People dealing with stress typically experience weight gain — high levels of the stress hormone cortisol can reduce self-control and amplify cravings. However, there are those who experience weight loss. And according to a new study published in Experimental Physiology, the differences may be explained by the varied ways the human body responds to psychological stress.
Study authors hypothesize mild psychological stress (as opposed to physical stress) can activate brown fat activity. Formally known as brown adipose tissue, brown fat increases body heat by burning calories, thus increasing insulin sensitivity and balanced blood sugar levels. Since brown fat has been shown to burn more calories than white fat, some experts believe it has potential to treat obesity.
To test their hypothesis, researchers asked five lean women to solve a series of math tests before giving them a relaxation video to watch. They took saliva samples to measure women’s cortisol levels and used infrared thermography to detect any temperature changes in skin areas where brown fat is abundant in humans, mostly the neck region.
While the math tests themselves did not stress women out, the anticipation of being tested did. Anticipation increased both levels of cortisol and "warmer brown fat," which suggests higher levels of cortisol are linked with more brown fat activity, thus more calorie-burning heat production.
Most adults only have between 50 and 100 grams of brown fat, study co-author Michael E. Symonds, a professor of The School of Medicine, University of Nottingham, said in a press release. While people who have a lower body mass index tend to have a higher amount of this type of fat, generally speaking, 50 to 100 grams may be enough.
"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," Symonds said. "There is an inverse relationship between the amount of brown fat and BMI, and whether this is a direct consequence of having more active fat remains to be fully established."
Of course, he said researchers still need "a better understanding" of the main factors controlling brown fact activity. But like the many studies before his, he agress this insight could lead to "sustainable interventions designed to prevent obesity and diabetes."
"In future, new techniques to induce mild stress to promote brown fat activity could be incorporated alongside dietary and/or environmental interventions," he concluded. "This is likely to contrast with the negative effects of chronic and more severe stress that can contribute to poor metabolic health."
It's not the first time we've heard mild stress can have positive health effects. According to Scientific American, a 2012 study found "only believing one's stressful experiences are harmful was correlated with illness and early mortality." SA quoted health psychologist Kelly McGonigal, who has seen certain levels of stress cause some people to feel and function better.
It's important to note these positive aspects are associated with mild levels of stress; chronic, high levels of stress can still be detrimental to health. Some stress relievers to consider: mindfulness meditation and adult coloring books.
Source: Symonds ME et al. Experimental Physiology. 2016.