Whether you’re exercising outdoors in the winter or simply spending time in a cold environment, feeling cold increases your metabolism, helping you regulate your body temperature better and burn more calories, says Dominique Gagnon, Ph.D., director of the Helsinki Sports and Exercise Medicine Clinic in Finland, who studies the effects of temperature on metabolism during exercise.
This occurs through thermoregulation. Thermoregulation is the process by which the body produces or releases heat to maintain a core temperature of approximately 98.6 °F, all controlled by a structure in the brain known as the hypothalamus. When it’s cold, your body has to work harder to stay warm, increasing your basal metabolic rate, or the rate at which you burn calories (energy) to perform necessary functions such as breathing and digestion.
The first line of defense against cold is vasoconstriction, which is the contraction of blood vessels in an attempt to conserve heat.
From there, two thermoregulatory mechanisms kick in, known as shivering thermogenesis and non-shivering thermogenesis. “Both processes require fuel to achieve this, which leads to increased calorie consumption,” explains Dr. Okobok.
Thermogenesis without shivering is how the body initially tries to generate heat without it muscle movement. It generates heat by activating brown adipose tissue (BAT), or specialized brown fat cells, which transfer energy from food and promote calorie burning. “BAT is a type of fat that is burned only to maintain body temperature when exposed to cold,” Okobok explains, adding that increased BAT activity can increase calorie expenditure.
Thermogenesis, accompanied by shivering, then occurs, and heat is generated by rapid, uncontrolled muscle contractions. “Under cold stress, shivering thermogenesis is the predominant form of heat production,” Dr. Gagnon says. “Shivering can generate up to five times more heat than you generate at rest,” he adds, explaining that muscles are one of the most metabolically active tissues in the body, so they can generate warmth by burning fuel (or calories).
Together, these processes can contribute to weight loss. “You burn more calories when it’s cold,” says Caroline Apovian, MD, professor of medicine and co-director of the Center for Weight Management and Wellness at Harvard Medical School in Boston, explaining that both BAT activation and thermogenesis can lead to increased calorie expenditure.
