Only 30 Grams of Protein Per Meal?
Tim Skwiat, MEd, CSCS, Pn2
This is a really good—and important—question, and it’s one that we hear quite frequently, albeit it in a number of different ways. It can be best summed up like this: “I heard that you should only consume 30 grams of protein per meal, and anything beyond that is wasted. Is that true?”
When asked this question, prominent protein and amino acid researcher Dr. Donald Layman (Professor Emeritus in the Department of Food Science & Human Nutrition at the University of Illinois) said:
“It is one of my biggest pet peeves in the area.”1
The short answer is: While there may be a limit on how quickly the body can absorb protein, this is presumption is not true, and there is really no evidence to indicate that 30 grams is the “magic number” that should be consumed per meal.
However, I wouldn’t be satisfied providing you a short answer—particularly without supporting evidence—and I hope that you wouldn’t be either.
A good starting point for some background on this question and the benefits of a high-protein intake is understanding the difference between protein “need” and “optimization,” which you can learn about it the following article:
For starters, as is outlined in that article, there are a host of metabolic advantages associated with a higher protein intake.2 Higher protein diets have been shown to:
- Accelerate fat loss and spare calorie-burning lean body mass when following a reduced-calorie diet.
- Prevent weight regain and contribute to long-term weight maintenance.
- Optimize 24-hour muscle protein synthesis and facilitate the maintenance or building of calorie-burning lean muscle mass.
- Boost metabolic rate.
- Preserve metabolic rate after weight loss.
- Increase satiety and improve appetite control.
- Improve carbohydrate metabolism and glycemic regulation.
- Increase calcium absorption.
As described in the section Establishing the ‘New Normal,’ a high-protein diet would involve an intake upwards of 0.8 – 1 gram of protein per pound of body weight per day. Thus, you can see that body weight is one of the factors that may dictate how much protein is consumed per meal. With that in mind, a 200-pound man and a 150-pound women would have significantly daily protein needs. If the 30-gram rule were in play, then each would have to spread their protein intake out over the appropriate number of meals (i.e., 7 and 5, respectively). However, the available evidence—both scientific research and real-world experience—tells us that, when it comes to body composition, meal frequency doesn’t matter when other variables (e.g., food choices, portion sizes) are controlled.
In one randomized controlled crossover trial published in The American Journal of Clinical Nutrition, researchers compared the effects of reducing meal frequency on a variety of health indicators in healthy, normal-weight adults. The study involved two 8-week treatment periods, during which time the participants consumed all of the calories (and protein, which was about 80 grams per day) needed for maintenance in either 3 meals per day or 1 meal per day.3
At the end of the study, the researchers found no effect of meal frequency on heart rate, body temperature, or the majority of blood chemistry variables. What they did find, however, was that the reduced meal frequency (i.e., 1 meal per day) result in a significant improvement in body composition marked by reduced body fat and modestly increased lean body mass, which one might have expected to drop.
In another randomized controlled crossover trial published in The American Journal of Clinical Nutrition, researchers from the University of Amsterdam provided further evidence that reduced meal frequency (a form of intermittent fasting) has no negative effect on lean body mass even when consuming an entire day’s worth of protein (80 – 100 grams) in a single 4-hour period.4
In a study published in The American Journal of Clinical Nutrition, French researchers a single protein feeding was more effective (in terms of protein synthesis) than four balanced protein feedings among a group of healthy older women.6 In a separate study published in The Journal of Nutrition, the same French researchers found no difference (in protein synthesis or breakdown) when healthy young women were given 0.77 grams of protein per pound of body weight per day either in one feeding or spread across four feedings.
Please see the section of the article above titled Show Me the Data for a litany of studies demonstrating that high-protein diets accelerate weight and fat loss and spare lean body mass.
The general consensus is that most folks will probably do best with 3 – 4 meals per day, spreading out their protein intake relatively evenly across those meals (rather than a “skewed” intake of protein). Please see the Balanced Bites section in the article cited above for more information.
