A study published in Oxford University’s Journal of Nutrition found that lean, resistance-trained men with high habitual protein intakes need much greater amounts to maximize whole-body anabolism. The recommendations for this type of protein consumer are severalfold higher than other populations.
 
It’s well established that dietary protein is crucial to exercise recovery, especially when it comes to resistance training exercises which predominantly engage non-skeletal muscle. The amount of protein needed for maintaining and maximizing muscle mass is a nutritional topic which is heavily investigated and debated. Research published in Oxford University’s Journal of Nutrition shows that whole-body anabolism requires a protein intake severalfold greater than current recommended dietary allowance.
 
In part, the purpose of this study was to determine if protein intakes for resistance-trained men could be higher without those participants seeing adverse health effects.
 
“What is noteworthy is that protein intakes that exceed the body’s capacity to incorporate amino acids into body protein stimulate irreversible oxidation and a subsequent increase in urinary urea production,” researchers noted. “Interestingly, the reported habitual protein intakes for resistance-trained men range between 2.0 and 4.0 [grams per kilogram of bodyweight daily].”
 
Using the indicator amino acid oxidation (IAAO) method, researchers analyzed the metabolic status of seven resistance-trained men, as they consumed significantly lower levels of dietary protein than usual and engaged in a resistance training routine. IAAO is a relatively novel technique, whereas researchers in the past investigated muscle-specific responses to protein through methods which narrowed a focus on skeletal muscle, overlooking the protein metabolism of the entire muscular system, the researchers said.
 
Additionally, resistance-trained athletes were shown to have distinct protein metabolism regulation after researchers used IAAO to trace specific amino acids.
 
The IAAO technique, while posing some limitations, is a much more noninvasive method of examining amino acid and protein intake requirements, and can be conducted in a much shorter time frame than previous methods. It can also be conducted on a wider variety of body types. In addition to being much less expensive, it is considered the best estimate of amino acid digestibility, though in can’t assess bioavailability, meaning that it is good for determining endpoint metabolism, but cannot actually analyze the biological mechanism affecting absorption of protein. Generally, IAAO can determine the availability of amino acids in food consumed by any given person within two weeks.
 
While previous studies have indicated that consuming more than 1.6 grams per kilogram of bodyweight per day provides no further benefit than that established upper limit, researchers determined through the use of IAAO that the upper limit actually shows a breakpoint protein intake of about 2 grams per kilogram of bodyweight per day before the threshold of whole-body anabolism is crossed in resistance-trained men.
 
“These findings are impactful as these authors reveal protein requirements that are severalfold greater than the RDA [Recommended Daily Allowance] and slightly higher for resistance trained men, who have habitually high protein intakes, on a nontraining day,” Paul T Reidy, Journal of Nutrition Editor, wrote.
 
What’s unclear, however, is where excess protein goes in resistance-trained men who eat above 2 grams of protein per kg of bodyweight daily. The seven men who were evaluated had habitually eaten 2.4 grams per kg of bodyweight daily leading up to the study. It is believed that high protein intakes could serve to promote visceral organ hypertrophy, an area which could have health risks associated with it and one that warrants further research.
 
“These questions remain: if this excess protein is impacting visceral protein metabolism and if so, what are the acute and chronic effects and implications?” Reidy continued. “These findings need to be confirmed in humans and we should consider what, if any, consequences of visceral organ hypertrophy exist and their implications for long-term health.”