There have been a lot of studies confirming the importance of protein supplementation to enhance post-exercise recovery. However these studies tested subjects in the morning after an overnight fast. Many athletes train in the afternoon or evening several hours after a meal. Reporting in the American Journal of Physiology, researchers for the first time examined the effects of protein and carbohydrate supplementation during resistance exercise performed in the evening in normal, fed conditions. Ten healthy men were studied in the evening 2 hours after dinner on two occasions. During one trial they consumed carbohydrate before and during a two hour resistance exercise workout. The carbohydrate supplement consisted of a beverage 50% glucose and 50% maltodextrin consumed before exercise (about 8 g) and then approximately 2-3 g were ingested every 15 min during the 2 hour exercise bout. During the other trial, subjects performed the exact same protocol except in addition to the carbohydrate, they consumed an equal amount of protein hydrolysate. The important findings were that the carbohydrate only supplement resulted in a negative whole body protein balance, whereas coingestion with protein resulted in a positive protein balance. Skeletal muscle protein balance was 49% higher after protein co-ingestion compared to the carbohydrate treatment. The results show that protein supplementation stimulates whole body and muscle protein synthesis rates during resistance exercise even in the fed state after a normal dinner. Thus, it appears that as far protein supplementation is concerned it does not matter what time of day you workout.

Beelen M, Koopman R, Gijsen AP, Vandereyt H, Kies AK, Kuipers H, Saris WH, van Loon LJ. Protein coingestion stimulates muscle protein synthesis during resistance-type exercise. Am J Physiol Endocrinol Metab. 2008 Jul;295(1):E70-7. Epub 2008 Apr 22.