To understand the answer, it helps to remember that fat is basically stored energy. Your body converts fat to usable energy for your muscles and other tissues through a series of complex metabolic processes. This causes your fat cells to shrink.
These metabolic activities also generate heat, which helps maintain your body temperature, and waste products. These waste products — water and carbon dioxide — are excreted in your urine and sweat or exhaled from your lungs.
March 17, 2015
- Body temperature and metabolism. In: Scanlon VC, et al. Essentials of Anatomy and Physiology. 7th ed. Philadelphia, Pa.: F.A. Davis Company; 2015.
- Fundamentals of human energy transfer. In: Katch VL, et al. Essentials of Exercise Physiology. 4th ed. Baltimore, Md.: Lippincott Williams & Wilkins; 2010.