Most endurance athletes know they need to fuel differently in the heat, but few appreciate how profoundly cold conditions alter their energy demands. Exercising in sub-zero temperatures can increase total caloric expenditure by 10–40% compared to the same effort in temperate conditions — a difference significant enough to send an under-prepared athlete into an energy deficit that compromises both performance and safety.
The mechanisms behind cold-weather calorie burn are distinct from heat stress and require a separate fueling strategy. Understanding shivering thermogenesis, brown adipose tissue activation, and how glycogen depletes faster in the cold will help you build an evidence-based winter nutrition plan that keeps you fueled from the first kilometre to the last.
Shivering Thermogenesis: Your Body's Emergency Heater
When core temperature drops below approximately 36.5 degrees C, the hypothalamus triggers involuntary muscle contractions — shivering — that generate heat as a byproduct of ATP hydrolysis. Shivering can increase metabolic rate by 200–600% above resting values and relies almost exclusively on carbohydrate and glycogen as fuel substrates, not fat. Even pre-shivering cold stress (the mild muscular tension athletes feel when standing at a cold start line) elevates metabolic rate by 25–50% above resting.
For a 70kg runner with a resting metabolic rate of approximately 1.3 kcal/min, 30 minutes of moderate shivering burns an additional 200–400 kcal — fuel that comes entirely from your glycogen reserves before you've even started your run. This is why athletes who stand in cold conditions at race start lines often begin their event already in a caloric deficit.
Brown Fat Activation and Non-Shivering Thermogenesis
Beyond shivering, cold exposure activates brown adipose tissue (BAT) — a metabolically active fat depot that burns energy to generate heat via uncoupling protein 1 (UCP1). Unlike white adipose tissue, brown fat is densely innervated by the sympathetic nervous system and is activated within minutes of cold exposure.
Regular cold exposure over 4–6 weeks measurably increases BAT volume and activity — a process called cold acclimatisation. While BAT primarily oxidises fatty acids, it also draws on circulating glucose. Research published in Cell Metabolism found that activated BAT can consume up to 150 kcal per hour in cold conditions. Athletes who regularly train in the cold develop higher non-shivering thermogenic capacity, meaning they can maintain core temperature with less shivering and more efficient fat utilisation — an adaptation that partially offsets the carbohydrate cost of cold exposure after several weeks of acclimatisation.
Accelerated Glycogen Depletion in Cold Conditions
Cold independently accelerates muscle glycogen use during exercise, independent of shivering. A study in the Journal of Applied Physiology demonstrated that glycogen utilisation rates were 35% higher during 60 minutes of cycling at 70% VO2max in 5 degrees C compared to 20 degrees C. The proposed mechanisms include increased epinephrine (adrenaline) levels in cold conditions, which stimulates glycogenolysis, and reduced free fatty acid mobilisation in cold muscle tissue, forcing a greater reliance on carbohydrate.
Practically, this means an athlete who would deplete glycogen stores at 90 minutes in temperate conditions may hit the wall at 60–65 minutes under cold conditions — a nearly 30% reduction in glycogen endurance. This has profound implications for event pacing, pre-race nutrition, and in-race fueling frequency.
Practical Fueling Adjustments for Winter Training
Given the increased carbohydrate demands, here are evidence-based adjustments for cold-weather sessions:
- Increase pre-exercise carbohydrate loading: Consume 3–5g of carbohydrate per kg body weight in the 3–4 hours before long cold sessions, compared to 1–3g/kg in temperate conditions
- Raise in-race carbohydrate intake by 30–50g per hour: If you typically consume 60g/hr, target 90g/hr in sub-zero conditions using dual-transporter gels
- Start fueling earlier: Take your first NorthLine Gold Standard gel at 30 minutes rather than 45–60 minutes to offset the accelerated early glycogen drain
- Increase feeding frequency: Every 20–25 minutes rather than every 30–45 minutes in cold conditions lasting over 90 minutes
- Increase overall caloric intake on cold training days: Target an additional 300–600 kcal on days involving prolonged cold exposure, primarily from complex carbohydrates and protein
- Carry gels in an inner layer pocket: Cold gels become viscous and difficult to consume; keeping them against your body prevents them from thickening in sub-zero temperatures
The Layering Strategy and Its Caloric Cost
The clothing layers athletes wear in winter also influence energy expenditure. Running in heavy winter gear increases the metabolic cost of locomotion by 5–15% due to increased mass, restricted movement patterns, and the effort of moving bulkier fabrics. A 2019 study found that running in full winter gear (jacket, thermal tights, gloves, hat) increased oxygen consumption by 8% compared to summer kit at the same pace — equivalent to roughly 50–80 additional kcal burned per hour for an average recreational runner.
This is compounded when athletes are post-exercise and cooling rapidly. After a cold run, the body continues burning calories at an elevated rate to restore core temperature — thermogenic afterburn can add 100–250 kcal of expenditure in the 30–60 minutes post-session. Consuming a recovery meal with 1–1.2g/kg of carbohydrate and 0.3g/kg of protein within 30 minutes of finishing addresses both glycogen resynthesis and thermal recovery.
Hydration in the Cold: The Blunted Thirst Problem
Cold conditions significantly suppress the thirst mechanism — research shows thirst response is reduced by up to 40% in cold compared to warm environments, even when fluid losses are identical. Cold-induced diuresis (increased urine production due to peripheral vasoconstriction) further compounds fluid losses, which athletes fail to register because they don't feel thirsty and aren't visibly sweating as heavily.
Despite lower absolute sweat rates in cold (typically 0.5–1.0L/hr versus 1.5–2.5L/hr in heat), dehydration still impairs thermoregulation and performance. Target 400–600ml of fluid per hour during cold sessions, using warm fluids where possible as they facilitate gastric emptying and provide additional warmth. NorthLine performance drinks served warm at 40–50 degrees C maintain electrolyte delivery without the thermal penalty of cold fluid ingestion.
For more detail on how to structure your winter nutrition across a full training block, see our article on winter running nutrition for cold weather. Build a precise hourly fueling plan for your next cold event with the Race Day Nutrition Planner, and calculate your fluid targets by temperature using the Sweat Rate Calculator.