Energy Metabolism Explained
'How your body uses, stores and burns energy'.
NOT MEDICAL ADVICE - CONSULT A DOCTOR FOR QUESTIONS
ABOUT YOUR HEALTH
This site hopes to explain how your body uses energy. A secondary goal is
that it may help you lose weight. Before we start off, the basics must be
After explaining where energy comes from we move on to how fuel is
transported and stored in your body. Then we treat how
it is converted into useable energy, and how
this energy is expended. Finally, there is a
page with some rambling on how I think a lot of people, including me, get
fat and how they can lose weight now that they understand how their
As this is a complicated subject, not everything is treated. This is mostly
about energy. It is not about healthy living and vitamins, sorry. Maybe
later. 1500 page books are written coverything just parts of the human
metabolism. When cramming everything in a few pages, something has to go.
All information found here can be checked with medical textbooks. Most of it
can be found in 'Advanced Nutritition and Human
Metabolism' by Groff &
Gropper. You will also see a lot of tiny
numbers, these are references to pages in books or websites which back
up the preceding paragraph.
Your body is like a machine, it requires energy to run. But food is not like
electricity in that it can be used to power you directly. It is far more
involved than that. These complications explain how it is possible to be
hungry while being overweight.
Food contains ingredients which your body can use as fuel. But even fuel is
not yet energy! If I give you fully charged battery, try using it to bake an
egg. Having an energy containing fuel does not mean that it is ready to use.
It all starts with food, and its metabolically active ingredients.
Metabolically active ingredients
You can see these ingredients mentioned on the packaging of most foods. With
the exception of fibers, all these carry energy. Fat contains 9 kcalories
per gram, carbohydrates and proteins in the order of 4
- Long carbohydrates
- Shorter carbohydrates ('sugars')
While fibers do not directly yield energy they are very important in making
digested food leave your body again and are generally useful to have in your
colon. There are indications that they may power intestinal bacteria which
help you digest other food.
Your body can extract at least the following three kinds of fuel from what
Fatty acids are made from fat. Longer carbohydrates are chopped up into
smaller ones, leading to glucose, which is stored as glycogen. Proteins get
converted to amino acids.
So the conversion of ingredients to fuels is:
- Fatty acids
- Amino acids
By now you may be confused about the relation between carbohydrates,
glucose, glycogen & sugar. If you want to know the details, see here.
- Fat -> fatty acids
- Fibers -> used for excreting ingredients
- Long carbohydrates -> shorter -> glucose
- Shorter carbohydrates ('sugars') -> glucose
- Proteins -> Amino acids
Next: Transport and storage.