The Principles That Don't Change

Before we get into race-specific numbers, there are a handful of rules that hold across every discipline, every distance, every condition. These are not suggestions. They are the load-bearing walls of the ANC fueling framework.

Carbs are the fuel. Full stop.

At race intensity, your body runs on carbohydrate. Fat is a background fuel — useful, always present, but not the limiting factor in performance. The limiting factor is how much carbohydrate you can absorb, store, and deliver to working muscle. Everything in this playbook is built around that reality.

In-race targets are flat g/hr — not body-weight scaled

Your gut's transport capacity is not meaningfully determined by your body weight. A 130-pound runner and a 180-pound runner have roughly the same intestinal transporter ceiling. What determines how much you can absorb is gut training — the deliberate, progressive practice of taking in carbs at race intensity over weeks and months. (Jeukendrup 2014, Cao 2025, ISSN 2025)

The dual-transporter rule

Single-transporter products (glucose or maltodextrin only) hit a hard ceiling around 60 g/hr. Above that, you need dual-transporter products — maltodextrin plus fructose in roughly a 2:1 ratio — which use separate intestinal pathways and allow absorption up to 90–120 g/hr, and higher in gut-trained athletes. Any target above 60 g/hr requires dual-transporter products. This is non-negotiable.

Race morning is a carb show — no protein, no fat, no fiber

The pre-race meal exists to top off liver glycogen and stabilize blood sugar. That is it. Protein slows gastric emptying. Fat sits in the gut. Fiber risks a bathroom stop you don't have time for. Save the whey shake, the eggs, the avocado toast, and the oatmeal-with-nuts for training and recovery. Race morning is white bagels, white rice, applesauce, sports drink, gels, bananas, and honey. Boring, fast-digesting, proven.

Heat does not change your carb target

This is one of the most common errors we see. Athletes feel off in the heat and cut carbs. Wrong direction. Heat changes your fluid and sodium needs — not your carbohydrate target. Carbs hold across all conditions. What changes:

• Heat (>78°F / 26°C): Fluid +15%, Sodium +20%. Carbs unchanged.
• Cool (<60°F / 15°C): Fluid −10%, Sodium −10%. Carbs unchanged.
• Humidity (>70% RH): Fluid +10%, Sodium +10%. Carbs unchanged.
• Altitude (>5,000 ft): Fluid +10%. Carbs unchanged.

Gut training is training

The gut is an organ. It adapts. Athletes who can absorb 100+ g/hr on race day got there by practicing 60, then 80, then 100 g/hr on long training sessions over 8–12 weeks. You cannot skip this step and expect race-day results. Practice your fueling in training the same way you practice your pacing.

Recovery is part of the fueling plan

Within 30 minutes of finishing any race or hard session: 1.0–1.2 g/kg carbohydrate + 0.4 g/kg protein, liquid preferred. Chocolate milk plus a whey shake is the ANC default — after the race, not before. This is not optional for athletes training or racing more than once per week.

5K

The 5K is over before exogenous carbohydrate can meaningfully contribute to performance. The lag between ingestion and oxidation is roughly 15 minutes — longer than most 5K races. So the fueling work for a 5K happens entirely before the gun.

Eat normally in the days before. Race morning, aim for around 1.5 g/kg of easily digested carbohydrate 2–3 hours out — bagel with honey, white rice, applesauce, a banana, sports drink. No protein, no fat, no fiber. No formal carb load required. No T-60 top-up needed. No in-race fueling.

The one exception: a carbohydrate mouth rinse. Swishing a 6% carb solution (roughly 100 ml of diluted sports drink) for 5–10 seconds at the start line — and spitting or swallowing — activates receptors in the mouth that signal the brain to reduce perceived effort. Studies show a 2–3% economy improvement via this CNS pathway, with no GI risk. (Carter/Jeukendrup/Jones 2004; Pottier 2010)

Recovery is standard: carbs + protein within 30 minutes. Appetite is usually fine after a 5K — real food works.

10K

At 35–70 minutes, the 10K sits in an interesting zone: long enough that carbohydrate availability starts to matter, short enough that in-race fueling is minimal. The work is mostly done before the start.

No formal multi-day carb load required — but eat carb-forward the day before. Race morning: 1.5 g/kg total, 75% at T-180, 25% at T-60. T-180 is carbs only (bagel, white rice, banana, sports drink). T-10 universal: one gel plus water.

In-race, most 10K athletes take the T-10 gel and ride it through the finish. For slower finishers (over 50 minutes), one mid-race gel is optional. The principle: if you're going to fuel, do it early enough for it to actually work.

Your exact targets — and whether you need anything beyond the T-10 gel — depend on your pace, your gut, and the conditions.

Half Marathon

The half marathon is where fueling starts to matter in a real way. At 1:15 to 2:30, glycogen is not the limiting factor for most athletes — but under-fueling will cost you in the final miles, and over-fueling will cost you in the first ones.

