Single stage ultramarathon fuelling calculator

Why Nutrient Timing and Composition Matter in Ultras
In single‑stage ultra‑marathons (durations of 20–24 h), athletes must attenuate caloric deficits by consuming 150–400 kcal per hour, divided into:

• Carbohydrate: 30–50 g/h to maintain blood‑glucose and delay fatigue

• Protein: 5–10 g/h to limit exercise‑induced muscle damage and support repair

• Fat: the remaining calories (≈1–18 g/h), often via savoury, energy‑dense foods PMC

Hydration & Electrolyte Balance

• Fluid: 450–750 mL/h (≈150–250 mL every 20 min) to prevent dehydration

• Sodium: > 575 mg per litre of fluid (or 300–600 mg/h) to maintain plasma volume

• Potassium & Magnesium: 200–300 mg/h K⁺ and 50–100 mg/h Mg²⁺ support neuromuscular function and reduce cramping PMC

Caffeine Strategy

• Pre‑race: 3–6 mg/kg 30–60 min before start

• In‑race: 1–2 mg/kg/h divided into small doses
  This dosing sustains alertness, offsets central fatigue, and may enhance fat oxidation in later stages PMC.

Probiotic Timing for GI Resilience
Four weeks of probiotic supplementation (e.g. Lactobacillus, Bifidobacterium strains) has been shown to reduce GI symptom severity and help athletes maintain pace in endurance events PMC. Schedule your first dose ~ 2 h before the start, then repeat every 12 h as tolerated.

Aligning with Circadian & Meal Windows
Digestive function and energy availability follow daily rhythms. Plan “real‑food” feeds around typical meal times—breakfast (06:00–10:00), lunch (12:00–14:00), dinner (18:00–20:00)—to maximise tolerance and thermic effect. Overnight, favour light, savoury foods before any rest period to minimise nocturnal GI slowdown.