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    Katherine Zeratsky, R.D., L.D.

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Question

Body fat: What happens to lost fat?

When you lose weight, where does the lost body fat go?

Answer

from Katherine Zeratsky, R.D., L.D.

Body fat breaks down during a series of complex metabolic processes.

When you burn more calories than you consume, your body uses fat (triglycerides) for energy. This causes your fat cells to shrink. In turn, triglycerides are broken down into two different substances — glycerol and fatty acids — which are absorbed into your liver, kidneys and muscle tissue. From there, the glycerol and fatty acids are further broken down by chemical processes that ultimately produce energy for your body.

These activities generate heat, which helps maintain your body temperature. The resulting waste products — water and carbon dioxide — are excreted in urine and sweat or exhaled from your lungs.

Next question
Metabolism: What's the best way to boost it?
References
  1. Stanfield CL, et al. Cell metabolism. In: Stanfield CL, et al. Principles of Human Physiology. 3rd ed. San Francisco, Calif.: Pearson/Benjamin Cummings; 2008:88.
  2. McArdle WD. Overweight, obesity and weight control. In McArdle WD. Exercise Physiology. 6th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2007:852.
  3. Stanfield CL, et al. The endocrine system: Regulation of energy metabolism and growth. In: Stanfield CL, et al. Principles of Human Physiology. 3rd ed. San Francisco, Calif.: Pearson/Benjamin Cummings; 2008:607.
AN01327 April 30, 2010

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