" Examining protein change theory and the upper limits of protein intake"

Throughout the years it is a question that is asked by both scientists, and laymen alike, yet a one true answer still remains to be clear. No, it’s not “what is the meaning of life?” There are more important things to worry about right now. The thing people really want to know is “How much protein should I consume each day to build muscle?”

The answer to this question will change depending on who you ask. I have heard all of the answers. Some say 2.75 grams per kg of lean mass per day, others say 2 grams per pound of bodyweight, and then there is the always popular answer to consume 1 gram of protein per pound of bodyweight. These are drastically different numbers, just where do they exactly come from, and which one is right, who should you trust?

There have been many studies that have set out to find exactly how much protein is needed for optimal growth. Unfortunately, the scientific community has had answers that seem as varied as the bodybuilding community at times. Different studies show varied muscle growth rates with drastically different protein intakes. How can this be?

Well, new research is showing that protein intake is not as clear cut as most make it out to be. So what does this new research say is the optimal protein intake? The simple answer may just be… more than you are taking in now.

Protein Spread and Change Theories

In a recent review published in The Journal of the International Society of Sports Nutrition, Bosse and Dixon review protein “spread” and “change” theories. This is an excellent review that not only gives an explanation for the inconsistent results of protein intake studies but also gives insight into the way we should view protein intake in general.

Protein spread theory states that when a study is being conducting that there must be a sufficient percentage difference in g/kg/day protein intake between groups during a protein intervention to result in muscle and strength differences. (1) Sometimes when studies compare high vs. low protein intakes there is not enough difference or spread of intake between the high and low groups to show a significant benefit from additional protein. This helps explain some of the inconsistencies of protein intake research.

Protein change theory is what should interest the average bodybuilder/ lifter the most. Protein change theory states that for strength and muscle gains there must be a sufficient increase in dietary protein from habitual intake to study intake. (1) This means once a study comparing protein intake establishes sufficient “spread”, the researchers must also ensure that the subjects are consuming sufficiently more protein than their typical, pre study intake.

This review pulls data from many different studies and shows that the results are not as chaotic as they may seem at first glance. It makes the most convincing argument for protein spread and change theories to date. For the full results of the review I highly suggest you read the review yourself.

While protein “spread” and “change” theories are both significant I want to focus most of our attention on protein change theory as this has the biggest implications in terms of practical application as well as telling us how our bodies react to protein and amino acids.

Protein Change Theory

What protein change theory shows is that the human body can essentially become used to a given amount of protein, and to further stimulate anabolism additional protein will be needed. When discussing protein intake one cannot simply compare grams per kg per day. Change from baseline intake must be considered. For example, let’s say we have two completely identical bodybuilders that both weigh 200 lbs. Our first bodybuilder has been consuming 200 grams of protein per day. Our second bodybuilder has been getting 275 grams of protein per day. Let’s now assume that our first bodybuilder increases his protein intake to 275 grams per day. Our second bodybuilder keeps his protein intake the same at 275 grams per day. As you see below, our two identical bodybuilders are now consuming identical protein intakes. The main difference though is that there is a difference in the % increase, and protein change theory tells us that this is important.

Even though these two bodybuilders are completely identical in every way, and are consuming the same amount of protein, the bodybuilder that had the biggest increase will likely now begin to grow at a faster rate.

There is one thing to note about this example though. While our first bodybuilder will likely now begin to grow at a faster rate, this will not last forever. The body will eventually begin to adapt to the higher protein intake and anabolism rates will begin to slow. This explains how people can have similar protein intakes yet have different rates of growth over a period of time. Protein change theory demonstrates metabolic adaptation at its finest.

Metabolic Adaptation

The human metabolism is a multitude of chemical reactions within the body and is incredibly complex. Protein change theory requires we consider metabolic adaptation when determining optimal protein intake. In previous articles and videos I have discussed the issue of metabolic adaptation and how it relates to fat loss, but these metabolic adaptations are also a determining factor in muscle growth and protein intake as well. The body will ALWAYS strive for homeostasis no matter the circumstance. One thing that very few people consider is that the human metabolism is not static. There are many things that affect the metabolism that are out of our control such as height, age, sex, and certain hormones. Things that we can control such as calorie/macronutrient intake, physical activity, and body weight/lean body mass will all cause the body to make changes in metabolic rate in order to achieve balance.

