Protein ingestion increases rates of protein synthesis (i.e., anabolism), but dose-response studies suggest that this anabolic response has an upper limit and that beyond 20-30 g of intake, any excess protein would instead be oxidized as fuel.
Thus, conventional wisdom holds that total protein intake should be spread throughout the day to maximize anabolic benefits, but a recent study 1 (December 2023) has challenged this notion, suggesting that the anabolic response may continue to increase in response to protein servings well above 20-30g.
Results showed that protein synthesis rates increased after ingestion of both 25 g and 100 g protein solutions, but the responses were greater in magnitude and duration after ingestion of the higher protein drink.
The 100 g dose far exceeds the estimated threshold of 20-30 g for maximal protein synthesis, and anabolic responses to this dose continued even 12 hours after ingestion, much longer than previously thought.
Many have interpreted these results as a challenge to the notion of an upper limit to the anabolic response to protein ingestion. However, upon closer examination, we find that these new results do not so much invalidate previously held beliefs as they significantly qualify them.
The protein used in this study was 80% casein, which is digested and absorbed exceptionally slowly compared to other proteins. In contrast, whey and many other protein sources are absorbed almost immediately—within 1 to 2 hours of ingestion.
In summary, these results therefore demonstrate that the magnitude and duration of the anabolic response to protein ingestion are not limited and have already been underestimated in vivo in humans.
1. Trommelen J, van Lieshout GAA, Nyakayiru J, Holwerda AM, Smeets JSJ, Hendriks FK, van Kranenburg JMX, Zorenc AH, Senden JM, Goessens JPB, Gijsen AP, van Loon LJC. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023 Dec 19;4(12):101324. doi: 10.1016/j.xcrm.2023.101324. PMID: 38118410; PMCID: PMC10772463.
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