Physiology

Brown fat and cold exposure: can shivering help you burn more?

Brown fat burns energy to make heat, and cold can activate it — but the extra calories are modest compared with diet and activity.

Most body fat is white fat, which stores energy. Brown fat is a different tissue packed with mitochondria that can burn fuel to produce heat instead of storing it, a process called non-shivering thermogenesis. Babies have relatively large amounts of brown fat to keep warm, and imaging studies have shown that many adults still have active brown fat, mostly around the neck, collarbones and spine. Cold exposure is the strongest natural trigger for this tissue, and regular cold exposure can increase its activity over weeks.

This has led to the idea of using cold showers, cold rooms or ice baths to boost fat loss. Research shows that cold exposure does increase energy expenditure, partly through brown fat and partly through shivering, and it may modestly improve how the body handles blood sugar. However, the amount of extra energy burned through brown fat in most adults is small, often estimated at tens to perhaps a little over a hundred calories per day during significant cold exposure, and the body may partly compensate by increasing appetite.

In practice, cold exposure is not a shortcut to fat loss, and its effect is far smaller than that of a consistent energy deficit, daily movement and strength training. Some people enjoy cold showers or cold-water swimming and report feeling more alert, which is a fine reason to include them if they are safe for you. Avoid extreme or prolonged cold, never swim alone in cold water, and talk to a doctor first if you have heart disease, high blood pressure or circulation problems, since sudden cold places a strain on the heart.

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