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There is a popular belief that the human body can't absorb more than 30 grams of protein per meal. Some also believe that the limit is 25 or less.

For example, This article states that "According to Dr. Helen Kollias, Ph.D. of Johns Hopkins Hospital, your body can absorb about 8 g to 10 g of whey protein per hour." This implies that there may be a limit for a single meal. On the other hand, this article states the opposite.

Is there any scientific consensuses of the protein limit in a single meal?

  • Given that the food you eat stays in the body for hours (not sure exactly how long until it's discharged, but let's take 6 hours as the average time between meals to be a good guess) the amount of protein absorbed from a meal becomes much greater than what the body can take up during that meal (in fact, unless it's a very long meal, digestion will not even have properly started until after the meal is fully consumed). – jwenting Sep 17 '13 at 5:49
  • Should Dr. Kollias not be a MD (medical doctor) and not a Ph.D.? If he is a Ph.D. then in what science exactly? – Martin Scharrer Sep 17 '13 at 8:27
  • @MartinScharrer you can have a PhD in medical sciences or related (like various biological and organic chemistry routines) without being an MD. – jwenting Sep 17 '13 at 10:39
  • @yrodro Proteins are absorbed in the small intestine as amino acids. At least three questions are possible from here: 1) What is the rate of amino acid absorption in the small intestine 2) Are all the amino acids absorbed at the same rate? (they are not). 3). What is the rate of synthesis of the body proteins from these dietary amino acids. I guess the question is about the absorption in the small intestine, but can you clarify this. The problem is that not all absorbed proteins (amino acids) from one meal are necessary converted to the body proteins. – Jan Sep 17 '13 at 15:09
  • @Jan: I only edited the title of the question. As it stood, it was pointless because the answer to "is there a limit to...?" is YES. You cannot for instance absorb 50 pounds of protein in one meal. It was exclusively a language issue, and I do not have anything to do with the question itself :) – yrodro Sep 17 '13 at 15:17
1

There is a very relevant article A Review of Issues of Dietary Protein Intake in Humans International Journal of Sport Nutrition and Exercise Metabolism, 2006, vol. 16, pages 129-152.

The rate at which the intestines absorb amino acids depends upon the protein source, and, according to table 2, this varies from a low of 1.3 grams per hour for egg protein to 8-10 grams per hour for whey isolate.

However:

Rudman et al. (27) found that the maximal rate of urea excretion (MRUE) in healthy individuals was 55 mg urea N ∙ h-1 ∙ kg-0.75, which is reached at an intake level of 0.53 g protein N/kg-0.75 At higher protein intakes there is no further increase in urea excretion rate, but a prolongation of the duration of MRUE, often in excess of 24 h

(the "-0.75" above is an exponent, as in kg^(-0.75))

So absorption by the intestines is not necessarily the only limit to consider.

In fact:

The dangers of excessive protein intake should not be underestimated and have been recognized historically through the excess consumption of lean wild meat by early American explorers leading to a condition referred to as “rabbit starvation syndrome,” in which symptoms included nausea and diarrhea followed by death within 2 to 3 wk

The review also states:

This “slow” and “fast” protein concept provides some clearer evidence that although human physiology may allow for rapid and increased absorption rate of amino acids, as in the case of WP (8 to 10 g/h), this fast absorption is not strongly correlated with a “maximal protein balance,” as incorrectly interpreted by fitness enthusiasts, athletes, and bodybuilders. Using the findings of amino acid absorption rates shown in Table 2 (using leucine balance as a measurable endpoint for protein balance), a maximal amino acid intake measured by the inhibition of proteolysis and increase in postprandial protein gain, may only be ~ 6 to 7 g/h (as described by RPT-WP, and casein) (38), which corresponds to a maximal protein intake of 144 to 168 g/d.

So yes there is a maximum rate somewhere in the 144-240 grams per day range, but it is not necessarily safe to approach the maximum.

  • Possibly off base on this, but isn't the issue with rabbit starvation syndrome more that suffers eat only protein, not that they eat lots of it? Wikipedia thinks so, and offers some good looking sources. en.wikipedia.org/wiki/Rabbit_starvation – John Doucette Jan 13 '16 at 20:42
  • @JohnDoucette even the Wikipedia article says "It has been observed that the human liver cannot safely metabolise much more than 221–301 g of protein per day (for an 80 kg/176 pound person)" in the " possible mechanisms" section. – DavePhD Jan 14 '16 at 12:59
  • That's true, but further down, the article cites this source: nap.edu/read/10490/chapter/12#694 which explains that that number is without a period of adaptation to a high protein diet. The Das and Waterlow 1974 source cited there apparently shows that exposure to a high protein diet in other animals increases protein uptake over time. Examine has a very well sourced article on the topic too, and it might be good to incorporate their findings into your answer: examine.com/faq/can-eating-too-much-protein-be-bad-for-you – John Doucette Jan 17 '16 at 21:20

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