REF-069 · Jeukendrup, 2004 · Nutrition, Vol. · Paper

Carbohydrate Intake During Exercise and Performance: Foundational Review (Jeukendrup 2004)

B+moderate evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

Overview

Jeukendrup's 2004 review sets out what was then accepted about carbohydrate feeding during exercise: it improves endurance capacity (time to exhaustion) and performance in prolonged exercise (>2 h), and more recent studies had also shown ergogenic effects in shorter, high-intensity exercise (~1 h at >75% of VO2max).

In prolonged exercise the mechanism is most likely maintenance of high carbohydrate oxidation rates and prevention of hypoglycaemia; in the ~1 h case the mechanism is less clear, with some evidence for central effects.

The review's distinctive contribution is the analysis of exogenous carbohydrate oxidation: a single carbohydrate is oxidised at up to about 1 g/min however much is ingested, whereas combinations using different intestinal transporters (e.g. glucose + fructose) raise exogenous oxidation rates by 20% to 50%.

Key Findings

Prolonged exercise (>2 h): carbohydrate feeding improves endurance capacity and performance; mechanism likely maintained carbohydrate oxidation and prevention of hypoglycaemia.
Shorter high-intensity exercise (~1 h at >75% VO2max): ergogenic effects also shown; mechanism less clear, some evidence for a central effect.
Oxidation ceiling: a single ingested carbohydrate is oxidised at rates up to about 1 g/min even when large amounts are ingested.
Multiple-transporter combinations (e.g. glucose + fructose) increase exogenous carbohydrate oxidation by 20% to 50%.
Open question at the time: improving delivery and oxidation efficiency so that less carbohydrate accumulates in the gut, reducing gastrointestinal problems in prolonged exercise.

Practical Application

Jeukendrup 2004 (narrative review): carbohydrate taken during exercise improves endurance capacity and performance when exercise lasts over 2 h and also in ~1 h efforts above 75% VO2max; a single carbohydrate source is oxidised at no more than about 1 g/min however much you eat, while glucose + fructose blends raise exogenous oxidation by 20-50% — so beyond the single-carbohydrate ceiling the type of carbohydrate matters, not just the amount.
For anything over 2 h, plan carbohydrate intake in advance; the benefit rests on keeping carbohydrate oxidation high and blood glucose up.
If you use more than a single-sugar product can deliver, choose multiple-transportable blends (glucose/maltodextrin + fructose) — that is the lever this review identified for higher usable intake with less gut accumulation (REF-064).
Not from this paper: the current dosing ranges by event duration (30-60 g/h; up to 90 g/h beyond 2.5 h) are in the later IOC consensus review REF-066.

Limitations

Narrative review from 2004: it organises the evidence but does not pool it, and the field has moved since (dosing ranges, gut training; not from this paper: the ≥100 g/h practice in REF-334).
The oxidation-rate analysis rests largely on laboratory tracer studies in trained men; it does not by itself give an event-specific dose.
Says nothing about gastrointestinal tolerance training or individual variation beyond flagging gut accumulation as a problem to solve.
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A: authoritative narrative review from the leading group on exogenous carbohydrate oxidation, not a systematic review

Content correction 2026-09-27
"30-60 g/h produces 15-25 min additional endurance", ">90 g/h benefits efforts >2.5 h", "50-100 g/h preserves muscle glycogen 20-30%", "taste-driven gain 2-4%", "sweet taste improves motor patterning" -> none of these are in the abstract; removed.
"Training 50-75 g/h, racing 75-90 g/h; all training >90 min and races >2 h; power loss in the final 30-60 min" -> house advice, not from this paper; removed (dosing ranges re-pointed to REF-066).
Added the review's actual findings: >2 h and ~1 h at >75% VO2max; ~1 g/min single-carbohydrate oxidation ceiling; +20-50% exogenous oxidation with multiple-transporter blends.
Level A -> B+ (narrative review from the leading group).