Many people report that they feel warmer throughout the day after taking a cold shower or bath. This could partly be due to enhanced circulation, but the stimulation of brown fat also seems a likely cofactor.
Brown fat is one of two types of fat in the body – the other being white fat, or what we normally just refer to as “body fat”. While white fat should be kept to a minimum, brown fat is beneficial because it helps burn calories and generate body heat. A study at the University of Maastricht in the Netherlands revealed that obese people have less brown fat than lean people .
A cold shower could be a good way to stimulate the body’s supply of brown fat. A branch of the aforementioned university found that in men, exposure to chilly temperatures increased the metabolic rate of brown fat 15-fold. Sustaining this rate alone could help a person shed 9 pounds a year. Women typically have twice as much brown fat as men .
In a Chinese experiment involving voles exposed to a 5° C environment, they found that the “thermogenic capacity” of brown fat increased; the cold-exposed voles had a higher content of uncoupling protein 1 in their brown fat, increasing their ability to convert stored calories into heat .
However, in one small study of six men, the researchers did not find that their adaption to cold was facilitated by brown fat . Hopefully future studies will find the most favorable conditions for activating brown fat and the precise benefits we can expect.
 Brown Fat: Don’t Try To Burn It
 Cold exposure does not decrease serum leptin concentration, but increases energy intake and thermogenic capacity in pregnant Brandt’s voles (Lasiopodomys brandtii).
 Effects of acclimitazation to cold baths on men’s responses to whole-body cooling in air.