How to Carb Load for an Ironman 70.3 Triathlon
Ask most triathletes how they carb load for a 70.3 and you'll get some version of big bowl of pasta or a pizza the night before." If that's you, you're not alone, but you're almost certainly leaving time on the course.
Carb loading can be the difference between finishing strong and an unpleasant shuffle to the line. But it isn’t just as simple as “eat more carbs”, because done badly, it can be a significant contributor to stomach upset during your race.
Done properly, carb loading means eating a specific amount of carbohydrate in the right window before your race, while cutting back on the foods that can negatively impact performance.
This guide walks you through how many carbs, which ones, and for how long, with a sample day you can copy.
I’ve worked with hundreds of triathletes as a Registered Sport Nutritionist (SENr), and I also love the 70.3 distance myself, with a personal best of 4:36. Carb loading is one of my favourite topics because it's such a powerful, low-effort lever, so let's get yours right.
Do you need to carb load for a 70.3?
This is where a lot of people, including some good coaches, get it wrong.
The thinking goes: a 70.3 is shorter than a full Ironman, so surely you don't need to bother as much about carb loading. That's a costly mistake, and here's why.
Your body runs on two fuels, fat and carbohydrate. Fat is effectively unlimited, with tens of thousands of calories stored even in a lean athlete. Carbohydrate is the one that runs out: you store only around 2,500 calories of it as glycogen (if you have carb loaded properly!).
A 70.3 is raced at a higher intensity than a full Ironman, which means you burn through a greater proportion of carbohydrate, so you actually empty those limited glycogen stores faster. That makes loading more important for a half, not less.
When you run out of carbs, you’ll “bonk”, or hit the wall: glycogen drops to a critically low level, your pace falls off a cliff, and you feel dreadful.
For most 70.3 athletes it happens on the run. Carb loading tops your glycogen up to its maximum, or even just above normal limits, so you push closer to the finish line while feeling strong. Carb loading needs a solid fuelling plan to go alongside it, and you can check out my full 70.3 triathlon fuelling guide in this article.
The payoff for proper carb loading is real.
Carb loading improves endurance performance by roughly 2–3%. Over a five-to-six-hour 70.3 that's somewhere in the region of nine to eleven minutes, just for eating well in the days before.
And that's before the mental side of finishing strong; feeling like you can keep pushing while others are slowing is an amazing feeling.
A thorough carb loading protocol was part of a key strategic piece of the work I did with Lizzie Rayner, a professional triathlete I support as a nutritionist. Dialling in her fuelling, carb loading included, was a big part of her step up: she's since won multiple pro races and is now ranked among the top 20 in the world.
Next, we’ll go through the timeframes for a proper carb load, because it’s an area that many triathletes get wrong. But if you’d like to watch the key concepts of this article in video format, check out the video below.
How many carbs do you need to carb load for a 70.3?
Here are the numbers I use:
Two days before the race: 6–8g of carbohydrate per kilogram of body weight.
The day before: 8–12g per kilogram.
The slightly lower figure two days out gives you leeway for any light training, walking around at registration, and just living your life, before you go all-in the day before.
To put real numbers on it:
I’m around 70kg, and that means I’d need 420–560g of carbohydrate two days out, then 560–840g the day before, which is around 2,800 calories from carbohydrate alone on that final day. That is a lot more than most people think, and it's one of the biggest reasons carb loading fails.
For perspective, here's the carbohydrate in some staples:
A cup of cooked pasta: ~45g
A cup of cooked white rice: ~45g
A slice of white bread: ~20g
A medium banana: ~27g
A 500ml bottle of sports drink: ~30–80g
I worked with a triathlete inside The Hub, my nutrition program for 70.3 and Ironman athletes, who'd done several 70.3s and never quite raced to her potential.
Her version of carb loading was a sprinkling of extra carbs the day before and a big pasta meal, and hopefully from the figures above, you can see how much it actually requires to get close to the right number of carbohydrates. When I added it up, she was getting less than half the carbohydrate she needed, so it was no surprise she kept fading late on. Fixing her carbohydrate loading strategy and developing a clear race nutrition plan allowed her to finish her races in a much faster time.
What to eat for when carb loading for a 70.3 triathlon, and what to avoid
For everyday eating I'd point you towards wholegrains, more fibre, plenty of veg, but this isn’t the time: Carb loading is when you have to do the opposite.
The trick is to go simple. White bread over wholemeal, white rice over brown, low-fibre cereals, and yes, sweets and sugary drinks earning their place.
Wholegrain foods carry more fibre, protein and sometimes fat, and those three are slow to digest. During a carb load they just leave you full and bloated, and there's a real chance they're still sitting in your gut on race morning, ready to cause trouble across the swim, bike and run.
Sweets and carbohydrate drinks, on the other hand, deliver simple carbs with almost no fibre, fat or protein, which makes them close to perfect here. This is the time to reach for your favourites, just steer clear of the high-fat ones like doughnuts and pizza.
Carb-rich drinks deserve a special mention. If you try to hit 700g of carbohydrate from solid food alone, it can feel really tough and make you feel bloated. One triathlete I worked with always felt miserable during carb loading until we shifted some of it into drinks, and it suddenly became manageable. Sports drinks typically have another added benefit: they often contain sodium, which helps maintain your hydration.
