Your metabolism is a collection of all the small chemical reactions taking place in your body that work to keep you alive. These reactions are fueled by burning up the calories that exist in all the food you eat. If you eat more calories than you need to power these reactions, the excess food energy will be stored as fat. Each person’s metabolism is different, just like every person is different. Throughout this summer, we’ll be exploring the different ways metabolisms work, and how understanding your own metabolism can help you become healthier.
As humans, we need to generate body heat to keep all of the chemical processes that run our bodies functioning.
“Maintaining proper body temperature is crucial,” says Yu Hua Tseng, Ph.D., Principal Investigator in the Section on Integrative Physiology and Metabolism at Joslin Diabetes Center. “In normal situations, we have to maintain the right temperature so all of the enzymatic processes in our body can function. In cold conditions, this is essential to produce heat in order to maintain this homeostasis.”
This heat generation is called thermogenesis, and it plays a big role in how many calories we’re burning at any given moment.
“At the cellular level, the mitochondria are processing the energy from food, and all of these enzymatic reactions are associated with some kind of heat production,” she said. “And we know that at more macro levels, when you exercise, it also produces heat. That’s why you sweat and feel warm when exercising.” If your body produces a lot of heat from these processes, both micro and macro, your metabolism will run faster and you’ll burn more calories while at rest.
There’s another heat production process that Dr. Tseng has been working on in her lab at Joslin. Brown fat is a type of fat that burns up excess calories by generating heat from your body, rather than storing that excess energy for later, which is the job of white fat. Activating brown fat can help counteract obesity-related conditions such as type 2 diabetes, because brown fat has also been shown to improve insulin sensitivity.
When brown fat is activated, it generates heat in your body, which then gets released into the atmosphere. Since that heat isn’t used for anything in your body, it could seem like it’s an energy wasting process. But people who are overweight or obese have too much stored energy in their bodies, in the form of white fat cells.
“In some extreme obese conditions, excess energy is stored in your liver or even muscles, which can cause insulin resistance.” says Dr. Tseng. “So, the idea of activating brown fat as a way to combust this excess energy is now an attractive area of research in both academia and industry for developing new treatment strategies to help combat obesity and various metabolic diseases.”
When brown fat is fully activated, it can burn between 200 and 300 extra calories per day. It is most successfully activated through cold exposure. A recent study of people with type 2 diabetes had volunteers sit in a 50 degree room for a couple of hours a day for 10 days in shorts and short-sleeved shirts.
“When I say cold, it’s not icy cold, it’s not like the winter in Boston,” she says. “It’s more or less like the temperature we have here in autumn. After this mild cold exposure, all ten volunteers with type 2 diabetes, as shown in that study, displayed increased brown fat activity and improved insulin sensitivity. This is very exciting.”
Dr. Tseng is working on understanding exactly what is happening on a cellular level to activate brown fat in the cold to see if she can create a drug that will mimic the effects. “Although cold works, it’s just not pleasant,” she says. “If you had to sit in a cold room for a few hours every day, perhaps not everybody could accept that.”
If cold isn’t your thing, evidence from mouse studies run by Laurie Goodyear, Ph.D., Senior Investigator and Co-Head of the Section on Integrative Physiology and Metabolism at the Joslin Diabetes Center, and Kristen Stanford, Ph.D., a post-doctoral fellow in the Section on Integrative Physiology and Metabolism at Joslin Diabetes Center, has shown that exercise can change white fat into brown fat. Some, like George King, M.D., Chief Scientific Officer at Joslin Diabetes Center, recommend combining these known brown-fat activators by working out in the cold to get the maximum benefit.
However you activate brown fat, increasing your level of the tissue raises your body temperature which could, in turn, increase your metabolic baseline.
“Brown fat is a natural defense system for obesity, diabetes and related diseases or conditions,” said Dr. Tseng. “As we learn more about how to regulate this unique fat tissue, we will be able to develop better remedies to help individuals who suffer from metabolic disorders.”