Intra-workout protein added nothing over carbs alone

Most research on protein and resistance training is conducted in the fasted state, yet most people actually lift having eaten. That gap matters, because if a meal has already supplied amino acids, adding more protein around the session may have little left to contribute. The practical question is whether protein consumed during a workout, on top of carbohydrate, buys extra muscle beyond the carbohydrate's calories alone. This trial also looked at whether baseline hormonal and fitness characteristics predicted who grew most.

Seventeen physically active young men completed an 8-week supervised resistance training programme, randomised to intra-workout carbohydrate plus protein (n = 8) or isoenergetic carbohydrate alone (n = 9), with all training performed in a non-fasted state. Assessments before and after included body composition, physical performance, blood variables and muscle biopsies. Muscle fibre cross-sectional area was analysed both by fibre type and distributionally across percentiles, rather than only as a group mean. Baseline testosterone, insulin-like growth factor 1, capillary density and maximal oxygen uptake were examined in relation to fibre cross-sectional area gains. The authors state that, given the limited sample size, the analyses should be considered exploratory.

There were no significant between-group differences for any outcome, with all p-values above 0.05 — intra-workout protein conferred no measurable advantage. Training itself, however, produced significant increases in lean mass, muscle strength, VO2max, fat oxidation capacity and fibre cross-sectional area. Type IIA fibre area rose from a median of 5232 μm2 to 5925 μm2, and distributional analysis showed the increase spanned the full percentile range, indicating a broad hypertrophic response, while type I fibres changed more modestly and less uniformly. A marked fibre-type transition occurred: type IIX fibres fell from about 1.2% to about 0.0%, and IIA/IIX hybrids from about 8.9% to about 4.4%. Baseline IGF-1 showed an exploratory association with fibre growth (p = 0.04), whereas testosterone, capillary density and VO2max did not.

This complicates the popular framing of intra-workout protein as a hypertrophy lever, at least when training is not fasted and calories are matched. It aligns with a broader shift in the field towards total daily protein and training stimulus mattering more than precise timing, though a single small trial cannot settle that. The fibre-type transition and the breadth of the type IIA response add mechanistic detail about how eight weeks of lifting remodels muscle. The IGF-1 association is intriguing as a possible predictor of responsiveness, but the authors flag it as needing confirmation in larger studies.

This is a reason to think that if you have eaten before training, sipping protein mid-session is unlikely to be the variable holding your progress back. What did reliably change here was everything driven by the training programme itself, across both groups. Because the trial included only 17 men and was explicitly exploratory, modest benefits cannot be ruled out, and a null result in a small study is weaker evidence than a null result in a large one. The findings speak to physically active young men, and other populations may respond differently.},