Bring your fibre down first
Slightly before the load itself, start cutting fibre. I'd transition to lower-fibre foods about three days out: the same white-over-wholegrain swaps, fewer vegetables, lower-fibre fruit. This is perhaps the single most important nutrient to reduce before your race, and is key to getting you to the start line feeling comfortable and not bloated.
I cover the gut side in more depth in the complete 70.3 fuelling guide, including in-race fuelling strategies.
How long should you carb load for a 70.3?
The evidence says 24 hours of proper loading is enough to max out your glycogen stores. My take for a 70.3 is to start about 36 hours out, which gives you room for the day-two figure above and covers any light pre-race pottering about.
One myth I’d love to kill: you do not need to go low-carb first to "deplete" before loading.
You get the same glycogen storage going straight from a normal diet into a load, and the depletion approach mostly just leaves you flat and miserable in the days before a big race. Keep the carbs flowing.
Will I gain weight during a carb load? And is it unhealthy?
Two worries come up constantly, so let's settle both.
You may see the scale rise a kilo or two, and that's completely normal. For every gram of glycogen you store, your body holds about 3 grams of water alongside it. That extra water is stored fuel and water, not fat, and it's working for you on race day.
The same mechanism is why you'll feel thirstier than usual, so drink a little more than normal and add electrolytes or a pinch of salt to your drinks across the loading days.
The potential performance increase outweighs any detriment from increased water weight, which is why it’s a strategy recommended for elite athletes chasing podiums all the way to age-groupers taking on their first 70.3
As for healthy, it's a short 48-hour window of higher carbohydrate intake. For most people that's completely fine, and there is no health risk or concern over vitamin or mineral deficiency over such a short spell.
The main exception is if you have a condition like diabetes, in which case get individual advice first.
A sample day-before carb loading plan (70kg athlete)
Here's what the day before could look like for a 70kg athlete, landing around 700g of carbohydrate. Scale the amounts to your own body weight, and notice it's front-loaded: more earlier in the day so you're not forcing food down at bedtime.
To help you further, I’ve created a free carbohydrate loading guide for you, with full day-by-day menus worked out for 60kg, 70kg and 80kg athletes, so you can see exactly what to eat and when to hit your numbers without doing the maths yourself.
| When | Example | ~Carbs |
|---|---|---|
| Breakfast | 2 bagels with jam, a banana, a glass of orange juice | ~140g |
| Mid-morning | Granola with milk, raisins and blueberries | ~90g |
| Lunch | 3 white tortilla wraps with smoked salmon and light soft cheese, orange juice | ~125g |
| Afternoon | Low-fat fruit yoghurt | ~55g |
| Dinner | White pasta with tomato sauce and breaded cod | ~90g |
| Evening | Low-fat rice pudding with a banana | ~90g |
| Across the day | Sports drink and fruit gums | ~115g |
A few things that make a real difference
Practise it once or twice at least four weeks out, ideally before a big training weekend. Even a single day is enough to check you tolerate the foods you've chosen, and it leaves you time to adjust so race week is stress-free.
It’s worth tapering your intake across each day; eat more in the morning and afternoon, less in the evening.
If you eat a mountain of food right before bed and the likelihood is you’ll feel over-full, bloated and have a poor nights sleep — not what you want before your race!
Frequently asked questions
How many carbs do you need to carb load for a 70.3?
Aim for 6–8g of carbohydrate per kilogram of body weight two days before the race, rising to 8–12g per kilogram the day before. For a 70kg athlete that's roughly 420–560g two days out and 560–840g the day before.
How long should you carb load for a 70.3?
About 24 hours of proper loading is enough to maximise glycogen, but I'd start around 48 hours out for a 70.3 to give yourself room. Separately, reduce your fibre intake from three days before.
Do you carb load the night before a 70.3?
Carb loading should be a structured nutrition plan over 48 hours, not a single giant meal the night before your race. Cramming it all into dinner tends to leave you bloated and sleeping badly, and you’ll miss the required carbohydrate targets.
Will carb loading make me gain weight?
You'll likely gain a kilo or two, but it's water, not fat. Every gram of stored glycogen holds about 3 grams of water with it, and so as your carb stores increase so does your water weight. Potential performance benefits are greater than any weight gain, which is why elite triathletes follow this strategy too.
Can you carb load in one day?
Yes. The evidence suggests 24 hours of proper loading is enough to top up your glycogen stores. However, I’d recommend 48 hours to account for light exercise, walking around the race village and to give yourself a little leeway.
Do you need to go low-carb before carb loading?
No. You get the same glycogen storage going straight from a normal diet into a load, and depleting first usually just leaves you feeling flat.
Once your tank's full
Carb loading fills the tank, but you still have to fuel on the day itself, across the swim, bike and run, at the higher intensity a 70.3 demands.
I cover this step by step in the complete 70.3 fuelling guide, which covers everything you need to create your own race nutrition plan and race as fast as possible.
If you'd rather not piece it together yourself and have expert guidance, that's exactly what I do inside The Hub, my nutrition program for 70.3 and Ironman triathletes. I’ll create a personalised carb loading plan based on your preferences, as well as a full race-day plan that you can refine over time with testing protocols and my continued support.