Carb load: a single-day T-1 load at 8 g/kg. For athletes finishing over 2 hours, a modest bump toward 8–9 g/kg is appropriate. Race morning: 1.5–2.0 g/kg, 75% at T-180, 25% at T-60. Carbs only — no protein, no fat, no fiber. T-10 universal: one gel plus water.

In-race, most athletes take 2–4 gels across the race depending on pace. The principle is simple: start early, stay on schedule, don't wait until you feel like you need it.

Your precise targets — carb load tier, race morning split, in-race g/hr, fluid, and sodium — are personal.

Marathon

The marathon is where fueling becomes decisive. The athletes who blow up between miles 18 and 22 are almost never out of fitness — they're out of fuel. The math is simple: at marathon pace, you burn carbohydrate faster than you can replace it from stores alone. Everything past mile 12 or so depends on what you put in your mouth during the race.

Carb load is sustained over T-2 and T-1. Most athletes should target the Standard tier. Race morning: 2.0–2.5 g/kg depending on your expected finish time, split 75% at T-180 and 25% at T-60. Carbs only at both meals — bagel with honey or jam, white rice with a little salt, applesauce, banana, sports drink. T-10 universal: one gel plus water.

In-race targets range from 60 g/hr at the conservative end to 90 g/hr at the aggressive end. Recent research (Sampson et al. 2024, Liverpool) showed elite marathoners at 120 g/hr had measurably lower oxygen cost versus 60 g/hr — the upper end is real and supported, but it requires gut training. Don't race at a number you haven't practiced.

Ultra Run

Ultra running introduces a challenge that shorter races don't: flavor fatigue, gut shutdown, and the psychological weight of fueling for 8, 12, 20+ hours. The math still applies — carbs per hour, fluid, sodium — but the execution requires real-food rotation, caffeine cycling, and a gut that has been trained for the long haul.

After hour 4, gel-only fueling becomes increasingly difficult for most athletes. Mix in real food: rice cakes, boiled potatoes with salt, broth, defizzed Coke, sandwiches. The goal is to keep the gut moving and the brain engaged.

Carb load is sustained at the Standard to Aggressive tier. Race morning: 2.5–3.0 g/kg, carbs only. In-race targets follow the same range as the marathon, but the execution window is much longer — which means gut training is even more critical.

Sprint Triathlon

At 60–90 minutes, the sprint triathlon is short enough that fueling is mostly a pre-race story. No multi-day carb load required — a carb-forward T-1 meal and normal hydration is sufficient. Race morning: 1.5–2.0 g/kg, 75% at T-180, 25% at T-60. Carbs only — no protein, no fat, no fiber.

In-race, most sprint athletes take one gel on the bike and nothing on the run. The race is simply too short for in-race fueling to make a meaningful difference — but starting the bike with a gel in the first few minutes keeps the system primed. T-10 universal: one gel plus water.

Recovery matters more than in-race fueling at this distance. Get carbs and protein in within 30 minutes of finishing, especially if you're racing again soon.

Olympic Triathlon

The Olympic distance sits at 2–3.5 hours — long enough that fueling is a real performance lever, short enough that the margin for error is smaller than athletes expect. Most athletes under-fuel the bike and pay for it on the run.

Carb load: sustained T-2 = T-1, Standard tier for most athletes. Race morning: 2.0 g/kg, 75% at T-180, 25% at T-60. Carbs only at both meals. T-10 universal: one gel plus water.

On the bike, targets range from 60 g/hr conservative to 90 g/hr aggressive. The run target is 78–85% of your bike rate — running mechanics increase GI permeability, which means the gut tolerates less per hour than on the bike. Plan accordingly.

Above 60 g/hr, dual-transporter products are required. Single-source glucose products will not absorb efficiently at the upper end.

70.3 / Half Iron

The 70.3 is where fueling becomes the race within the race. At 4–7 hours, you cannot wing it. The athletes who run well off the bike are almost always the ones who fueled the bike well — consistently, on schedule, without waiting to feel hungry.

The bike is your fueling window. The aero position is more forgiving on the gut than the mechanical jostling of running. Once you start the run, absorption capacity drops. If you arrive at T2 under-fueled, you will not catch up. This is not a maybe — it is a physiological certainty.

Carb load is sustained over T-2 and T-1, with the Standard tier (10 g/kg/day MID) as the default for most athletes. Race morning: 2.5 g/kg, 75% at T-180, 25% at T-60. Carbs only — no protein, no fat, no fiber. A typical T-180 looks like a white bagel with honey or jam, applesauce, banana, and 16–20 oz of sports drink. T-60: one gel with water. T-10 universal: one gel plus water — primary caffeine dose here if you're using a Performance protocol.

Bike targets range from 80 g/hr conservative to 100 g/hr aggressive. Run targets are 78–85% of your bike rate. Above 60 g/hr, dual-transporter products are mandatory. Gut training to your target rate is required before race day.

Full IRONMAN

A full IRONMAN is 8.5 to 17 hours of continuous output. There is no distance in endurance sport that demands more from your fueling system — or punishes fueling errors more severely. The athletes who finish strong are not the ones who went hardest. They are the ones who fueled most consistently.

