Benefits
Muscle size and strength with resistance training
In a 12-week randomized trial in 44 young men, a nightly protein drink (27.5 g of protein) before sleep led to larger gains in one-rep max strength, thigh muscle cross-sectional area and type II muscle fiber size than a placebo drink. The abstract describes a protein supplement without naming the protein type, and this is the only long-term pre-sleep trial cited here.
Overnight muscle protein synthesis after evening exercise
In 16 young men who lifted weights in the evening, 40 g of casein taken 30 minutes before sleep was digested and absorbed overnight, raised whole-body protein synthesis and made net protein balance positive compared with placebo. Muscle protein synthesis was about 22 percent higher, a borderline result (p=0.05). In another study, evening exercise raised overnight synthesis from 30 g of casein by 37 percent.
Slow, sustained amino acid release
In a tracer study in healthy adults, casein gave a slower, longer, moderate rise in blood amino acids than whey, probably because it leaves the stomach more slowly. Casein lowered whole-body protein breakdown by 34 percent while whey did not, and net leucine balance over 7 hours was more positive with casein. These were whole-body measures after one meal, not muscle growth.
Short-term muscle response compared with whey and soy
In young men given drinks matched for 10 g of essential amino acids, micellar casein raised muscle protein synthesis less than whey hydrolysate or soy, both at rest and after leg exercise. The groups were small (6 men each) and synthesis was measured for a few hours, so the result shows a slower response rather than less muscle gained over time.
Mechanism of action
Clotting in the stomach
Casein forms clumps in acidic stomach contents, which slows how fast it leaves the stomach. In the tracer study cited here, this was the likely reason casein produced a slower, longer rise in blood amino acids than whey, which gave a sharp but short rise.
Leucine and the mTOR pathway
Like other complete proteins, casein supplies leucine, which switches on the mTOR signal that starts muscle protein synthesis; this pathway is worked out mainly in laboratory research. In the comparison study cited here, casein raised blood leucine less than whey and gave a smaller short-term synthesis response.
Less whole-body protein breakdown
After a single meal in healthy adults, casein lowered whole-body protein breakdown by 34 percent while whey did not. This was measured across the whole body, not in muscle specifically, and over 7 hours after one meal.
Clinical trials
Randomized placebo-controlled trial of a nightly pre-sleep drink with 27.5 g of protein, 15 g of carbohydrate and 0.1 g of fat versus a noncaloric placebo during a 12-week progressive resistance training program. (Snijders et al. 2015, J Nutr)
44 healthy young men aged about 22.
Strength rose more with protein than placebo (+164 vs +130 kg in summed one-rep max, p<0.001). Quadriceps cross-sectional area grew more with protein (+8.4 vs +4.8 cm2, p<0.05), as did type II muscle fiber size. The abstract describes a protein supplement and does not name the protein type. One co-author worked at DSM.
Trial in which young men did evening resistance exercise, had a recovery drink, and then took 40 g of labelled casein or a placebo drink 30 minutes before sleep, with overnight tracer measurements. (Res et al. 2012, Med Sci Sports Exerc)
16 healthy young men.
Casein was digested and absorbed during sleep and kept blood amino acids raised through the night. Whole-body protein synthesis (311 vs 246 micromol/kg over 7.5 h) and net protein balance (+61 vs -11) improved versus placebo (p<0.01). Muscle protein synthesis was about 22 percent higher, a borderline result (p=0.05).
Randomized study of 30 g of labelled casein before sleep, with or without resistance exercise earlier in the evening; there was no casein-free group. (Trommelen et al. 2016, Med Sci Sports Exerc)
24 healthy young men (12 per group).
About 57 percent of the casein-derived phenylalanine appeared in the blood overnight. Overnight myofibrillar protein synthesis was 37 percent higher with prior exercise (0.055 vs 0.040 percent per hour, p<0.001), and more casein-derived amino acids were built into new muscle protein. It compared exercise with no exercise, not casein with placebo.
Tracer study in which healthy adults ate one meal of labelled casein or whey with the same leucine content, with whole-body leucine kinetics measured for 7 hours. (Boirie et al. 1997, Proc Natl Acad Sci U S A)
Healthy adults (group sizes are not given in the abstract).
Whey caused a sharp but short rise in blood amino acids, while casein caused a longer, moderate rise. Whey raised whole-body protein synthesis by 68 percent and casein by 31 percent; casein lowered protein breakdown by 34 percent and whey did not. Net leucine balance over 7 hours was more positive with casein. Whole-body measures only.
Acute study of three groups given a drink with 10 g of essential amino acids as whey hydrolysate, micellar casein or soy protein isolate, at rest and after one-leg resistance exercise. (Tang et al. 2009, J Appl Physiol)
18 healthy young men (6 per group).
Whey raised blood leucine and essential amino acids more than casein or soy. At rest, muscle protein synthesis was about 93 percent higher after whey than casein; after exercise it was about 122 percent higher than casein and 31 percent higher than soy. Soy raised synthesis more than casein at rest (64 percent) and after exercise (69 percent). Casein gave the smallest response. Small groups and a few hours of measurement.
Systematic review, meta-analysis and meta-regression of randomized controlled trials lasting at least 6 weeks that combined resistance training with dietary protein supplements. (Morton et al. 2018, Br J Sports Med)
1863 healthy adults across 49 trials.
Protein supplements increased one-rep max strength by 2.49 kg, fat-free mass by 0.30 kg and muscle fiber size versus control. The effect on fat-free mass shrank with age and was larger in people already resistance trained, and there was no further gain above about 1.62 g/kg/day of total protein. Protein supplements in general, not one protein type. The senior author has received support from the US National Dairy Council.