Does cold exposure really help with weight loss?

According to a new study led by the Leiden University Medical Center (LUMC) and presented at the European Congress on Obesity (ECO) in Dublin, Ireland (17-20 May 2023), the metabolic response to cold exposure varies based on the time of day and the gender of individuals. More specifically, cold exposure in the morning might be more effective in boosting metabolism and burning fat in men, whereas the same effect may not be observed in women.

Brown fat, also known as brown adipose tissue (BAT), is a type of fat that is activated in response to cold temperatures. Its primary function is to generate heat and maintain body temperature by burning calories, particularly from fat.

The study revealed that the optimal timing for cold exposure closely aligns with the circadian cycle. “There may also be a sex difference in how the body responds to cold exposure in terms of boosting metabolism at a specific time point. It appears that delivering cold exposure therapies in the morning may be more beneficial for men,” said co-author Mariëtte Boon, an expert in fat metabolism at Leiden.

In rodents, the metabolic activity of brown fat fluctuates throughout the day and reaches its peak just before waking up. This is logical from a biological standpoint, since heat production decreases during nighttime and the body needs to raise its core temperature upon waking. However, it remains unknown whether humans exhibit a circadian rhythm in brown fat activity and if it differs between men and women when exposed to cold.

To investigate further, the researchers conducted a randomized crossover study involving 24 lean adults, consisting of 12 men (aged 18-31 years; BMI 18-26 kg/m²) and 12 women (aged 18-29 years; BMI 18-26 kg/m²). Participants underwent a personalized cooling protocol using water-filled mattresses for 2.5 hours in the morning (7:45 am) and evening (7:45 pm), with a day’s interval between the sessions.

The water temperature was gradually decreased until shivering occurred or until it reached 9°C. Following this, participants were exposed to stable cold for an additional 90 minutes. Energy expenditure and supraclavicular skin temperature (a proxy for brown fat activity) were measured four times during the experiment: at the start under thermoneutral conditions (32°C), during the cooling down phase, the stable cold phase, and at the end of cooling.

The analysis revealed that, in men, cold-induced energy expenditure and skin temperature were higher in the morning compared to the evening. However, in women, there was no significant difference in cold-induced energy expenditure and skin temperature between the morning and evening. 

Interestingly, women exhibited greater tolerance to cold in the morning, meaning they started shivering at a lower temperature in the morning than in the evening. Additionally, women showed higher levels of circulating free fatty acids, triglycerides, and cholesterol after cold exposure in the morning compared to the evening.

Some limitations of the study include the inability to establish strong causal conclusions about the direct effects of cold exposure on cardiometabolic health, and the fact that unmeasured lifestyle or genetic factors may have influenced the results, despite efforts to control diet and sleep.

“Nevertheless, this is an important first step investigating the effects of circadian rhythm on the effects of cold exposure on (fat) metabolism. We are currently studying whether repeated bouts of cold exposure in the morning improves cardiometabolic health in individuals with obesity. At the very least, our findings indicate that administering interventions at specific times should be considered when targeting lipid metabolism,” Boon concluded.

The study is published in the Journal of Clinical Endocrinology & Metabolism.

More about cold exposure and fat burning

Research suggests that cold exposure could potentially help burn fat, but it’s not entirely clear how significant or practical this effect is.

Humans have two types of fat: white fat and brown fat. White fat stores energy and is the kind of fat that builds up when we consume more calories than we burn. On the other hand, brown fat burns energy to generate heat and can help maintain body temperature in cold conditions.

When your body is exposed to cold, it tries to keep your core warm, and one way it does this is by activating brown fat, which burns calories to generate heat. Therefore, theoretically, exposure to cold could help burn more calories and potentially reduce fat stores.

There’s some evidence that regular cold exposure can increase brown fat activity and potentially help with weight loss. A study published in the Journal of Clinical Investigation in 2014 found that people who were exposed to cold temperatures for two hours a day for six weeks burned more energy and had a decrease in body fat. 

However, more research is needed to understand the potential benefits and risks of cold exposure for fat burning and weight loss. Also, it’s not clear how cold the exposure needs to be or how long it needs to last to have a meaningful effect.

Moreover, cold exposure might have side effects, such as hypothermia, frostbite, or cardiovascular strain, especially in people with certain health conditions. Therefore, it’s important to talk to a healthcare provider before trying cold exposure as a weight loss strategy.

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By Andrei Ionescu, Earth.com Staff Writer

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