How much protein can the body absorb per meal? That might very well be one of the most frequently asked questions in exercise and nutrition.
First, let us clarify the question. There is often a certain misunderstanding about what this really means.
Taken literally, as in how much protein can be absorbed before an excess is eliminated through the feces, the amount is higher than is practically relevant. It is possible to concentrate the entire protein intake of a day into a single meal. The intestinal capacity to absorb protein is not limited to the amount of protein in a can of tuna. This also makes sense from an evolutionary perspective. If that had been the case, and gorging when the opportunity presented itself had only resulted in a protein-rich bowel movement, humankind probably would not have survived to see modern times.
The actual question is probably “how much protein can the body use in a single meal for muscle-building?” The answer to this question is a bit more complex. Just because the protein from a meal has been absorbed does not mean that it will be utilized to synthesize muscle protein.
What does the science say?
Anabolic Response to Protein Intake at Rest
In one study, 34 subjects of varying ages were given servings of lean meat providing either 30 or 90 grams of protein.1 One group received a serving of 113 grams of meat, providing 220 calories. The other group were served 340 grams of meat, providing 660 calories.
Mixed muscle fractional synthesis rate was calculated for 5 hours following the meal. Both the small and the large meal increased muscle protein synthesis approximately 50%. Regardless of age, 30 grams of protein stimulated muscle protein synthesis just as much as 90 grams.
Previous research has shown that acute muscle protein synthesis is not energy-dependent, and this study confirm those earlier findings. Despite a threefold increase in energy content, the larger serving did not result in any more muscle protein being synthesized than the smaller serving, in either young or elderly.
The conclusion of the study is that instead of eating one or two large, protein-rich meals per day, dividing the daily protein intake into multiple moderate-sized meals might be a more effective way to optimize muscle growth.
Several other articles, however, conclude that there probably is no practical upper limit to the anabolic response to the amount of protein consumed in a single meal.2 3 This perspective is based on a number of studies and analytical models. The more protein and carbohydrate consumed within the context of a single meal, the better the protein balance, that is to say the difference between protein synthesis and protein breakdown.
Muscle Protein Balance Determines Anabolism or Catabolism
Muscle fiber hypertrophy is the result of a positive muscle protein balance. This is achieved when muscle protein synthesis over a certain period exceeds that of muscle protein breakdown. If muscle protein synthesis is larger than muscle protein breakdown, the result is anabolism and muscle hypertrophy.
The muscle protein balance during a single moment in time or a short period is not relevant over time. It might be of academic interest, but it does not translate to either hypertrophy or muscle loss. Even if the measured protein balance is, for example, negative at a certain time and under a certain condition, the protein balance of the entire day can still be positive.
The important thing is not muscle protein synthesis or muscle protein breakdown per se.4 It is quite possible for large amounts of muscle protein breakdown to occur during the course of a day, for example through physical activity, with the end result still being a positive muscle protein balance at the end of the day.
The More Protein the Better?
No practical upper limit to the anabolic response to the amount of protein consumed in a single meal seems to exist, as stated above. How can this be, when the protein synthesis response to an intake of 90 grams of protein in one meal is no greater than that of 30 grams? The answer can be found in protein breakdown. Even if the stimulatory effect on protein synthesis does not increase further, when more than 30 grams of protein is consumed, the insulin response to larger meals directly correlate with energy intake. Eating more energy from protein and carbohydrate in one meal means a larger insulin response. This in turn leads to a more robust decrease of protein breakdown.5
Does this mean that eating one large, protein-rich meal per day is just as good as spreading the protein intake over a number of smaller meals in terms of hypertrophic potential? Unfortunately, things are not that simple.
The “no upper limit to the anabolic response to the amount of protein in a single meal”-perspective does not originate from studies on muscle protein synthesis. Instead, more protein consumed in one meal means greater whole body protein synthesis. In fact, measuring muscle protein breakdown correctly is easier said than done. A needle biopsy is used to collect cells from a muscle, and in the process, the muscle fibers are damaged. This makes it hard to determine if naturally occurring processes or the invasive procedure itself caused the observed muscle damage.
Instead of measuring breakdown directly through invasive biopsies, indirect biomarkers of muscle protein breakdown like creatine kinase levels in the blood are used. Those results do not correlate directly with actual muscle protein breakdown. High levels of creatine kinase can also be the result of activities that stimulate muscle growth, like resistance training. In that case, are those high levels actually detrimental to hypertrophy? Probably not.
The substantial decrease in protein breakdown observed after a large protein intake cannot be tied directly to a certain amount of muscle protein. It could likely be a decrease in protein breakdown in the gut, skin, intestines, and other organs. That does not have to be something negative, but it is probably not the intended goal when consuming protein. In addition, it is not certain that a constantly positive organ protein balance is something desirable. Who wants a growing liver and a growing gut?