The common view of the human body seems to be that it is almost like a bank where we deposit and withdraw calories. The typical “calories in vs. calories out” argument for fat loss and muscle growth is a perfect example of this view, explaining that we must expend more calories than we consume to lose weight and we must consume more calories than we expend to gain weight. The truth is that this is only part of the picture. The human body is less like a bank and more like the stock market. We can make deposits and withdrawals but the market is always fluctuating according to and reacting to what is put in and what comes out. Like the stock market, we have to consider the state of the market before we determine what we will put in and take out.  

Many people still cannot quite grasp how protein can be subject to the body’s metabolic adjustments. The common belief regarding protein intake is that you simply need to make sure that sufficient amino acids are available for the body to build muscle. While this is true it is not the whole story of protein, and it is oversimplifying the role of amino acids and proteins within the body.

Protein and Amino Acids as Signaling Molecules

By now we have all heard it a million times. Proteins are made up of amino acids and amino acids are the building blocks of muscle tissue…etc, etc. I have read that line a million times in magazines and articles. This is usually where the information about amino acids stops in most articles. This is what gives many people the idea that there is a magic amount of protein that is sufficient or optimal. If amino acids are only used as substrate then one would be led to think that you simply need to supply enough substrate to get the job done. It doesn’t work quite like that.

While it is true that amino acids were long considered simply substrates for protein synthesis, they have more recently shown to also act as modulators of intracellular signal transduction pathways that are typically associated with growth-promoting hormones such as insulin and IGF-1. This means particular amino acids not only serve as substrates for protein synthesis but are also modulators of the process as well. (2) This has been found to be especially true of the amino acid leucine and it’s regulation of the mTOR pathway.

Since amino acids are signaling molecules and not simply substrate then this will make them subject to the body’s metabolic adaptations. It appears that over time the body will become less sensitive to the anabolic response of amino acids, therefore more protein will be necessary to further drive change. This means that optimal protein intake is no longer a static number.

Protein Synthesis and Net Anabolism

This is still not the whole story of protein intake. While amino acids act as the modulators of protein synthesis, there is a limit to how much protein synthesis can be stimulated so there must be another way in which protein can signal growth. Several studies have shown that stimulation of muscle protein fractional synthetic rate can be maxed out with an intake of 20-30 grams of protein. (3) When determining what is best for muscle growth it is foolish to look solely at protein synthesis rates. Protein intakes that are above the maximum amount required to stimulate synthesis can still be beneficial. A prevailing thought among bodybuilders is that if you take in too much protein at one time the excess amino acids will just be wasted. This is rather silly when you think about it. Before modern times, humans did not have access to steady protein intakes. Homo sapiens would frequently kill an animal and stuff themselves to capacity with meat. There was no way to stick this protein away and save it for later, they had to eat it now. It would be rather inefficient of the body to let these amino acids go to waste since significant protein meals could be days apart in these times.

Total muscle growth is not simply the result of protein synthesis. Instead we must look at net anabolism. To determine net anabolism we must consider both muscle protein synthesis AND muscle protein breakdown. Contrary to what many think, the body is constantly in a simultaneous state of synthesis and breakdown. When synthesis outpaces breakdown we have anabolism, when breakdown exceeds synthesis we have catabolism.

Additional protein intake once maximum protein synthesis has been achieved can still lead to increased net anabolism by attenuating breakdown, rather than further stimulating protein synthesis. When protein is consumed in large amounts protein synthesis levels will begin to increase, but only to a point. Once the maximum protein synthesis rate is reached, intracellular amino acid levels will begin to rise. If protein intake continues to increase, total anabolism will continue to rise even without a corresponding increase in protein synthesis. This response seems to happen because the continued rise of intracellular amino acid levels signal to limit the rate of protein breakdown. (4) It is thought that this signal to decrease breakdown is due to the action of insulin and has no limit, as protein breakdown will continue to decrease with ever increasing protein intake. (5, 6) This is what takes place at a single feeding, so it is reasonable to assume that this will apply to every feeding during the day. This not only shows that the extra daily protein intake will lead to growth, but also that there is no “limit” to how high a single bolus of protein should/could be. In other words, anyone that says you can’t take in more than a certain amount of protein in one meal is just wrong.

