A British study, published in the journal Experimental Physiology, suggests that a low level of stress could boost the activity of so-called "brown fat," which is capable of burning the "white fat" associated with excess weight, obesity and sedentary lifestyles.
Five studies published in 2009 showed that, as well as having the white adipose tissue -- or white fat -- that stores lipids and excess calories, human adults also have brown adipose tissue -- or brown fat -- which generates body heat by "burning" calories. Brown fat was more commonly associated with hibernating mammals which, at the end of the winter, start to burn fatty acids that in part come from white adipose tissue. Babies also have reserves of brown fat to protect them from hypothermia.
British researchers have now discovered that stress could activate adult brown fat reserves, principally by increasing levels of the stress hormone cortisol.
The team, led by Professor Michael E. Symonds from the UK's University of Nottingham, asked five slim, healthy young women to participate in two monitored sessions. For the first, they were given a series of mathematical problems in the aim of creating a low level of stress. For the second, they were asked to watch relaxation videos.
The scientists evaluated their stress levels by measuring the level of cortisol in participants' saliva. Brown fat activity was measured via infrared thermography, detecting temperature changes in skin in the neck (above the collar bone), where brown fat levels are highest in the human body.
The results showed that the anticipation of the maths test increased cortisol levels and that the temperature increased in the area of brown fat being monitored. In other words, the low or moderate level of stress induced stimulated this region of brown fat to produce heat by burning calories.
"Most adults only have between 50-100g of brown fat but because its capacity to generate heat is 300 times greater (per unit mass) than any other tissue, brown fat has the potential to rapidly metabolize glucose and lipids," explains Professor Symonds.
There also appears to be an inverse relationship between a person's brown fat reserves and their BMI (Body Mass Index), as people with lower BMIs tend to have more brown fat.
The study could open up new research directions for obesity treatment, where triggering low levels of stress could be investigated as a possible means of therapy, along with physical activity and a healthy diet, which can also affect brown fat activity. These positive results contrast with the effects of chronic or severe stress, which can reduce metabolism and can lead to other conditions.
© AFP/Relaxnews 2023