Eat 60 to 90 grams of carbs every hour, and start in the first 15 minutes of the bike. Most athletes don’t. In a study of 221 endurance athletes, 70.3 racers averaged just 65 g/h of carbohydrate, and the spread was huge (plus or minus 25 g/h). That means plenty of athletes sit under 50. In short: the average racer under-eats, and the run is where it shows.
This plan gives you the hour-by-hour numbers. It also gives you a way to scale them to your body and your finish time.
Why the bike is your only real fuelling window
The average age-group 70.3 takes about 5:53 for men and 6:20 for women. The bike is the longest leg, at roughly half of your race time. It’s also the only leg where you can eat and drink freely.
You can’t eat in the swim. On the run, your stomach bounces around and your gut tolerates less. So the bike has to carry the load.
Think of the bike as filling a gas tank before a long stretch with no stations. Fill it early and fill it often. A tank you top up late is a tank that was empty for hours.
The data backs this up. A study of 823,459 age-group athletes found that bike and run splits predict overall 70.3 results better than swim splits (Sports Medicine - Open, 2023). Swim fuelling worries are small. Bike fuelling mistakes are big.
How many carbs per hour?
The joint position statement from the American College of Sports Medicine and two dietitian groups sets the range for events over an hour at 30 to 90 g/h. The top end needs more than one type of sugar (Thomas et al., 2016). In short: for a 70.3, the middle and upper part of that range is your zone.
Why more than one type? Your gut absorbs glucose through one door and fructose through another. A drink with both, at a 2:1 glucose to fructose ratio, lets more carbs through. In studies, this raised carb burning by up to 65% over glucose alone (Jeukendrup). Translation: two doors move more people than one.
For most age-groupers, a newer review suggests 60 to 90 g/h. Start at 60 and build in training (Podlogar and Wallis, 2022).
Real racers sit below the target line. The gap between 65 and 90 is where finish times go to die.
The 70.3 race-day nutrition plan, hour by hour
These numbers assume a 70 kg athlete and a bike of about three hours. Scale grams by your body mass and your pace. The sodium column is a starting range, not a rule.
| Race time | Segment | Carbs | Fluid | Sodium | Notes |
|---|---|---|---|---|---|
| T-3 h | Breakfast | ~140 g (2 g/kg) | 400-500 ml | 300-500 mg | Low fiber. Foods you’ve tested. |
| T-60 to -15 min | Pre-start | 20-30 g | Sips | Optional | Caffeine here if you use it. |
| 0:00 | Swim | 0 | 0 | 0 | Just swim. |
| Bike hour 1 | First 10-15 min | 60 g | To thirst | 300-600 mg | Start eating early. |
| Bike hour 2 | Mid-ride | 75-90 g | To thirst | 300-600 mg | Mix drink and gels. |
| Bike hour 3 | Final hour | 75-90 g | To thirst | 300-600 mg | Last big carb dose. |
| T2 | Transition | 10-20 g | Sips | 0 | Quick gel on the way out. |
| Run hour 1 | First half | 45-60 g | Sip at every aid station | 300-600 mg | Small, steady amounts. |
| Run hour 2 | Second half | 30-60 g | Sip at every aid station | 300-600 mg | Cola and gels often go down best. |
Breakfast follows the research range of 1 to 4 g of carbs per kg, one to four hours before the start. In short: eat a big, boring, low-fiber breakfast about three hours out. If you need a deeper plan for the days before, read our guide to carbohydrate loading before a marathon. The same logic applies to a long-course race.
Front-load the bike. Your gut handles food better while you’re seated and steady. On the run, it has less tolerance and absorbs less. Bank the carbs early.