Takeaways and Implications

Protein change theory offers some interesting takeaways and implications as far as protein intake is concerned. Let’s examine the three main takeaways from the newer research:

There is no upper limit or maximum amount of protein that will not lead to further growth.

We now know there is no reasonable limit to protein intake within a given meal or within a day. We need to throw out the idea of there being a “limit” as to how much protein is of use within the body.

Protein intake and its effect on muscle growth is highly dictated by how much protein is currently being consumed and how much is added to that baseline level. This means adding additional protein added to the diet is very likely to stimulate extra growth and there appears to be no point at which this will not hold true.  BUT this does not mean that you should begin eating 600 grams of protein just yet. Which bring me to takeaway number two.

Protein intake must be kept high but adjusted for the individual metabolism.

Protein change theory shows that there is no set “optimal protein intake” that will fit everyone. This means there is no magical amount of grams per bodyweight that will work as a cookie cutter plan for everyone to use. While it seems on the surface that more protein is always better, this is not necessarily true. It is important to keep in mind that nothing within the human metabolism is isolated and everything works in relation to everything else.

Different people will have different macronutrient requirements and it is important to remember that carbohydrates and fats carry their own anabolic and performance benefits. If protein intake is too high, then carb and fat intake will need to be kept unacceptably low in order to avoid exceeding calorie requirements. In the long run this will ultimately hinder muscle growth. On the other hand, if protein intake it set too high and without lowering carbohydrate and fat intake then calorie levels will be too high and body fat levels will sky rocket.

People with an endomorphic body type will have vastly different macronutrient breakdowns than those with ectomorphic qualities. So the goal for any metabolic type should to be to consume as much protein as possible while not exceeding your caloric needs, and also not interfering with the needed intake of other macronutrients.

I realize this is vague, but learning the ins and outs of an individual metabolism is not a simple process. When I work with clients it can take weeks to truly know their metabolism.

Protein intake may need to slowly increase over the course of a bodybuilder’s career.

If protein change theory holds true, it implies that over the course of time there should be an increase in the average protein intake for a lifter. It seems as though the body can become less sensitive to the effects of amino acids over time so it could feasibly take higher and higher amounts to further stimulate growth.

Once again, this does not mean that you should be consuming a thousand grams of protein once you are in your 50’s. This still should not interfere with other macronutrient needs, but a slight increase in the average protein intake over the course of a bodybuilding career may be a good idea.

Where We Go From Here

It should be noted that there are many other factors regarding protein intake that affect growth such as protein source, timing of ingestion (refractory response), and amino acid make up. Those issues open up an entirely new can of worms and each one could be the topic of its own article. For now we can take the new information and use it to adjust our protein intake accordingly.

There is still plenty of research to be done, but what we know about protein and amino acids has increased dramatically in recent years. Protein change theory is still a relatively new idea and the details are not fully understood quite yet, but ideas such as this may lead us to a better understanding of protein intake as a whole. Every new discovery makes things that much clearer for us within the bodybuilding world. Who knows? Maybe someday years from now we will know all there is to know about protein and amino acids. Then we can finally get around to solving that meaning of life thing.

1. J. Bosse, B. Dixon. Dietary protein to maximize resistance training: a review and examination of protein spread and change theories
. J Int Soc of Sports Nutr 2012,
Published: 8 September 2012.
2. S.R. Kimball, L.S. Jefferson. Role of amino acids in the translational control of protein synthesis in mammals.  Seminars in Cell and Developmental Biology; 2005 Feb; V. 16 Issue 1, p. 21-27.
3. 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 Sep;109(9):1582–1586PubMed PMID:19699838. Pubmed Central PMCID: 3197704. Epub 2009/08/25. Eng.
4. Wolfe RR, Miller SL. Amino acid availability controls muscle protein metabolism. Diabetes Nutr Metab. 1999 Oct;12(5):322–328PubMed PMID: 10741346. Epub 2000/03/31. Eng