Issue 07 · 19 August 2026
A special issue on one question: which parts of the carbohydrate loading protocol actually matter. Eight papers from 1981 to this year, including the only meta analysis of loading protocols that exists, the closest thing to a head to head comparison of depletion against a taper, and a count of how many performance trials were ever blinded.
Issue 07: Sixty years of carb loading, and two blinded trials
25:25 · 19 August 2026
What sixty years of carb loading actually settled
Four beats, in the order the papers came. Every figure here appears on a study page in this issue, verified at its source.
The protocol got shorter, and nothing was lost
Three arms of one 1981 trial, run in the same runners with the same units, plus a later trial that removed the depletion phase altogether.
The first three rows are one trial and share their units, millimoles of glucosyl units per kilogram of wet tissue. The fourth is a separate trial with different methods and is placed on the day axis only, not on the same scale. Its result was maximal glycogen in type I, IIa and IIb fibres within 24 hours. Run times did not differ between the first three arms.
Six things were tested. Three predicted the overshoot
Meta regression across the cycling trials in the only quantitative meta analysis of loading protocols. Bars are R squared, the share of the variation between studies each factor explains.
Adding the top two factors to one model dropped heterogeneity from 92.4 to 66.1 percent, which says the trials have been disagreeing about protocol rather than about physiology. The bottom row is the one worth sitting with: how fit the athlete was explained none of the difference.
The knob that matters is the one being missed
Measured intake in the 48 hours before a race, against the loading guideline, in female triathletes at the 2024 IRONMAN World Championships.
Six of twenty three reached the guideline. The interviews say the reason was not that they did not know it: travel, nerves, food access and how it feels to eat that much.
Mean intake was 6.4 plus or minus 2.1 grams per kilogram. Higher carbohydrate intake correlated with faster finish times, which is a correlation across twenty three athletes at one event and not a demonstration that the carbohydrate caused it.
The muscle filled. The stopwatch did not notice
A placebo controlled trial over 100 kilometres, with carbohydrate taken during the ride as a racer would.
+18%
Muscle glycogen. 572 against 485 millimoles per kilogram of dry weight after loading, a significant difference.
no change
100 km time. 147.5 against 149.1 minutes, p = 0.4. Loading was numerically faster by about one percent, which seven riders cannot resolve.
And of the fourteen loading trials with a performance outcome, two were double blind and placebo controlled. Both of those also fuelled during the test, and neither found a benefit.
Two blinded trials finding nothing is not the same as nothing being there. The glycogen literature is solid. It is the step from a fuller muscle to a faster race that has barely been tested.
In this issue
Trained runners went through three exercise and diet regimens before a 20.9 kilometre run. The classical severe depletion arm and a moderate carbohydrate arm reached the same muscle glycogen, and no arm produced a faster run.
International Journal of Sports · Sherman et al. · 1 May 1981 · PMID 7333741
Eight endurance trained men ate 10 grams of high glycaemic index carbohydrate per kilogram a day and did no training. Muscle glycogen roughly doubled within 24 hours and then stopped moving, and every fibre type had already reached its ceiling.
European Journal of Applied · Bussau et al. · the University of Western Australia · 28 May 2002 · PMID 12111292
Twenty five men were put through either a depletion protocol or a taper only protocol and then fed identically for six days, with muscle glycogen measured every day by magnetic resonance. On day five the two protocols were level. On day seven the depletion group pulled ahead.
American Journal of Physiology, · Goforth et al. · the Naval Health Research Center · 5 August 2003 · PMID 12902321
The only quantitative meta analysis of carbohydrate loading protocols pooled 30 studies and then tested which parts of the protocol predicted the size of the glycogen overshoot. Two variables mattered and four did not, and one of the four was maximal oxygen uptake.
Frontiers in Physiology 16:1620943 · Solem et al. · the Norwegian School of Sport Sciences · 18 August 2025 · PMID 40901614
An earlier trial had reported that women could not supercompensate muscle glycogen at all. When carbohydrate was prescribed per kilogram of lean body mass instead of as a share of habitual energy intake, women loaded as well as men.
European Journal of Applied · James et al. · the University of Western Australia · 1 October 2001 · PMID 11718281
Among female triathletes at the 2024 IRONMAN World Championships, 6 of 23 reached the 8 to 12 g/kg carbohydrate loading guideline, with a mean intake of 6.4 g/kg. Interviews found the shortfall was not a knowledge gap.
