Carb loading for a half marathon is simpler than most runners think. At our Samford gym we coach plenty of people towards their first 21.1 km, and the question we hear in race week is always the same: do I need to eat a mountain of pasta? The short answer is no, but a little planning over the last two days makes a real difference to how the final 5 km feels.
Do you need to carb load for 21.1 km?
It depends on how long you will be out there. A runner finishing in about 90 minutes can get by on normal eating plus a good breakfast. Most recreational runners take two hours or more, and for them a short, sensible load is worth doing. It is not the full three-day load used for marathons. Think of it as eating a bit more carbohydrate, and a bit less of everything else, for two days.
How much carbohydrate?
A common sports nutrition guide is 7 to 10 g of carbohydrate per kilogram of body weight a day for the 36 to 48 hours before an event of 90 minutes or more. For a 70 kg runner that is roughly 500 to 700 g a day. That sounds like a lot, so in practice we suggest the lower end and a few easy habits rather than counting every gram.
Carb loading for a half marathon: the two-day plan
| When | What to do | Examples |
|---|---|---|
| Two days out: breakfast | Bigger carbohydrate serve than usual | Porridge with banana and honey, plus toast |
| Two days out: lunch and dinner | Carbohydrate covers half the plate | Rice bowls, pasta, wraps, potatoes |
| Day before: snacks | Carbohydrate snacks between meals | Fruit, rice cakes with jam, fruit toast, juice |
| Day before: dinner | Familiar, carbohydrate-focused, normal size | Pasta or rice with a simple sauce and lean protein |
| Race morning | Small carbohydrate breakfast 2 to 3 hours out | White toast with honey, a banana, a sports drink |
Keep protein steady, trim the rest
The carbohydrate has to fit somewhere, so the other parts of the plate get a little smaller. Keep a normal serve of protein at each meal. Cut back on rich, fatty foods, which fill you up without adding carbohydrate.
Many runners also eat less fibre in these two days. Big bowls of beans, bran cereal and raw salad take up room that carbohydrate could use, and they can feel heavy on race morning. Swap brown rice for white and wholegrain bread for sourdough, keep vegetables cooked and moderate, and go back to your usual high-fibre eating after the race.
Practise in training
Never try carb loading for the first time in race week. Do a shortened version before your longest training run, two or three weeks out, and note how you feel. Our half marathon plan marks where that test run sits in the build.
Fluids and salt
Stored carbohydrate holds water, so expect the scales to be up 1 to 2 kg by race morning. That is normal and a sign the load worked. Drink steadily through both days and add a little salt to meals if the forecast is hot. Our electrolyte drinks guide covers race-day fluid.
During the race
If you will run more than about 75 minutes, plan to take 30 to 60 g of carbohydrate an hour, from gels, chews or a sports drink, starting around the 40 minute mark. Our guide to energy gels for running explains how to practise it.
After the race
Once you are done, go back to normal eating, with plenty of protein, carbohydrate, fruit, vegetables and wholegrains. Some of our runners also stir a soluble fibre powder into a drink during ordinary training weeks; if you are comparing brands, this guide to the best PHGG in Australia sets out what is in each jar.
Common questions
Do I need to carb load for a half marathon?
If you expect to take two hours or more, a short two-day load is worth doing. Faster runners can usually get by on normal eating and a good breakfast.
When should I start carb loading for a half marathon?
About 36 to 48 hours before the start. Longer loads are for marathons and longer events.
Is pasta the best food for carb loading?
It is a good choice, but rice, potatoes, bread, fruit, juice and porridge all work. Pick what you already eat often.
Why am I heavier after carb loading?
Stored carbohydrate holds water, so a gain of 1 to 2 kg is normal and expected.
When to get it checked
If you keep fading in the last part of long races despite fuelling well, or a niggle appears every time your long runs go past 15 km, see an exercise physiologist. We can look at your training, strength work and fuelling together.