When not on the trails, your body is constantly repairing itself and adapting to stress. Each little adaptation requires fuel and hydration too. If you put bad stuff in, bad stuff will come out. Inadequate fueling can increase injury risk and decrease progression by slowing down adaptation and healing.

Fueling and hydration is a limiting factor in these power-plant reactions, but, unlike other factors like genetics, it is under your control. By strategically considering what you eat and drink before, during and after runs, you can be healthier, happier and faster

HYDRATION

The first, easiest step in taking control of your fueling and hydration is having adequate fluids to avoid dehydration. Proper hydration lets your body clear waste products and is essential for nearly every bodily function, including running.

General Hydration Tips

After you wake up each day, drink a glass of water. While you were dreaming, your body was still humming along performing basic tasks, all of which use a bit of water. So when you wake up, a glass of water can make sure that you aren’t getting behind when you’re counting sheep.

Throughout the day, stay hydrated as feels natural to you. There are conflicting approaches to hydration, with some experts saying it is over-emphasized, and others insisting on the typical advice of eight glasses a day (not accounting for exercise). When the experts disagree, it’s always helpful to look at what people actually do. Most elite runners carry a water bottle around with them throughout their days. A few more sips of water is a simple thing to do, and it likely won’t hurt, so be sure to keep the water flowing during training.

The body is less adept at absorbing plain water than it is water with some electrolytes. So consider adding a pinch of salt or an electrolyte tab to your bottle.

Although some electrolytes are good, drinking sugar water is not. Most of your fluids should not come with a few spoonfuls of sugar, like you’ll find in most juice and sports drinks. Avoid too many liquid calories, which have been linked to negative health outcomes like Type II diabetes.

Finally, at the end of the day, make sure you aren’t going to bed dehydrated. You shouldn’t be waking up to pee constantly, but if you find yourself parched when you wake up, you might want to experiment with a small glass of water before bed.

Hydration Before, During and After Trail Runs

During runs, most activity below 60 minutes does not require rehydration until after it is completed. If you start the run hydrated, you shouldn’t need to be attached to your bottle at all times. Some runners complain of dry mouth as soon as 10 minutes into a run, and a lot of the time this feeling is a learned response, rather than a physiological signal. If you are one of those runners, it may be helpful to have a half a piece of gum to chew so you generate saliva to overcome that parched feeling.

On runs longer than 60 minutes, the amount of hydration needed depends on your sweat rate. Every body is different, and the variation in sweat rates can be astounding. In general, smaller athletes require less fluid, and bigger athletes require more. But there are some 100-pound runners that sweat like broken fire hydrants and some 250-pound runners that are camels. In addition, temperature and dew point play a big role in how much you lose to sweat. On hot, humid days, you’ll need more water no matter what your sweat rate.

So while there is a ton of variation, most runners require between 12 to 24 ounces of fluid per hour, depending on sweat rate and weather conditions. The sweet spot seems to be around 16 ounces per hour in cool weather. It is helpful to have some extra calories in your fluids, which aids absorption and staves off bonking. Sports drinks and mixes are almost always better than plain water when available.

Up to 90 minutes, many runners can get by with little or no hydration. But beyond two hours, be sure you are hydrating properly—there is no physiological benefit in training your body to be dehydrated. Plan your runs around water sources, invest in water-purification straws or tablets, or stash bottles along your route. While it’s possible (and sometimes beneficial) to run without food, running without water is a recipe for disaster.

After you finish running, there are few more pleasant experiences than a tall glass of cold water. So, indulge, you earned it! In general, assuming a bit of normal dehydration from running, it is good to rehydrate whatever sweat loss you failed to keep up with during exercise (see CALCULATE YOUR SWEAT RATE below). If you’re feeling adventurous, you can mix water and juice, or even add a scoop of protein powder (or Ovaltine!).

Hydration is essential, but, like usual, there can be too much of a good thing. Avoid overhydration, which can cause severe kidney damage and even death. Called hyponatremia, overhydration is a major risk if you aren’t strategic about guzzling fluids.