Signals for Anabolism
A common notion is that protein consumed is protein that ends up as muscle protein, that amino acids from a protein-rich meal are the amino acids that form new body protein, including muscle protein. This is true to some extent, but it is far from the whole story. Only 10–15% of the protein in food and drink end up as muscle protein. The rest synthesize other fat-free tissue in the rest of the body or is utilized as energy.6
Why eat so much protein day in and day out then, if only a few grams are turned into muscle mass? Signals! Following protein ingestion, amino acid levels in the blood increase. Cells react to the availability of amino acids, which initiates multiple biochemical processes to synthesize muscle protein.7
The amino acids incorporated into muscle protein do not have to originate from the protein just consumed. Instead, amino acids freed through muscle protein breakdown are re-used, and incorporated into muscle protein as a response to the increased levels of amino acids in the blood.
Around 75% of all muscle protein broken down on a daily basis is recycled in this way and contributes to the synthesis of new muscle protein. Only 25% is catabolized. This means that an amino acid ingested as part of a protein-rich meal can contribute to muscular hypertrophy, even if its own individual fate is to oxidize into energy.
Effective Muscle Protein Synthesis Requires Effective Muscle Protein Breakdown
Recent research has indicated that suppression of muscle protein beyond what is accomplished through everyday life and nutrition might not be desirable if the goal is to maximize hypertrophy. This might sound paradoxical, but the perspective is backed by both logic and physiological mechanisms.
A new review article postulates that there are no known benefits with respect to skeletal muscle hypertrophy by strategies that suppress muscle protein breakdown.8 If anything, such strategies might even be counterproductive, since a robust muscle protein synthesis requires a robust system of muscle protein breakdown, to efficiently remove damaged proteins and maintain a functional proteolytic response.
Since amino acids resulting from muscle protein breakdown are re-used as discussed previously, suppresssing muscle protein would also decrease the number of available building blocks for new muscle protein. This does not mean that maximal muscle protein breakdown is something to strive for. The take home message would instead be that trying to manipulate muscle protein breakdown and suppress it is unnecessary at best and might even be counterproductive. If the focus is on stimulating muscle protein synthesis, muscle protein breakdown will take care of itself. It seems to be a necessary and vital part of muscle growth.
Anabolic Response to Post-Exercise Protein Intake
Is there any difference in how much protein can be utilized for muscle-building purposes, if the protein meal is preceeded by strength training?
The answer is yes, but the differences do not seem to be dramatic. After resistance training, amino acid sensitivity is enchanced, which implies that a smaller dose of protein would be needed to stimulate muscle protein synthesis maximally post-exercise compared to an intake in the resting state.
In one study from 2008 subjects were given 0, 5, 10, 20 or 40 grams of egg albumin protein after a leg workout.9 Muscle protein synthesis peaked at 20 grams of protein, after which it plateaued. The double amount of protein only marginally increased muscle protein synthesis further.
In a 2014 study, subjects ingested 0, 10, 20 or 40 grams of whey protein post-exercise.10 The results were the same, with a plateau at 20 grams of protein, after which a further intake mostly increased amino acid oxidation. The results from this study also indicate that 10 grams of protein is not a large enough dose to stimulate muscle protein synthesis significantly.
Whole-Body Workouts Require More Protein
The results of a 2016 study indicate that a post-exercise protein intake larger than 20 grams can be beneficial, under certain circumstances.11 In this study, the subjects ingested 20 or 40 grams of whey protein following a whole-body workout. In previous studies, only the effect of protein intake after working one muscle or one muscle group had been studied.
After the whole-body workout, muscle protein synthesis was stimulated to a greater extent following ingestion of 40 grams of protein compared with 20 grams. The response was not double that of 20 grams, but 22% greater. Over the course of a longer period of time, 22% more muscle protein synthesized following each workout would amount to a significant difference.
It was also found that the amount of lean body mass did not affect the anabolic response to the amount of protein ingested. Instead it might be how many muscles that have been worked that sets the limit on how much protein can be utilized post-exercise.
The “Muscle Full”-Effect
If 30 grams of protein per intake can be used to synthesize new muscle protein, wouldn’t consuming this amount of protein every hour result in even larger gains in muscle mass? The idea is an compelling one, but one that does not seem to be practically feasible. This is because of a phenomenon called “muscle full”, which occurs when the blood is constantly flooded with amino acids in large amounts.
As previously mentioned, a large and sudden influx of amino acids in the blood stimulates protein synthesis. After this stimulation, there is a refractory period in which amino acids do not further stimulate protein synthesis. In fact, if plasma amino acids are continuously elevated, protein synthesis falls back to baseline, even with increased amino acid availability. This was first shown through amino acid infusion, but has later been demonstrated through oral protein intake.12
After protein intake, plasma amino acid levels must decrease before protein synthesis can be stimulated again by another protein intake. This “muscle full”-effect does not seem to happen post-exercise, so a protein intake immediately after working out can be followed by a protein-rich meal an hour later without impairing the amino acid response.
This “muscle full”-effect also indicates that it is not a good idea to sip on amino acid-rich beverages throughout the day. This practice provides too little amino acids at one time to achieve a robust stimulation of muscle protein synthesis, and it might also lessen the response to regular protein-rich meals by keeping plasma amino acid levels slightly elevated.
Old Muscle Requires More Protein
Someime after the age of 60, a phenomenon called amino acid resistance manifests itself.13 This means that an older individual requires more protein per intake to fully stimulate muscle protein synthesis compared to a younger individual.
