Do You Burn More Calories When You Are Cold or Hot?

Cold wins, and it is not particularly close. When your body is exposed to temperatures below its comfort zone, it activates powerful heat-generating mechanisms that can dramatically increase calorie burn. Heat, by contrast, raises your metabolic rate only modestly. One field study measuring the same individuals across different climates found that people in cold environments burned roughly 1,550 extra calories per day compared to temperate or hot conditions, while hot-climate energy expenditure was statistically the same as temperate.

Why Cold Is a Calorie-Burning Machine

Your body has two main strategies for generating heat when temperatures drop, and both cost energy. The first is shivering, the involuntary contraction of skeletal muscles that you feel as trembling. Shivering can substantially raise your metabolic rate because your muscles are doing real mechanical work, just not the kind that moves you anywhere. Research has shown that leaner individuals shiver more intensely and produce more metabolic heat during cold air exposure than people with more body fat, because fat acts as insulation and delays the point at which shivering kicks in.¹

The second strategy is non-shivering thermogenesis, which happens largely through brown adipose tissue, or brown fat. Unlike the white fat that stores energy, brown fat burns it to produce heat. A landmark study found that brown fat was active in 96% of healthy men during cold exposure but completely inactive at comfortable room temperature.² A systematic review and meta-analysis confirmed that acute cold exposure consistently increases both brown fat activity and the body’s overall energy metabolism.³

These two systems work together on a spectrum. In mild cold, brown fat handles most of the extra heat production without you feeling any shivering at all. As the temperature drops further or exposure lasts longer, shivering takes over as the dominant heat source. Both pathways burn calories, but shivering is the bigger energy hog in genuinely cold conditions.

What Heat Does to Your Metabolism

Heat does raise your metabolic rate, but the effect is smaller and works through different pathways. When your core temperature rises, the chemical reactions in your cells speed up slightly. One study quantifying this relationship found that oxygen consumption increased as core temperature climbed, with an overall factor suggesting metabolic rate roughly doubles for every 10°C rise in body temperature.⁴ That sounds dramatic, but in practice your core temperature only fluctuates by a degree or two before your cooling systems kick in, so the real-world calorie increase is modest.

The body’s main response to heat is not generating more energy but dissipating it. Your heart pumps more blood to the skin, and sweat glands ramp up production. Sweating itself requires some energy to produce, but the actual cooling comes from evaporation, a physical process that draws heat from your skin without requiring additional metabolic work. Research on men exercising in 45°C heat found that sweat rate increased by about 30%, but much of that sweat dripped off without evaporating, making it metabolically wasteful.⁵ Your body works harder to cool you down, but most of that effort goes into cardiovascular adjustments and fluid management rather than calorie-burning heat production.

The Numbers Side by Side

The clearest comparison comes from a study that tracked the same people living and working in temperate, hot, and cold environments. Total energy expenditure in the hot climate was statistically identical to the temperate climate. But in the cold, participants burned about 1,550 additional calories per day.⁶ That is a striking gap, and it puts into perspective just how metabolically expensive it is for a warm-blooded animal to maintain a 37°C core in a freezing environment.

The same study uncovered an interesting wrinkle about physical activity. Being active in the cold actually reduced the thermoregulatory cost, because exercising muscles generate their own heat as a byproduct, essentially doing double duty. In the heat, though, physical activity increased thermoregulatory costs, because the body had to work even harder to dump the extra heat from both the environment and the exercise.⁶ So the relationship between exercise and temperature runs in opposite directions depending on whether you are trying to stay warm or cool.

Exercising in Cold Versus Hot Conditions

If you exercise in the cold, your oxygen consumption tends to be higher than it would be for the same workout in a warm gym. This happens because your body is still generating heat to stay warm on top of the energy you need for the exercise itself. At lower workout intensities, this difference is noticeable. As you ramp up the effort, though, the gap narrows, because exercise heat production eventually overwhelms the cold stress and your body no longer needs to shiver or activate as much brown fat.⁷

Exercising in cold conditions does come with tradeoffs. Higher-intensity activity in the cold increases respiratory heat loss from breathing cold air, and body movement can pump cold air underneath clothing, undermining insulation.⁸ So while you burn a few more calories, you also lose heat faster, which can become a safety concern in extreme cold.

