Expert: Walter Hintz - 12/28/2007

Question
QUESTION: If a human inhales O2 and exhales CO2 where does the carbon come from? Is there a form of 'fusion' inside the body that we gain energy from? in theory (silly but worth asking because of the carbon addition) can I lose weight from breathing?

ANSWER:    Hi dan
We get our Carbon from eating organic compounds.  Energy is then stored in chemical bonds of carbohydrates, lipids and proteins.  When we need energy we oxidize these compounds and CO2 is released as a byproduct.
Actually you so lose small amounts of weight when breathing because you expell water in the breath but a water balance is maintained so you get it right back by eating and drinking

---------- FOLLOW-UP ----------

QUESTION: How is energy gained from the oxidization process?

Answer
Oxidation involves Redox reactions (oxidation/reduction) Enzymes stimulate the chemical reactions whereby oxygen combines with glucose breaking it down and releasing in teh form of heat and producing CO2 and H2O.  This is a simplification.  The chemical process is much more complicated.  I do not know what you know about organic chemistry.