As you’ll see in that section, researchers have made per-meal suggestions for protein intake based on maximizing muscle protein synthesis (MPS). In other words, a per-meal protein amount of about 0.18 grams of protein per pound of body weight optimally stimulates MPS and ingestion of protein beyond that amount does not appear to have any further impact on MPS.7,8 These findings have been similar among healthy young folks regardless of the type of food (i.e., protein supplements or whole food), whether at rest or after exercise, and regardless of fitness level.9–12
With that being said, a key finding to point out here is that the amount of protein needed to maximally stimulate MPS in healthy older men is substantially higher than the amount needed by healthy younger men. In other words, in addition to body weight, age also appears to be an important contributing factor when determining protein needs.
While larger amounts of protein can indeed be consumed and digested, they do not appear to further stimulate MPS, but they are oxidized at a higher rate, resulting in the production of urea.11,12 As Professor Layman has said on a number of occasions, “The notion that [protein] oxidation is bad I think is totally misleading.”1 As an adult, the body strives for balance/homeostasis, and increased protein oxidation concomitant with a higher intake is reflective of that (i.e., nitrogen balance). That being said, if we can swing the equation in favor of positive nitrogen balance while still consuming more protein, that may be worth discussing, which we will below.
Before moving on, one important thing to note is that these findings are based off acute protein-only feedings. In other words, it’s unknown how mixed meals may influence MPS.
With these MPS findings in mind, it’s plausible that the notion that the body can only “use” 30 grams of protein per feeding may have been born. However, if you go back to the article cited above, you’ll see that there are myriad benefits and metabolic advantages to high-protein diets beyond stimulating MPS.
For instance, high-protein diets increase satiety and improve appetite control.13,14 High-protein meals boost satiety, which means that protein-dense foods are much more likely to make you feel full and satisfied.13 What’s more, diets rich in high-quality proteins improve appetite control and reduce cravings, as well as reduce daily food intake.15
All foods that you eat requires calories to be burned in order to digest, absorb, and assimilate their nutrients. This is referred to as the Thermic Effect of Feeding (TEF). There is a general consensus in the scientific literature that protein stimulates TEF to a greater extent than other macronutrients (e.g., carbohydrates, fat).16 In fact, protein-rich foods are estimated to boost metabolic rate by as much as 30%, whereas as fats and carbohydrates are typically estimated to be in the 5 – 10% range.13
In other words, protein-rich foods have the greatest TEF, boosting the metabolism THREE to SIX TIMES more than carbs or fats.
This means that you burn more calories each day when you consume a high-protein diet, and it also means that protein-rich foods provide less metabolizable energy (than carbs or fats).17 This latter point is important to note. Going back to the section above about MPS, this means that “extra” protein that is oxidized provides less energy (i.e., calories) than carbs or fats, and as a result, the calories from protein are less likely to be stored as fat.
This leads to another great question. If you’re not eating protein, what else will you eat?
Along these lines, Professor Steve Simpson formulated the protein leverage hypothesis, which essentially posits that protein can reduce the intake of other nutrients (e.g., carbs, fats) due to a homeostatic mechanism based around a protein “seeking” behavior.18 In other words, protein is the driving force for appetite, and our bodies are programmed to eat toward a protein target.
Professor Simpson describes, “Interestingly, if protein in the diet is diluted, even by a small amount by extra fat and carbohydrate, the appetite for protein dominates and they will keep eating in an attempt to attain their target level of protein.”
A number of randomized controlled trials have tested Professor Simpson’s protein leverage hypothesis, and they have found that lower protein intakes are associated with the consumption of more snacks between meals and greater daily caloric intake than higher-protein diets.19,20
Further, in a recent meta-analysis (a high-level statistical analysis of the current body of research) published in the journal Obesity Reviews, a research team from the University of Sydney (including Professor Simpson) found that the amount of protein in the diet was negatively associated with total daily caloric intake. In other words, higher protein diets were associated with lower caloric intake, and lower protein intakes were associated with higher caloric intake, thus strongly supporting the the protein leverage hypothesis in lean, overweight, and obese humans.
One of the factors that may contribute to limiting how quickly the body can digest and absorb protein is saturation of the digestive enzymes responsible for the breakdown of protein (i.e., proteolytic enzymes). You see, the body has a limited number of digestive enzymes—which decline as a result of aging, environmental pollution, stress, processed foods, irradiated foods, not consuming enough raw foods, genetically modified food, and cooking methods—and that means the body can only digest protein at a certain rate.