What the plan adds up to
Here’s the simple math. Your fuelled time is your finish time minus about 45 minutes for the swim and first transition. Multiply by your hourly intake. These are plain arithmetic, not study results.
| Finish time | Fuelled time | 60 g/h | 75 g/h | 90 g/h |
|---|---|---|---|---|
| 5:00 | ~4.25 h | 255 g | 319 g | 383 g |
| 5:30 | ~4.75 h | 285 g | 356 g | 428 g |
| 6:00 | ~5.25 h | 315 g | 394 g | 473 g |
| 6:30 | ~5.75 h | 345 g | 431 g | 518 g |
A 6:00 finisher at 75 g/h needs about 394 g of carbs on course. That’s roughly 16 gels at 25 g each. Slower finishers need more total food, not a higher hourly rate. Their bike window is longer, so they have more time to eat it.
Sodium and fluid: don’t overthink it
Many coaches start athletes at 300 to 600 mg of sodium per hour. That’s a coaching rule of thumb, not a consensus guideline. Use it as a starting range and adjust with a sweat test.
Here’s why. Sweat sodium varies about four times between athletes, from roughly 20 to 80 mmol/L. At 40 mmol/L and a sweat rate of 1 L/h, you lose about 0.9 g of sodium per hour. Translation: a salty sweater and a light one need very different plans.
To test your sweat rate, weigh yourself before and after an hour at race effort. Each kilogram lost equals about one litre of sweat.
On fluid, skip the “drink as much as you can” advice. A 17-expert panel found that drinking to thirst is enough to prevent both dehydration and exercise-associated low blood sodium. Overdrinking is the main driver (Hew-Butler et al., 2015). If you gain weight during a race, you’re drinking too much.
Thirst is a decent gauge. Trust it.
Caffeine: when to take it
Studies commonly use 3 to 6 mg of caffeine per kg of body mass, taken 60 to 90 minutes before exercise. For a 70 kg athlete, that’s 210 to 420 mg. Lower doses often work and cause fewer jitters and stomach upset.
Many athletes also take a caffeinated gel late on the bike or early on the run. Try it in training first. Race day is the wrong time to meet your caffeine limit.
Gut training: build the number before race day
Serious stomach trouble hit 14% of 70.3 racers and about 31% of full Ironman racers in the same study. A history of stomach problems was the best predictor. In short: if your gut has failed you before, it will likely fail again unless you practise.
The fix is practice. In one study, two weeks of repeated carb feeding during runs cut stomach symptoms by about 60% (Costa et al., 2017). Your gut is a muscle in this sense. Load it a little more each week and it adapts. Our full breakdown is in how long gut training takes to work.
A simple ramp over 8 to 12 weeks looks like this. Start long rides at 40 g/h. Move to 60 g/h, then 75 g/h, and finish near your race target. If a step causes trouble, hold there another week.
Case study: Dan’s run fix
Take a triathlete I’ll call Dan, 41, 70 kg, with a 5:50 70.3 goal. This is an illustrative example. In his first race, he averaged about 45 g/h on the bike and skipped most food on the run. By mile 5 of the half marathon, his pace fell off a cliff.
Over ten weeks, he built his long-ride intake from 40 to 75 g/h. He tested sodium with a sweat check and settled near 500 mg/h. He ran bricks to practise eating off the bike (see our brick workouts guide).
At his next 70.3, Dan took in about 75 g/h on the bike and 45 g/h on the run. He held his pace to the end and finished at 5:35.
Dan didn’t get fitter in the last race. He got fed.
Common mistakes that cause the run blow-up
- Waiting until you feel hungry to start eating on the bike.
- Trying a new gel or drink on race morning.
- Overdrinking plain water and ignoring sodium.
- Eating too much in the last 20 minutes of the bike, then arriving at T2 sloshing.
- Skipping fuel on the run because you feel full.
Your fuel plan is a rehearsal, not a guess. AthleteOS builds your race-day fuel plan in grams of carbs, fluid and sodium per hour, then ramps your long-session fuel targets through the build. Log what you actually ate with the Fuel feature, and your plan adapts if sessions get missed or the forecast turns hot. Start your 14-day trial and try it on your next long ride.