Triathlon
Half-Ironman 70.3 Nutrition Plan: Bike-to-Run Fueling Without Stomach Problems
A 70.3 nutrition plan for triathletes who need enough carbs and sodium on the bike without starting the run bloated, nauseous, or empty.
Quick answer
A strong 70.3 nutrition plan uses the bike as the main fueling window. Most athletes should practice 60-90g carbs per hour on the bike, steady fluids and sodium based on sweat rate, then switch to smaller, more frequent carbs on the run. The main objective is to arrive at T2 fueled but not overloaded.
A half-Ironman is not three separate nutrition problems. It is one long digestive challenge with a swim start, a bike fueling window, and a run that exposes every mistake you made earlier.
The best 70.3 nutrition plan gets you to the run with enough carbohydrate, enough fluid, enough sodium, and a stomach that still wants to cooperate.
Why 70.3 Fueling Is Different From Marathon Fueling
Marathoners fuel while running. Triathletes have a major advantage: the bike. Cycling usually allows higher intake because there is less gut jostling. That means the bike leg is where you do most of the fueling work.
The mistake is treating the bike like a buffet. Too much fuel, too little water, or drinks that are too concentrated can turn the run into a survival shuffle.
The 70.3 Nutrition Timeline
| Timing | Main Goal | Common Mistake |
|---|---|---|
| Night before | Top off carbs with familiar foods | Eating a huge, high-fiber dinner |
| 3-4 hours pre-race | Carb breakfast plus fluids | Skipping breakfast because of nerves |
| 15-30 minutes pre-swim | Small carb top-up if practiced | Trying a new gel on race morning |
| Bike | Most race carbs, fluids, and sodium | Front-loading too aggressively |
| Run | Smaller frequent carbs and controlled fluids | Trying to fix bike underfueling all at once |
Bike Fueling Targets
Many 70.3 athletes start with 60-75g carbs per hour on the bike and progress toward 90g per hour if they tolerate it. The higher end usually requires gut training and products that combine glucose and fructose sources.
- Use the first 10-15 minutes of the bike to settle before aggressive fueling.
- Sip regularly instead of taking large boluses of fluid.
- Separate carb concentration from hydration when possible so you can adapt to heat.
- Practice opening, grabbing, and consuming fuel while riding at race effort.
Run Fueling Targets
The run is where you protect the plan. You usually cannot absorb as much as you can on the bike, so the run strategy should be smaller and steadier: gels, chews, sports drink, and water in amounts you already practiced in brick sessions.
| Run Scenario | Fueling Approach |
|---|---|
| Cool conditions | Gels or chews every 25-35 minutes with water, adjust based on pace. |
| Hot conditions | Prioritize cooling and fluid access while keeping carb intake steady. |
| Nausea starting | Slow intake briefly, rinse mouth, sip water, resume with smaller carbs. |
| Energy fading | Take fast carbs with water and avoid stacking multiple concentrated products. |
How to Practice the Plan in Brick Workouts
A brick workout tells the truth. Fueling that feels perfect on the bike can feel awful after the first mile of running. The goal is not to prove you are tough. The goal is to find what still works when your stomach is under race-like stress.
- Practice race breakfast before a long ride or race simulation.
- Use planned bike carbs for at least 2 hours before running off the bike.
- Start the run with the exact fuel timing you expect to use on race day.
- Record bloating, burping, side stitches, nausea, sloshing, and energy dips.
- Change one variable at a time: carb amount, fluid amount, sodium, or product type.
Anchor the Plan to the Bike and Brick
A 70.3 build throws a lot at you — swims, rides, runs, and bricks all in the same week — but you do not have to optimize every session. Anchor your fueling to the two that matter most: the long ride and the brick. Use the bike, where digestion is easiest, to practice taking in real race-level carbs (often 60-90g per hour) and to arrive at the run fueled rather than scrambling. Treat the brick as your full dress rehearsal for the bike-to-run transition. Fuel those two sessions properly, let the easy swims and aerobic runs ride on roughly normal meals, and the week's nutrition largely sorts itself out.
Connecting each session to the right daily targets and building the breakfast-bike-run-recovery race plan is something MAVR assembles from your schedule. But the anchor-to-the-key-sessions approach is the part that actually keeps a 70.3 build from quietly wearing you down, and it needs no app to apply.
MAVR turns triathlon training into a clear fueling plan for bike, run, recovery, and race day.
Frequently Asked Questions
How many carbs per hour should I take in a 70.3?
Many athletes start around 60-75g carbs per hour on the bike and use a lower, more tolerable intake on the run. Well-trained athletes may handle 90g per hour on the bike, but this should be practiced before race day.
Should I eat solid food during a half-Ironman?
Some athletes tolerate solid food early on the bike, but many race better with drink mix, gels, chews, or simple low-fiber foods. The run usually favors simpler fuel because digestion is harder.
Why does my stomach fail on the run?
Common causes include too much fuel late on the bike, drinks that are too concentrated, dehydration, heat stress, high intensity, or a product you have not practiced. Brick sessions help identify the cause.
What should I eat for breakfast before a 70.3?
Eat a familiar carb-focused breakfast 3-4 hours before the start. Options include bagels, rice, oatmeal, banana, applesauce, sports drink, or low-fiber cereal. Keep fat and fiber low and avoid new foods.
Written by
MAVR Sports Nutrition Team
The MAVR sports-nutrition team translates peer-reviewed endurance research (Jeukendrup, Burke, the ISSN) into daily fueling for runners and triathletes.