What do you need to know about food in the mountains?

What is the best food to eat during a demanding mountain day?
And the day before?
How do our eating habits influence our performance?
These are some of the questions answered in this article by doctor, runner, and nutrition expert Jorge García-Dihinx, providing the necessary arguments to adopt a balanced diet that helps us feel better both during physical activity and in daily life.
Mountain sports, such as hiking, climbing, mountaineering, backcountry skiing, and trail running, involve medium or long-duration activities performed at moderate intensities, with some moments of explosiveness.

In this brief article, we won’t go deep into nutrition for explosive activities, but rather focus on the daily diet for mountain sports, which are mostly endurance activities lasting hours in the mountains.
Nutrition for these beautiful outdoor sports includes both our daily diet in normal life and what we eat on days of mountain activity.

Our daily nutrition will determine our metabolic health when developing our sport. If our daily diet leads to weight gain or illness (Metabolic Syndrome/Pre-Diabetes), we will struggle in the mountains.
In short, the three macronutrients that provide energy from food are carbohydrates (CH), proteins, and fats. Micronutrients, which refer to vitamins and minerals, are also essential but do not provide energy (calories).

CARBOHYDRATES (CH) are primarily a source of quick energy, providing 4 kilocalories (kcal) per gram. The main sources we will talk about here are starches or polysaccharides (chains of many glucose molecules), such as rice, pasta, cereals, bread, and potatoes. These are absorbed relatively quickly (except their whole grain variants, which contain protective fiber, ideal for daily use but not for the day before a race).

Legumes have more fiber and cause a smaller spike in blood sugar than white bread or white rice, making them healthier for daily meals. Vegetables are high in volume and fiber, with few calories and many nutrients, making them a good choice for daily meals, but not before a race or intense activity.

PROTEINS, among other functions, are used as building blocks for muscle structure (the bricks). We also get 4 kcal per gram from proteins, although their use as an energy source is "inefficient" and they are only used in cases of energy deficiency (which is undesirable).
The main sources of protein are animal products: eggs, meat, poultry, fish, although we can also get protein from legumes, soy, some cereals, and nuts. Animal protein is more bioavailable, more complete, and has a higher nutritional density. For example, to get the protein from a chicken breast, we would need to consume 5 cups of quinoa, with the additional calories (which you’ll need to burn... during the week).

Protein experts recommend at least 30 g of protein in each of the three meals to reach the threshold of 2.5 g of leucine, which is necessary for muscle repair.
While the official recommendation is 0.8 g/kg of body weight, it is ideal for athletes to aim for 1-2 g/kg. It’s important to note that 100 g of meat, poultry, or fish does not contain 100 g of protein, but rather around 20 g (20%).

FATS serve as a source of energy and also provide the best energy storage in our body. For each gram, we get 9 kcal, more than double the energy provided by carbohydrates and proteins.
We find fat alongside protein in animal foods (eggs, meat, fatty fish like salmon or sardines), as well as in full-fat dairy, nuts, and oils.
Although we’ve been repeatedly told that “good” fats are unsaturated (avocados, nuts, fish) and “bad” fats are saturated (meats, coconut, butter), I’m sorry to tell you that the only "bad" fats are industrial fats or trans fats from ultra-processed foods (partially hydrogenated vegetable oils in a trans position to extend shelf life).
Just remember that the best food in nature is breast milk, which, in addition to providing more than half of the calories from fat, contains saturated fat, which is essential for brain development, both for babies and for us.

Should we eat carbohydrates?
Although there are countless diets and trends today, the concept that we need a diet rich in carbohydrates (CH) for sports is still valid. Carbohydrates provide quick energy, especially for moments of explosiveness, when we need glycolytic energy.
However, most mountain activities are long-duration, medium-intensity, aerobic efforts, where we need a long-lasting fuel that doesn’t make us dependent on gels or bars every hour.
We need an almost inexhaustible energy source that allows us to keep moving without continuously eating. That fuel is fat. In fact, even though we use glucose as the main energy source for more explosive moments (such as in a Vertical Kilometer), most of the time in the mountains, our muscles and heart burn fatty acids as the main fuel.

