High Altitude Nutrition | A Primer

On the morning of 31st May 2021, Resilient Nutrition athletes Adri Brownlee and Dan Dowding stood on top of the world. After years anticipating the moment, they’d finally realised their dreams and climbed Everest. Determination, careful planning, and expert guidance from Nims Dai and the Elite Exped team of experienced mountaineers and guides led them to the summit, but their preparation was instrumental too, a key component of which was their nutrition. Since the Resilient Nutrition team supported Adri and Dan before and during their Everest expedition, in this blog we’ll cover some of the nutrition strategies the two of them implemented. Before we start though, please note that this blog isn’t about Everest alone – it’s relevant to anyone venturing above 3,000 metres or so.


Key takeaways

  • The degree to which altitude affects you depends on how high you go. Shocker, I know.
  • Consuming enough iron at altitude supports production of new red blood cells, which are needed to transport oxygen around your body. At high altitude, supplementing 100-200 mg iron each day works for many people, but you should supplement iron under medical supervision.
  • You’ll burn more calories at rest and during activity at altitude, making you prone to weight loss. You’ll therefore need to eat more carbohydrate, fat, and protein to maintain your weight and your health.
  • Hypoxia, low humidity, and increased breathing rate hamper hydration at altitude, so you’ll need more fluid to compensate.
  • If you’re not an elite endurance athlete, supplementing 8 mmol nitrate (about 500 mg), ideally in the form of beetroot juice or shots, 2 h before endurance exercise might acutely boost performance.
  • If you’re struggling with acute mountain sickness, supplementing 120 mg Gingko biloba per day might help a little.

What happens to your body at altitude?

If you can understand some of the changes that happen in your body at altitude, you can understand how nutrition can support how you function. We’ll therefore walk through some of the key biological changes you'll experience at high altitude. Before we do so, I want to be clear that the degree to which you experience the changes laid out below depends on the heights you reach and the time you spend at them. Near sea level (at 0 to 500 m), you won’t experience any of these effects. By the time you’re at moderate altitude (2000 to 3000 m), these changes will be taking effect. And by extreme altitude (over 5500 m), they’re in high gear.


Your body makes more red blood cells at altitude, which requires dietary iron

One of the most prominent changes you’ll experience at altitude is a boost in your red blood cell numbers. This is driven by a hormone named erythropoietin (EPO), which you’ve probably heard of because many endurance athletes have been caught doping with it. Red blood cells contain haemoglobin, a protein that helps transport oxygen to your cells, supporting energy production. As iron is needed to make haemoglobin, you need to consume more iron at altitude.

The problem is that excess iron intake leads to “iron overload” (“haemochromatosis”), which can lead to a host of negative consequences in many body systems. While there’s probably less risk of iron overload at altitude, supplementing iron is best done under the supervision of a medical professional, and you might want to get a blood test assessing your red blood cells and iron profile 4 to 6 weeks before exposure to altitude. This will give time to optimise your iron status before entering high altitude, but please note that if you want to adapt to altitude then the most important thing is your iron intake while at altitude, not your iron status before you go.

Now, let’s say you and your doctor decide it’s smart to supplement iron at altitude (which it usually is). How much iron should you take?

To maximise the effects of altitude on your haemoglobin, taking 100 to 200 mg elemental iron per day usually works well, and most studies showing this have had people consume iron salts (e.g., ferrous sulphate). Digestive discomfort is perhaps the most common side effect people get when supplementing iron, and you might be able to reduce this by splitting your daily dose in two, with half your supplemental iron in the morning and half in the evening. The only downside to this is that consuming all your supplemental iron as one dose might be slightly better at boosting your haemoglobin.

To enhance how well you absorb iron, take it with a rich source of vitamin C, such as a citrus fruit. Note also that certain plant-borne chemicals (e.g., tannins, which are present in tea) reduce iron absorption.

Finally, as haem iron (found in animal foods, such as red meat) is much better absorbed than non-haem iron, the above is likely especially relevant to vegans and vegetarians!


You burn a lot more calories at altitude, so you need to eat more

Next, you’ll burn more calories at altitude – both at rest, and during exercise. As a result, many people struggle to meet their energy needs at altitude, making them prone to injuries and the other problems Emily Jevons outlined in this blog. Crucially, eating enough is necessary for healthy immune function and sex hormone levels, and the latter help ensure that you’ll make plenty of new red blood cells at altitude – it’s not just your iron intake that determines your iron status and haemoglobin!

You might be wondering whether altitude will change how much carbohydrate and fat you burn. It’s not clear whether altitude increases reliance on carbohydrate or fat more than at sea level, and you’ll almost certainly just burn more of both. Muscle protein breakdown goes up too, so since it can be hard sourcing high-quality protein at altitude, snacks such as Rebuild Long Range Fuel come into their own. All of this means you probably just need to eat more in general at altitude, which you can make easier by choosing more calorie-dense foods (e.g., dried fruit is more energy dense than fresh fruit). It also makes sense to monitor your bodyweight to ensure you’re not losing large amounts of weight while you’re up there.

