# Divergent serum metabolomic, skeletal muscle signaling, transcriptomic, and performance adaptations to fasted versus whey protein-fed sprint interval training

PMID: 34747202
Journal: American journal of physiology. Endocrinology and metabolism
Published: 2021 Dec 1
Authors: Aird TP, Farquharson AJ, Bermingham KM, O'Sulllivan A, Drew JE, Carson BP

## Question

How do fasted, whey protein concentrate-fed, and whey protein hydrolysate-fed conditions affect acute and 3-week metabolic and performance adaptations to sprint interval training?

## Summary

In recreationally active but aerobically untrained men, 3 weeks of Wingate sprint interval training improved mitochondrial enzyme activity and aerobic/anaerobic performance regardless of whether sessions were done fasted, after whey protein concentrate, or after whey protein hydrolysate. Protein feeding changed acute amino-acid and muscle-signaling responses and did not blunt training adaptations.

## Population

- Twenty-eight healthy recreationally active male participants aged 18-35 years who were aerobically untrained, protein sufficient, and nonobese.
- Sample size: 28
- Age: 18-35 years; group means 23.6-26.1 years
- Sex: Male
- Fitness level: Recreationally active but aerobically untrained; VO2max <50 mL/kg/min
- Health status: Healthy, nonobese, protein sufficient

## Methodology

- Randomized double-blind parallel-group nutrition and sprint interval training study
- 3 weeks plus acute biopsy/metabolomic testing
- Laboratory Wingate cycling, muscle biopsies, blood metabolomics, and performance testing
- Randomized and controlled study design.

## Protocol

- Wingate SIT with preexercise feeding condition.
- Modality: Cycle ergometer sprint interval training.
- Work intervals: 30 s all-out sprint.
- Recovery: 4 min active recovery.
- Sets or repetitions: 4 sprints in sessions 1-3, 5 sprints in sessions 4-6, 6 sprints in sessions 7-9.
- Intensity: All-out against resistance equivalent to 7.5% body mass.
- Session duration: 5-min warm-up, sprint/recovery set, 3-min cool-down.
- Frequency: Typically 3 sessions/week with 48-72 h between sessions.
- Program length: 9 sessions over 3 weeks.
- Progression: Sprint count progressed from 4 to 5 to 6.
- Fasted vs whey protein conditions.
- Modality: Same SIT protocol with different preexercise drink.
- Work intervals: 30 s all-out sprint.
- Recovery: 4 min active recovery.
- Sets or repetitions: Same progression.
- Intensity: All-out at 7.5% body mass resistance.
- Session duration: Same SIT session.
- Frequency: Same training frequency.
- Program length: 3 weeks.
- Progression: Same sprint progression.

## Outcomes

### Amino acids
Status: improved
WPH and WPC increased amino-acid availability versus fasted conditions.

Protein feeding increased 17 amino acids plus total BCAA, EAA, AA, and NEAA tAUC versus FAST (all p<0.05); WPH exceeded WPC for several amino-acid summaries

### Gene expression
Status: mixed
Protein did not blunt acute increases in key mitochondrial/metabolic genes; WPH enhanced CD36 response.

PGC-1alpha, PDK4, SIRT1, and PPAR-delta increased after acute SIT independent of nutrition; WPH beneficially altered CD36 mRNA expression

### Mitochondrial enzymes
Status: improved
Citrate synthase and beta-HAD activity increased after 3 weeks in all nutrition groups.

Authors reported augmented CS and beta-HAD after training with no nutrition-condition effect

### Performance
Status: improved
Aerobic and anaerobic performance improved after 3 weeks regardless of nutrition condition; WPH showed preliminary advantages for some anaerobic components.

Training improved aerobic mean power and Wingate measures within groups; mean-power adaptations did not differ significantly between nutrition groups

## Practical Insights

- Preexercise whey protein did not compromise short-term SIT performance or mitochondrial enzyme adaptations compared with fasted training.
- Fasted SIT is not required to preserve acute mitochondrial gene-expression responses in this context.
- The study is mechanistic and uses invasive measures; practical claims should be modest.

## Limitations

- Small parallel groups and some outcomes had n=8-10 per group.
- Only healthy young men.
- Only 3 weeks of training.
- Some between-group effect sizes suggested limited power.
- Industry funding from Carbery Food Ingredients.

## Safety And Adherence

- Across 241 exercise sessions, 10 incidences of gastrointestinal distress were observed.
- Participants were informed of risks and screened with PAR-Q/7D-PAR.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/34747202/) (pubmed)
- [DOI](https://doi.org/10.1152/ajpendo.00265.2021) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8906818/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.