Posted on January 24th, 2018 by John Armstrong
For those of us who are marathon training, our Sunday runs are starting to get seriously long. Once you are running for over 2 hours, you should think seriously about nutrition.
On marathon day, nutrition is crucial. Your body’s ability to store fuel is often the limiting factor on marathon ability. Your body’s main fuel reserve for running is called glycogen. This is the main way carbohydrates are stored in the human body for use by your muscles. Your body can also use fat reserves when you are running, but this is a much less effective source of energy on race day. Many runners will run out of glycogen at about mile 18 or 20. This is often called “hitting the wall” for self-explanatory reasons.
This is why on race day you should definitely be taking on board fuel as you run. There are many options: you can carry energy gels and/or eat the various energy gels, sweets and drinks they hand out at most big marathons. Personally, I eat 3 jelly babies every 5k during a marathon until I can’t stand them any more plus one energy gel at the start and a caffeinated gel towards the end. I also make sure I know where the water stations are so I get a drink immediately after eating anything.
What works for me may not work for you. But you should start trying to figure out what you intend to do on race day. How much can you take on without getting a stomach upset? Does Lucozade agree with you etc? We all respond quite differently.
Start experimenting on your long runs with nutrition to find out what works. If you practice taking on fuel, your body will learn how to make the most of it. There is some debate about how much fuel you should take on during training. Personally, I think you should do all or almost all of your long runs (>2hrs) taking on a reasonable amount of food to stop your training runs being too exhausting and to aid recovery. You should certainly do a few dry runs where you try out your race day strategy as close as you can.
There is some (in my view slightly unconvincing) evidence that doing some training runs where you allow yourself to run on low glycogen can help you develop the ability to use fat as a fuel on race day. So some people do recommend running occasional “glycogen depletion” runs. The reason I find the evidence is unconvincing is that although in the experiments they were able to show athletes who had experienced glycogen depletion training had better fat metabolism, they didn’t actually have better times. You might wonder about the effect of glycogen depletion on weight loss, surprisingly the evidence suggests that glycogen depletion runs don’t help with weight loss (having said that, anyone who drinks sports drinks when they are not doing sport is on a fast-track to weight gain, we’re talking about moderate carb consumption as part of a greater than 2hr run here).
Despite the pretty clear evidence that you need to eat to get the most out of your marathon, I know that a lot of people worry about doing so. One obstacle that I know stops some people trying gels etc is that they taste pretty revolting. Also I know a lot of you don’t like eating rubbish processed food. And it’s absolutely true that eaten when you’re not running, gels are just the kind of pure sugary junk you should avoid. But so long as you eat a balanced diet when you’re not choking down your High 5’s, you shouldn’t worry about taking them when you run. The fact is that on race day, the flavour and the lack of fibre are not important considerations. On the other hand, be warned that failing to take on energy during the race will cost you dear.
Here are two links to some science. I’m not claiming to have read the articles in full, but I think I’ve managed to extract the gist of both.
The first paper Metabolic Factors Limiting Performance in Marathon Runners has a number of references to back up the basic claim that you need to eat while you run to achieve your best performance. They also develop a mathematical model that can supposedly be used as a marathon pace/energy calculator. I’d be very skeptical about their calculator as they don’t really seem to have tested it much.
The second paper is Training in the fasted state facilitates re-activation of eEF2 activity during recovery from endurance exercise. This title says it all: namely that they study the effect of glycogen depletion exercise not on performance but on some rather technical aspect of how your cells function. One might conjecture this cellular change could make you run faster but in the time trials they conducted they didn’t observe a difference.