Literature Review: The Anabolic Response to Protein Ingestion During Recovery From Exercise Has No Upper Limit in Magnitude and Duration in Vivo in Humans | Part I

Oftentimes in the realm of medicine and research, a landmark study is betrothed upon us. These studies tend to cause a chasm or shift within the scientific community. After all, this should be the aim of research; to challenge what is known and create a stage for critical thinking. Well… that just happened in the world of sports nutrition, and it’s taking the world by storm.

On December 19th, I started my routine indoor cycling on my smart trainer. Right before the pedals started churning, I glanced at an alert email from Cell Press- one of the most prestigious medical journals in research. I skimmed the alert, seeing words like “anabolism” and “timing.” At the time, I didn’t think much of it and went on with my intervals. As I ended my workout two hours later, I realized that this study just tossed a hand grenade into the realm of sports nutrition, our understanding of protein intake, and anabolism.  

Before we begin diving into this paper, we need to understand a few key terms. Anabolism is the synthesis of new molecules in the body, such as glycogen, from the exogenous molecules that we eat. Simply put: carbs, fat, and proteins that we ingest are turned into complex molecules. These processes require ATP- the energy currency of the cell. Next up are Amino Acids: the building blocks of protein. There can be hundreds if not thousands, of amino acids in a single protein molecule. The body spends a relatively enormous amount of energy to break down these protein bonds- releasing the individual amino acids from them. What’s more, amino acids play an important role as signaling molecules for complexes like mTOR. Finally, we need to understand that this study utilized isotope tracing to track the metabolic fate of each amino acid that was administered to the candidates.

Image: Schematic diagram showing anabolism and catabolism

Now, for the sake of not driving everyone mad, I am not going to get into isotope tracing but will quote the brief description from the study:

“Stable isotope methodology allows the assessment of dietary protein-derived  amino acid kinetics and the metabolic fate of ingested-protein-derived amino acids” (Trommelen et al., 2023.)

Now let’s dive into the details. The study, titled “The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans,” is a “hand grenade” because it challenges the previous notion that anabolism does indeed have an upper limit in humans (Chan et al., 2019.) In other words, at 100 grams of protein ingested after a workout, there is no demarcation to how much of those amino acids can be used by the body for biological processes like tissue repair and muscle hypertrophy.

Also Read: How Much Protein Should I Eat Before a Race?

It is important to note that many past studies around anabolism have either used 25 grams of protein as their test material or did not perform this research in vivo. Furthermore, most previous studies only measured the anabolic response for up to 6 hours. Trommelen et al. used both a 100-gram protein drink as well as an observational period of 12 hours.

Second, Trommelen et al. found that there was no increase in the amount of oxidation of these amino acids in vivo. This is a vital finding because it demonstrates that excess protein is not oxidized, as believed in current academia. In layman’s terms: the excess protein we ingest is not going to waste- it is being used by the body in a constant state of tissue turnover. The anabolic response to protein ingestion has no upper limit. 

Also Read: How Much Protein is Too Much?

Because there is so much to unpack here, I am going to publish this into a multipart series. Please stay tuned for part II of this series. In the meantime, I invite you to sign up for my newsletter and to read the study here.

References

Chan, A. H., D’Souza, R. F., Beals, J. W., Zeng, N., Prodhan, U., Fanning, A. C., Poppitt, S. D., Li, Z., Burd, N. A., Cameron-Smith, D., & Mitchell, C. J. (2019). The Degree of Aminoacidemia after Dairy Protein Ingestion Does Not Modulate the Postexercise Anabolic Response in Young Men: A Randomized Controlled Trial. The Journal of Nutrition, 149(9), 1511–1522. https://doi.org/10.1093/jn/nxz099

Trommelen, J., van Lieshout, G. A. A., Nyakayiru, J., Holwerda, A. M., Smeets, J. S. J., Hendriks, F. K., van Kranenburg, J. M. X., Zorenc, A. H., Senden, J. M., Goessens, J. P. B., Gijsen, A. P., & van Loon, L. J. C. (2023). The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Reports Medicine, 4(12), 101324. https://doi.org/10.1016/j.xcrm.2023.101324

About protein intake:

To maximize muscle growth and recovery after a workout, the combination of BCAAs (branched-chain amino acids) and protein plays a crucial role. These essential amino acids, found in protein-rich sources, are particularly effective in promoting muscle protein synthesis. When considering the best post-workout drink for building muscle, it's essential to include a source of quality protein. Many fitness enthusiasts turn to milk as an excellent post-workout beverage due to its ideal protein composition. The balance of whey and casein proteins in milk provides a sustained release of amino acids, aiding in muscle repair and growth. Determining how much protein you need depends on various factors such as your body weight, activity level, and fitness goals. As a general guideline, individuals aiming to build muscle should consume an adequate amount of protein, typically ranging from 1.2 to 2.2 grams per kilogram of body weight. Tailoring your post-workout nutrition to include both BCAAs and an optimal protein source, like milk, ensures you provide your body with the necessary building blocks for muscle recovery and growth.