protein can you consume in one sitting to affect protein synthesis? This is probably highly individual, I would imagine you can consume more after a workout, in which an abundance of AA can could enhance protein synthesis.

However, consuming 50-60 grams of whey protein by itself, in one sitting, not after a workout, will probably end up with a lot of it getting converted to glucose (via gluconeogenesis). If is consumed in a meal with other foods like fat, it is really tough to say what exactly would happen. Like someone pointed out earlier, there is a ton of variables that go into speed of digestion, based on your body, what you eat, etc.

[quote]schanz_05 wrote:
However, consuming 50-60 grams of whey protein by itself, in one sitting, not after a workout, will probably end up with a lot of it getting converted to glucose (via gluconeogenesis). If is consumed in a meal with other foods like fat, it is really tough to say what exactly would happen. Like someone pointed out earlier, there is a ton of variables that go into speed of digestion, based on your body, what you eat, etc. [/quote]

Here’s a quote:

[quote]The mechanism by which amino acids are absorbed is conceptually identical to that of monosaccharides. The lumenal plasma membrane of the absorptive cell bears at least four sodium-dependent amino acid transporters - one each for acidic, basic, neutral and amino acids. These transporters bind amino acids only after binding sodium. The fully loaded transporter then undergoes a conformational change that dumps sodium and the amino acid into the cytoplasm, followed by its reorientation back to the original form.

Thus, absorption of amino acids is also absolutely dependent on the electrochemical gradient of sodium across the epithelium. Further, absorption of amino acids, like that of monosaccharides, contributes to generating the osmotic gradient that drives water absorption.

The basolateral membrane of the enterocyte contains additional transporters which export amino acids from the cell into blood. These are not dependent on sodium gradients. [/quote]

If I’m incorrect, please let me know. I don’t get offended if someone teaches me something. I don’t know much about how the digestive system works, but I think with anything, the body can only absorb so much. The idea of receptor saturation, requirement of enzyme cofactors, etc seems like a recurring theme in biology.

[quote]anime wrote:

[quote]schanz_05 wrote:
However, consuming 50-60 grams of whey protein by itself, in one sitting, not after a workout, will probably end up with a lot of it getting converted to glucose (via gluconeogenesis). If is consumed in a meal with other foods like fat, it is really tough to say what exactly would happen. Like someone pointed out earlier, there is a ton of variables that go into speed of digestion, based on your body, what you eat, etc. [/quote]

Here’s a quote from the website I linked to:

[quote]The mechanism by which amino acids are absorbed is conceptually identical to that of monosaccharides. The lumenal plasma membrane of the absorptive cell bears at least four sodium-dependent amino acid transporters - one each for acidic, basic, neutral and amino acids. These transporters bind amino acids only after binding sodium. The fully loaded transporter then undergoes a conformational change that dumps sodium and the amino acid into the cytoplasm, followed by its reorientation back to the original form.

Thus, absorption of amino acids is also absolutely dependent on the electrochemical gradient of sodium across the epithelium. Further, absorption of amino acids, like that of monosaccharides, contributes to generating the osmotic gradient that drives water absorption.

The basolateral membrane of the enterocyte contains additional transporters which export amino acids from the cell into blood. These are not dependent on sodium gradients. [/quote]

If I’m incorrect, please let me know. I don’t get offended if someone teaches me something. I don’t know much about how the digestive system works, but I think with anything, the body can only absorb so much. The idea of receptor saturation, requirement of enzyme cofactors, etc seems like a recurring theme in biology.[/quote]

What that is talking about is absorption of amino acid’s from the blood stream into a particular cell. So, like I said in my earlier post the transporter’s are only necessary for the AA’s to cross a cell membrane. Now, there could be the possibility that all of the AA transport receptor’s become saturated, not allowing AA’s into certain cells. But, to reiterate on an earlier point, the proteins will have already been digested into AA’s and circulating in the blood stream.

[quote]schanz_05 wrote:
What that is talking about is absorption of amino acid’s from the blood stream into a particular cell. So, like I said in my earlier post the transporter’s are only necessary for the AA’s to cross a cell membrane. Now, there could be the possibility that all of the AA transport receptor’s become saturated, not allowing AA’s into certain cells. But, to reiterate on an earlier point, the proteins will have already been digested into AA’s and circulating in the blood stream. [/quote]

He is talking about absorption of amino acids by the intestines into the cytoplasm of intestinal cells from what I read. It could be that the amino acid transporters are able to transport amino acids so quickly that the transporters never become saturated. Here’s another quote

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CG0QFjAI&url=http%3A%2F%2Fjournals.cambridge.org%2Farticle_S0029665185000167&ei=qxE-T8nWC6q0iQLtyN2QAQ&usg=AFQjCNFy2NwPwuYviNpMLmxH3zC6Yq6v0Q

[quote]
Although it has become clear that brush-border hydrolysis, and consequent
utilization of the monosaccharide transport system, is the predominant method of
absorption of the luminal products of carbohydrate digestion in man, it now
appears certain that two major mechanisms are involved in the absorption of the
luminal products of protein digestion: (I) transport of liberated free amino acids by
group specific active amino acid transport systems, and (2) uptake of unhydrolysed
peptides by mechanisms independent of the specific amino acid entry mechanisms.[/quote]

The second mechanism is not the main way protein is absorbed.

[quote]anime wrote:

[quote]schanz_05 wrote:
What that is talking about is absorption of amino acid’s from the blood stream into a particular cell. So, like I said in my earlier post the transporter’s are only necessary for the AA’s to cross a cell membrane. Now, there could be the possibility that all of the AA transport receptor’s become saturated, not allowing AA’s into certain cells. But, to reiterate on an earlier point, the proteins will have already been digested into AA’s and circulating in the blood stream. [/quote]

He is talking about absorption of amino acids by the intestines into the cytoplasm of intestinal cells from what I read. It could be that the amino acid transporters are able to transport amino acids so quickly that the transporters never become saturated. Here’s another quote

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CG0QFjAI&url=http%3A%2F%2Fjournals.cambridge.org%2Farticle_S0029665185000167&ei=qxE-T8nWC6q0iQLtyN2QAQ&usg=AFQjCNFy2NwPwuYviNpMLmxH3zC6Yq6v0Q

[quote]
Although it has become clear that brush-border hydrolysis, and consequent
utilization of the monosaccharide transport system, is the predominant method of
absorption of the luminal products of carbohydrate digestion in man, it now
appears certain that two major mechanisms are involved in the absorption of the
luminal products of protein digestion: (I) transport of liberated free amino acids by
group specific active amino acid transport systems, and (2) uptake of unhydrolysed
peptides by mechanisms independent of the specific amino acid entry mechanisms.[/quote]

The second mechanism is not the main way protein is absorbed.[/quote]

Yes you are right, that’s what I get for not reading the link and just looking at the excerpt. So, basically I was just a step ahead of you. What you’re saying is that you think the transporters that move AA’s to the enterocytes for absorption might become saturated, causing AA’s that don’t get transported into enterocytes soon enough, to be passed out through the colon?

Could be a possibility, I don’t know enough about that process to take a stance one way or another. It would just depend on how long AA’s will sit there before the body decides to pass it down through the colon.