Muscles communicate with the rest of our tissues through myokines. These are chemicals released from the muscle by various conditions such as exercising or a change in temperature. These myokines have benefits on organs, such as our nervous and cardiovascular system, as well as disease protection for cancer, dementia, osteoporosis, and type 2 diabetes.
Our bodies contain two types of adipose tissue, which are distinguished as white fat and brown fat. White fat is the reservoir of our excess calories and it is used to provide energy when too few calories are coming into the body (for instance when dieting or starving) or during prolonged periods of exercise. Brown fat (that color because it contains a cellular component, mitochondria, that gives it its brownish hue) is the furnace of the body. These mitochondria generate heat and use up calories to keep our bodies warm in cold environments. Adults have very little brown fat. What they do have is located in the upper back, in the hollow between the collarbone and shoulder and along the spine. Newborns have much more, about 5 percent of their total body mass. Newborns are susceptible to the cold and cannot shiver to generate heat. The brown fat prevents them from suffering from hypothermia.
Even the small amount of brown fat we have as adults uses up or “burns” calories when the body is exposed to cold. In a study in the Journal of Clinical Investigation by endocrinologist, Dr. Andre Carpentier, men were kept in a cold environment so they were chilled, but not shivering. The heat-burning brown fat increased their metabolic rate by 80 percent, even though they were just sitting in an under-heated room.
A new “hormone” has recently been discovered, Irisin. Iris (Greek mythology) is the personification of the rainbow and messenger of the gods. She is also known as the swiftness goddess of the sea and the sky. Irisin is released from exercising muscles and turns white fat cells (the kind we want to get rid of) into cells that act like brown fat cells. Dr. Pontus Bostrom and colleagues, who discovered the white to brown fat cell conversion, reported in the journal Nature that these new fat cells are not identical in color to the brown cells we have from birth. He named them brite, or brown-in-white, cells. They act like brown cells by increasing heat, burning calories and decreasing elevated glucose levels.
Although most of the research has been carried out in mice, some studies on humans found a significant increase in this hormone, as well as metabolic rate in humans after 10 weeks of regular exercise. It has also been suggested that the increased metabolic rate seen for a couple of hours following completion of exercise may be due to the continuing fat burning by these newly-formed brite cells.
Studies using mice suggest that increasing the level of Irisin, which is identical in humans, causes the white fat to become brite. Obese mice did not have to go on a treadmill to increase their Irisin levels. They were genetically manipulated into producing a high level of this hormone. The mice increased their energy production, thus using up calories and losing weight while improving glucose tolerance and future weight gain.
Irisin might be the magic weight-loss pill everyone has been waiting for! Would taking it in pill form eliminate the need to exercise to lose weight and decrease elevated glucose levels? An editorial in the April 19th 2012, New England Journal of Medicine suggests that Irisin would be beneficial for those who are unable to exercise because of severe muscle or skeletal disability or cardiovascular conditions. But for now, there is no substitute for exercise, which gives so much more health benefits than weight loss!
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