The human body burns more calories when exposed to cold temperatures. The body constantly works to maintain a stable internal temperature, known as thermal homeostasis, around 98.6°F (37°C). When the external environment cools, the body must increase its energy expenditure to compensate for accelerated heat loss. This necessary increase in energy consumption pulls from stored fuels, resulting in a higher rate of calorie burn.
The Core Mechanism: Thermogenesis
The process of heat production is termed thermogenesis. This heat generation is metabolically demanding, requiring the consumption of stored energy, which increases calorie expenditure in the cold. Thermogenesis ensures the core temperature remains within a life-sustaining range. The body offsets heat loss by producing heat internally, breaking down fuel sources like fat and glucose. The colder the environment, the more robust the thermogenic response must be, leading to a higher rate of calorie consumption.
Two Pathways for Cold-Induced Calorie Burn
The body employs two distinct pathways to generate the necessary heat, both of which consume energy. The most noticeable response is Shivering Thermogenesis (ST), triggered by a significant drop in skin temperature. Shivering involves the rapid, involuntary contraction and relaxation of skeletal muscles. This highly energy-intensive muscular activity can increase the body’s heat production fivefold, representing a substantial, short-term increase in calorie burn.
The second pathway is Non-Shivering Thermogenesis (NST), occurring primarily through the activation of Brown Adipose Tissue (BAT). BAT is a specialized fat cell rich in mitochondria that burns fuel specifically to produce heat, not energy for movement. Unlike white fat, brown fat is metabolically active and consumes glucose and fatty acids. NST is often the body’s initial response to milder cold exposure before the onset of visible shivering.
Quantifying the Calorie Cost of Cold
The amount of extra energy burned depends heavily on the intensity and duration of the cold exposure. Mild cold exposure, such as temperatures between 61–66°F (16–19°C), often activates BAT and initiates non-shivering thermogenesis. This milder exposure can result in a measurable increase in daily energy expenditure, sometimes increasing the Resting Metabolic Rate (RMR) by 10%. More extreme or prolonged cold triggers shivering, causing a dramatic spike in energy use. The total calorie cost is highly individualized and is influenced by factors like body composition and the volume of active brown fat.
Exercising in the Cold: An Added Metabolic Boost?
When exercising outdoors, the metabolic scenario shifts. Exercise itself is a powerful thermogenic process, generating internal heat that often reduces the need for cold-induced mechanisms like shivering or BAT activation. The body’s primary energy demand shifts to fueling muscle movement. The total calorie burn is the sum of exercise demands plus the additional cost of working in a cold environment. This extra expenditure comes from the energy required to carry heavier winter clothing, the inefficiency of moving on cold surfaces, and the effort to warm inhaled cold air.