Trail running nutrition looks complicated because it has more variables than road racing: longer durations, changing effort levels on uphills and downhills, heat variability, and mandatory gear that limits how much food you can carry. This guide breaks down the practical math and gives product-specific guidance for GU Energy Gel 24-Pack , Maurten Gel 100 (Box of 12) , Spring Energy Long Haul Endurance Fuel (Box of 12) , Tailwind Nutrition Endurance Fuel (50-serving bag) , Skratch Labs Sport Hydration Drink Mix (20-serving bag) , and Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack) .
For trail runs under 4 hours, 150-200 calories per hour from gels or chews with an electrolyte drink is sufficient. Over 4 hours, add real food and increase sodium to 500-1000mg per hour in heat. For 100-mile races, plan a gel-to-real-food transition around mile 50-60. Gut training in long runs before the race is as important as the product you choose.
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Calorie targets: the math that drives everything else
The human gut can absorb roughly 60 to 90 grams of carbohydrates per hour depending on the carbohydrate sources used (glucose-only transport is capped at 60g/hr; glucose plus fructose blends can reach 90g/hr). That translates to 240 to 360 calories per hour from carbohydrates alone.
In practice, most trail runners target 150 to 250 calories per hour at race pace. Pushing to 300 calories per hour from the start of a 100-mile is a recipe for GI distress later; the gut tolerates high calorie intake better when it is trained and when pace is moderate.
Start the math from your expected finish time. A 12-hour 50-mile requires roughly 1800 to 3000 calories from gels and food over the race. At 100 calories per GU Energy gel , that is 18 to 30 gels, which is why most 50-mile runners carry 6 to 8 gels and supplement with aid station food rather than carrying everything.
GU Energy Gel 24-Pack
The trail running gel category standard: 100 calories per gel, 20 flavors including caffeinated options, 24 gels per box.
Gels in the first half: why they work and when they stop
The advantage of gels in the first half of a trail race is that they are calibrated, fast-absorbing, and easy to consume while running hard on technical terrain. A GU gel delivers 100 calories in a 32g packet you can consume in three seconds without slowing. Maurten Gel 100 (Box of 12) uses hydrogel technology that may reduce stomach disruption by keeping carbohydrates encapsulated longer.
The problem with gels in the second half of long races is sweetness fatigue. After 40 gels over 25 hours, the taste and consistency of most gels triggers nausea in even well-trained guts. This is physiological, not a willpower issue. Elite ultramarathon runners plan their gel-to-real-food transition at roughly the halfway point of their expected finish time.
Spring Energy Long Haul Endurance Fuel (Box of 12) real-food pouches bridge the gap: real whole-food ingredients that digest more comfortably than synthetic gel formulas while still being packable and consumable on the move. They are thicker than gels, so they require more deliberate swallowing, but they are the best packaged option for the second half of long races.
GU Energy Gel 24-Pack
The trail running gel category standard: 100 calories per gel, 20 flavors including caffeinated options, 24 gels per box.
Maurten Gel 100 (Box of 12)
Hydrogel-technology race gel used by UTMB elite athletes: neutral taste, 25g carbohydrates per gel, designed to reduce GI distress.
Spring Energy Long Haul Endurance Fuel (Box of 12)
Real food pouches made from brown rice, coconut oil, and banana: easier to digest late in a race than any gel when sweetness fatigue hits.
Electrolyte math: sodium is the variable most runners get wrong
Electrolytes are not optional on efforts over 4 hours in moderate temperatures. Hyponatremia, which is dangerously low blood sodium, kills ultramarathon runners. Cramping is the early warning sign, but cramping without dehydration almost always means sodium deficit, not fluid deficit.
Sweat sodium concentration varies enormously by individual. Some runners lose 600mg per liter, others lose 2000mg per liter. The simplest field approach is to start with 500mg sodium per hour from dedicated electrolyte products, separate from any sodium in gels or food. Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack) capsules allow precise titration: start at 500mg per hour, observe how your body responds at hours 4 and 8, and adjust upward if cramping or swelling occurs.
Do not rely solely on sport drink sodium. Skratch Labs Sport Hydration Drink Mix (20-serving bag) provides 380mg sodium per serving, which is useful for hydration but insufficient as a primary electrolyte source for heavy sweaters in hot conditions. Combine it with dedicated electrolyte capsules if you are running in heat.
Tailwind Nutrition Endurance Fuel (50-serving bag) includes 303mg sodium per serving and works as a combined calorie-electrolyte product for shorter efforts and cool conditions. For events over 12 hours in heat, supplement with additional sodium even if using Tailwind.
Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack)
Research-backed electrolyte capsules with 1500mg sodium per capsule, used by elite ultramarathon runners for sweat rate-matched replacement.
Skratch Labs Sport Hydration Drink Mix (20-serving bag)
Low-osmolality electrolyte drink mix with real fruit flavoring: fast-absorbing, easy on the stomach, and beloved by runners with sensitive guts.
Tailwind Nutrition Endurance Fuel (50-serving bag)
Complete liquid calorie and electrolyte solution in a drink mix: 100 calories and 303mg sodium per serving, no separate gels needed.
Gut training: the step most runners skip
The nutrition products you choose matter less than training your gut to accept them at race pace. The gut capacity to absorb carbohydrates and tolerate volume is trainable over 8 to 12 weeks of consistent practice.
