A sleep method claiming that "sleeping in the cold helps you lose weight" is going viral on social media, particularly across Europe. On platforms like TikTok and Instagram, the so-called "cold-sleep diet"—which involves lowering indoor temperatures to 16–18°C before bed—has gained significant traction. Users have shared reviews claiming their body fat has decreased and they feel "lighter" in the morning.
The method is based on the principle that the human body increases energy expenditure to maintain its core temperature in cooler environments, burning fat in the process. However, medical experts note that there are clear limits to this as a reliable weight-loss strategy.
Brown Fat Activation: Possible but Limited
In a cold environment, the body utilizes more energy to maintain thermal homeostasis. This process can activate brown fat, which generates heat and burns calories. Some studies suggest that exposure to cool environments can indeed influence metabolic activity.
However, these metabolic changes are generally minor. Because they account for a relatively small portion of total daily energy expenditure, they are unlikely to produce meaningful weight loss on their own. During sleep, when physical movement is restricted, any additional calorie burn is even more limited. Ultimately, significant weight changes require a combination of dietary adjustments and increased physical activity.
Risks to Sleep Quality and Immunity
Lowering the temperature too far carries several risks. If the indoor environment is excessively cold, the body remains in a state of tension to maintain its core temperature, making it difficult to reach deep sleep stages. This can lead to frequent waking, increased fatigue, and a decline in overall sleep quality.
Furthermore, diverting excessive energy to maintain body temperature can burden the immune system. Prolonged exposure to cold may increase the risk of the common cold, muscle stiffness, and blood vessel constriction.
For older adults or individuals with chronic health conditions, cold-sleep environments may even raise the risk of hypothermia. Experts recommend maintaining a temperature of approximately 18–22°C for comfortable, healthy sleep, emphasizing that forcing an overly cold environment can ultimately do more harm than good.
