Ironman 70.3 Nutrition Plan: What to Eat During a Half Ironman

A 70.3 nutrition plan is not really three sports.

It's one awkward swim, one long bike buffet, and one half marathon where your stomach starts making executive decisions without asking you first.

That is why the bike matters so much. You cannot eat during the swim. You probably cannot fix a bad plan during the run. So the race usually comes down to whether you can get enough carbs, fluid, and sodium in during the 56-mile ride without turning your gut into a science fair volcano.

For most age-group athletes, the starting point is simple: build the whole day around 60-90 g of carbs per hour on the bike, a little less on the run if needed, fluid based on sweat rate, and sodium matched to your conditions. The IRONMAN 70.3 nutrition guide makes the same basic point: nutrition is personal, but carbs, sweat rate, sodium loss, gut tolerance, and race duration drive the plan.

The trick is turning those ideas into bottles and gels you can actually carry.

The 70.3 fueling target

The old endurance baseline was 30-60 g/hr of carbohydrate. That still works for shorter events and cautious first-timers. But for a 70.3, most athletes are racing long enough that the better target is usually higher, especially on the bike.

The Academy of Nutrition and Dietetics, Dietitians of Canada, and ACSM position stand supports higher carb intakes, up to around 90 g/hr, during very long events when glycogen gets drained. And glucose-fructose products can help because they use more than one absorption pathway. Asker Jeukendrup's GSSI review explains the multiple-transportable-carbohydrate idea in more detail.

Normal-person version: if you're trying to take in more than about 60 g/hr, mixed glucose-fructose fuel usually works better than forcing a pile of glucose-only gels through one gut lane.

Here is the practical range I would start with:

Athlete	Bike carb target	Run carb target
First 70.3, cautious gut	50-60 g/hr	35-50 g/hr
Solid age-grouper, practiced fueling	60-80 g/hr	45-65 g/hr
Gut-trained, faster, using mixed carbs	80-100 g/hr	60-75 g/hr

Do you need 100 g/hr because some pro talked about it on a podcast? Probably not.

A 70.3 is harder than full-Ironman effort, and higher intensity pushes blood away from the gut. That means the biggest number your stomach can survive in training is not automatically the best race-day number. Your goal is enough fuel to run well, not a heroic bottle recipe that only works when you're sitting upright in the kitchen.

Race morning is boring on purpose

Race morning is not the time for a fiber-forward breakfast, a new protein bar, or whatever suspicious muffin came in the hotel lobby bag.

Keep it familiar and carb-heavy. Many athletes do well with 1-3 g of carbohydrate per kg of body weight 2-4 hours before the start, with the lower end fitting later wake-ups and nervous stomachs. If you want the deeper breakfast math, the pre-race breakfast guide walks through timing by event length.

For a 70 kg athlete, that might mean:

• 2 bagels with jam and a banana
• oatmeal with maple syrup, banana, and sports drink
• rice, honey, and a small amount of egg if that is already normal for you

The last phrase matters. Already normal for you.

If you like a pre-swim gel, take it 10-20 minutes before the start with a few sips of water. If caffeine is part of your plan, do not blow the whole dose before the cannon. A 70.3 has plenty of late-race suffering available, supply and command. Save some ammo for the run if caffeine sits well for you.

The swim just needs you topped off

You are not eating in the water unless something has gone deeply wrong.

The swim job is simple: start with liver glycogen topped off, blood sugar stable, and your stomach calm. If you under-eat breakfast because you're nervous, you start the bike already behind. If you over-eat breakfast because you're scared of bonking, you start the swim feeling like a washing machine.

Neither is ideal.

So keep the swim plan boring: breakfast early, optional gel close to the start, then nothing until you are settled on the bike. Once you hit T1, do not immediately start inhaling calories while your heart rate is still acting like you got chased out of the water. Get moving, breathe, then start the plan.

The bike is where you build the run

The bike leg is the most important fueling window in a Half Ironman.

You have bottles. You have pockets. Your gut is steadier than it will be on the run. You can sip every few minutes instead of trying to shove food down at an aid station while your legs are arguing with gravity.

My boring answer for most athletes is drink mix plus backup gels. Drink mix handles the steady carb drip. Gels cover missed sips, dropped bottles, wind, course chaos, and the moment when your fancy bottle plan launches itself into a ditch.

A simple 70-80 g/hr bike setup could look like this:

Per bike hour	Carbs
One bottle with 40-50 g drink mix	40-50 g
One gel every 30-40 minutes	25-30 g
Water as needed, separate from the carb bottle	0 g

For a 3-hour bike split, that puts you around 210-240 g of carbs before T2. That is a real run setup, not snack-and-hope energy.

If you prefer all-liquid fuel, fine. Maurten 320, SiS Beta Fuel, Skratch Super High-Carb, Neversecond, Gatorade Endurance, they can all fit a 70.3 plan if the math works and you have trained with them. But carry at least one backup gel. Bottles disappear. Aid stations get weird. Late-race you is not exactly the CFO of the operation.

And set a timer. Every 10-15 minutes, sip. Every 30-40 minutes, gel if that is part of the plan. Waiting until you feel hungry on the bike is like waiting until your tire is flat to think about air pressure.

