RESEARCH: Studies from 17 to 23 Aug 2026

This week’s quick summary:

1. High-dose carbohydrate intake and running economy in elite marathoners

2. Pacing patterns and performance across 79,000 marathon finishers

3. Adding moderate training volume benefit to performance

4. How Ethiopia’s elite distance runners actually train

5. Benefits of supershoe running on running economy on inclines

Study date: Dec 2025

Professional cyclists have increasingly pushed carbohydrate intake during racing beyond 90g/h, a rate previously identified as close to the ceiling for exogenous glucose-fructose oxidation. Whether or not these higher doses result in metabolic advantages in elite athletes had not been directly tested. In this study, the authors focused on marathon runners an set out to “evaluate the effects of carbohydrate (CHO) ingestion at rates of 60g/h, 90g/h, and 120g/h on whole body substrate metabolism, exogenous CHO oxidation, and gastrointestinal (GI) symptoms in elite male marathon runners”.

STUDY INTERVENTION

1. 8 elite male marathon runners (personal best 2:22:54 ± 0:05:37) completed three 120-minute running trials, each preceded by 24 hours on a high-carbohydrate diet (8g/kg) and a pre-exercise meal (2g/kg).

2. Each trial involved ingesting carbohydrate at 60g/h (maltodextrin:fructose 1:0), 90g/h (2:1), or 120g/h (1:1), with the glucose and fructose isotopically labelled (U-13C) to distinguish exogenous from whole-body oxidation.

3. Running trials comprised 15 minutes at 95% lactate threshold, 90 minutes at 94% lactate turnpoint, and a final 15 minutes back at 95% lactate threshold.

KEY RESULTS

1. Whole-body carbohydrate oxidation increased with dose (120g/h: 3.07g/min; 90g/h: 2.46g/min; 60g/h: 2.09 g/min), and the same dose-response pattern held for exogenous carbohydrate oxidation in the second hour of exercise.

2. Running economy improved at the highest dose, with an 8.1mL O2/kg/km lower oxygen cost at 120g/h compared with 60g/h.

3. Moderate or severe gastrointestinal symptoms were common across all three doses, with peak nausea, stomach fullness, and abdominal cramps greatest at 120g/h.

AUTHORS’ CONCLUSION

• Carbohydrate ingestion at 120g/h confers a metabolic advantage over lower doses in elite male marathoners by better maintaining whole-body carbohydrate oxidation, raising exogenous oxidation, and improving running economy.

• Gut-training strategies are warranted before applying such high intake rates in practice, given the prevalence of gastrointestinal symptoms across all doses tested.

RESULT CONFIDENCE

• Only 8 athletes were tested, all male, so the findings can’t yet be assumed to generalise to female marathoners or to runners with different gut tolerance and training histories.

PRACTICAL TAKEAWAY

This study showed that in elite male marathoners, carbohydrate intake at 120g/h produced greater whole-body and exogenous carbohydrate oxidation and a measurably lower oxygen cost of running than 60 or 90g/h, but also came with the highest gastrointestinal symptom burden of the three doses.

My recommendation for marathoners considering intake above 90g/h is to treat it as a deliberate choice that considers both the advantages and disadvantages. The metabolic and running-economy benefit is real, but a structured gut-training plan is needed to ensure that GI issues do not negate the benefit during a race.

However, this does not mean all athletes should be pushing up their carbohydrate rates in races. A personalised glucose-dosing approach in trained cyclists found that a calculated individual dose, averaging just 65g/h, achieved peak exogenous oxidation statistically identical to a blanket 90g/h dose, while producing meaningfully lower perceived exertion and stomach fullness. Taken together, the two studies map out a spectrum: 120 g/h appears to be the current physiological ceiling for well gut-trained elite athletes chasing every last percentage point of economy, but most athletes may get nearly the same oxidation benefit, with a more comfortable gut, by finding their own individual dose rather than assuming higher is always better.

RELATED RESEARCH

• Study archive: Nutrition - CHO

• Carbohydrate dose influences liver and muscle glycogen oxidation and performance during prolonged exercise

• Graded carbohydrate ingestion up to 120g/h attenuates the reduction in critical power following 3h of moderate-intensity exercise in a dose-dependent manner

• Exogenous glucose oxidation during exercise is positively related to body size