REF-1541 · Gejl et al., 2017 · Medicine & Science in Sports & Exercise · Paper · PubMed

Does restricting carbs between two sessions add anything in elite men?

With doubles 3 days a week for 4 weeks, VO2max and time-trial power rose about 5% with no clear group difference. Tests the fuel, not doubling.

Main caveat: Abstract only. Arm sizes, arm means, sports and training content could not be read.
moderate evidenceMeasured on highly trained to elite athletes

Twenty-six elite male endurance athletes were matched and randomised to continue regular endurance training for 4 weeks with or without carbohydrate manipulation on three days a week.

Those days held a 1-h high-intensity bike session in the morning, 7 h of recovery on an isocaloric diet that was high (414 ± 2.4 g) or low (79.5 ± 1.0 g) in carbohydrate, then 2 h at moderate intensity on the bike, with or without carbohydrate.

VO2max, maximal fat oxidation and power in a 30-min time trial were tested before and after; the time trial followed 90 min of intermittent exercise, with carbohydrate before training and with both carbohydrate and placebo after.

Across all athletes VO2max and time-trial power rose 5 ± 1% (P < 0.05), and glycogen (18 ± 5%), citrate synthase (11 ± 5%) and pACC (38 ± 19%) rose, with no differences between groups. HAD and CPT1b did not change. Our reading: at this level, restricting carbohydrate between sessions showed no added gain over 4 weeks.

Because both arms did the same doubles, the rise is not attributable to the double, and the study has no bearing on it either way.

Protocol

Design: matched, then randomised into two groups (pairing not stated); 4 weeks of regular endurance training with the manipulation on 3 days a week.
Manipulation days: morning 1-h high-intensity bike session; 7-h recovery; isocaloric diets at 414 ± 2.4 g or 79.5 ± 1.0 g of carbohydrate; afternoon 2-h moderate bike session with carbohydrate in the high arm and without in the low arm, as we read the abstract's wording.
Tests: VO2max, maximal fat oxidation, a 30-min time trial after a 90-min intermittent preload.
Biopsies: glycogen, citrate synthase and HAD activity, CPT1b protein, phosphorylated acetyl-CoA carboxylase.
Not in the abstract: arm sizes, sports, the rest of the training week, blinding of tests, the size of second-session work, power or perceived exertion in training, biopsy timing, adverse effects, funding and interests.

Key Results

MeasureBoth groups, change over 4 weeksGroup difference
VO2max+5 ± 1% (P < 0.05)none reported
30-min time-trial power+5 ± 1% (P < 0.05)none reported
Muscle glycogen+18 ± 5% (P < 0.05)none
Citrate synthase activity+11 ± 5% (P < 0.05)none
pACC+38 ± 19% (P < 0.05)none
HAD activity, CPT1b proteinunchanged
Post-training time trial: performance was similar after carbohydrate and placebo during the preload, per the authors.
The abstract gives pooled changes only, so a reader cannot see each arm's mean or the interval on the difference.
No clear difference, not "similar." A null in about 13 men an arm (our arithmetic) leaves room for a small real effect either way, and at this level a small effect can matter (our inference).

Mechanisms

Measured: the muscle markers named showed no group difference after 4 weeks of restriction on three days a week.
Not reported in the abstract: acute signalling after the low-carbohydrate session, glycogen in the afternoon session itself, whether the second session's work was matched.
Not measured: any training on single-session days as a comparison, and any effect in women.

Practical Application

Does restricting carbs between two sessions add anything in elite men? With doubles 3 days a week for 4 weeks, VO2max and time-trial power rose about 5% with no clear group difference. Tests the fuel, not doubling.
Good for: a male endurance athlete at a high level weighing a low-carbohydrate gap on double days: no added gain showed here in performance or in the muscle markers named.
Good for: reassurance that eating about 414 g between sessions showed no clear cost in those adaptations, compared with 79.5 g, at matched energy.
Not good for: whether to do double days at all. Both arms did them.
Not good for: recreational athletes or women. Not from this paper: the active-people result in REF-1549 points the other way in a different population, and both tested the fuel.
Not good for: ruling out any benefit. Not from this paper: the pooled view for trained athletes is in REF-218, where the effect was not significant.

Limitations

Abstract only. Arm sizes, arm means, sports and training content could not be read.
Tests the fuel only. Any effect of doubling cannot be seen, in either direction.
Four weeks, men only. Nothing on longer restriction, or on women.
Regular training continued alongside, whose content is not in the abstract, so the share of the week under manipulation is unknown.
Pooled reporting. Individual and per-arm change are not printed.
Funding and conflicts could not be read.
How this entry was checked and changed
Why this level

parallel RCT with n = 26 (the rubric's 20-39 band). Read from the abstract only; no open copy in PubMed Central or Europe PMC. It sits at the low edge: arm sizes, group means and effect sizes are not in the abstract, and it is a null with no equivalence test