Efficacy Of A 13 C ‘Breath Test’ To Determine Protein Anabolism After Physiological Feeding And Exercise
Bibliographic record
Abstract
Dietary amino acids that are not oxidized are retained in the body to support net protein anabolism, which is important for individuals aiming to maintain or enhance lean body mass. There are limited methodologies with which to measure protein anabolism noninvasively in response to physiological stimuli (e.g. single meal feeding and exercise), which represents a challenge for research in vulnerable populations. PURPOSE: To determine the efficacy of a novel, noninvasive stable isotope ‘breath test’ to measure differences in anabolism in response to a physiological anabolic stimulus. METHODS: Fifteen healthy men were randomized to a rested (FED; n=7; 23±5y; 77±4kg; 14±3% body fat; mean±SD) or post-resistance exercise (EX-FED; n=8; 22±2y; 78±10kg; 13±5% body fat) condition. Participants consumed a mixed carbohydrate (0.75g/kg body weight) complete amino acid (0.25g/kg) beverage modeled on the composition of egg protein, with a leucine content of 20mg/kg enriched to 5% with L-[1-13C]leucine, which is primarily metabolized within skeletal muscle. CO2 production was measured hourly via indirect calorimetry, and breath samples were collected every 20-30min during the 5h postprandial period to determine 13CO2 enrichment via isotope-ratio mass spectrometry. Dietary leucine kinetics are expressed as the cumulative percentage of 13C excreted (%LEU) and total exogenous leucine oxidation (OX) over 5h. Dietary net leucine balance (BAL) was determined by the difference between leucine intake and OX. RESULTS: %LEU was lower (P=0.03) in EX-FED (14.2±1.9%) vs. FED (16.3±1.2%). Similarly, OX was lower (P<0.01) in EX-FED (60.8±6.5μmol/kg/5h) vs. FED (70.2±5.3μmol/kg/5h), which resulted in a greater (P<0.01) BAL in EX-FED (90.5±6.5μmol/kg) vs. FED (81.1±5.3μmol/kg). CONCLUSION: We demonstrate that a novel, noninvasive breath test based on oral [13C]leucine ingestion can detect greater anabolism with resistance exercise in young men. Muscle protein enrichment analysis is ongoing to determine the extent to which these whole-body outcomes reflect those within skeletal muscle. Further validation will enhance the applicability of this new technique to a variety of populations experiencing growth (e.g. children) and/or atrophy (e.g. clinical populations).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".