How Altitude Affects Sports Nutrition: Tips for Highland and Mountain Events
The first time I raced above 2,000 metres I got everything wrong. I fuelled and drank the way I would at sea level, and by halfway I had a pounding headache, a stomach that wanted nothing to do with food, and legs that belonged to someone else. The course was no harder than anything I had done in Scotland. The air was just thinner, and I had not adjusted a single thing for it.
Altitude sports nutrition rarely gets covered properly because most of us train at low elevation. But if you have a Highland ultra, an Alpine sportive or a mountain marathon on the calendar, the physiology changes enough that your normal fuelling plan needs a rethink. This guide covers what happens to your body above roughly 1,500 metres and the practical adjustments that keep you moving.
What altitude does to your body
At sea level, atmospheric pressure is roughly 1,013 millibars. At 2,000 metres it drops to around 795, so every breath delivers roughly 20% fewer oxygen molecules; at 3,000 metres it is closer to 30% fewer. Your body notices immediately, and the responses that matter for fuelling are these:
- Breathing rate goes up. Ventilation increases to compensate, and because mountain air is cold and dry you lose far more water through respiration: roughly 1 to 2 litres per day more than at sea level, before you add sweat.
- Urine output increases. Altitude diuresis is a real physiological response. In the first few days at elevation your kidneys excrete more fluid as part of acclimatisation, compounding the dehydration risk.
- Appetite drops. Hypoxia suppresses hunger hormones. Studies at 3,000 to 4,000 metres consistently show a 10 to 40% reduction in voluntary food intake, and many athletes report that food simply tastes wrong.
- Carbohydrate becomes the preferred fuel. Carbohydrate yields more energy per litre of oxygen than fat (roughly 5.05 kcal versus 4.7 kcal), so your body shifts towards glycogen at altitude. Efficient, but it drains your stores faster.
- Resting metabolic rate rises. Basal metabolic rate increases by 10 to 30% in the first week at elevation. You burn more calories sitting still, at exactly the point where you least feel like eating.
Together that is a nasty combination: more fluid lost, more carbohydrate burned, more energy needed, and less desire to consume any of it. That is why an altitude sports nutrition plan cannot be a copy of your sea-level plan.
Carbohydrate targets for altitude sports nutrition
At sea level, the standard advice for events over two and a half hours is 60 to 90 grams of carbohydrate per hour, using a mix of glucose and fructose so you can absorb more than 60 grams. At altitude, the case for the top end of that range is stronger, not weaker. Your body is already leaning on glycogen, and running out at 2,500 metres is a far bigger problem than running out on a flat road near home.
The complication is appetite. If you struggle to eat 90 grams an hour normally, you will find it harder still with a suppressed appetite and a queasy stomach. Rules that have worked for me and athletes I have coached:
- Start fuelling in the first 20 minutes, not after the first hour. You are preventing a deficit, not catching one up. Hunger cues are unreliable up high, so eat by the clock.
- Little and often beats big and rare. 15 to 20 grams every 15 minutes is far easier on a hypoxic gut than 60 grams every 45 minutes. Small chewable portions let you dose precisely.
- Bias towards a 1:1 glucose to fructose ratio. Fructose uses a separate intestinal transporter, so a blended source increases total absorption without adding volume to your stomach.
- Treat 70 to 80 grams per hour as a realistic ceiling unless you have trained your gut for more. Above that, nausea risk at altitude climbs sharply.
- Front-load carbohydrate in the 48 hours before. 8 to 10 grams per kilogram of bodyweight per day is the standard carb-loading target, and it matters more at elevation.
Hydration and electrolytes above 1,500 metres
Dehydration is the most common reason people feel awful on mountain days, and it is often mistaken for altitude sickness because the symptoms overlap: headache, fatigue, poor concentration, loss of appetite. The difference is that dehydration is largely within your control.
Increase fluid intake by 500 ml to 1 litre per day, starting the day before you go up. During the event, aim for 500 to 750 ml per hour depending on temperature and sweat rate, and do not wait until you are thirsty. Thirst is a lagging indicator at the best of times and is blunted further by altitude.
Electrolytes matter, but keep it proportionate. Sodium losses in cold mountain conditions are often lower than in a hot summer sportive because you sweat less; 300 to 600 mg of sodium per litre of fluid is enough for most people. Overdoing salt in the hope of fixing altitude symptoms does nothing useful and can upset your stomach.
Managing appetite and the altitude stomach
Appetite suppression at altitude is real and you cannot willpower your way past it. What you can do is make the food you carry as easy to get down as possible:
- Small physical volume. A soft, chewable piece you can pop in one-handed is far more likely to get eaten than a bar you have to unwrap and chew for two minutes while breathing hard.
- A clean, fruity flavour. Sickly sweet or artificial tastes become repulsive when you are hypoxic. Real fruit flavours stay palatable longer, and tart profiles in particular cut through nausea.
- Low fibre and low fat during the effort. Both slow gastric emptying, and a slow-emptying stomach at altitude is a recipe for feeling sick. Save the sandwiches for afterwards.
- Familiarity. Never introduce a new product at a mountain event. Practise your altitude fuelling on hard sea-level sessions until it is automatic.
Cold plays a role too. Gels turn thick and unpleasant below 5 degrees, and some bars become hard to bite. Pastilles hold their texture across a wide temperature range, which is one reason many mountain athletes have moved towards them above the treeline.
Recovery when you sleep up high
If you are staying at elevation for more than a night, recovery nutrition becomes part of the altitude plan. Sleep is measurably worse above 2,000 metres because of periodic breathing, and poor sleep slows glycogen resynthesis and muscle repair. Add the raised metabolic rate and the oxidative stress of hypoxia, and your body has more repair work to do on less rest.
The basics do not change: 1 to 1.2 grams of carbohydrate per kilogram of bodyweight in the first hour after finishing, alongside 20 to 30 grams of protein, then a proper meal within two to three hours. What changes is the emphasis on antioxidants. Hypoxia increases production of reactive oxygen species, and there is reasonable evidence that foods high in anthocyanins, such as tart cherry, help moderate the inflammatory response and support sleep through their natural melatonin content.
What We Use at FTP Endurance Fuel
Most of our team ride and run in the Scottish Highlands, modest altitude by Alpine standards but with plenty of cold, wind and long exposed days. What comes with us on every mountain outing is our energy pastille, for the reasons above: small enough to eat every 15 minutes without breaking rhythm, a 1:1 glucose to fructose blend so you can absorb the higher hourly targets, and a texture that does not change whether it is 2 degrees on a summit or 20 in the valley.
For the effort itself we use the Mixed Fruit Pastilles, which stay palatable hour after hour as appetite fades. For recovery evenings at elevation, the Tart Cherry Pastilles double as a carbohydrate top-up and a source of anthocyanins from real Montmorency cherry. The 1 kg bulk packs let you decant exactly what you need into a jersey pocket, which keeps weight down on multi-day trips.
Mountains do not forgive sloppy fuelling. Go up with full glycogen stores, eat by the clock from the first 20 minutes, drink more than feels necessary, and keep the food simple and small. Get those right and thin air becomes a challenge rather than a wall. To test a mountain-ready setup before your next big day, the Taster Pack is the easiest way to see whether pastilles work for you.
