Fueling the Long Run

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title: "Fueling the Long Run" excerpt: "A science-backed guide to carbohydrate loading, mid-run fueling, and hydration strategies that keep you strong through the final miles." date: "2026-03-15" tags: ["Nutrition", "Marathon", "Endurance"] featured: false

Why Fueling Matters

Your body stores roughly 2,000 calories of glycogen — enough for about 90 minutes of hard running. After that, you're running on fumes. The difference between a strong finish and a devastating bonk often comes down to what you ate, when you ate it, and how your gut was trained to handle it.

The 48-Hour Carb Load

Carb loading isn't about eating a mountain of pasta the night before. Modern protocols spread the load across 48 hours:

• Two days out: Increase carbs to 8–10g per kg of bodyweight
• Day before: Stick to familiar, low-fiber carbs — white rice, bread, pretzels
• Race morning: 1–2g per kg, 2–3 hours before the gun

A 70kg runner targeting 8g/kg needs about 560g of carbs per day during the load. That's roughly 2,240 extra calories from carbs alone.

Mid-Run Fueling Strategy

The gut is trainable. If you practice fueling during long runs, your body adapts to absorb more carbohydrate per hour.

The Targets

| Duration | Carbs per Hour | |----------|---------------| | Under 60 min | None needed | | 60–90 min | 30g | | 90 min – 2.5 hr | 30–60g | | Over 2.5 hr | 60–90g |

Multiple Transportable Carbs

To absorb more than 60g/hr, you need both glucose and fructose. This dual-transport approach uses separate intestinal pathways:

• Glucose sources: Maltodextrin, rice-based gels
• Fructose sources: Many commercial gels blend both
• Ideal ratio: 2:1 glucose to fructose

Timing

Start fueling early — within the first 30–45 minutes. By the time you feel hungry, you're already behind.

Hydration: The Sweat Rate Approach

Forget the "8 glasses a day" rule. Your hydration needs are individual and depend on sweat rate:

1. Weigh yourself before a 60-minute run (no bathroom, minimal clothing)
2. Run for 60 minutes at race effort
3. Weigh yourself again
4. The difference (in kg) equals your sweat rate in liters per hour

Most runners lose 0.5–1.5L per hour. Aim to replace 50–80% of sweat losses during the race — trying to replace 100% often causes GI distress.

Electrolytes

Sodium is the primary electrolyte lost in sweat (400–1800mg per liter). If you're a salty sweater (white marks on your kit), you'll need more:

• Light sweater: 300–500mg sodium per hour
• Heavy sweater: 500–1000mg sodium per hour

Race Day Fueling Mistakes

1. Trying something new — never test a new gel or drink on race day
2. Starting too late — waiting until mile 10 to take your first gel
3. Ignoring the gut — if you never practice fueling, your gut won't cooperate
4. Over-hydrating — hyponatremia (low sodium from excess water) is dangerous

Train Your Gut

The single most important fueling advice: practice everything in training. Your long runs are rehearsals for race day. Use the same gels, the same timing, the same fluids.

Start with 30g of carbs per hour during long runs. Over 4–6 weeks, gradually increase to your race-day target. Your gut adapts remarkably well when given consistent practice.

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