There are three things you need to get through the deadly Khumbu Icefall - energy, mental strength, and concentration. How did I get my energy? Simple. High-calorie, tasty foods, such as Resilient Nutrition’s Energise Long Range Fuel. Can’t go wrong with a dark chocolate and hazelnut shot of pure electricity! - Adri Brownlee


Altitude promotes dehydration, so you need to drink more

If you track your bodyweight at altitude, you’ll probably notice that you lose up to 2% of your weight over the first few days. Don’t fret – this is completely normal. The combination of low humidity, little oxygen in the air, and increased breathing rate all increase how quickly you lose fluid, and this is compounded by increased urination (diuresis) on initial exposure to altitude. You’ll therefore need to take in more fluid to stay hydrated.

As at sea level, drinking enough to avoid thirst is a good start, as is monitoring the colour of your first urination each morning: If you’re well hydrated, it should be the colour of apple juice or lighter.


Less oxygen in the air at altitude compromises endurance performance

Then there’s the fact that as there’s less oxygen in the air at altitude, sustaining a given physical workload is harder. Wouldn’t it therefore be great if there was a nutritional strategy to reduce the oxygen cost of exercise?

Of the different substances that counter the performance-impairing effects of being at altitude, nitrates might be particularly helpful for some of us. Commonly consumed in the form of concentrated beetroot juice, nitrates are a precursor to nitric oxide, a gas that improves blood flow and oxygen delivery to cells. Through these mechanisms and others, nitrate supplementation can increase the oxygen content of blood in arteries and improve exercise economy, meaning that less oxygen is needed to complete a given endurance task.

Just drink beetroot shots then, right?

Not so fast. For one, elite endurance athletes with high-functioning cardiorespiratory systems seem less likely to benefit from supplementing nitrates. Another potential issue is that the compromising effects of altitude on things like oxygen delivery to cells might serve as important signals in stimulating adaptations to exercise, and by supplementing with nitrates you might impair these signaling mechanisms.

So, if you’re not an elite athlete and are just looking for a short-term performance boost at altitude, try consuming about 8 mmol nitrate (about 500 mg), ideally in the form of a beetroot shot, about 2 h before exercise at altitude. If you don’t like the taste of beetroot or find it impractical, there are some encapsulated nitrate products out there too (e.g., a red-spinach extract named Oxystorm). However, I suspect pill-based nitrate products probably aren’t quite as effective as beetroot, for beetroot contains performance-enhancing substances other than nitrate too.

Regardless of the product you use, don’t use mouthwash around consuming the nitrate, for the bacteria in your mouth are key to ultimately converting dietary nitrate to nitrite, which ultimately gets converted to nitric oxide.


Being at altitude increases “oxidative stress”, but you needn’t supplement antioxidants

Altitude exposure also increases your body’s production of “reactive oxygen and nitrogen species” (RONS). (You’ve probably heard of reactive oxygen species in relation to antioxidants, which help quench these species.) RONS have many important roles in health and how we adapt to exercise, and your body normally has enough antioxidant “capacity” to counter its production of RONS. But when the RONS exceed your capacity to handle them, the result is enough “oxidative stress” to damage important structures in your cells, including your DNA. While we don’t know much about the consequences of increased RONS at altitude, excess oxidative stress might hamper recovery, and a group of scientists speculate it might contribute to acute mountain sickness. 

To counter this increase in oxidative stress, some people have proposed supplementing with antioxidant vitamins, such as vitamin C. One of the problems with this strategy is that supplementing with high-dose antioxidant vitamins actually seems to interfere with how your body adapts to exercise, for oxidative stress is an important signal for triggering beneficial adaptations to training. It’s probably better to just consume an antioxidant-rich diet comprising an array of colourful fruits and vegetables. Since high altitude-environments aren’t exactly ideal growing conditions for plants, if it’s hard to source fresh fruits and vegetables when you’re up in the mountains, pack plenty of dried fruits, and consider taking a good “greens” powder with you.


Countering acute mountain sickness

Finally, since I mentioned it, acute mountain sickness leads to symptoms such as fatigue and headaches. If you experience mountain sickness, you might find Ginkgo biloba supplementation helpful. While it’s not clear how Gingko biloba counters mountain sickness, potential mechanisms include antioxidant effects and improved bloodflow. If you try it, start with 120 mg Ginkgo biloba per day.


Be strong, crack on

I hope you find these tips helpful next time you’re up among the clouds. As always, preparation is key to success, so be sure to have at least a rough nutrition plan for your trip!

If you want some extra help planning your expedition we offer an assessment and planning service here.