Let’s take whey protein for example. Under normal circumstances, the maximum rate of absorption of whey protein is 8 – 10 grams per hour.21 Could the addition of proteolytic enzymes (i.e., enzymes that digest proteins) enhance the rate of absorption? That’s a great question, and it’s precisely one that researchers set out to answer in a recent study published in the Journal of the International Society of Sports Nutrition.22
In the study, on two separate occasions, a group of 41 healthy men drank a whey protein shake (containing 42.5 grams of protein)—first without any additional digestive enzymes, and then on a separate day, with the added proteolytic enzymes. The researchers measured the participants blood and urine at various points afterward (30 minutes, 1 hour, 2 hours, 3 hours, 3 ½ hours, and 4 hours) to assess the levels of amino acids (i.e., the building blocks of protein), which represents how much protein has been absorbed (in the blood) and the amount of nitrogen excreted (in the urine).
After drinking the whey protein shake by itself, the participants’ blood levels of amino acids (representing absorption) peaked after 4 hours, about 30% greater than baseline. After the participants drank the whey with added digestive enzymes, their levels of amino acids also peaked at 4 hours, however, in this case, they had increased by as much as 127% relative to baseline.
Over the course of the 4-hour time period, the addition of the protease enzymes led to a 3.5 TIMES greater increase in amino acid absorption.
Remember that the researchers also measured the amount of nitrogen excreted in the urine as well. This measure is a rough approximation of whether our muscles are in a state of balance (i.e., nitrogen in equals nitrogen out), growth (i.e., positive nitrogen balance), or breakdown (i.e., negative nitrogen balance). The researchers found that when the participants consumed the whey with the addition of proteolytic enzymes, they excreted less nitrogen, indicating a positive nitrogen balance and a more favorable environment for recovery and muscle growth.
This research indicates that protease supplementation significantly increases the rate of absorption of whey protein in liquid form. Thus, the researchers speculate that the rate-limiting step in the digestion process may be saturation of the body’s endogenous proteolytic enzymes.
One of the reasons that I point this out is because BioTrust Low Carb (my personal protein supplement of choice and what I recommend to my clients) contains a patented, research-backed specialized blend of proteolytic enzymes called ProHydrolase®, which has been shown to substantially increase the rate of digestion of the proteins found in BioTrust Low Carb. Based on the findings from the study above, this increased rate of digestion likely means greater blood levels of amino acids (i.e., absorption) and less urinary nitrogen excretion (i.e., positive nitrogen balance).
[Another side benefit of ProHydrolase and enhanced protein digestion is the mitigation of GI discomfort (e.g., nausea, bloating, gas, cramping) associated with inadequate digestion of proteins.]
Researchers from Deerland Enzymes recently assessed the impact that ProHydrolase had on the breakdown of the proteins in BioTrust Low Carb, and the results were nothing short of amazing. Two samples of BioTrust Low Carb were tested for protein breakdown—one sample with ProHydrolase and one without. After just 15 minutes, 20% of the initial protein with ProHydrolase was already digested. After 60 minutes, 96% of the protein had been broken down with the addition of ProHydrolase. The protein samples without ProHydrolase showed little to no breakdown at all time points measured, which is consistent with the rate of digestion described in the study above.
The section above indicates that the body has a certain capacity to digest proteins limited by the amount of endogenous proteolytic enzymes. So, you may be asking yourself whether supplementation with digestive enzymes may be a good idea with other protein-containing meals to maximize protein absorption and utilization. This is a very good question, and while we can’t say for certain, it does seem to be a plausible conclusion.
In general, orally administered digestive enzyme products containing proteases have very few side effects. Issues tend only to arise in cases of hypersensitivity (i.e., allergic reaction) to the source of the enzymes, which may be bovine-, porcine-, or plant-based (e.g., fungal, papaya, pineapple).23
As you already know, the body has a finite number of endogenous proteolytic enzymes for protein digestion. Further compounding that, there are a number of additional factors that can affect the body’s natural digestive enzyme production and supply, including (but not limited to) aging, environmental pollution, stress, processed foods, irradiated foods, not consuming enough raw foods, genetically modified food, and cooking methods.
