How Does Food Energy Become Our Body’s Energy?

How Does Food Energy Become Our Body's Energy?
On a daily basis we acquire energy from foods in the form of carbo-
hydrates, protein, fat, and alcohol. However, we cannot use these mol-
ecules for energy directly. These substances must first engage in chemical
reaction pathways that break them down and allow for us to capture
much of their energy in a form that we can use directly. With the excep-
tion of alcohol, these food energy molecules are also stored in our body to
be used as needed.
   To be more specific, when these energy molecules are broken down
some of their energy is captured in so-called "high-energy molecules." By
far the most important high-energy molecule is adenosine triphosphate
or, more commonly, ATP. Figure 1.6 displays a simplified version of ATP.
When energy is needed to power an event in our body it is ATP that is
used directly. So, the energy in carbohydrate is used to generate ATP,
which in turn can directly power an energy-requiring event or operation
in our body. As you might expect, the release of the energy from these
little molecular powerhouses is controlled. Specific enzymes are employed
to couple ATP with an energy-requiring chemical reaction or event and
the transfer of energy.
    Adenosine triphosphate (ATP) is the principal energy molecule to
    power body activities.
   Interestingly, not all of the energy released in the breakdown of carbo-
hydrates, protein, fat, and alcohol is incorporated in ATP. It seems that
we are able to capture only about 40 to 45 percent of the energy available
in those molecules in the formation of ATP. The remaining 55 to 60 percent
of the energy is converted to heat, which helps us maintain our body
temperature  . The final product of the chemical reaction
pathways that breakdown carbohydrates, proteins, fat, and alcohol is
primarily carbon dioxide (CO2), which we then must exhale, and water
(H2O), which helps keep our body hydrated.