It’s curious that carbohydrates are considered the preferred source of fuel for athletes, even though our glycogen reserves (our form of storing glucose) are very limited.
Our body only stores between 1% and 3% of its energy in the form of glycogen because it is very heavy, being full of water, hence the name "Carbo-HYDRATE."
Therefore, glycogen weighs 6 times more than the same amount of energy stored as fat.
We have about 75-100 g of glycogen storage in the liver and up to 250-350 g in the muscles. These 400-500 g of glycogen, at 4 kcal per gram, give us a maximum of 1,600-2,000 kcal.
After consuming those calories, we often hit “the wall” after 30 km in a marathon, unless we’ve been eating something during the race. However, compared to the small energy reservoir from carbohydrates (glycogen), the fatty acid reservoir is practically unlimited, weighing 6 times less and generating more than double the energy per gram (9 kcal versus 4 kcal).

Even a very lean athlete (like me) with 8% body fat (around 5 kg) would have, say, 5,000 g of fat, providing 45,000 kcal. That’s more than 20 times the energy from the glycogen in our muscles and liver.
This is where Metabolic Flexibility comes into play, meaning the ability of our body to switch between fuels based on needs. If we’re consuming refined carbs like white bread, rice, pasta, potatoes, pizza, juices, and ultra-processed foods (with added sugars), our metabolism will continually rely on glucose as the primary fuel in the mountains.

This will make it difficult for us to access fatty acids as fuel (which is much greater), leading to several problems:

1. Need to eat often: We’ll need to replenish "sugars" periodically during our activity, relying on gels, bars, bread, or sugary drinks.

2. No access to fats as fuel: Each time we ingest glucose, insulin rises to lower blood glucose levels (which is harmful to arterial walls at high levels). Insulin prioritizes burning the recently ingested energy and blocks access to body fat for fuel.
   Insulin inhibits lipolysis, turning us into carb-dependent machines, unable to tap into the huge fuel we carry in our adipocytes. You’ve probably seen many mountaineers with bellies, right? All that energy they carry daily, but can’t access.
   It’s like being a fuel truck, but only having access to the small fuel tank under the driver’s seat (glycogen), without access to the large tank attached (fat).

3. The wall or the bonk: Another issue with being carb-dependent is that the brain also becomes glucose-dependent. When our body sees that glycogen reserves are running low, it will cut off energy flow to the muscles (to prevent death), leading to what’s known as the "bonk" or "wall."

Metabolic Adaptation
However, an athlete with metabolic flexibility becomes a keto-adapted athlete. At low to medium intensities (below 60-65% VO2max), their muscles will primarily burn fats.
At the same time, in long-duration activities without food, the liver will begin to produce ketone bodies for the brain, which will become metabolically adapted with hybrid energy, using both glucose and ketone bodies (mainly Beta-Hydroxy-Butyrate), which in prolonged fasting periods can account for up to 60-70% of the brain’s energy.

So this brain, with continuous access to two types of fuel, won’t limit our athletic performance when glucose drops after hours without eating. We won’t hit the wall or the bonk.
The liver, during prolonged fasting, can provide 30% of the brain’s energy through gluconeogenesis (producing new glucose) and the remaining 70% from ketone bodies. This helps prevent a coma during long fasts, such as a hunger strike or long mountain challenges with little access to food.

In a keto-adapted person, their muscles learn to burn fatty acids while sharing ketone bodies with the brain, which can’t use fatty acids for energy. Everyone is happy.
The muscles because they have almost unlimited access to energy (>45,000 kcal), and the brain, with its hybrid fuel, is ready for long mountain activities.
This metabolic flexibility or adaptation doesn’t happen overnight; it requires 2 to 4 weeks (sometimes longer) to fine-tune the machinery that improves fat burning in the muscles and ketone body utilization by the brain.
We can speed up this process if, from time to time, we train in a fasted state, always at very low intensities, forcing our body to be more efficient in burning fatty acids.

