Pre-sleep casein protein ingestion: new paradigm in post-exercise recovery nutrition

Abstract

[Purpose] Milk is a commonly ingested post-exercise recovery protein source. Casein protein, found in milk, is characterized by its slow digestion and absorption. Recently, several studies have been conducted with a focus on how pre-sleep casein protein intake could affect post-exercise recovery but our knowledge of the subject remains limited. This review aimed at presenting and discussing how pre-sleep casein protein ingestion affects post-exercise recovery and the details of its potential effector mechanisms. [Methods] We systematically reviewed the topics of 1) casein nutritional characteristics, 2) pre-sleep casein protein effects on post-exercise recovery, and 3) potential effector mechanisms of pre-sleep casein protein on post-exercise recovery, based on the currently available published studies on pre-sleep casein protein ingestion. [Results] Studies have shown that pre-sleep casein protein ingestion (timing: 30 minutes before sleep, amount of casein protein ingested: 40-48 g) could help post-exercise recovery and positively affect acute protein metabolism and exercise performance. In addition, studies have suggested that repeated pre-sleep casein protein ingestion for post-exercise recovery over a long period might also result in chronic effects that optimize intramuscular physiological adaptation (muscle strength and muscle hypertrophy). The potential mechanisms of pre-sleep casein protein ingestion that contribute to these effects include the following: 1) significantly increasing plasma amino acid availability during sleep, thereby increasing protein synthesis, inhibiting protein breakdown, and achieving a positive protein balance; and 2) weakening exercise-induced muscle damage or inflammatory responses, causing reduced muscle soreness. Future studies should focus on completely elucidating these potential mechanisms. [Conclusion] In conclusion, post-exercise ingestion of at least 40 g of casein protein, approximately 30 minutes before sleep and after a bout of resistance exercise in the evening, might be an effective nutritional intervention to facilitate muscle recovery.