Mild stress stimulates the activity of, and heat production by, brown fat associated with raised cortisol, according to a study published online on February 8, 2016, in Experimental Physiology. The article is titled “Brown Adipose Tissue Activation As Measured by Infrared Thermography by Mild Anticipatory Psychological Stress in Lean Healthy Females.” Brown adipose tissue (BAT), also known as brown fat, is one of two types of fat found in humans and other mammals. Initially only attributed to babies and hibernating mammals, it was discovered in recent years that adults can have brown fat too. Its main function is to generate body heat by burning calories (as opposed to the function of white fat, which is to store excess calories). People with a lower body mass index (BMI) therefore have a higher amount of brown fat. To induce a mild psychological stress in the current study, five healthy lean women had to solve a short math test in the first run, but in the second run, the test was substituted for with a relaxation video. To assess stress responses, the scientists measured cortisol in the saliva. To measure the activity of brown fat, the researchers used infrared thermography to detect changes in temperature of the skin overlying the main area of brown fat in humans (namely, in the neck, or supraclavicular, region). Although the actual math tests did not elicit an acute stress response, the anticipation of being tested did, and led to raised cortisol and warmer brown fat. Both were positively correlated, with higher cortisol linked with more fat activity and thus more potential heat production. Professor Michael E.
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