Want the bike and run numbers matched to your pace, body size, and weather? Build a personalized carb, fluid, and sodium plan in about 60 seconds with the free EnduranceOS planner.

The run is where simple wins

The 70.3 run is not a great place to get cute.

Running bounces the gut. Heat builds. Intensity creeps up because now you can smell the finish line and everyone around you is making bad choices with confidence. If your bike fueling was solid, the run plan does not need to be impressive. It needs to be followable.

For most athletes, that means gels, sports drink, water, maybe cola later if it has worked in training. Bars and heavy chews can work for some people, but the run is usually where dense food starts filing complaints.

A simple run plan:

• gel at T2 or in the first 10 minutes if your stomach is calm
• gel every 25-35 minutes after that
• water with gels
• sports drink or cola only if it fits the carb count
• small caffeine top-up late if you practiced it

If you rode well and start the run with a decent fuel cushion, you do not need to force 90 g/hr while running. Many athletes run better on 45-65 g/hr than they do chasing a bike-style target at half-marathon effort.

And if your gut starts to turn? Slow the intake. Do not quit entirely. Small sips, water, a little sports drink, maybe one gel stretched over several minutes. Total shutdown is how a manageable wobble becomes a death march.

The race stomach problems post gets into the causes, but the short version is usually pacing, heat, carb concentration, or trying something your gut has never seen before.

Fluids and sodium are not side quests

Carbs get most of the attention because bonking is obvious. Hydration mistakes can be sneakier.

The ACSM fluid replacement position stand is clear that sweat rate and sweat electrolyte loss vary a lot between athletes, which is why custom fluid plans make more sense than universal rules. A smaller athlete in cool conditions and a big salty sweater racing in July are not doing the same event from a hydration standpoint, even if they have the same bib color.

Start with sweat rate. If you have not measured it, use the sweat rate guide before race day.

For many 70.3 athletes, a reasonable first pass looks like:

Condition	Fluid target	Sodium starting point
Cool day, smaller athlete	400-600 ml/hr	300-500 mg/hr
Moderate conditions	500-800 ml/hr	500-800 mg/hr
Hot day or salty sweater	700-1,000+ ml/hr	800-1,200 mg/hr

Those are starting points, not commandments.

Also count what is already in your plan. Drink mix, on-course sports drink, gels, chews, broth, salt caps, all of it counts. Plenty of athletes accidentally stack a high-sodium drink with salt tabs and then blame the gel when their gut goes sideways.

Female athletes and smaller athletes deserve special attention here. Absolute fluid and sodium needs are often lower because body size and sweat rate are often lower, but individual spread is still huge. Do not let some 180 lb guy's salt plan become your default because he sounded confident in a Facebook group.

A sample 6-hour 70.3 plan

Here is what this can look like for a middle-of-the-road athlete racing around six hours.

Assumptions: 70 kg, practiced mixed-carb fueling, moderate weather, bike split around 3:00, run split around 2:00.

Timing	Fuel	Target
3 hours before start	Bagel, banana, sports drink, familiar breakfast	120-180 g carbs
10-20 min before swim	Optional gel with water	20-30 g carbs
Bike hour 1	Bottle with drink mix plus one gel	65-75 g carbs
Bike hour 2	Bottle with drink mix plus one gel	70-85 g carbs
Bike hour 3	Bottle with drink mix, gel early, stop heavy intake near T2 if gut feels full	60-80 g carbs
Run hour 1	Two gels with water, sports drink only if counted	45-65 g carbs
Run hour 2	One to two gels, cola or caffeine if practiced	35-60 g carbs

Fluid might land around 500-800 ml/hr, more if it is hot and your sweat rate supports it. Sodium might land around 500-800 mg/hr, but that depends heavily on your sweat profile and what is already in the bottles.

Is this plan perfect for everyone? No.

That is the point. It is a starting template. Your training decides whether it becomes your race plan.

Practice the whole chain

Do not wait for the big Saturday ride to practice this.

Practice fueling on the sessions where it feels almost silly: a 75-minute trainer ride, a short brick run, a weekday tempo. Long sessions prove the plan. Short sessions build the habit. You want the timing to feel automatic before race day, because race-day brain departments are not exactly known for calm bookkeeping.

Run through the full setup at least twice before the race:

• same breakfast
• same drink mix concentration
• same gels
• same bottle placement
• same watch alerts
• same caffeine timing
• same sodium plan

If the exact plan only works when you are fresh, cool, and riding inside with Netflix on, it is not ready yet.

The gut training guide is worth pairing with this post. Higher carb targets are not just bought. They are trained.

The plan is the boring part, and that is good

A good 70.3 nutrition plan should feel almost disappointingly simple.

Eat a carb-heavy breakfast you trust. Start the bike calmly. Use the bike to build the run. Keep the run plan gel-first and easy to follow. Match fluid and sodium to your sweat rate and the weather. Count grams, not vibes.

That is how you avoid showing up to mile eight of the run with one gel, half a bottle, and a tiny bag of hope rattling around like a nutrition plan.

The EnduranceOS planner turns your race, pace, body size, weather, and experience level into carb, fluid, and sodium targets for the whole day. It takes about 60 seconds, and it's free.