Let’s start at the most basic level. Your body has a basal metabolic rate (BMR), which varies from person to person. There are lab-based ways to get exact with BMR, but a general online calculator will do the trick for most people. BMR is higher for men who have higher body-mass indexes (BMI), and lower for women with lower BMIs. For example, the BMR for a 5’2”, 25-year-old woman weighing 110 pounds is 1200 calories per day, assuming she is sedentary. Meanwhile, a 6’5”, 250-pound man of the same age has a BMR of 2070 calories per day.

Your BMR is the baseline number of calories it takes to maintain bodily functions without going into an energy deficit. Going below that number is called negative energy availability, which is good if you are trying to lose weight, but is also connected to running-related injuries and overtraining due to lack of fuel to repair stressed physiological systems.

Add exercise to the mix and things get a lot trickier. It varies a lot, so we won’t break it down here, but running one mile can burn up to 100 calories, with variation for age, gender, weight and running experience. In other words, if you run lots, you need to eat lots.

Failing to fuel enough can work in the short-term for some people that need to lose weight. But long-term negative-energy availability while training can lead to overuse injuries, reduced libido and countless other maladies that make running (and life) far less enjoyable. So the stakes are high when it comes to running-related fueling.

At the threshold level, make sure you are getting enough calories for your goals. That is step number 1—avoid thinking that less is more and skinny is fast. Instead, reframe it in this way: “strong is fast.” To be strong, you must fuel.

Carbohydrates are the final of the triumvirate, and they are essential for energy during exercise. While the general wisdom is turning toward limiting simple carbs in your diet like white bread and sugar, some carbs are necessary to keep your body efficient at high-intensity levels. A good rule is to not skimp on carbs before, during and immediately after runs, then to have carbs in moderation the rest of the time.

Beyond that simple overview, one of the best diet tips is perhaps the easiest: don’t overthink it. Set some rules, like eat lots of fat and don’t binge on potato chips every day. But after that, listen to your body and don’t stress about day-to-day choices and variation in your life and body composition. For many runners, salvation is achieved when they throw out their scale entirely and stop counting calories.

While the body is a machine, viewing it in terms of quantified inputs and outputs can take some of the soul away from day-to-day life, and it can lead to perverse outcomes like eating disorders and body image dysmorphia. Viewing diet through general, flexible principles rather than strict, quantified rules can be liberating, and ultimately it can lead to better health outcomes for some runners.

PRO SNACKS

No food is perfect. But across a number of top runners, there are some foods that you’ll see again and again in fridges (and Instagram posts). Here are the top 5.

1. Full-fat yogurt. Full-fat yogurt provides a nearly ideal macronutrient profile when mixed with a dollop of honey. Plus it has probiotics, which could improve gut health and prevent mid-run stops in the bushes.

2. Nuts and nut butters. There is almost no diet that says nuts are bad, which is remarkable because nearly every food is controversial if you know the right person to ask. Countless runners practically live off of almond butter.

3. Jerky. Jerky is a great source of protein, and jerky sponsorships are now common among pro runners.

4. Bananas. Zach Miller, winner of the 2016 North Face 50 Miler, is lovingly called “Banana Boy” by some of his closest friends. Why? He has been known to eat almost a dozen a day on occasion.

5. Eggs. Eggs with yolks are a wonderful source of many essential nutrients, and an omelet is a great option for post-long-run brunch.

Now, we can get into the nitty gritty of fueling. What exactly should you eat around your runs? The unsatisfying answer is that it depends on your background and your physiology. But there are a few general rules to understand.

Before runs, most of your fuel is held in two places: your glycogen stores (basically stored carbohydrates) and your fat stores (the jiggle that helps you wiggle). Glycogen stores are usually topped off from meals many hours before you actually run, and they can fuel high-intensity exercise for 90 to 120 minutes in most people when fully fueled. Your fat stores are longer-term still and can burn nearly indefinitely at low intensity.

Glycogen burns hot, so when training is more intense, you need glycogen to support it. Fat burns long and strong, so lower-intensity exercise uses fat. In practice, most trail running mixes those two energy sources. That is why most runners could go three hours without keeling over and being unable to move, although they may have to slow down.

