Carb Loading Is a Two-Day Job, Not One Dinner
You have a pasta dinner booked for the night before your marathon, and in your head that is your carb loading. It is not. Carb loading is a two-day job, and one dinner cannot fill a tank that takes 48 hours to fill. The runners who get this wrong do not find out at the start line. They find out at 35k, when the legs go and the pace falls off a cliff.
Here is what is at stake. Your muscles hold enough fuel for about 30 kilometres, or roughly 18 miles, at marathon effort. The last 12 are the ones that decide your day. Get this right and the final 10k is just hard. Get it wrong and the race turns into damage control. Nobody ever gives you a number, you just get told to eat more carbs, which is useless advice when you are standing in a supermarket two days out. This article gives you the number and the timing.
Why Runners Run Out of Fuel Around 35k
I made this mistake before my first marathon. I ate the biggest bowl of pasta the night before, went to bed feeling like I had nailed it, and had eaten completely normally for the two days before that. At 35k my legs stopped answering and I thought I had under trained. I had not. I turned up to a four hour race carrying about two hours worth of fuel. After coaching over 200 runners, this is still the one most of them get wrong.
It shows up the same way every time. You wake up feeling full and read that as ready. The first 20k feels easier than it should. Then somewhere after 20k the legs get heavy, your pace drops 10 or 15 seconds a kilometre, and you cannot lift it no matter how hard you push. You did not lose fitness in the last 10k. You ran out of fuel, and every minute you give away is a minute you spent nine months earning.
Your Number and Your Timing
Start 48 hours out, not the night before. Aim for 8 to 10 grams of carbohydrate per kilo of body weight every single day. At 70 kilos, that is 560 to 700 grams a day. You are not adding food on top of what you already eat. You are swapping fat and fibre out and putting carbohydrate in their place.
Your muscles will hold far more glycogen than normal, but only if you keep feeding them long enough to fill up. One meal tops up the surface. Two days fills the tank. If you only manage one day, you get about half the benefit.
The research backs this. A 2011 study in the International Journal of Sports Medicine followed 257 London Marathon runners and matched equal ability runners against each other. Those eating more than 7 grams per kilo the day before ran faster and held their pace. The low carbohydrate group slowed the most between 35 and 40k. That is the part of the race this protects. I had a runner fall apart at 35k in two marathons. He changed nothing in training. We only changed the number and the timing for the two days before, and in his third marathon he held pace to the finish and took 3 minutes off.
What to Eat and When
Do not just eat as much as you can for three days. You will turn up heavy, sluggish and sitting on a stomach that has not cleared. The total only changes a little. The composition changes. Expect the scales to go up a kilo or two. That is water bound to the glycogen, not fat, and it comes straight back off. Do not panic and do not try to correct it.
Two days out, work out your number: body weight in kilos times eight. At 70 kilos that is 560 grams. Write it down, because you will not hit it by guessing. Then make every meal white: white rice, white bread, white pasta, skinless potatoes, bananas, honey, jam and sports drinks. Cut the salad, vegetables, nuts and anything high in fat. Eat four meals and two or three snacks, because you cannot physically fit this much food into three sittings.
On race morning, three hours out, have 1 to 2 grams per kilo of something you have eaten hundreds of times before. Nothing new. If you only get one thing right, start Friday morning for a Sunday race, not Saturday night.
If you want someone to look at your build to race day, book a free video call with me and we will go through your goal, your training and what is missing.