Nutrition planning for ultra-distance events in extreme cold requires a different approach from temperate conditions. The body must cover both prolonged exercise costs and the substantial thermogenic energy needed to maintain core temperature.
This article examines:
- Key physiological changes in extreme cold
- Changes in substrate oxidation
- Actual competition energy requirements
- Nutritional strategies for practice
- Common mistakes that compromise performance
We explore changes during sport in freezing or high-altitude conditions, propose corresponding nutrition strategies and review common competition mistakes.
Physiological processes and homeostatic adaptations in extreme cold
The main biological priority during cold exposure is maintaining a stable body temperature. When cold exceeds the body’s heat production, a cascade of neuroendocrine responses activates to prevent hypothermia.
Thermogenesis mechanisms and their metabolic impact
Cold-induced thermogenesis has two mechanisms: shivering and non-shivering thermogenesis.
Shivering involves involuntary skeletal muscle contractions with very low metabolic efficiency. Most energy spent contracting these fibres dissipates as heat rather than producing movement.
This study assessed cold’s impact on substrate oxidation at rest and during activity and on basal metabolic expenditure, finding that the latter can increase fivefold.
Non-shivering thermogenesis occurs at the molecular level in brown adipose tissue (BAT). Noradrenaline release activates BAT, lipolysis and glycolysis, increasing energy availability.
Changes in substrate oxidation
Extreme cold shifts exercise substrate preference towards carbohydrates, particularly non-mitochondrial glycolysis and muscle glycogen use. Shivering, when present, adds further glucose demand.
Starting competition with maximised muscle glycogen stores becomes even more important than in normal temperatures.
This article proposes that low glycogen availability accelerates peripheral fatigue and disables shivering, increasing vulnerability to hypothermia.
Haemodynamic and cardiovascular responses
Sympathetically mediated peripheral vasoconstriction is another important response. It reduces blood flow to skin and superficial tissues to preserve supply to vital organs.
This increases peripheral vascular resistance and mean arterial pressure. Redistributing blood towards the core also activates mechanoreceptors, sending a signal interpreted as fluid overload.
This apparent overload triggers diuresis and greater urinary excretion. Cold, dry air also increases respiratory water loss.
Haematological and oxygen transport adaptations
When competition combines cold and altitude, acclimatisation mechanisms activate to maximise oxygen transport.
Altitude stimulates erythropoietin production to raise haematocrit and oxygen transport. This affects iron requirements, discussed below.
Dilutional pseudoanaemia is common: total red blood cell mass increases, but plasma volume rises more, resulting in a lower relative concentration.
Intense exercise raises hepcidin, a peptide hormone that temporarily inhibits intestinal iron absorption for 3–6 hours afterwards. This complicates nutritional management of iron stores.
Nutritional strategies
Energy requirements
Energy requirements increase by varying amounts, but this rise must be anticipated. Military studies report daily expenditure above 4,000 kcal during sub-zero expeditions.
An initial recommendation could be to increase total energy intake by 10–15% compared with normal temperatures, then assess progress alongside other factors.
Macronutrient distribution
Since muscle glycogen is the main fuel, maximising stores before competition is essential. Prioritise carbohydrates over other macronutrients during the preceding 24–72 hours.
Depending on event demands, intake during competition may be around 60–90 g/hour. This is highly individual and depends on tolerance and total energy expenditure.
Dietary fats are important throughout the day because their energy density helps meet very high requirements. Prioritise polyunsaturated sources such as omega-3 for their anti-inflammatory role.
Key micronutrients
Iron and vitamin C: adequate pre-competition iron stores are essential for the reasons discussed. Pair dietary iron with vitamin C to maximise absorption.
Vitamin B12 and folate: crucial for red blood cell formation. Low levels are associated with reduced haemoglobin synthesis.
Hydration: water, carbohydrates and electrolytes
Despite apparently lower sweat rates, cold-induced diuresis and respiratory losses make dehydration a serious risk.
Calculate sweat rate using pre- and post-exercise body weight, the weight of all fluids consumed and, if applicable, urine output.
A general sodium recommendation may be 600–1,000 mg/hour, potentially higher. Beyond replacing sweat losses, higher sodium concentrations in sports drinks improve fluid retention and counter cold-induced diuresis. They may also slightly increase thirst, encouraging drinking.
INDYA · Professional nutrition software
Personalised nutrition planning, continuous client follow-up and comprehensive practice management in one platform designed for nutritionists and nutrition teams.
TRY INDYA FREECommon mistakes when managing cold during competition
Cold-induced appetite suppression
Cold exposure may reduce appetite through increased leptin, making energy requirements even harder to meet.
Careful pre-event and in-race nutrition planning is therefore particularly important.
Dehydration and thirst perception
As discussed, cold may reduce thirst and encourage dehydration.
Tips to encourage fluid intake include:
- Warm drinks such as tea or herbal infusions accompanied by carbohydrates
- Increasing sports drink sodium concentration
- Keeping bottles close to the body during exercise to prevent cooling or freezing.
Frozen food and drinks
Body heat helps prevent competition supplies from freezing. Starting with a warm drink also helps maintain body temperature.
Higher drink osmotic concentration delays freezing: use bottles containing higher carbohydrate and sodium concentrations.
Energy gels containing thickeners such as pectin may also freeze more slowly for the same reason.