The notion that we’re born with a finite number of enzymes during our lifetime, stems from research conducted by Dr. Edward Howell, a noted pioneer in the field of enzyme research, who coined the Enzyme Nutrition Axiom, which states:
“The length of life is inversely proportional to the rate of exhaustion of the enzyme potential of an organism. The increased use of food enzymes promotes a decreased rate of exhaustion of the enzyme potential. Another rule can be expressed as follows: Whole foods give good health; enzyme-rich foods provide limitless energy.”24
Thus, age is inversely correlated with enzyme production, as the organs responsible for producing digestive enzymes become less efficient. This is particularly interesting to note because evidence suggests that suggests that older folks tend to be less sensitive to a specific dose of protein. In other words, whereas 20 grams of protein may be sufficient to stimulate muscle protein synthesis in healthy, young folks, it may take significantly more protein (e.g., up to 40 grams) to elicit the same response in older folks.25 While there are likely to be a number of factors in play, some speculate that the body’s supply of proteolytic enzymes (or lack thereof) may play a contributing role.
Further, food choices also affect the body’s ability to produce digestive enzymes. Dr. Howell discusses this at length; in fact, he states, “The increased use of food enzymes [e.g., supplemental enzymes, raw foods] promotes a decreased rate of exhaustion of the enzyme potential.”
For instance, raw, whole foods provide food enzymes, which help promote their digestion. Cooking methods (e.g., heating) destroys food enzymes, and by the same token, processed foods are void of said food enzymes. Certain micronutrients (e.g., magnesium, zinc, iron) are also required for optimal enzyme function. Via dietary displacement, if someone is eating predominantly nutrient-sparse foods, that means s/he is also eating fewer nutrient-dense foods, which contribute these vital nutrients for enzyme production.
Another factor that may affect digestive enzyme supply is stress. Stress initiates the sympathetic branch of the nervous system—the “fight or flight” response—which works in direct opposition with the parasympathetic nervous system, also known as the “rest and digest” branch of the nervous system. The parasympathetic division stimulates digestion whereas the sympathetic branch typically inhibits it.
The digestive system is densely innervated by both branches of the nervous system, and the sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion.27 When the parasympathetic branch of the nervous system is activated, digestive enzymes are released; on the other hand, when the sympathetic nervous system is activated saliva production is reduced and many digestive system functions are slowed or stopped.
With all of this in mind, supplementation with a high-quality digestive enzyme product (containing ample proteases) may be a good idea for many folks who are looking to optimize protein absorption.
- There doesn’t appear to be a “magic number” for protein to which we need to limit ourselves on a per meal basis.
- Factors that seem to be most important are body weight and age. Protein intake can be calculated on a daily (0.72 – 1g per pound of bodyweight), and it’s a good idea to spread this out over 3 – 4 meals (at least 0.18g per pound of body weight).
- On a per meal basis, muscle protein synthesis (MPS) may be optimized at 0.18g of protein per pound of body weight.
- However, are numerous metabolic advantages and benefits to consuming a high-protein diet beyond muscle protein synthesis, including improved satiety, increased metabolic rate, and positive dietary displacement (i.e., eating more protein-rich foods means eating less “other stuff”).
- The body’s ability to digest protein may be limited by its endogenous production and supply of proteolytic enzymes. Choosing a protein supplement with a blend of proteolytic enzymes appears to be an effective solution to increasing protein absorption and augmenting nitrogen balance.
- There are a number of factors that may impact the body’s supply of digestive enzymes, including age, stress, food choices, whether food is cooked or raw, and environment. Supplementation with digestive enzymes may be a safe, effective strategy to decrease the rate at body’s natural supply is exhausted as well as enhance protein digestion and absorption.
- Lennon D. Donald Layman, PhD – Leucine Kinetics, mTOR Activation & the Anabolic Response to Protein. http://sigmanutrition.com/episode123/.
- Pasiakos SM. Metabolic Advantages of Higher Protein Diets and Benefits of Dairy Foods on Weight Management, Glycemic Regulation, and Bone: Benefits of higher protein…. J Food Sci. 2015;80(S1):A2-A7. doi:10.1111/1750-3841.12804.
- Stote KS, Baer DJ, Spears K, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. 2007;85(4):981-988.
- Soeters MR, Lammers NM, Dubbelhuis PF, et al. Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. Am J Clin Nutr. 2009;90(5):1244-1251. doi:10.3945/ajcn.2008.27327.
- Jakobsen LH, Kondrup J, Zellner M, Tetens I, Roth E. Effect of a high protein meat diet on muscle and cognitive functions: a randomised controlled dietary intervention trial in healthy men. Clin Nutr Edinb Scotl. 2011;30(3):303-311. doi:10.1016/j.clnu.2010.12.010.