Gut training protocol: practice consuming your target race nutrition (specific products, specific amounts) on your long training runs starting 8 weeks before your race. Run with full vest weight, target the same calorie intake per hour you plan for race day, and deliberately train at race-level effort for the first 60 to 90 minutes before eating.
If your target race uses GU gels , do not do your long runs on Maurten . Race day is not the time to introduce new flavors, textures, or formulations. Aid station food is the exception; you cannot always predict what will be at aid stations, so practice flexibility by using different real food options in training.
Testing your nutrition at a shorter tune-up race 4 to 6 weeks before your goal event is the best possible gut training. Nothing replicates race-day gut stress except racing.
GU Energy Gel 24-Pack
The trail running gel category standard: 100 calories per gel, 20 flavors including caffeinated options, 24 gels per box.
Maurten Gel 100 (Box of 12)
Hydrogel-technology race gel used by UTMB elite athletes: neutral taste, 25g carbohydrates per gel, designed to reduce GI distress.
Spring Energy Long Haul Endurance Fuel (Box of 12)
Real food pouches made from brown rice, coconut oil, and banana: easier to digest late in a race than any gel when sweetness fatigue hits.
Practical nutrition planning by race distance
50K (6 to 9 hours): 150 to 200 calories per hour from gels and chews, 300 to 500mg sodium per hour, plain water or Skratch Labs Sport Hydration Drink Mix (20-serving bag) for hydration. 12 to 18 gels total. Carry a full load; aid stations are supplemental.
50 miles to 100K (10 to 20 hours): same gel strategy for the first half, transition to real food at aid stations around hour 8 to 10. Increase sodium to 500 to 750mg per hour in daylight heat. Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack) capsules ensure sodium coverage independent of food choices.
100 miles (20 to 36 hours): gel-heavy for hours 1 to 12, transition to real food by hour 15, use Spring Energy Long Haul Endurance Fuel (Box of 12) pouches for the last 10 hours as a bridge between gel and aid station food. Increase sodium aggressively if it is warm. Plan at least one hot food stop at a key crew point to reset the gut.
Skratch Labs Sport Hydration Drink Mix (20-serving bag)
Low-osmolality electrolyte drink mix with real fruit flavoring: fast-absorbing, easy on the stomach, and beloved by runners with sensitive guts.
Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack)
Research-backed electrolyte capsules with 1500mg sodium per capsule, used by elite ultramarathon runners for sweat rate-matched replacement.
Spring Energy Long Haul Endurance Fuel (Box of 12)
Real food pouches made from brown rice, coconut oil, and banana: easier to digest late in a race than any gel when sweetness fatigue hits.
GU Energy Gel 24-Pack
The trail running gel category standard: 100 calories per gel, 20 flavors including caffeinated options, 24 gels per box.
GU Energy Gel 24-Pack
The trail running gel category standard: 100 calories per gel, 20 flavors including caffeinated options, 24 gels per box.
Maurten Gel 100 (Box of 12)
Hydrogel-technology race gel used by UTMB elite athletes: neutral taste, 25g carbohydrates per gel, designed to reduce GI distress.
Spring Energy Long Haul Endurance Fuel (Box of 12)
Real food pouches made from brown rice, coconut oil, and banana: easier to digest late in a race than any gel when sweetness fatigue hits.
Tailwind Nutrition Endurance Fuel (50-serving bag)
Complete liquid calorie and electrolyte solution in a drink mix: 100 calories and 303mg sodium per serving, no separate gels needed.
Precision Fuel and Hydration PH 1500 Electrolyte Capsules (30-pack)
Research-backed electrolyte capsules with 1500mg sodium per capsule, used by elite ultramarathon runners for sweat rate-matched replacement.
Skratch Labs Sport Hydration Drink Mix (20-serving bag)
Low-osmolality electrolyte drink mix with real fruit flavoring: fast-absorbing, easy on the stomach, and beloved by runners with sensitive guts.
FAQ
Frequently asked questions
How early in a trail race should I start eating?+
Start fueling within the first 20 to 30 minutes, before you feel hungry. Hunger is a lagging indicator; by the time you feel hungry, you are already behind on calories. Most experienced ultramarathon runners follow a strict schedule (one gel every 30 to 45 minutes) regardless of hunger in the first third of a race, then shift to appetite cues in the second half when GI state is a better guide.
What should I eat at a trail race aid station?+
Prioritize salty foods over sweet ones at aid stations, especially if you have been fueling on gels. Potatoes with salt, broth, and PB and J sandwiches are classic ultramarathon aid station staples because they are easy to digest, provide sodium, and break the sweetness of gel fueling. Avoid anything that requires significant digestion (heavy protein, fats) in the first half of a race when blood flow to the gut is limited by race effort.
Can I use caffeine gels in a trail race?+
Yes, strategically. Caffeine improves performance and alertness but causes GI distress at high doses, especially when the gut is already stressed late in a long race. Most experienced runners use caffeinated gels starting at hour 6 to 8 when alertness begins to flag, not from the race start. GU Roctane and the caffeinated GU Energy gel variants contain 35 to 70mg per packet. Time caffeine intake to the toughest sections of your race rather than loading it throughout.