70.3 Nutrition Plan: The Complete Half Ironman Guide

Quick answer: A 70.3 nutrition plan comes down to four numbers. Carb load at 10 to 12 grams of carbohydrate per kilogram of body weight per day for the 36 to 48 hours before the race, eat 2 to 3 grams per kilogram at breakfast 2 to 3 hours before your wave, take in 70 to 90 grams of carbohydrate per hour once you are on the bike, and drink to your own measured sweat rate rather than to a generic bottle-per-hour rule. For a 72kg athlete that is roughly 720 to 864g of carbohydrate a day in the two days before, 145 to 215g at breakfast, and about 2 gels plus a bottle of sports drink every hour on the bike. Everything else in this article is how to make those four numbers work in a real race.

The half Ironman is the distance that punishes a vague plan. A Sprint or Olympic race is short enough that you can get away with underfuelling and still finish respectably. A full Ironman is slow enough that most athletes take fuelling seriously by default. The 70.3 sits in the awkward middle: fast enough that your gut is under real pressure, long enough that you cannot run 21.1km on what you ate for breakfast.

That is why so many age-groupers post a good swim, a strong bike and then walk aid stations from the 8km mark. The bike split was not the issue. The fuel that was supposed to carry the run was never taken in.

Nutrition is the fourth leg of triathlon, and it is the only one most athletes never train. If you can swim, bike and run but you are still guessing at the food, this is the leg that will cost you the most time on race day.

What does a 70.3 nutrition plan actually need to cover?

A complete 70.3 nutrition plan covers five windows, and each one has its own job:

• Race week (days 5 to 3 out): normal eating, tapered training, no experiments.
• Carb load (36 to 48 hours out): topping up muscle glycogen (the storage form of carbohydrate sitting in your muscles and liver).
• Race morning (2 to 3 hours out): refilling liver glycogen, which drains overnight while you sleep.
• The bike (about 2:15 to 3:15 for most age-groupers): the only leg where you can comfortably eat, so this is where the run gets fuelled.
• The run (about 1:30 to 2:30): topping up with what your gut will still tolerate at race pace.

Miss any one of those and the others cannot cover for it. A brilliant bike nutrition plan will not rescue an athlete who skipped the carb load, because you cannot eat 400g of carbohydrate in three hours to make up for the 800g you did not eat the day before.

How many carbs per hour do you need in a 70.3?

For most age-group athletes, the target is 70 to 90 grams of carbohydrate per hour across the bike and run combined.

Here is the evidence behind that. A single carbohydrate source such as glucose can only be absorbed and burned at around 60 grams per hour, because the transporter that carries it across your gut wall gets saturated. Add fructose (the sugar found in fruit, which travels through a completely different doorway into your bloodstream) and total oxidation climbs to roughly 90 grams per hour in events lasting longer than about 2.5 hours (Jeukendrup, 2014, Sports Medicine). Contemporary reviews have pushed that ceiling higher again in trained athletes who have deliberately practised it (Podlogar & Wallis, 2022, Sports Medicine).

The interesting part is what athletes actually do. When researchers measured real intake at Ironman 70.3, the average was 65 grams of carbohydrate per hour, with a spread of plus or minus 25 grams, and higher carbohydrate intake was significantly associated with faster finishing times (Pfeiffer et al., 2012, Medicine & Science in Sports & Exercise). So the average half Ironman athlete is sitting below the ceiling, and the ones eating more are getting to the finish line sooner.

One caveat matters more than the table itself. The number you can absorb is the number you have practised, not the number you read here. If you have been training on 45 grams per hour and you take 90 grams on race day, your gut will let you know about it, and not in a good way. Build up over 8 to 12 weeks in your long rides. I go into the ceiling and how to raise it in detail in Carbs Per Hour for Triathlon: Why More Isn't Always Faster.

How should you carb load in the 48 hours before a 70.3?

If your race is longer than 90 minutes, then carb loading is worth doing, and a 70.3 is comfortably in that territory. The joint position stand from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine puts the target at 10 to 12 grams of carbohydrate per kilogram of body weight per day for the 36 to 48 hours before competition (Thomas, Erdman & Burke, 2016, Journal of the Academy of Nutrition and Dietetics).

For a 72kg athlete that is 720 to 864 grams of carbohydrate a day. To make that tangible, it is roughly double a normal training day, and it is close to impossible to reach if you are still eating a big salad with your dinner. Volume is the enemy here. You need carbohydrate that is dense, low in fibre and easy to get through.

