Hi Lenwine! This is a really good—and important—question, and it’s one we hear quite frequently, albeit in different ways.
In terms of a “limit” on how much protein can be consumed/used in a single meal, this will likely always be a topic of some debate. Our “foundational” recommendations are typically 0.45 to 0.68 grams of protein per pound of body weight per day to optimize fat loss while preserving/building lean body mass. That multiplier may increase upwards of 1 gram per pound of body weight in more active individuals. That is, protein intake may be in line with your energy needs/expenditure.
While this equation is in terms of body weight, we tend to agree with you that lean body mass may be more accurate. However, this opens the door to questions on the accuracy of body composition testing. Lean body mass may be an even better measure for obese populations. But because the body composition testing is likely to be even more skewed in this population, goal body weight may be a better figure to plug into the equation.
For someone as lean as yourself, using body weight would be perfectly fine.
Can You Absorb More than 30 grams of Protein at One Time?
The short answer is: While there may be a limit on how quickly the body can absorb protein, there is really no evidence to indicate 30 grams is the “magic number” that should be consumed per meal.
In fact, 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
A good starting point is understanding the difference between protein “need” and “optimization.” For starters, there are a host of metabolic advantages associated with a higher protein intake,2 including:
- Accelerating fat loss and sparing calorie-burning lean body mass when following a reduced-calorie diet.
- Preventing weight regain and contributing to long-term weight maintenance.
- Optimizing 24-hour muscle protein synthesis and aiding muscle mass maintenance or building.
- Boosting metabolic rate.
- Preserving metabolic rate after weight loss.
- Increasing satisfaction and improving appetite control.
- Improving carbohydrate metabolism and glycemic regulation.
- Increasing calcium absorption.
A high-protein diet would involve an intake upwards of 0.8 – 1 gram of protein per pound of body weight per day. So 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 woman would have significantly different 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 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, 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 periods: participants consumed all of the calories (and protein—about 80 grams per day) needed for maintenance in either 3 meals per day or 1 meal per day.3 The researchers found no effect of meal frequency on heart rate, body temperature, or the majority of blood chemistry variables.
What they did find was the reduced meal frequency (i.e., 1 meal per day) resulted in a significant improvement in body composition with reduced body fat and modestly increased lean body mass.
In two other studies, French researchers found a single protein feeding was more effective (in terms of protein synthesis) than three to four balanced protein feedings.6
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.
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
Another 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, age also appears to be an important contributing factor when determining protein needs.
It’s plausible the notion that the body can “use” only 30 grams of protein per feeding may have been born with these findings in mind. However, there are numerous 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 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, as well as reduce daily food intake.15
All foods you eat require calories to be burned 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 greater 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 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 you burn more calories each day when you consume a high-protein diet, and it also means protein-rich foods provide less metabolizable energy (than carbs or fats).17 This means “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.
If You’re Not Eating Protein, What Else Will You Eat?
Protein is the driving force for appetite, and our bodies are programmed to eat toward a protein target.18 As Professor Steve 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 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 research team from the University of Sydney (including Professor Simpson) found 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 protein leverage hypothesis in lean, overweight, and obese humans.
Adding Digestive Enzymes to the Protein Equation
Another factor 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.
One of the issues with whey protein in particular seems to be its rate of absorption. For whey protein to be effective (i.e., digested, absorbed, and assimilated), it must be broken down into smaller peptides within 90 minutes of consumption. Undigested whey protein will essentially not be utilized by the body. What’s more, inadequate digestion of whey protein will often result in GI discomfort, like gas, bloating, and nausea.
Could the addition of proteolytic enzymes (which digest proteins) enhance the rate of absorption? That’s a great question, and it’s one researchers set out to answer in a recent study.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). This 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, they had increased by as much as 127% relative to baseline.
That is, over the 4-hour time period, the addition of the protease enzymes led to a 3.5 TIMES greater increase in amino acid absorption.
The researchers also measured the amount of nitrogen excreted in the urine. This 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 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 protease supplementation significantly increases the rate of absorption of whey protein in liquid form. Thus, the researchers speculate the rate-limiting step in the digestion process may be saturation of the body’s internal proteolytic enzymes.
Since it appears the body has a certain capacity to digest proteins limited by the amount of proteolytic enzymes, you may be asking yourself whether supplementation with digestive enzymes is a good idea with other protein-containing meals to maximize protein absorption and use? Good question! While we can’t say for certain, it does seem to be plausible.
In general, taking digestive enzyme products containing proteases have very few side effects. Issues tend to arise only 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
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.
Whew! That’s a lot of information on one Q&A. If you have any comments or other questions you would like one of our coaches to answer, please feel free to comment below.