Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Page numbers: 1560-1569
Summary of background and research design:
Background: Resistance training stimulates both protein synthesis and protein breakdown and, in the presence of adequate protein, net protein synthesis occurs. The result is an increase in muscle strength and size. It is known that a large amount of recovery and protein rebuilding occurs during sleep. It is unknown if protein ingestion immediately before sleep (in addition to a post-workout protein supplement) aids further in the development of muscle size and strength.
Hypothesis: Consumption of protein before bed will increase concentrations of amino acids in the blood and increase muscle protein synthesis during sleep.
Subjects: Recreationally active men (n = 15), age about 21-24 y
Experimental design: randomized, double-blind, placebo-controlled, crossover study
Protein – 450 g (about 2 cups) water with 40 g of isotopically labeled casein + strawberry flavor and artificial sweetener
Placebo- the same beverage without the protein (no calories)
Protocol: Before the study, the participants were evaluated for body composition including whole body fat percentage and percent fat in the trunk and legs. They were familiarized with the proper technique for leg press and leg extension. One repetition maxima were determined for each participant for both exercises. On the day of the test, each participant followed a standardized diet. At 4:30 pm, they reported to the laboratory and at 4:45 they consumed a standardized dinner. At 6:30 pm, the participants received a primed infusion of isotopically labeled phenylalanine (an amino acid whose fate can be traced) for analysis of protein turnover. A basal blood sample was also collected. A primed continuous tracer (isotopically labeled phenylalanine and tyrosine) was then started at 7:00 pm, also for determination of protein turnover. The participants rested for one hour, then began exercising at 8:00 pm. They performed a specific lifting routine focusing on the lower body. At the end of the exercise (9:00 pm), another blood sample was collected. They then consumed a post-workout beverage that consisted of 60 g carbohydrates and 20 g whey protein. At 11:30 pm, a muscle biopsy was acquired from the quadriceps, after which the participant consumed one of the test beverages (protein or placebo). The participant slept between 12:00 midnight and 7:00 am, when a second muscle biopsy was acquired. Blood samples were collected throughout the entire laboratory stay (18 total samples) and were analyzed for plasma concentrations of glucose, insulin, amino acids, and isotopically labeled phenylalanine and tyrosine. Rate of amino acid appearance and disappearance were calculated, from which fractional synthesis rate (FSR) of mixed muscle protein was then estimated.
Summary of research findings:
- Plasma glucose concentrations during the night were 5.1 ± 0.1 mM in the protein group and 5.2 ± 0.1 mM in the placebo group (not statistically different).
- Plasma insulin concentrations were significantly higher 15 and 30 min after beverage consumption (p < 0.01) but did not differ at other time points throughout the night.
- Essential amino acid concentrations in the plasma increased after the recovery beverage (consumed immediately after exercise) in both groups, and returned to baseline within 2.5 hours.
- After consumption of the test beverage, those in the protein group exhibited elevated essential amino acid concentrations at every time point throughout the night compared to the placebo group. During the night, maximum essential amino acid concentrations were about 1750 ± 150 µM in the protein group compared to about 700 µM for the placebo group.
- The rate of protein appearance in muscle tissue was significantly greater in the protein group vs. the placebo group. In fact, 50% ± 2% of the protein in the beverage was observed circulating the system as amino acids during the 7.5 hour period and was therefore available for protein synthesis.
- The fractional synthesis rate (FSR), or rate of muscle protein synthesis, was about 22% greater in the group that consumed protein before bed vs. the placebo (p = 0.05).
- The increase in FSR, in addition to a decrease in protein breakdown in the protein group, led to a net protein balance of +61 ± 5 in the protein group and -11 ± 6 in the placebo group.
Key practice applications: Protein ingestion before sleep was effectively absorbed and metabolized and led to significantly greater net protein synthesis compared to a calorie-free control. These data suggest that consumption of protein before bedtime will lead to a greater rate of recovery and a greater amount of protein synthesis, thereby resulting in greater strength and muscle size.
Limitations: The baseline diet in both groups contained about 1.2 g/kg body weight of protein. The protein treatment group received 40 g more protein than did the placebo group. Thus, because protein intake was not equalized between the two groups, it is not clear if the benefits observed in the protein group were specifically due to the timing of protein ingestion before bed or just the result of a higher overall protein intake. An improvement in the design would have been to equalize the protein intakes between groups, but have the placebo group take the 40-g protein treatment at a different time during the day.
Key search terms for this article (5-7 terms): protein, timing, before bed, sleep, casein, recovery