While scientists don't know all the details of how the endocrine system -- the system of the body that controls hormonal release and inhibition -- affects fat, it is clear that hormones play a significant role in how the body uses fat as energy and also how fat gets stored.
Fat Burners
In response to physical stressors, such as exercise, you need to increase the availability of energy to keep going strong and keep the body functioning at optimal capacity. This sudden energy demand triggers multiple organs to release hormones that will stimulate glucose and fat -- two primary energy sources -- to be released into the blood. The hormones epinephrine, norepinephrine, cortisol and growth hormone all contribute to increased fat release and usage during prolonged exercise.
Fat Storage
When too much energy is available -- like in the case of consistent overeating -- your body will store some of that energy, saving it for "stressful" times. As a fat storage hormone, insulin is released from the pancreas and helps remove glucose from the blood by enhancing glucose uptake into muscle and fat cells. Estrogen, the developmental hormone released by the ovaries, also increases fat storage, especially in the hips and thighs.
Other Hormones
Leptin, a hormone produced in fat cells, may also indirectly contribute to increased fat storage. When fat reserves are perceived as being low, leptin is released and signals the brain to signal the hunger drive. After eating, leptin release declines. In rare cases, leptin release isn't turned off as it should be, resulting in overstimulation of the hunger drive, overeating and ultimately, excessive fat storage.
Special Circumstances
While cortisol typically burns fat, studies have linked it with excessive abdominal fat. Emotional stress triggers the release of the same hormones associated with physical stress, but it doesn't include the heavy demand for energy. When stress is effectively managed, this has little effect. However, in a study published in the 2008 "Annals of the New York Academy of Sciences," chronic stress, when combined with high-sugar and high-fat diets, significantly increased abdominal fat deposits.
References
- "Human Anatomy and Physiology"; Elaine Marieb; 2001
- "Physiology of Sport and Exercise"; Jack Wilmore, David Costill; 2004
- "The Annals of the New York Academy of Sciences": Chronic Stress, Combined with a High-Fat/High-Sugar Diet, Shifts Sympathetic Signaling toward Neuropeptide Y and Leads to Obesity and the Metabolic Syndrome; Lydia Kuo, et al.; Dec 2008
- "Nature: International View of Science"; Leptin and the Regulation of Body Weight in Mammals; Jeffrey Friedman, Jeffrey Halaas; October 1998
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