Upper Limits of Protein Intake

Upper Limits of Protein Intake

The history of protein intake and digestion  

A recent study from Luc van Loon’s lab has challenged the notion that our bodies can only digest 20-40 grams of protein per sitting. Instead, ingesting higher amounts of protein post exercise leads to a dose-response increase in protein absorption, muscle protein synthesis rates and whole body protein balance. While there are some limitations to the study, it opens the door to further research in this area. In turn, it may result in greater practicality and convenience when it comes to getting your proteins in. 

 Contrary to the popular “myth” that the body can only utilize 30 grams of protein at once, new research suggests that there is “no upper limit” to the anabolic response to protein ingestion.

Historically, we were led to believe that eating more than 20-30 grams of protein at once would be ‘wasted’ protein and there is no benefit from eating more than this in one sitting. The advice was then to evenly distribute your protein intake throughout the day, i.e., get protein in at every meal if you wanted to maximise absorption and muscle synthesis.  

From an evolutionary context, this may not have been the case. The reality then was more likely to consume large amounts of protein (when food was caught or available) rather than splitting your protein over 5 – 6 meals a day.  

Earlier studies measuring the anabolic response to protein using smaller doses (45g) of protein and in very short timeframes (6 hours or less) is what ultimately lead us to these conclusions. This is important because it means studies did not push the upper limits of large protein consumption nor were the impacts measured over longer periods of time, which seems to now have brought on new thoughts around protein consumption.  


Photo Credits:  Luc van Loon’s study

What happens with greater protein doses?  

In Luc van Loon’s study, 36 healthy men between ages 18 and 40 were given a single dose of milk protein of 0 grams, 25 grams, or 100 grams. They took blood samples and muscle biopsies up to 12 hours after ingestion to determine the time, magnitude of the anabolic response and the fate of the protein ingested. Prior to consuming the protein drink, the men participated in a single weight training session.

The results showed amino acids were higher for up to 5 hours with the 25 grams, and even higher and up to 12 hours (protein was still being digested) with the 100 grams compared with the controlled condition (0 grams).  

When muscle protein synthesis rates were measured over the 12-hour period, similar findings were observed. That being the 100 grams of protein increased muscle protein synthesis greater than 25 grams, and both increased protein synthesis more than the control condition (0 grams).

Interestingly, the larger muscle protein synthesis response was the result of a more prolonged response to 100 grams of protein.  

Specifically, muscle protein synthesis rates were 20% higher with 100 grams in the first 4 hours after ingestion, compared to 25 grams. Muscle protein synthesis rates were 40% higher in the 100 grams during 4–12 hours. Resulting in an overall 30% larger protein synthetic response in 100 grams compared to 25 grams. This shows over time that a larger dose of protein can be fully utilized by the body.

Mammalian target of rapamycin or mTOR is one of the key regulators of protein synthesis. Although mTOR activation (amino acids stimulate mTOR, especially Leucine) was elevated the first 4 hours after protein ingestion, this elevation did not last the entire 12 hours.  

This surge in mTOR seems necessary to encourage protein synthesis and at the same time it seems mTOR does not need to be constantly elevated if muscle growth is on the menu.  



Photo Credits:  Luc van Loon’s study

So what now?

It looks like the 20g – 30g of protein per serving no longer holds water when it comes to what the body can digest at one sitting. Given enough time the body will digest around 85% of the protein ingested (up to 100g or until new findings suggest otherwise) and oxidise the rest. 


Photo Credits: Canva

Some practical implications  

The study used milk protein, which was predominantly casein protein. Casein takes longer to digest and prolongs the anabolic response compared to other proteins. Would other faster absorbing proteins powders (whey protein isolate, whey protein, pea protein, etc) or whole foods (tofu, chicken, beef, etc) have the same effect? 

The study was done on a bunch of healthy athletic males whose ages ranged from 18 – 40 years of age. They also carried out a strength training session prior to the ingestion of the protein. Would these results be repeated on females, non-athletes, other age groups and at normal mealtimes without a pre-exercise session? 

The study is not suggesting athletes consume more protein at one sitting or should aim to get all their protein in one sitting. Rather it’s about asking if the old notion of our body only being able to digest 20g – 30g of protein in one sitting, is still valid. 

If you foresee yourself not being able to eat a protein source later in the day, then this new study suggests that stacking up a little more protein in one meal will still optimise muscle protein synthesis and not go to waste. It’s nice to know this option is officially on the table should you need it. 

Consuming 100g of protein (about 15 large eggs or 3 cans of tuna) in one sitting is a lot and not something most people will do or could do. So, distributing the load over the day may be more practical. It’s more important to get your total protein intake over a 24 hour, weekly and monthly period rather than the exact timing of the day and now it doesn’t matter whether it’s through larger or smaller doses either. 

One thing to consider is that if you do decide to abstain from eating for several hours, then the extra aminos circulating in the body may end up being used as a fuel source. This is not necessarily a bad thing but may not be the ideal approach if you are attempting to optimise protein synthesis. Instead, a lighter carbohydrate based snack may result in you using those carbohydrates as your fuel source and saving those amino acids for the guns!  


At Active Vita, we added Branched Chain Amino Acids (BCAAs) to our Energy Drink Mix as during exercise, our body can break down muscle and use it as a fuel source. The BCAAs therefore, help minimize potential muscle damage from exercise, reduce creatine kinase levels (an enzyme released when muscle tissue is damaged), and reduce perceived muscle soreness.

As long as you meet your total daily protein intake requirement, the timing and source (animal vs vegetarian) of protein don’t seem to be of major concern. Failing to meet your protein levels means the timing and type of protein becomes very important. 

Getting your overall protein intake is the priority here. Sedentary individuals could aim for 1g per kg of body weight while active individuals can bump this up to 2-3g per kg of body weight. If you are a 60kg athlete, then that’s 120g of protein per day if you go with 2g per kg of body weight. 

The above protein intake recommendations may be achieved through a balanced diet. If you need to top up your protein levels, then additional supplementation may be an option and has been shown to contribute to overall protein synthesis. Achieving your ideal protein intake is an art and science - so experiment and see what works best with your lifestyle. 



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