This can either be accomplished by increasing the amount of protein-rich food eaten within the context of a meal or by adding a protein supplement to a regular meal. The first alternative can be impractical, since protein is the most satiating of the macronutrients, and old age is often followed by a decrease in appetite.
A meal providing a sub-optimal amount of protein can be “rescued” by adding 5 grams of the amino acid L-leucine to a meal, thus improving its anabolic properties to that of a normal protein-rich meal. This effect can be seen both in young and old individuals.14 15
The evidence suggests that there is indeed a limit to how much protein can be utilized from one meal for muscle building purposes. That limit seems to be around 30 grams of protein at rest. A higher protein intake in one sitting decreases protein breakdown, but it is unclear how much of this decrease is comprised of muscle protein breakdown. Decreasing muscle protein synthesis in this manner might not even be beneficial to achieve muscular hypertrophy.
Post-exercise, this limit seems to be around 20 grams of protein per intake, if one or two muscles have been exercised. Following a whole-body workout, 40 grams of protein leads to a more substantial increase in muscle protein synthesis, although double the amount of protein does not equal double the protein synthesis.
It doesn’t have to be more complicated than spreading the daily protein intake out over the day with moderate servings of protein of around 30–40 grams each. Meals of 40 grams of protein seem like a sensible approach, even with the upper plateau at around 30 grams where larger amounts do not increase protein synthesis further. There is likely an individual response to protein intake, so a small safety margin might be prudent, and certainly will not hurt.
Note that all protein in the diet should be included when calculating protein intake, not just protein sources like meat, fish, and poultry. A bowl of oatmeal with milk and eggs provides protein from all three sources, not just the milk and eggs. Even if one food article in isolation does not provide a complete protein, with adequate proportions of each of the nine essential amino acids necessary for muscle protein synthesis, it is automatically complemented when part of a varied diet.
For individuals older than 60–65 years of age or for vegans, it might be prudent to increase the protein content of each meal by 5–10 grams. In the first case because of the previously mentioned amino acid resistance of old age, and in the second because vegetarian protein sources do not provide the same amounts of the essential amino acids used to synthesize muscle.
Don’t Worry Too Much About Small Details
In conclusion: don’t fret overly much over minor details. Fanaticism doesn’t build muscle. You don’t have to eat every third hour to gain muscle mass or become stronger. One meta-analysis examined the effect of meal frequency on body composition and found no significant difference between few and many meals.16 If there is such a difference, it certainly is not a large one.
Do you like eating a few large meals per day rather than many small meals? Maybe you practice intermittent fasting? No problem. You can reach your body goals with such feeding practices as well. This has been shown in practice many times. It is also quite possible that such a meal pattern makes it easier to lose body fat or to keep a low body fat percentage.
Nothing will go horribly wrong if you don’t consume some form of protein every third or fourth hour. Strength training is the number one factor for muscle mass and strength. The total protein- and energy intake per day, over longer periods of time, make it possible for your training routine to give you the results you desire. Meal- and protein frequency might be the icing on the cake, but it will not be the things that make or break your progress. The best results are often the results you get from doing what you like, not forcing yourself to follow a diet or a training program you feel aversion to.
It might not be 100% optimal to eat your entire daily protein intake in a few large meals, but the differences won’t be crucial.
Ninety-seven percent optimal can get you pretty far, as well.
- J Am Diet Assoc. 2009 Sep;109(9):1582-6. A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects.
- Clin Nutr. 2013 Apr;32(2):309-13. Is there a maximal anabolic response to protein intake with a meal?
- Clin Nutr. 2018 Apr;37(2):411-418. Update on maximal anabolic response to dietary protein.
- J Am Coll Nutr. 2005 Apr;24(2):134S-139S. Dietary protein to support anabolism with resistance exercise in young men.
- Clin Nutr. 2013 Apr;32(2):309-13. Is there a maximal anabolic response to protein intake with a meal?
- PLOS One, November 10, 2015. Post-Prandial Protein Handling: You Are What You Just Ate
- Nutrients. 2012 Jul; 4(7): 740–758. Exercise and Amino Acid Anabolic Cell Signaling and the Regulation of Skeletal Muscle Mass.
- Nutrients 2018, 10(2). Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training.
- Am J Clin Nutr. 2009 Jan;89(1):161-8. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men.
- Am J Clin Nutr. 2014 Jan;99(1):86-95. Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise.
- Physiol Rep. 2016 Aug;4(15). The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein.
- Am J Clin Nutr. 2010 Nov;92(5):1080-8. Muscle full effect after oral protein: time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling.
- FASEB J. 2005 Mar;19(3):422-4. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle.
- Nutr Metab (Lond). 2011 Oct 5;8:68. Skeletal muscle protein metabolism in the elderly: Interventions to counteract the ‘anabolic resistance’ of ageing.
- J Physiol. 2012 Jun 1;590(11):2751-65. Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men.]
- Nutr Rev. 2015 Feb;73(2):69-82. Effects of meal frequency on weight loss and body composition: a meta-analysis.