Runner's Dilemma #30 — How Many Energy Gels for a Full Marathon?
Runner's Log | Runner's Dilemma #30
How Many Energy Gels for a Full Marathon?
In three days, I'm going for a sub-4 full marathon.
If I were far faster than that, I probably wouldn't be worrying about any of this.
But since I honestly don't know whether sub-4 is possible, I end up worrying about everything.
When should I use CrampFix, the shot that's supposed to help when a cramp hits?
Should I drink water at every aid station?
What should I eat starting three days before the race, and what should dinner the night before be?
And what about breakfast on race morning?
So many questions.
So I looked into them one by one.
A Marathon Is Fuel Tank Management
Your body has a fuel tank that stores carbohydrates. It's called glycogen.
But the tank has a fixed size, so over a full marathon you start to see the bottom.
That leaves three jobs.
2. Keep topping it up as you run (III)
3. Run so the tank doesn't empty too fast (pacing)
I. Three Days Out: What Should I Eat?
This isn't the time to build anything more through training. It's the time to fill up through food.
The method is simple. For the two days before the race, raise the share of carbohydrates like rice, bread, and pasta.
Studies describe starting to eat plenty of carbohydrates 36 to 48 hours before the race.
So rather than cramming it all into one dinner the night before, it's better to fill up well before that. Carbohydrate storage isn't something that finishes in a single evening meal.
So here's how my remaining three days go.
| Day | What to do |
|---|---|
| Thu (D-3) | Eat as usual. Just avoid very greasy or unfamiliar food |
| Fri, Sat (D-2, D-1) | More easy-to-digest carbs than usual (rice, noodles, potatoes, bread) |
| Sun | Eat breakfast and start |
That said, there's no need to suddenly change everything you normally eat. What matters more is this:
Food I eat often and that has always sat well in my stomach. That's the safest choice.
Two Days Out: Things to Be a Little Careful With
| Be a little careful with | Examples | Why |
|---|---|---|
| High-fiber food | Multigrain rice, beans, broccoli, raw vegetables, salad | Can cause bloating or an upset gut |
| Greasy food | Fried food, pork belly, cream sauce | Can feel heavy |
| Unfamiliar food | A restaurant you've never tried, a new supplement | Trouble if your stomach reacts |
| Alcohol | Beer, soju | Better to skip before a race |
Fiber, greasy food, and unfamiliar food are things carb-loading guides commonly agree on.
As for alcohol, I'll skip it this weekend.
If your stomach is sensitive, there's also talk of resting spicy food, dairy, and carbonated drinks for these two days, but that varies by person.
If you've eaten something regularly without trouble, there's no need to cut it out.
One more thing. Eating this way can make your weight go up a little.
That's because carbohydrates are stored along with water.
There's no need to worry if your weight is slightly up before the race.
II. The Night Before and Race-Morning Breakfast
The Night Before
There's apparently no single "best last meal."
I'll make the night before not the day I eat the most, but the day I eat the most familiar things.
The usual rice or pasta, with easy-to-digest side dishes, and just a little more than normal.
Race-Morning Breakfast
Eat too much breakfast and your stomach may bother you while running. Eat nothing and you may run short of energy early on.
So I eat 2 to 3 hours before the start.
Something I've eaten before that digests easily, like rice or porridge, bread with jam, or a banana.
But I don't normally eat breakfast. For me, eating breakfast on race morning is itself something I've never done.
So on the day I'll keep it light: plain rice wrapped in seaweed, no fillings.
Caffeine
There's plenty of research showing caffeine can help exercise performance.
And caffeine isn't only in coffee. It's also in energy drinks, cola, green tea, caffeine gum and capsules, and in gels that contain caffeine.
I plan to have my usual cup of coffee.
Trying it for the first time on race day, if you don't normally drink it, is risky.
And one thing matters here too.
That goes for supplements you don't normally take, or anything you suddenly decide to try because you heard it's good.
III. So, How Many Gels?
Now for the part I've been most curious about.
Energy Gels: 7, Plus 1 Spare
The tank keeps draining while you run. So you top it up along the way.
But gels aren't the only source. The sports drink at the aid stations contains carbohydrates too.
