Evidence A · Strong
Acute
The primary fuel of exercise. For athletes with metabolic flexibility (low-carb adapted), 30–60 g/h is the sweet spot. For conventional athletes, 60–90 g/h (up to 120 g/h in elite races).
Dose (low-carb)30–60 g/h
Dose (conventional)60–90 g/h (up to 120)
TimingStarting from 60–90 min into the race
RatioGlucose:Fructose 1:0.8 ideal
Strategies
- Constant base: Palatinose / SuperStarch (UCAN) — slow release, no insulin spike.
- Climbs / race finish: traditional gels (malto + fructose) for a fast hit.
- 40 ml gels: the TSA rule allows as many as fit in a 1L Ziploc bag (≈15–20 gels).
Why glucose:fructose 1:0.8?
The gut has two different transporters for glucose (SGLT1) and fructose (GLUT5). Combining the two in an optimized ratio lets you absorb ~90 g/h without saturating either transporter on its own. Modern gels (Maurten, Tailwind, SiS Beta Fuel) use this ratio.
Carb-loading before the race
- 3 days before: 8–10 g/kg/day of carbohydrate.
- Each g of glycogen carries 3–4 g of water — expect to gain 1–2 kg.
- That weight "disappears" during the race as you burn through the stores.
Evidence
- Jeukendrup — Carbs during endurance exercise PubMed
- Carb intake during endurance: updated review ScienceDirect