Protein is built from amino acids, and the authors note that the ability of a protein to stimulate muscle building depends on which amino acids it contains rather than on its bulk. The effect is attributed mainly to the essential ones, and within those to a group of three called branched chain amino acids, of which leucine is the one most often singled out. The authors also note the timing claim they are testing, that the window for taking them is immediately after exercise, because no benefit has been seen two hours later.
Drawn from the paper's introduction.
The authors point out that the earlier work claiming a benefit from this kind of supplement was not comparative, which leaves open whether the benefit came from the amino acids or from taking something at all. Their stated gap is that no study had demonstrated the benefits of a branched chain amino acid rich supplement taken alongside exercise therapy in patients undergoing surgery for gastrointestinal cancer.
Drawn from the paper's introduction.
Single centre, single blind randomised controlled trial. Fifty patients with gastric or colorectal cancer scheduled for surgery were enrolled and one withdrew consent, leaving a full analysis set of 24 in the test group and 25 in the control group. Both groups received perioperative exercise therapy and took a jelly immediately after exercising. The test jelly carried 10 g of protein including 2,400 mg of branched chain amino acids, of which 1,400 mg was leucine, plus 15 g of carbohydrate. The control jelly carried no protein and 22.5 g of carbohydrate.
The two primary endpoints were percentage changes in thigh skeletal muscle area, from pre-intervention to nine weeks after discharge and from two weeks after surgery to nine weeks after discharge.
Quadriceps area change from pre-intervention to nine weeks after discharge was 3.24 plus or minus 6.63 percent in the test group and 2.34 plus or minus 16.59 percent in the control group, p equals 0.812. From two weeks after surgery to nine weeks after discharge it was 8.40 plus or minus 7.57 percent and 4.44 plus or minus 12.93 percent, p equals 0.229.
No significant differences were observed in hamstring area, isometric knee extension or flexion strength, or six minute walk distance. A mixed model adjusted for age and primary cancer did not change any conclusion.
Background intake was measured and did not differ. Protein intake at nine weeks after discharge was 1.29 plus or minus 0.30 against 1.39 plus or minus 0.36 grams per kilogram, p equals 0.298, with no difference at any of the four timepoints, and energy intake matched likewise. Adherence to cardiopulmonary training, muscle strengthening and jelly intake all exceeded 80 percent in both groups with no difference between them.
| Quadriceps area change, pre-intervention to nine weeks after discharge | 3.24% vs 2.34%, p=0.812 |
| Quadriceps area change, two weeks post surgery to nine weeks after discharge | 8.40% vs 4.44%, p=0.229 |
| Hamstring area change | 1.46% vs 1.71%, p=0.954 |
| Protein intake at nine weeks | 1.29 vs 1.39 g/kg, p=0.298, and no difference at any of four timepoints |
| Adherence | above 80% for exercise and supplement in both groups |
| Test supplement | 10 g protein, 2,400 mg branched chain amino acids, 1,400 mg leucine |
| Baseline age imbalance | 77.0 vs 72.7 years, p=0.034 |
| Registration | UMIN000036022 |
Proposed by the authors This is the explanation the authors offer in their discussion. This study did not test it.
The explanation the authors reach for is that the exercise swamped the supplement. Alongside endurance work the participants did strength training every day, and they argue the muscle building effect of that was prominent enough that any contribution from the amino acids could not be detected.
They then name the comparison itself as the second reason. In the earlier trials that found a benefit the control group took nothing after exercising, whereas here the control group took a carbohydrate supplement containing no amino acids, which they describe as a deliberate choice to test the supplement more accurately.
The conclusion they draw from the wider literature is that what matters is increasing overall protein intake rather than altering its distribution across the day.
Drawn from Discussion, PMC13626774.
The case for timing an amino acid supplement to the end of a session looks weaker once the comparison is something rather than nothing, and once ordinary food intake is measured rather than assumed.
Older adults recovering from surgery for gastric or colorectal cancer, following a supervised exercise programme for one week in hospital and nine weeks after discharge.
The same comparison at a higher branched chain amino acid intake, which the authors name themselves, and in a population whose ordinary protein intake is lower than it was here.
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