Carbs during an ultra — the honest guide

People who finish a 50K+ without hitting the wall don't do it by luck. They do it because they planned nutrition as seriously as training. This is the guide I wish I'd read before my first 50K.

The basics: why carbs mid-race

Your body stores ~400-500 g of glycogen between muscle and liver. At ultra pace (~Z2), you burn 60-80 g/h. Do the math: without refueling, that stash lasts 5-6 hours, tops. Before then, when glycogen drops, pace drops, HR climbs at the same effort, and the wall starts. Topping carbs during the race stretches the engine.

How many grams per hour — the real curve

The classic "60 g/h" recommendation falls short. Modern evidence (Jeukendrup, Burke et al) shows the trained athlete can absorb a lot more:

30-60 g/h: beginner, first ultra. Without prior gut training.

60-90 g/h: intermediate ultrarunner who trained nutrition.

90-120 g/h: elite or athlete with a trained gut, mixing glucose + fructose.

The trick to the upper ceiling (>90 g/h) is the glucose:fructose 2:1 mix. Each sugar uses a different intestinal transporter (SGLT1 vs GLUT5), so together you absorb more without saturating. That's why modern gels come with that ratio — it's not marketing, it's physiology.

Sources that work (and don't)

### YES, work

Gels: 22-30 g per sachet. 2:1 ratio if your gut tolerates it.

Sports drink: 30-40 g per 500 ml bottle. Iso/hypo mix.

Bananas: 25-30 g per unit, easy to digest.

Dates: 18-20 g per piece, very concentrated.

Real food: boiled salted potato, rice, white bread with dulce de leche, bread with honey. In long ultras (>6h) the sweetness gets old — alternating with savory saves the mind.

### NO, don't work mid-race

Fat (avocado, whole nuts). Slow gastric emptying, nausea under effort.

Plain protein (high-protein bars). Same reason.

Fiber (whole apple, heavy whole-grain bread). Causes runs + cramps.

Hypertonic drinks (warm Coke without water). Pulls water into the gut and dehydrates more.

Training the gut: the part nobody does

The intestine adapts like a muscle. If you've never eaten 90 g/h in training, you won't pull it off in a race. Progressive plan:

Week 1-2: on long runs (>90 min), 40-50 g/h. Try different brands. Log what sits well.

Week 3-4: bump to 60-70 g/h. You start noticing the pace holds better in the final hours.

Week 5-6: target 80-90 g/h. Do this at least 2-3 times before your A race.

Week 7-8: race simulation. 4-5 hour run with your exact nutrition plan. This is a REHEARSAL, not a stomach test: use what you'll use on race day.

Hydration: the other half

Without enough water, carbs don't absorb (blood concentration spikes and the stomach shuts down). Practical rule:

Cool weather (50-65°F / 10-18°C): 400-600 ml/h.

Temperate (65-77°F / 18-25°C): 500-800 ml/h.

Hot (>77°F / 25°C): 700-1000 ml/h + electrolytes (Na 400-700 mg/h).

If you wear a hydration pack, you carry enough for 2-3 hours + refill at aid stations. If you run with a bottle, mark the km where you know aid is. Running out of water at hour 4 is game over.

Mistakes that cost dearly

1. Waiting until you're hungry to eat. Too late. Start at 30-45 min in and keep the cadence.

2. Trying a new gel on race day. Easiest to avoid, most common offender. Your gut won't forgive the surprise.

3. Sweet only for the first 6 hours. By hour 7-8, sweet triggers gag reflex. Carry savory (pretzels, salty snacks).

4. Forgetting sodium. In heat + effort you lose 800-1500 mg Na/h. Water alone dilutes blood sodium → hyponatremia (dangerous, not just inconvenient).

5. No plan B. Pack emergency gels and powdered drink, in case an aid station ran out of your brand.

Sample plan for a 50K (5-7 hours), trained amateur

| Hour | Action |

|---|---|

| -2 to -1h pre | 80-100 g CHO + 500 ml water + salt. Coffee optional 30 min before. |

| 0:30 | First gel (25 g) + 200 ml water. |

| 1:00-5:00 | 60-80 g/h: alternate gel + drink + 1 solid fruit every 90 min. |

| 5:00+ | If you're truly hungry, solid sandwich. If sweet won't go down, savory. |

| Last hour | Drop solid carbs, just drink + fast gel. |

| Post | 1.0-1.2 g CHO/kg + 20 g protein within 30 min. |

Race day isn't the time to improvise

Carry a sheet with your exact plan and a watch that beeps every 30 min. Sounds excessive — but by hour 6 of an ultra your brain is mush and you don't make good nutrition calls. Let the decision be made in advance.

Eating in an ultra isn't complicated. But it has to be trained, rehearsed, respected. When you do it right, the last two hours are sustained pace and you pass people who quit on nutrition.