So you can't just count gels. You have to think about gels and sports drink together.
Studies talk in terms of "grams of carbohydrate per hour."
In my case, taking the gels and the sports drink together into account, I plan to take one gel about every 30 minutes.
One gel usually contains around 20 to 30g of carbohydrate.
More isn't automatically better, and taking a lot suddenly can upset your gut.
Here's how I think about timing.
Not after I get hungry, but while I still feel fine, a little at a time. I start about 45 minutes in and take one at regular intervals.
This plan is calculated for a sub-4 at 5:41/km pace.
| Gel | Where | Elapsed time |
|---|---|---|
| 1 | 8km | 45 min |
| 2 | 13km | 1h 10m |
| 3 | 17km | 1h 37m |
| 4 | 21km (halfway) | 2h |
| 5 | 26km | 2h 28m |
| 6 | 30km | 2h 53m |
| 7 | 35km | 3h 19m |
In both of my long runs, my legs turned heavy after 30km.
Gels are easier on the stomach when taken with water.
Some products are made to be taken without water, though, so check what kind of gel you're using.
Water at Every Aid Station?
Until now, I thought I had to at least take a sip of water at every aid station.
But apparently that's not necessarily true. If it's hot or you're sweating a lot, you may need more, but drinking a lot at every stop isn't good either. Drinking too much can actually put your body at risk, and you need to be especially careful over long distances.
So here's my approach.
- If I'm thirsty, I drink.
- If it's hot or I'm sweating a lot, I pay a bit more attention.
- If I'm not thirsty, I don't force myself to drink a lot.
I sweat a lot. The white salt marks left on my running vest suggest I lose quite a bit of sodium in my sweat.
Sports drinks replace some of that salt. But their sodium concentration is fairly low (it varies by product, so check the label), and if I only drink half a cup at each aid station, the amount isn't much.
So I'll use sports drink as the base. I'll only add electrolyte tablets if I've used a product before, and I won't try anything new three days before the race.
CrampFix: An Emergency Option for When a Cramp Is Coming
From what I found, muscle cramps aren't caused simply by a lack of water or salt.
In a study that followed Ironman triathletes, what predicted cramps wasn't dehydration or sodium, but running faster than usual and having had cramps before. Getting swept up in the race atmosphere and pushing the pace early could be the biggest cramp risk of all.
Anti-cramp shots are described as working not by supplying water or salt to the muscle, but by strongly stimulating sensation in the mouth and throat to reduce cramping. But the evidence wasn't strong.
I found two studies. In one, the time before a cramp set in got longer; in the other, the effect was small and short-lived. I also can't confirm that the product I have is the same one used in those studies.
So rather than taking it from the start, I think it's more realistic for me to carry it as an emergency option for when a cramp seems to be coming.
Of course, this shouldn't be tried for the first time on race day either. It can be spicy or harsh enough to upset your stomach.
The Whole Plan on One Page
| When | What to do |
|---|---|
| Fri, Sat | More easy-to-digest carbs than usual. No alcohol, nothing new |
| Night before | Familiar food, a solid meal, but no overeating |
| 2-3 hours before | A light breakfast like seaweed-wrapped rice (try it once beforehand) |
| Before the start | My usual amount of coffee |
| From 8km | One gel every 30 minutes (7 total + 1 spare) |
| Aid stations | Water or sports drink when thirsty. Don't force it |
| Cramp warning | CrampFix |
| The whole way | Don't do anything new on race day |
I did the 35km long runs. I ran 20km at race pace. I finished my last training run.
There isn't much more I can do now.
Eat well, sleep well, keep my body relaxed, and run on race day the way I prepared.
But having come this far, I have to give it a try.
A promise to my son is turning out to be a scary thing.
"Well, with the injuries... Fine. I'll break 4 this fall."
References: Carb-loading guides · Secondary sources citing ACSM nutrition and athletic performance guidance · International Society of Sports Nutrition position stand on caffeine (2021) · Craighead et al., Muscle & Nerve (2017) · Behringer et al., European Journal of Applied Physiology (2017) · Study of predictors of cramping in 210 Ironman triathletes (2011).
This post is general guidance and is not a substitute for a nutrition or hydration plan tailored to an individual.
