Table 1.
Summary of findings from studies that measured blood leucine concentration profiles and post-prandial rates of muscle protein synthesis at rest in older adults.
| References | Participants | Study design/Intervention | Muscle fraction for post-prandial MPS measurement | Evidence supporting “leucine trigger” hypothesis | Blood leucine concentration profile | Post-prandial rates of MPS profile |
|---|---|---|---|---|---|---|
| Fuchs et al. (22) | Healthy, untrained males (71 ± 1 yr) | Double-blinded, Parallel RCT 6 g BCAA (n = 15) 6 g BCKA (n = 15) 30 g milk protein (n = 15) |
Myofibrillar 0–5 h | No | Peak plasma leucine concentrations: BCAA (45–60 min) > Milk (75–90 min) > BCKA (45–60 min). Overall plasma leucine concentrations: BCAA > Milk > BCKA. |
Milk (0.022 ± 0.002%/h) = BCAA (0.022 ± 0.002%/h) = BCKA (0.021 ± 0.001%/h) at 0–2 h from BL. Milk (0.039 ± 0.004 %/h) > BCAA (0.024 ± 0.005 %/h) = BCKA (0.024 ± 0.005%/h) at 2–5 h. |
| Devries et al. (23) | Healthy, untrained females (69 ± 1 yr) | Single-blinded, parallel RCT 15 g milk (4.2 g LEU) (n = 11) 15 g milk + soy (1.3 g LEU) (n = 11) |
Myofibrillar 0–4 h | Yes | Peak and overall plasma leucine concentrations: Milk > milk + soy. | Milk>milk + soy; +53% from BL vs. +13% from BLCorrelation between peak plasma leucine concentrations and MPS:(r = 0.57, P = 0.01) |
| Reitelseder et al. (24) | Healthy, moderately active males (69 ± 1 yr) | Single-blinded, RCT 0.45 g/kg LBM WH (n = 10) 0.45 g/kg LBM CAS (n = 9) |
Myofibrillar 0–3 h | No | Overall plasma leucine concentrations: WH > CAS at 15–90 min. | CAS (0.045 ± 0.003%/h) = > WH (0.043 ± 0.004%/h) |
| Kouw et al. (25) | Healthy, untrained males (72 ± 1 yr) | Double-blinded, parallel RCT PLA (n = 12) PRO20 [20 g casein (n = 12)] PRO20 + LEU [20 g casein and 1.5 g LEU (n = 12)] PRO40 [40 g casein (n = 12)] |
Myofibrillar 0–7.5 h | Yes | Peak plasma leucine concentrations: PRO20 + LEU (396 ± 20 μM) > PRO40 (316 ± 19 μM) > PRO20 (269 ± 10 μM) at 30–180 min. PRO40 > PRO20 + LEU at 180–480 min. | L-[ring-2H5]-phenylalanine) PRO40 (0.044 ± 0.003%/h) > PRO20 + LEU (0.039 ± 0.002%/h) > PRO20 (0.037 ± 0.003%/h) > PLA (0.033 ± 0.002%/h). L-[1-13C]-leucine PRO40: (0.058 ± 0.003%/h) > PRO20 + LEU (0.056 ± 0.002%/h) > PRO20 (0.046 ± 0.004%/h) = PLA (0.047% ± 0.004%/h). |
| Gorissen et al. (26) | Healthy, untrained males (71 ± 1 yr) | Double-blinded, parallel RCT 35 g wheat (n = 12) (2.5 g LEU) 35 g WPH (n = 12) (2.5 LEU) 35 g micellar casein (n = 12) (3.2 g LEU) 35 g whey (n = 12) (4.4 g LEU) 60 g WPH (n = 12) (4.4 g LEU) |
Myofibrillar 0–4 h | No | Peak plasma leucine concentrations: 35g whey (580 ± 18 μM) > 60g wheat (378 ± 10 μM). | 35 g micellar casein > Whey > Wheat at 0–4h60 g WPH > 35 g whey at 2–4 h. Micellar casein (0.050% ± 0.005%/h) > 60 g WPH (0.049% ± 0.007%/h) > 35 g WPH (0.032% ± 0.004%/h). |
| Churchward-Venne et al. (27) | Healthy, untrained males (71 ± 1 yr) | Parallel RCTn = 32 25 g bovine milk serum casein 25 g casein protein |
Myofibrillar 0–5 h | No | Overall plasma leucine concentrations: Casein > Bovine milk serum casein at 30–180 min. | Bovine milk serum casein = casein at 0–2 h.(0.038 ± 0.005 vs. 0.031 ± 0.007%/h). Casein > Bovine milk serum casein at 2–5 h.(0.067 ± 0.005 vs. 0.052 ± 0.004 %/h). |
| Mitchell et al. (28) | Healthy, middle-aged sedentary to recreationally active males WPC (52.6 ± 3.9 yr) MPC (52.1 ± 6.4 yr) | Double-blinded RCT 20 g WPC (2.3 g LEU; n = 8) 20 g MPC (2.1 g LEU; n = 8) |
Myofibrillar 0–3.5 h | No | Plasma leucine concentrations: WPC > MPC at 45 and 75 min | WPC (0.021 ± 0.018 %/h) > MPC (0.019 ± 0.009 %/h) at 0–210 min MPC (0.057 ± 0.018 %/h) > WPC (0.052 ± 0.024 %/h) at 0–90 min |
| Wall et al. (29) | Healthy, untrained males (74 ± 1 yr) | Parallel RCT CAS + LEU [20 g casein (n = 12)] CAS [20 g casein and 2.5 g LEU (n = 12)] |
Mixed 0–6 h | Yes | Overall plasma leucine concentrations: CAS + LEU > CAS at 30–180 min. | CAS + LEU (0.0078 ± 0.001 %/h) > CAS (0046 ± 0.001 %/h) at 0–2 h. CAS + LEU (0.023 ± 0.002 %/h) > CAS (0.019 ± 0.001 %/h) at 2–6 h. CAS + LEU (0.049 ± 0.003 %/h) > CAS (0.040 ± 0.003 %/h) at 0–6 h. |
| Pennings et al. (30) | Healthy, untrained males (74 ± 1 yr) | Parallel RCT 20 g whey (n = 16) 20 g casein (n = 16) 20 g casein hydrolysate (n = 16) |
Mixed 0–6 h | Yes | Peak plasma leucine concentrations: Whey (526 ± 21 μM) > casein hydrolysate (381 ± 14 μM) > casein (282 ± 13 μM). | Whey (0.15 ± 0.02%/h) > Casein hydrolysate (0.10 ± 0.01%/h) > Casein (0.08 ± 0.01%/h). Strong positive (r = 0.66) correlation between plasma leucine concentrations and mixed MPS. |
| Koopman et al. (31) | Healthy, untrained males (64 ± 1 yr) | Crossover, Double-blinded trialn = 10CAS (35 g intact casein) or CASH (35 g hydrolyzed casein) |
Mixed 0–6 h | Yes | Overall plasma leucine concentrations: CASH: 42.7 ± 2.3 > CAS: 32.6 ± 1.8 μmol·6 h/kg (AUC). | CASH (0.068 ± 0.006 %/h) > CAS (0.054 ± 0.004 %/h). |
AUC, area under curve; BCAA, branched-chain amino acids; BCKA, branched-chain keto acids; BL, baseline; LEU, leucine; MPC, milk protein concentrate; MPS, muscle protein synthesis; PLA, placebo; RCT, randomized controlled trial; WPC, whey protein concentrate; WPH, wheat protein hydrolysate.
Values are presented as means ± SE.