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.

Probiotics and GI Symptoms
In a small trial, 24 recreational runners took a multi-strain probiotic (Lactobacillus and Bifidobacterium) or a placebo daily for 28 days before a marathon. The probiotic group reported less severe GI symptoms in the final third of the race and slowed less over that stretch, although finish times did not differ (Pugh et al. 2019). This was a marathon, not an ultramarathon, and the benefit followed four weeks of daily use beforehand, not doses taken on race day.

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.