Shivering, Like Moderate Exercise, May Boost Weight Loss
US researchers found that shivering and bouts of moderate exercise are equally capable of converting energy-storing ’white fat’ into the fat-burning ‘brown fat’.
For most people, body fat has a bad reputation. But scientists consider it as one of the most ‘fascinating organs’ which has more functions than people thought. There are various types of body fat and they include the ‘white’ and ‘brown’ fats. Past research has shown that when stimulated, brown fats may actually help the body burn more calories.
According to the latest research, about 50 grams of white fat stores more than 300 kilocalories of energy. The same amount of brown fat could burn up to 300 kilocalories a day.
The research team, led by Dr Paul Lee, of Sydney’s Garvan Institute of Medical Research uncovered a way that fat and muscle communicate with each other through specific hormones – turning white fat cells into brown fat cells to protect us against cold.
Results showed that exposure to cold increases the levels of irisin – the hormone produced by muscles, and FGF21 which is produced by brown fats. Specifically, around 10-15 minutes of shivering resulted in equivalent rises in irisin as an hour of moderate exercise. In the laboratory, irisin and FGF21 turn human white fat cells into brown fat cells over a period of six days.
Before, it was thought that brown fats vanish in early infancy, but new studies suggest that this type of fat is present in most, if not all, adults. Research also suggests that adults with more brown fat are slimmer than those without.
"Excitement in the brown fat field has risen significantly over last few years because its energy-burning nature makes it a potential therapeutic target against obesity and diabetes," said Dr Lee. "White fat transformation into brown fat could protect animals against diabetes, obesity and fatty liver. Glucose levels are lower in humans with more brown fat."
In the current study, Lee and his team sought to understand the activation of brown fats. According to them, it was already known that cold temperature simulates brown fat but it was unclear how the body signals that message to its cells.
"When we are cold, we first activate our brown fat because it burns energy and releases heat to protect us. When that energy is insufficient, muscle contracts mechanically, or shivers, thereby generating heat. However we did not know how muscle and fat communicate in this process." In an experiment, the researchers exposed the volunteers to increasing cold, from 18 to 12 degrees until they shivered and took blood samples after to measure their hormone levels.
The team identified two hormones that were stimulated by cold – irisin and FGF21. “These hormones fired up the energy-burning rate of human white fat cells in the laboratory, and the treated fat cells began to emit heat – a hallmark of brown fat function." Dr Lee said.
"We speculate exercise could be mimicking shivering – because there is muscle contraction during both processes, and that exercise-stimulated irisin could have evolved from shivering in the cold." he added. The team hopes that their findings be used as basis for future studies to develop new therapies for obesity.
Their work was published in the journal Cell Metabolism.
Source of this article:
Irisin and FGF21 Are Cold-Induced Endocrine Activators of Brown Fat Function in Humans
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