- Arnal MA, Mosoni L, Boirie Y, et al. Protein pulse feeding improves protein retention in elderly women. Am J Clin Nutr. 1999;69(6):1202-1208.
- Moore DR, Churchward-Venne TA, Witard O, et al. Protein Ingestion to Stimulate Myofibrillar Protein Synthesis Requires Greater Relative Protein Intakes in Healthy Older Versus Younger Men. J Gerontol A Biol Sci Med Sci. 2015;70(1):57-62. doi:10.1093/gerona/glu103.
- Morton RW, McGlory C, Phillips SM. Nutritional interventions to augment resistance training-induced skeletal muscle hypertrophy. Front Physiol. 2015;6. doi:10.3389/fphys.2015.00245.
- Cuthbertson D, Smith K, Babraj J, et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB J Off Publ Fed Am Soc Exp Biol. 2005;19(3):422-424. doi:10.1096/fj.04-2640fje.
- Symons TB, Sheffield-Moore M, Wolfe RR, Paddon-Jones D. A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects. J Am Diet Assoc. 2009;109(9):1582-1586. doi:10.1016/j.jada.2009.06.369.
- Moore DR, Robinson MJ, Fry JL, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr. 2009;89(1):161-168. doi:10.3945/ajcn.2008.26401.
- Witard OC, Jackman SR, Breen L, Smith K, Selby A, Tipton KD. Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise. Am J Clin Nutr. 2014;99(1):86-95. doi:10.3945/ajcn.112.055517.
- Halton TL, Hu FB. The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J Am Coll Nutr. 2004;23(5):373-385.
- Westerterp-Plantenga MS, Nieuwenhuizen A, Tomé D, Soenen S, Westerterp KR. Dietary Protein, Weight Loss, and Weight Maintenance. Annu Rev Nutr. 2009;29(1):21-41. doi:10.1146/annurev-nutr-080508-141056.
- Leidy HJ. Increased dietary protein as a dietary strategy to prevent and/or treat obesity. Mo Med. 2014;111(1):54-58.
- Westerterp KR. Diet induced thermogenesis. Nutr Metab. 2004;1(1):5. doi:10.1186/1743-7075-1-5.
- Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997;94(26):14930-14935.
- Simpson SJ, Raubenheimer D. Obesity: the protein leverage hypothesis. Obes Rev Off J Int Assoc Study Obes. 2005;6(2):133-142. doi:10.1111/j.1467-789X.2005.00178.x.
- Gosby AK, Conigrave AD, Lau NS, et al. Testing Protein Leverage in Lean Humans: A Randomised Controlled Experimental Study. Morrison C, ed. PLoS ONE. 2011;6(10):e25929. doi:10.1371/journal.pone.0025929.
- Martens EA, Lemmens SG, Westerterp-Plantenga MS. Protein leverage affects energy intake of high-protein diets in humans. Am J Clin Nutr. 2013;97(1):86-93. doi:10.3945/ajcn.112.046540.
- Bilsborough S, Mann N. A review of issues of dietary protein intake in humans. Int J Sport Nutr Exerc Metab. 2006;16(2):129-152.
- Oben J, Kothari SC, Anderson ML. An open label study to determine the effects of an oral proteolytic enzyme system on whey protein concentrate metabolism in healthy males. J Int Soc Sports Nutr. 2008;5(1):10. doi:10.1186/1550-2783-5-10.
- Lorkowski G. Gastrointestinal absorption and biological activities of serine and cysteine proteases of animal and plant origin: review on absorption of serine and cysteine proteases. Int J Physiol Pathophysiol Pharmacol. 2012;4(1):10-27.
- Howell E. Enzyme Nutrition. Penguin Group US; 1995. http://lib.myilibrary.com?id=717976. Accessed April 20, 2016.
- Breen L, Phillips SM. Nutrient interaction for optimal protein anabolism in resistance exercise: Curr Opin Clin Nutr Metab Care. 2012;15(3):226-232. doi:10.1097/MCO.0b013e3283516850.
- Browning KN, Travagli RA. Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions. Compr Physiol. 2014;4(4):1339-1368. doi:10.1002/cphy.c130055.