Carb Loading Explained

Carb loading is a deliberate increase in carbohydrate intake in the two to three days before a race, aimed at maximizing glycogen stores in your muscles and liver before the start. It's genuinely useful for some race distances and mostly unnecessary for others, which is where a lot of the confusion around it comes from.

When carb loading actually matters

For a 5K or 10K, normal glycogen stores are generally more than enough, and carb loading isn't necessary. For a half marathon, a modest increase in carbohydrate the day before can help some runners, though it's optional rather than essential for most people. For a full marathon, where hitting the wall becomes a genuine risk without adequate glycogen stores, a deliberate carb loading approach in the final two to three days is considerably more worthwhile.

How it works

Your muscles and liver store a limited amount of carbohydrate as glycogen, which is the primary fuel source for sustained running effort. Increasing carbohydrate intake while keeping training minimal in the final days before a marathon allows those stores to fill more completely than they would under normal training and eating.

A simple, practical approach

For most recreational marathoners, carb loading doesn't need to be complicated or extreme. A practical version looks like shifting the balance of your meals toward more carbohydrate-rich foods, rice, pasta, bread, potatoes, and fruit, for the two to three days before the race, while keeping portion sizes reasonable rather than dramatically overeating.

• Increase the proportion of carbohydrates at each meal, rather than adding entirely new, unfamiliar foods
• Keep meals familiar; this isn't the time to try new dishes or cuisines
• Don't confuse carb loading with simply eating more of everything
• Pair it with reduced training volume during tapering, since you're not burning through glycogen as fast

Common mistakes

Overeating in general, rather than specifically shifting toward carbohydrates, is a common mistake that can leave runners feeling heavy or bloated on race morning rather than well-fuelled. Trying unfamiliar high-carb foods for the first time during loading days is another; stomach issues from an unfamiliar meal are a bigger risk than slightly under-loading.

How this fits into race week overall

Carb loading is just one part of a broader race week eating plan; see what to eat the week before a marathon for a fuller day-by-day approach, and how to fuel a marathon for what happens during the race itself.