Exercising in the heat changes your fuel mix rather than your total calorie output. One study found that during exercise in hot conditions, muscle glycogen oxidation jumped by about 25% compared to exercising in cool conditions, while the body’s ability to use ingested carbohydrates dropped.⁹ In other words, heat makes your muscles burn through their stored fuel faster without necessarily increasing your total energy expenditure. That shift matters for endurance athletes who need to manage fuel stores, but it does not mean you burn more total calories running in summer versus winter.

Body Fat, Sex, and Who Burns More

Your body composition is one of the strongest predictors of how many extra calories you burn in the cold. Research dating back decades has established that the metabolic response to cold is inversely related to body fat percentage: the less fat you carry, the more calories you burn to stay warm.¹⁰ Fat acts as a thermal blanket, slowing heat loss and delaying the trigger for shivering and brown fat activation. People with very low body fat start shivering sooner and shiver harder, driving their metabolic rate up further.

What about sex differences? Men and women show the same overall percentage increase in resting energy expenditure after cold exposure, about 6.5% in one controlled study.¹¹ Where the sexes diverge is in the hormonal and metabolic fine print: women showed larger swings in leptin, adiponectin, and blood glucose after cold exposure than men did. But these hormonal differences did not translate into a different calorie burn. A cold-water immersion study reinforced this finding, showing no significant gender differences in total metabolic heat production or fat oxidation once body size and body fat were accounted for.¹² The practical takeaway is that body composition drives the calorie-burn difference far more than biological sex does.

Can You Train Your Body to Burn More in the Cold

Repeated cold exposure does reshape your body’s response, and part of that reshaping involves brown fat. One study had participants undergo ten consecutive days of mild cold acclimation and found that non-shivering thermogenesis increased from about 11% above resting to about 18% above resting. At the same time, the volume of detectable brown fat expanded by roughly a third, and the metabolic activity of existing brown fat increased.¹³ Your body essentially builds a bigger furnace the more often you use it.

Cold adaptation goes well beyond brown fat. A comprehensive review describes how repeated cold exposure triggers changes across virtually every organ system: the liver adjusts glucose and fat metabolism, the thyroid gland amplifies heat-generating capacity, the gut microbiome shifts in ways that alter nutrient absorption, and immune function is modulated.¹⁴ Chronic cold exposure also appears to ramp up fatty acid burning in brown fat tissue at the cellular level, increasing the machinery that breaks down fat for fuel.¹⁵

Heat acclimation goes the other direction metabolically. When people adapt to exercising in the heat over a period of days, their bodies become more efficient. One study found that heat-acclimated individuals significantly reduced metabolic heat production during the same workload, meaning they generated less internal heat while doing the same amount of work.¹⁶ In other words, your body learns to waste less energy on heat it then has to get rid of. That is great for athletic performance in hot weather but means you burn fewer calories for the same effort over time, the opposite of what cold acclimation does.

The Comfort Zone and Why It Matters for Weight

Your body has a range of ambient temperatures where it can maintain its core temperature just by tweaking blood flow to the skin, without activating shivering, sweating, or any extra metabolic machinery. This is called the thermoneutral zone.¹⁷ While you are in this zone, you burn the fewest possible calories for a given level of physical activity. The lower boundary of this zone, the point below which your body starts producing extra heat, varies between individuals and even between sexes. Research has shown that the thermoneutral zone for women shifts toward warmer temperatures compared to men, meaning women start needing to generate extra heat at a milder cold than men do.¹⁸

Modern life keeps most people firmly inside this zone for nearly all of their waking and sleeping hours. Air conditioning in summer and central heating in winter mean your body rarely has to expend extra energy on temperature regulation. Some researchers have proposed that this perpetual thermal comfort contributes to rising obesity rates, because an energy expenditure pathway that our ancestors relied on has been effectively shut off.¹⁹ The hypothesis does not claim that temperature alone explains the obesity epidemic, but that it is one of many environmental factors that have tilted the energy-balance equation toward surplus.