Train low in carbs and compete high in carbs
The FatMax zone, where we burn the most fat, occurs at low or moderate intensities (Z1 and Z2), when we can talk while progressing with skis, walking, jogging, or climbing.
However, in mountain races or any activity that requires high caloric expenditure entering glycolytic energy zones above Z3 (Z4-Z5), glucose will again be the chosen fuel for the body.

Therefore, it’s a good idea to fill up on glycogen in the two days before a competition or intense activity, or at least the night before.
In daily life, we can maintain metabolic flexibility with a relatively low-carb diet based on vegetables, eggs, meat, fish, dairy, some legumes, berries, and nuts.
But then, for the weekend, we can periodically load up on more refined carbohydrates like rice, pasta, bread, potatoes, oats, quinoa, fruit, etc.

What to bring to the mountains?
Fats will NOT be the primary fuel for activity, both in the mountains and in races, as their digestion is slow and demanding, requiring a lot of energy and pulling blood toward the digestive system. This blood and energy should be preserved for our muscles.
So, even though we eat eggs and nuts in our daily diet, we shouldn’t bring these foods to the mountains. More than once, we've ended up with frozen fingers while backcountry skiing in winter after stopping to eat some nuts, with the digestive system drawing all the blood to digest them, leaving our fingers frozen.
Blood is what provides temperature to the skin.
Therefore, even though our daily diet may be low in carbohydrates, during sports activities, we’ll need quick-digesting energy sources like dried fruit, which has no water weight, such as apricots, dates, prunes, figs, etc.
Fresh fruit like bananas, melon, or a pear will also provide both energy and hydration (although it will increase the weight for minimalists).
In summary, at home, consume fats and proteins; in the mountains, keep glucose on hand, but not fat!

Macronutrients in intense activities
When we load up on carbohydrates (CH) the day before a race, ski outing, or intense activity, it’s because we don’t consume many carbs daily. On activity days, if we’re going at Z3 intensity or higher

On those days, for example, it is better to have white bread or white rice rather than whole grain (for easier digestion and faster emptying), and to reduce other sources of fibre (legumes, vegetables).
During the activity, dried fruit (dates) or chunks of banana, melon (classics in mountain race aid stations) or the classic glucose gels +/- caffeine are recommended.
These quick sources of glucose, such as a gel or a sugary drink, will come in handy "during" the race or activity, but they should never be consumed just before the start (at rest), as the insulin peak may cause a rebound hypoglycemia shortly after starting to run, making you feel miserable.
After an activity lasting more than 90 minutes, in addition to carbohydrates, protein should also be replenished due to muscle breakdown. For example, combine rice with meat or with protein shakes or a good glass of cold milk, which also hydrates.
The anabolic window for protein intake after an activity to regenerate all the muscle damage is relatively wide in men, and it is not mandatory to consume it right after the race. However, women should replenish protein within the following 60-90 minutes after a long activity, as their anabolic window (due to hormonal reasons, especially if you're in the second half of your cycle) is much shorter.
Hence, recovery protein shakes or a large glass of cold milk after a long route.

Conclusions
In summary, we can maintain a low glycemic index diet on a day-to-day basis, with real food, including vegetables, legumes, eggs, meat, fish, berries, nuts, and dairy. The day before a long route (or two days before a mountain outing or competition), we can load up on glycogen with more refined carbohydrates such as white rice, pasta, bread, potatoes, and cereals, without overdoing juices or sugary drinks.
In this way, our keto-adapted body will rely on fats (unlimited energy) at medium intensities during our mountain route (on foot or with skis) and will preserve glycogen for high-intensity moments, such as a vertical climb with crampons, a difficult climbing move, or any explosive mountain race.
We won't deplete that glycogen during the normal activity, as it will be reserved for those explosive moments or the final sprint that will help you win that mountain race.