Three rules make it work:

• Cut the fibre, not the food. Swap wholemeal for white, skip the raw veggie sides, and choose juice over whole fruit for a day or two.
• Add carbohydrate to drinks. Sipping 500ml of juice or sports drink adds 50 to 60 grams without adding a single mouthful of food.
• Spread it across six feeds, not three. You are a human, not a snake. Three enormous meals will leave you bloated and heavy.

The full 48-hour protocol with actual meals is in Carb Loading for Triathlon: The 48-Hour Plan With Meals, so I will not repeat it here.

What should you eat on 70.3 race morning?

Liver glycogen drains overnight, so you wake up on race morning with a partly empty tank no matter how well you loaded. Breakfast is what refills it.

Aim for 2 to 3 grams of carbohydrate per kilogram of body weight, eaten 2 to 3 hours before your wave goes off. For a 72kg athlete that is 145 to 215 grams. In real food, that is something like 2 slices of white toast with honey, a banana, a small tub of low-fat yoghurt and a 600ml sports drink.

If your wave is at 6:30am and you cannot face eating at 3:30am, then eat what you can at 4:30am and top up with 30 to 45 grams of liquid carbohydrate in the 30 minutes before the swim start. A sports drink or a gel with water both work. Do not skip breakfast because it feels early. Nerves are not a nutrition strategy.

And never try anything new on race day. If the race is offering a branded breakfast you have never eaten, eat your own.

How much fluid and sodium does a 70.3 nutrition plan need?

This is where generic advice does the most damage, because sweat rate and sweat sodium vary enormously between athletes. Sweat sodium concentration ranges from around 200 to more than 2000 milligrams per litre depending on the individual, and both testing method and conditions change the answer (Baker, 2017, Sports Medicine). A ten-fold range means there is no sensible one-size-fits-all sodium number.

What you can do is measure your own. Weigh yourself naked before and after a one-hour ride in race-like conditions, add back what you drank, and you have your sweat rate in litres per hour. The method is in Sweat Rate Test at Home: The 60-Minute Method.

Then apply it:

• If your sweat rate is under 800ml per hour, then aim to replace roughly 500 to 600ml per hour on the bike.
• If your sweat rate is 800ml to 1.2 litres per hour, then aim for 600 to 800ml per hour and add a sodium source.
• If your sweat rate is over 1.2 litres per hour, then you need 750ml or more per hour plus deliberate sodium, and you should plan bottle exchanges rather than hoping.

You are aiming to finish the race having lost less than about 2% of your body weight. For a 72kg athlete that is 1.4kg, which is smaller than most people assume. As a starting point for sodium, 500 to 1000 milligrams per litre of fluid covers most athletes, with heavy and salty sweaters at the top of that range. There is more on how to work out where you sit in Sodium for Triathletes: How Much You Need by Sweat Type.

How do you fuel the run when your stomach has had enough?

The run is where 70.3 nutrition plans fall apart, and the reason is mechanical. Running jostles the gut, you are working at a higher intensity, and blood that was helping you digest gets sent to your working muscles instead. It is the same reason digestion shuts down when you are running away from a lion, because the blood is in your heart, your lungs and your legs, not your stomach.

Three adjustments make the run survivable:

• Drop the target slightly, do not abandon it. If you were taking 90 grams per hour on the bike, then plan for 60 to 70 grams per hour on the run.
• Go more liquid, less solid. Gels with water, defizzed cola and sports drink all clear the stomach faster than a bar.
• Front-load the last 30 minutes of the bike. Take your final gel with 20 to 30 minutes of riding left, so it is absorbed before you start running.

Worth knowing: in that same 70.3 and Ironman field, higher carbohydrate intake was linked to more nausea and flatulence as well as faster times (Pfeiffer et al., 2012). Some gut discomfort at the top end of intake is normal and manageable. Vomiting at 12km is not, and it usually means the plan was never trained.

What does a worked 70.3 nutrition plan look like?

Say you are a 72kg athlete targeting a 5:30 finish, racing somewhere warm like the Sunshine Coast. Here is how the numbers turn into a plan. This is a hypothetical example, not a prescription, so treat it as a template to adjust rather than a plan to copy.

Total on-course carbohydrate for that athlete is roughly 340 to 390 grams across 4 hours and 45 minutes of bike and run. Write it on your top tube. Set a watch alarm every 20 minutes. Do not rely on remembering, because by the 60km mark you will not be doing your best thinking.