Carb load is sustained over T-2 and T-1. Standard tier (10 g/kg/day MID) for most athletes; experienced gut-trained athletes may move to Aggressive or Advanced. Race morning: 3.0 g/kg, 75% at T-180, 25% at T-60.

T-10 universal: one gel plus water.

Bike targets range from 90 g/hr conservative to 120 g/hr aggressive for standard athletes, and up to 140 g/hr for Advanced + Aggressive athletes with proven gut tolerance. Run targets are 78–85% of your bike rate. Dual-transporter products are mandatory throughout. Gut training to your target rate is not optional.

The run is where IRONMAN races are decided — and the run is fueled by what you did on the bike. Every gel you skip on the bike is a mile you walk on the run.

Ultra Triathlon

Double Iron and beyond. At 20+ hours, fueling is no longer just a performance variable — it is a survival variable. The principles are the same: carbs per hour, dual-transporter products above 60 g/hr, fluid and sodium scaled to conditions. But the execution window is so long that real-food rotation becomes essential, caffeine must be cycled strategically, and gut management becomes as important as any training variable.

Carb load: 10–12 g/kg/day sustained. Race morning: 3.0 g/kg, carbs only. In-race bike targets range from 80 g/hr conservative to 110 g/hr aggressive. Run targets are 78–85% of bike rate. Real food after hour 4 is not optional — it is necessary for gut variety and psychological sustainability.

Gran Fondo / Century

A century or gran fondo is one of the most forgiving fueling environments in endurance sport: no run leg, bigger bottles, jersey pockets, and aid stations with real food. The challenge is not logistics — it's discipline. Athletes who feel good in the first two hours tend to under-fuel, then pay for it in hours three and four.

Carb load: Standard tier (9–10 g/kg/day MID). Race morning: 2.5–3.0 g/kg, carbs only. In-race targets range from 70 g/hr conservative to 100 g/hr aggressive. Above 60 g/hr, dual-transporter products are required.

The rule is the same as every other distance: start fueling in the first 20 minutes, stay on schedule, and don't wait until you feel like you need it.

Gravel 50 mi

At 3–5 hours, a gravel 50 sits in the same fueling territory as a 70.3 bike leg — long enough to require a real plan, short enough that most athletes can execute it with gels and drink mix alone. Real food at hour 3+ is optional but welcome.

Carb load: Standard tier (9 g/kg/day MID). Race morning: 2.5 g/kg, carbs only. In-race targets range from 60 g/hr conservative to 90–100 g/hr aggressive. Above 60 g/hr, dual-transporter products are required.

Gravel 100 mi

Unbound 100 and races like it are 6–10 hours of sustained output on variable terrain. The fueling challenge is real: high targets, long duration, and conditions that can shift dramatically across the day. Real food after hour 4 is strongly recommended — a mix of gels, chews, and solid food keeps the gut engaged and the brain from revolting against another gel.

Carb load: Standard to Aggressive tier (10–11 g/kg/day MID). Race morning: 3.0 g/kg, carbs only. In-race targets range from 80 g/hr conservative to 110–120 g/hr aggressive, with gut-trained athletes capable of 120–150 g/hr at peak windows. Glucose:fructose ratio of approximately 1:0.8 above 90 g/hr. Dual-transporter products mandatory above 60 g/hr.

Gravel 200 mi

Unbound 200 is in a category of its own. At 11–20+ hours, this is ultra endurance cycling — and the fueling demands reflect that. Real-food rotation is mandatory after hour 4. Caffeine must be cycled deliberately: 1–3 mg/kg pre-race, then 1–2 mg/kg every 3–4 hours, with a daily cap around 6 mg/kg. Recovery nutrition continues through the next 24 hours.

Carb load: Standard to Advanced tier (10–12 g/kg/day MID). Race morning: 3.0 g/kg, carbs only. In-race targets range from 80 g/hr conservative to 120 g/hr aggressive, with gut-trained peak windows of 120–150 g/hr. Dual-transporter products mandatory throughout.

100-Mile MTB

Leadville and races like it add altitude to the fueling equation. At elevation above 5,000 feet, fluid needs increase by roughly 10% — but carbohydrate targets do not change. The altitude effect on carbs is minimal; the altitude effect on hydration is real. Plan accordingly.

Carb load: Standard to Aggressive tier (10–11 g/kg/day MID). Race morning: 3.0 g/kg, carbs only. In-race targets range from 80 g/hr conservative to 110–120 g/hr aggressive. Dual-transporter products mandatory above 60 g/hr. Real food after hour 4 recommended.

Build Your Personalized Plan

This playbook gives you the principles and the framework. Your personalized plan — exact carb load tier, race morning split, in-race g/hr by tier, fluid targets, sodium targets, product recommendations — lives at racefuelplanner.com.

The numbers in this playbook are ranges. Your number is specific. It depends on your finish time, your gut training history, the race conditions, your sweat rate, and your tier. Build it properly.