The big day is here. You trained right, slept well and feel ready to go. You’ve spent hours scouring over maps and amassed the gear that will best set you up to succeed in your objective. Everything seems to be ready, but what should you bring to eat. There’s that apple in the fridge and maybe an old Clif Bar at the bottom of your other pack. Shouldn’t your food be as dialed as the rest of your trip?

In this edition of Therm-a-Rest Beta, contributor Jenny Abegg guides us through the crucial nutrition that is required before, during and after a big day in the hills.

Whether you’re out for a big day of skiing, biking, running, climbing, or kayaking, energy output needs to be replaced with energy input. Nutrition is essential. Unfortunately, it can be hard to sort through the many theories of proper nutrition: There are fad diets and ketosis, solyent, the protein craze, and remind me, does eating fat help you lose weight or gain it? As a highly practical person, it’s altogether too much, especially during days when food is more a fuel for my body’s machine than an elaborately prepared and shared meal.

On a big endurance day in the mountains or on the trail, I have just a few, simple demands of my food: I need it to be lightweight, easy to eat, and energizing. In this article I’ll provide all you need to know for eating right on your next big day out.

Lightweight: Calories & Caloric Density

We all know what calories are: they’re listed on all the packaged food we eat, on the menu board in Starbucks, and some of us count them on a daily basis. Another word for calories is energy, and essentially, the goal during a long day outside is to put as much energy back into the body as it expends. For the purpose of moving quickly and efficiently, most of us have the goal of doing this with food that is as light and un-bulky as possible.

Food can be boiled down to three main components—carbohydrates, proteins, and fats. Carbohydrates and proteins each contain 4 calories per gram; fats contain 9 per gram. Thus, in terms of energy-dense foods (light and un-bulky), fats are a clear winner. 

I’ll introduce another term here: Basal Metabolic Rate (BMR), which essentially means the number of calories you’d burn if you stayed in bed all day. My basal metabolic rate is about 1400 calories. On a big day running or climbing, I might burn anywhere from 1500 – 4500 calories. Add that to my BMR, and my body might need to eat upwards of 6000 calories. Now, if I tried to fuel my body using fresh fruits and vegetables for a day such as this, I’d need a few sherpas to follow me carrying bags full of food. If I ate just carbohydrates and proteins (with 4 calories/gram as we learned above), I’d also be bringing more bulk than is ideal. This is the concept of “caloric density.”

To calculate the caloric density of any food, simply divide the number of calories by its weight. Obviously foods higher in fats will have a greater density than others. 

Easy to Eat: Performance Bars & Gels vs. Other Foods

Let’s continue with caloric density for a second here, comparing one of my favorite energy bars, the Clif Bar Peanut Toffee Buzz, with a Snickers bar. Both contain 250 calories, but the Clif Bar weighs 68g, and the Snickers bar 52.7g. It doesn’t take much math to determine which bar gives you more bang for your buck (and is cheaper too!). The same goes for energy chews vs. fruit snacks, minus potentially a few amino acids or electrolytes thrown into the former. 

However, where energy bars (and their less expensive, less flashy counterparts) absolutely shine is their convenience. Eating every 30 minutes/hour while moving is essential throughout the day, and having a bar in my pocket or chalk bag is the easiest way I have found to do this. In general, it’s prudent to eat about 200 calories an hour, and drink about 16oz of water.

That said, a bit of creativity and a combination of both bars and other foods is often my choice. Cheese is extremely calorie dense, as are homemade no-bake energy balls made with dates, nuts, and coconut. Some of these foods I save for when I actually take a break to rest and eat, while I mostly consume convenient energy bars, candy bars, or gummies while on the go.

Energizing: The Big Debate

Calories matter, yes, but your body won’t last for long purely off candy, say, or butter. The nutrients that make up your calories are important too. This is one of those hotly contested topics, where people in one camp hail the fast-burning carbohydrate while the other side lauds slow-burning fats and disdain sugar for its tendency to spike blood sugar.

I tend to opt for a healthy mix of both, bringing cheese, nuts and peanut-butter products for long-lasting energy, but also consuming candy bars, gummies, and even cookies when I need an instant pick-me-up. It is my opinion that most people will need to use trial and error to determine what is best for their bodies. Bottom line though, more important than specific nutrition is simply consuming calories constantly throughout the day.

Before and After

Although what you eat during activity is of great importance, the food and water you consume both the day before and immediately following your long push are equally vital.

Throughout the day before, it’s essential to be extremely on top of hydration, drinking enough so that urine is clear and copious throughout the day and adding electrolyte tablets such as Nuun, to ward against hyponatremia (diluting sodium levels in your blood by drinking too much water). Be sure not to skimp on food the day before, and specifically eat a nutrient-rich and carbohydrate-heavy dinner (think whole grains, beans, and fruits) to buffer your glycogen supply. In the morning of your big day, consume easy-to-digest carbs and try to slowly down a liter of water throughout your pre-activity routine.

After your enduro day, nutrition is extremely important to aid in recovery. Your first meal should occur soon after completing your mission, and be a mixture of carbohydrates and protein to replenish energy and begin to repair muscles. Hydrating continues to be important during this stage.

Shopping List

We’ve determined how to pack foods that are lightweight, nourishing, and easy to consume. To bring these theories down to earth, here’s a look at what I might eat before, during, and after a big (14-18 hour) day of alpine rock climbing.

Dinner: brown rice and black beans with fresh greens, sautéed veggies, and an oil/vinegar dressing

Breakfast: Yogurt & granola & banana


  • 3 energy bars
  • 2 snickers bars
  • 3 packs of energy chews/fruit snacks
  • baggie of peanut butter m&ms
  • block of cheese
  • 8 medjool dates

Immediately following the activity: peanut butter & banana, egg burrito

As you can see, there are many ways to stay energized and moving on a long endurance day, and every athlete’s food consumption will vary slightly from the next. Food and water can be powerful tools, and when used well, enable our bodies to be the best machines they can be. If you can spend an enjoyable day in the great outdoors, avoid bonking, and end feeling like you pushed your body to its healthy limit—I’d say you’re doing something right.