European Journal of Sport · Fortis et al. · Liverpool John Moores University · 1 July 2026 · PMID 42274547
Seven well trained cyclists rode a 100 kilometre time trial twice, once after carbohydrate loading and once after a placebo controlled moderate carbohydrate diet, eating carbohydrate during both rides. Loading raised muscle glycogen significantly and did not change the time.
Journal of Applied Physiology · Burke et al. · the Australian Institute of Sport · 1 April 2000 · PMID 10749820
A systematic evaluation of the carbohydrate loading performance literature found that only two of fourteen studies were double blind and placebo controlled. Both of those also fuelled athletes during exercise, and neither found a performance benefit.
International Journal of Sport · Jones et al. · Liverpool John Moores University · 24 June 2026 · PMID 42342234
Where the protocol argument actually sits
Opinion Our reading of what these eight papers add up to. Everything above this line came from the papers. This part did not.
The protocol most people picture comes from the late nineteen sixties. Several days of very low carbohydrate paired with hard training to empty the muscle, then several days of flooding it. The depletion half of that came out of a single elegant experimental design, one legged cycling, in which only the leg that had worked overshot. That is a good reason to think depletion matters. It is not the same thing as a trial that gave one group a depletion phase and another group none, and then compared them.
The worry usually raised about carbohydrate loading is that athletes do a one day version of a protocol built to run for a week, and that this is why it disappoints. It is a reasonable worry and the evidence does not support it. Sherman's runners reached the same muscle glycogen on a moderate diet as on a severe one, in 1981. Bussau's athletes hit their ceiling in twenty four hours with no depletion at all, in every fibre type. Goforth ran the closest thing to a head to head, and the depletion group did finish ahead, on day seven. On day five, which is where a real taper sits, the two protocols could not be told apart.
The meta analysis is the useful document here, because it is the only one that tests the knobs rather than the outcome. Two things predicted the size of the overshoot: how carbohydrate rich the diet was, and how empty the muscle was when loading began. Three things did not: the gram dose, the size of the depleting bout, and the athlete's maximal oxygen uptake. That last null deserves more attention than it will get. The idea that better trained athletes have less to gain from loading is widespread, and across sixty years of these studies aerobic fitness explained none of the variation in how much glycogen was stored.
The same lesson turns up in the most consequential error this literature has made. For six years the field carried the claim that women cannot supercompensate at all, on the strength of one trial. Change the denominator of the dose from a share of habitual energy intake to grams per kilogram of lean body mass, and the difference does not appear. The failure was not in the women and it was not in the physiology. It was in the prescription.
Then there is the field data, which is the least glamorous paper in this issue and possibly the most useful. At the IRONMAN World Championships, six of twenty three women reached the loading guideline, and the average intake was closer to an ordinary training day than to a loading day. The interviews say knowledge was not the missing piece. Travel, nerves, food access and how it feels to eat that much were. If the meta analysis is right that how carbohydrate rich the diet is drives the number, then the protocol failure that matters is not a skipped depletion phase. It is a dose that never arrived.
Which leaves the question everyone actually cares about, and here our confidence should drop. Burke's cyclists loaded, gained about eighteen percent more muscle glycogen, and rode a hundred kilometres in the same time. And of the fourteen loading trials with a performance outcome, twelve could not separate the diet from the belief in the diet. The two that could, both of which also fed the athletes during the test, found nothing.
It would be easy to land that harder than the evidence allows, so here is the other side. Two blinded trials is a thin basis for a null. Burke's loading condition was numerically faster by about one percent, which is a margin that decides races and a margin seven riders can never resolve. The depletion protocol did store more glycogen by day seven, and that is a real finding rather than a rounding error. And nobody has ever run a one day loading protocol with a performance test on the end of it, which is a strange gap given how long the one day protocol has been on the table.
So the honest position is narrower than either camp would like. The muscle physiology is settled and reproducible. Give a trained athlete a carbohydrate rich diet and a rest and glycogen overshoots, in men and in women, at almost any level of fitness, and faster than the classical calendar assumes. What is not settled is the last step, from a fuller muscle to a faster race. The field has spent sixty years measuring the first step very well and reporting it as though it were the second.
That is the gap worth naming. The problem is not that athletes are doing the protocol wrong. It is that the protocol was validated on a proxy.
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