Your pre-run meal is focused on topping off your glycogen stores and optimizing your blood sugar for the activity ahead. For most elite runners, something small—around 200 to 300 calories—a couple of hours before does the trick, like an energy bar or a banana and peanut butter. However, there are some people who can’t eat for many hours before running, and others that can eat a full meal right before heading out the door. Physiologically, it doesn’t matter all that much as long as you have been eating well in the days preceding the run.

During runs, your body burns through the glycogen and fat as you traverse the trail. For intense runs less than 90 minutes, you don’t need to refuel. And for lower-intensity events less than two to three hours, you don’t need anything, since your body will likely be burning your nearly bottomless fat stores.

However, over 90 minutes, unless you are a fat-adapted runner (see FAT ADAPTATION AND FASTED RUNNING below), you’ll need to refuel strategically. Running burns anywhere from 500 to 1000 calories an hour for most people. Meanwhile, most stomachs can only tolerate around 300 calories per hour during exercise. So no matter what, you will be operating on a deficit, and the key is to prevent the deficit from becoming too large and causing a bonk, where you run out of fuel to continue moving forward well at all.

You can get those approximately 300 calories per hour through whatever source you tolerate best. Energy gels are the most reliable options. A gel at 60 minutes and every 30 minutes after, supplemented by sports drink, can work wonders for energy levels and performance. Other options are energy bars, or even more outside-the-box treats like peanut-butter-and-jelly sandwiches. But, if you train your stomach over time, it usually has a remarkable ability to handle almost anything. Clare Gallagher famously won the Leadville 100 in the 2nd-fastest time ever while fueling with frosting and candy. While that approach is not recommended long term, it shows that the key is to limit the calorie deficit, rather than to consume the perfect foods all the time.

FAT ADAPTATION AND FASTED RUNNING

The body is astonishingly adaptable, and that is especially evident in how it can be trained to utilize fat. Over time, with specific dietary choices, an athlete can burn more fat at higher levels of exertion, theoretically leading to more efficiency on the trails.

After Runs

You may have heard about the “glycogen window,” the period of time after runs when the body is most apt at taking up calories and replenishing glycogen stores. While there is some scientific truth to that, in practice, many top runners don’t abide by any specific system of refueling. Therefore, like diet generally, it might be best to remove some of the rules and constraints, focusing on what your body is telling you, rather than what articles (or books) are telling you.

As a general rule, focus first on rehydration after you finish your run. Then, let yourself be guided by hunger, with the qualification that you should be sure to get well-rounded foods with carbs, protein and fat in your body within an hour or two of running if possible. Have fun with post-run foods, and don’t be afraid of giving yourself a reward. Positive psychology works, and it’s really fun to train yourself like a puppy on occasion.

1. Don’t wake up starving.

If you find yourself waking up with an almost-uncontrollable urge to eat, you are underfueling. Because underfueling can cause numerous health issues for runners, it’s essential to look for signals of needing more.

2. Overtraining is insidious.

Overtraining syndrome takes many forms, from hormone deficiencies to overuse injuries, and it doesn’t just happen to pro runners. Some physiologists say that what we consider overtraining is partially due to inadequate fueling. So be especially aware of fueling well when training hard.

3. Everything in moderation.

By our nature, we runners can be a bit obsessive and a tad compulsive. So practice the old axiom: everything in moderation, even moderation. Have a pizza sometimes. Have a few of them other times. But don’t have a few of them all the time.

You Are What You Eat

The next time you are running down a trail at full speed, think about what your body is going through. Really aim to feel your quads and hip bones absorbing impact, your feet pushing off the ground with epic force and your muscles contracting at full strength. Then think of the saying, “You are what you eat.”

In that moment, what do you want to be? You don’t want to be a jelly donut probably. But you also don’t want to be a sprig of lettuce. Instead, you want to be a three-egg omelet with mushrooms and spinach, or whole-grain avocado toast with a side of sweet-potato fries. In other words, when the going gets tough, you want to be fueled by food that is built to go the distance.

Food is strength, and strong is fast. Make fueling and hydration choices that make you strong, and you’ll be healthily hammering out miles on the trails for decades to come.