What goes wrong with most 70.3 nutrition plans?

After two decades of working with triathletes, the same five errors come up again and again:

1. Fuelling the bike you are on instead of the run you are about to do. Everything you eat on the bike is being banked for the half marathon.
2. Copying a pro's numbers. A 62kg professional going 3:50 has a different energy cost, a different gut and a different eight years of practice behind them.
3. Set and forget. The plan that worked in June in Tasmania is not the plan for September on the Sunshine Coast. Heat changes fluid and sodium needs.
4. Race-day novelty. This is the brand new gel, the course-supplied drink you have never tasted, or the pre-race coffee twice your usual size.
5. Training fasted all season and expecting the gut to cope. Your gut adapts to what you ask of it, so ask it in training, not in transition.

If you want to compare products before you build your plan, I have run the numbers on the main ones in Best Triathlon Gels Compared (2026). Not all gels are created equal, and the carbohydrate ratio matters as much as the flavour.

Frequently asked questions about 70.3 nutrition

Q: How many carbs per hour do you need in a 70.3?
Most age-group athletes should aim for 70 to 90 grams of carbohydrate per hour across the bike and run combined. Research measuring real intake at Ironman 70.3 found an average of 65 grams per hour, and higher intakes were associated with faster finishing times (Pfeiffer et al., 2012). The number you can actually absorb is the one you have practised in training, so build up gradually over 8 to 12 weeks rather than changing it on race day.

Q: What should you eat the morning of a half Ironman?
Eat 2 to 3 grams of carbohydrate per kilogram of body weight, 2 to 3 hours before your wave. For a 70kg athlete that is 140 to 210 grams, which looks like 2 slices of white toast with honey, a banana, a small yoghurt and a 600ml sports drink. Keep fibre, fat and protein low, and top up with 30 to 45 grams of liquid carbohydrate in the 30 minutes before the swim if your start is early.

Q: How long before a 70.3 should you start carb loading?
Start 36 to 48 hours out, which for a Sunday race means from Friday morning. The target is 10 to 12 grams of carbohydrate per kilogram of body weight per day (Thomas, Erdman and Burke, 2016). Loading for a full week is unnecessary for this distance and usually just leaves you feeling heavy on the start line.

Q: Do you need real food in a 70.3 or are gels enough?
Gels and sports drink alone are enough for a half Ironman for most athletes, because the race is short enough that palate fatigue is manageable. Some athletes prefer a bar or chews in the first hour of the bike for the chewing sensation and a bit of variety. If you use solid food, take it early on the bike where digestion is easiest, never on the run.

Q: Why does your stomach shut down on the run in a 70.3?
Running mechanically jostles the gut, and at race intensity blood is redirected away from your digestive system towards your working muscles, which slows gastric emptying (how fast food leaves your stomach). Higher carbohydrate intakes are associated with more nausea and flatulence, though also with faster times (Pfeiffer et al., 2012). Reduce your intake target by roughly 20 grams per hour on the run, switch to liquid carbohydrate, and take your last bike gel 20 to 30 minutes before T2.

Q: How much sodium do you need in a half Ironman?
Start with 500 to 1000 milligrams of sodium per litre of fluid, and adjust based on your own sweat testing. Sweat sodium concentration varies from around 200 to more than 2000 milligrams per litre between individuals (Baker, 2017), so a generic salt tablet protocol is a guess. Heavy sweaters racing in heat sit at the top of that range, and light sweaters in cool conditions often need very little.

Bottom line

A 70.3 nutrition plan is not complicated, but it is specific. Load at 10 to 12 grams per kilogram for 36 to 48 hours, eat 2 to 3 grams per kilogram at breakfast, take 70 to 90 grams of carbohydrate per hour once you are racing, and drink to a sweat rate you have actually measured. Then rehearse the whole thing in at least three long training sessions before race day, because an untrained plan is really just a Hope and Pray strategy.

If some of this looks like the gap between what you have been doing and what you should be doing, do not stress. It is a very fixable gap, and you did not know what you did not know. The athletes who get this right are not more disciplined than you, they just stopped guessing and got taught the numbers for their own body.

That is exactly what we do inside the Triathlon Nutrition Academy, where you build your own periodised race nutrition plan with an Advanced Sports Dietitian instead of copying someone else's. You can register your interest for the next cohort at dietitianapproved.com/academy.