Cold Exposure for Weight Loss in Practice

Given that cold clearly increases calorie burn, it is natural to wonder whether deliberate cold exposure can help with weight loss. The evidence here is less encouraging than the metabolic data might suggest. A review of intermittent cold exposure studies found that while cold consistently increased brown fat activity and improved metabolic markers like glucose tolerance and insulin signaling, it did not reliably reduce body weight or fat mass.²⁰ The review also noted that combining cold exposure with exercise did not seem to provide additional benefit beyond exercise alone, at least when the exercise happened during the cold exposure.

One reason cold exposure may not translate into weight loss is appetite. A study comparing hunger and food intake after mild cold exposure versus comfortable temperatures found a trend toward increased hunger in the cold, though the actual amount of food people ate at a buffet was not significantly different between conditions.²¹ The extra calories burned may simply be offset by eating slightly more over time. The body is quite good at defending its energy stores, and bumping up thermogenesis often leads to compensatory behaviors that claw back the deficit. Most of the rodent studies showing dramatic fat loss from cold housing involve conditions that no human would replicate voluntarily.

That said, cold exposure may still offer metabolic health benefits that go beyond the scale. Improved insulin sensitivity, better glucose handling, and increased brown fat activity are all potentially valuable, particularly for people at risk for metabolic disease. The extra calorie burn from cold showers or time spent outdoors in winter is real, just not likely large enough on its own to move the needle on weight.

Populations That Evolved in the Cold

Perhaps the most striking evidence of how cold shapes metabolism comes from human populations that have lived in frigid environments for thousands of years. Indigenous Siberian groups show significantly elevated basal metabolic rates compared to reference values, with men showing increases ranging from 7% to 19% above predicted levels and women from 3% to 17%.²² These elevations persist even after accounting for body size and composition, suggesting they are not just a product of physique.

The mechanism appears to involve both short-term acclimation and longer-term genetic adaptation, with thyroid hormones playing a central role. Indigenous Siberian populations appear to have a greater capacity to upregulate their basal metabolic rate during severe cold, possibly through genetic variants that affect thyroid hormone regulation.²³ Twin studies have confirmed a significant genetic component to thyroid responses to environmental stress, meaning some of this metabolic flexibility is heritable rather than purely learned. These populations burn more calories at rest, all the time, as part of a biological strategy refined over generations of living in the cold.

Why Feeling Hot After a Workout Is Not the Same as Burning More

A common misconception worth addressing: people often feel like they are “burning more” in hot weather because they sweat more, breathe harder, and feel more exhausted. But most of that sensation reflects cardiovascular strain and fluid loss rather than increased calorie expenditure. Your heart beats faster to shuttle blood to the skin for cooling. You lose water and electrolytes through sweat. Your perceived effort goes up. None of those things mean you are burning significantly more energy than you would for the same workout in a cool room.

If anything, the opposite may be true for repeated hot workouts. As the heat acclimation research shows, your body adapts to heat by becoming more efficient, sweating earlier, maintaining a lower core temperature, and reducing internal heat production for the same workload. An athlete who trains through a hot summer actually burns slightly fewer calories per session by August than she did in June, even at the same pace, because her body has gotten better at not wasting energy as excess heat. The discomfort of exercising in the heat is real, but discomfort and calorie burn are not the same thing.

Cold discomfort, by contrast, is directly linked to calorie expenditure. When you feel cold, your body is spending energy to warm you, whether through brown fat activation, shivering, or increased muscle tone. The worse you feel in the cold (up to a point), the more calories you are actually burning. It is one of the few situations where subjective misery and metabolic cost track together reasonably well.