There are no data available to substantiate the claim that people cannot fully digest, absorb or
assimilate more than 30 grams of protein in one sitting and that any additional protein is either
converted to fat or goes out through the stool. Protein metabolism is affected by a vast number of
factors, both biological and environmental, like exercise, protein intake, total energy intake,
proper digestion, zinc supplementation, hormonal regulation, steroid use, disease (diabetes,
cirrhosis), obesity, pesticides in food and even temperature. Digestion and absorption alone depend
on a multitude of factors, including chemical composition of the diet to the efficiency of
mechanical mixing, gastric secretion of hydrochloric acid, adequate production of proteolytic
enzymes, and transporter activity.
So old-time bodybuilders were not wrong when they advocated the use of digestive enzymes and
hydrochloric acid tablets. Protein can only be absorbed in the form of amino acids or very small
peptides, bigger molecules being too large to pass through the intestinal wall into the
bloodstream. But it is still best to get one's high-quality protein from regular meals because
chemically similar amino acids compete for absorption. A solid mixed meal releases amino acids only
sparingly but steadily for several hours. The protein from food can thus be totally absorbed,
whereas a concentrated solution containing only free amino acids is less efficiently absorbed on an
empty stomach. Also, di- and tripeptide-rich hydrolysates are transported very quickly across the
intestinal wall, which can result in more amino acids being oxidized by the liver, a reason why
some champions mix their protein supplements with peanut butter.
Considering the variables, it is impossible to determine exactly how much protein the body can
process at one time. It is not that the thirty gram figure is always false. It is rather that it is
not necessarily true. In fact, strength athletes take in an average of 30-40 grams of high quality
protein per meal, and according to Paddon-Jones and Rasmussen, this dose is enough to "stimulate
muscle protein synthesis in both young and older individuals." But to maintain that anything in
excess is always wasted is unreasonable. In the past decade, a group of French researchers
repeatedly showed that people consuming 80% of their daily protein intake at a single sitting -
which is referred to as the pulse pattern - demonstrate higher nitrogen retention, higher protein
synthesis and a better protein-sparing effect when compared to people following some "spread
protein-feeding pattern". Of course, this does not prove the superiority of one pattern over the
other as far as sports nutrition is concerned, since none of the subjects tested appeared to be
involved in any athletic activity. But it does indicate that the human body has the ability to
digest and assimilate much more than only 30 grams of protein at a time.
This conclusion also seems logical when considered in light of evolution. Modern humans evolved as
hunter-gatherers over a 200,000-year period until finally the Neolithic revolution broke out. Since
preserving food was not an option in the early days of mankind, every time our prehistoric
ancestors killed one of the megafauna animals such as mammoths or woolly rhinoceroses (whose
hunting was probably a cause of extinction), they stuffed themselves full to bursting, knowing that
they would probably be reduced to a state of semi-starvation again in the future. Periodic
starvation was a common occurrence back then. Hunter-gatherers, however, were tall and brawny
because they had evolved to adapt to periods of game scarcity. Thus, they were obviously
predisposed to use more than 30 grams of protein per meal. And as their descendants, so are we.
Of course, if you eat more than 100 grams of protein within a two-hour span, it is doubtful that
the body will fully digest and absorb it all. Furthermore we know that large amounts of fast-
absorbed protein cause the body to waste a significant portion of amino acids through liver
oxidation. But it remains unclear what the upper limit is, or whether generalization is possible.
The response to food is highly person-specific and an upper limit may vary greatly between
individuals. For example, the intestinal extraction of dietary amino acids is known to increase
with age. Similarly, advanced resistance athletes and people who are used to taking large amounts
of protein seem more effective in utilizing it, not to mention athletes on anabolic substances.
Indeed, the human body is wonderful in that it can adapt to almost anything it is forced to deal
with. Thus, while on a high-protein diet, the metabolism adjusts and amino acid transport
upregulates to accommodate high levels of protein intake.
So what have we learned so far? That discussing the 30-gram rule is pointless and irrelevant. In
fact, we should feel more concerned about meal composition, daily caloric intake and macronutrient
ratios. Nutrient timing is crucial as well, since protein deprivation and resistance training both
increase muscle sensitivity to amino acids. For example, there are times in a day when a high-
protein meal is most welcome and more protein can probably be used by the body: at breakfast and
around training time. It is also beneficial to eat protein-rich foods along with healthy fats
before going to bed. Now, in the real world, you will not find many athletes counting every gram or
calorie. That is simply impossible. They count portions instead and, unless they are vegans - which
is not that common among strength athletes - they only count animal-derived foods as protein foods.
(1) Arnal and al. Protein pulse feeding improves protein retention in elderly women. American
Journal of Clinical Nutrition. 1999 Jun;69(6): 1202-8.
(2) Arnal and al. Protein feeding pattern does not affect protein retention in young women. Journal
of Nutrition. 2000 Jul;130(7):1700-4.
(3) Arnal and al. Protein turnover modifications induced by the protein feeding pattern still
persist after the end of the diets. American Journal of Physiology Endocrinology and Metabolism.
2000 May; 278(5):E902-9.
(4) Hirst, Barry, Dietary regulation of intestinal nutrient carriers, Proceedings of the Nutrition
Society (1993), 52, 315-324
(5) Di Costanzo, Jacques, Paleolithic nutrition: a model for the future? Current Opinion in
Clinical Nutrition and Metabolic Care: March 2000 - Volume 3 - Issue 2 - pp 87-92
(6) Paddon-Jones D, Rasmussen BB: Dietary protein recommendations and the prevention of sarcopenia.
Current Opinion in Clinical Nutrition and Metabolic Care: January 2009 - Volume 12 - Issue 1 - p
Emmanuel Legeard, PhD, is a professional sports writer and has authored over 200 articles and two
books on training and sports performance. As a trainer and consultant, he has worked with athletes
at every level, from novice to Olympic trials. He is a Certified Strength and Conditioning
Specialist (CSCS) with distinction (*D) through the National Strength and Conditioning Association
(NSCA) and a Certified Sports Nutritionist (CISSN) through the International Society of Sports
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