The incredible shrinking
Everything you want to know about fat cells & fat
By Tom Venuto, NSCA- CPT, CSCS
Q: Dear Tom: would you
please try to explain in laymen's terms exactly how
fat cells work and what happens when you start to
burn body fat. I heard a statement that the fat cell
has to get moved into the muscle cell for it to be
released or burned. Thought you could explain a
Earlier this week someone in our
burn the fat discussion
forum wrote, "I haven't LOST any fat... I know
EXACTLY where it went! I got a chuckle out of that
because I "got" the joke, but truth is, most people
really don't know how fat cells work, how the fat
burning process takes place, or where the fat goes
when it's burned, so this is a really good question.
When you "lose" body fat, the fat cell (also called
an adipocyte) does not go anywhere or "move into the
muscle cell to be burned", as it was suggested to
you (although that's not too far off). The fat cell
itself, (unfortunately) stays right where it was -
under the skin in your thighs, stomach, hips, arms,
etc., and on top of the muscles - which is why you
can't see muscle "definition" when your body fat is
Fat is stored inside the fat cell in the form of
triaglycerol. The fat is not burned right there in
the fat cell, it must be liberated from the fat cell
through somewhat complex hormonal/biochemical
pathways. When stimulated to do so, the fat cell
simply releases its contents (triaglycerol) into the
bloodstream as free fatty acids (FFA's), and they
are transported through the blood to the tissues
where the energy is needed.
A typical young male adult stores about 60,000 to
100,000 calories of energy in body fat cells. What
triggers the release of all these stored fatty acids
from the fat cell? Simple: When your body needs
energy because you're consuming fewer calories than
you are burning (an energy deficit), then your body
releases hormones and enzymes that signal your fat
cells to release your fat reserves instead of
keeping them in storage.
For stored fat to be liberated from the fat
cell, hydrolysis (lipolysis or fat breakdown),
splits the molecule of triaglycerol into glycerol
and three fatty acids. An important enzyme called
hormone sensitive lipase (HSL) is the catalyst for
this reaction. The stored fat (energy) gets released
into the bloodstream as FFA's and they are shuttled
off to the muscles where the energy is needed. As
blood flow increases to the active muscles, more
FFA's are delivered to the muscles that need them.
An important enzyme called lipoprotein lipase (LPL),
then helps the FFA's get inside the mitochondria of
the muscle cell, where the FFA's can be burned for
energy. If you've ever taken a biology class, then
you've probably heard of the mitochondria. This is
the "cellular powerhouse" where energy production
takes place and this is where the FFA's go to be
burned for energy.
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When the FFA's are released from the fat cell, the
fat cell shrinks and that's why you look leaner when
you lose body fat - because the fat cell is now
smaller. A small or "empty" fat cell is what you're
after if you want the lean, defined look.
It was once believed that the number of fat cells
could not increase after adulthood, only the size of
the fat cells could increase (or decrease). We now
know that fat cells can indeed increase both in size
(hypertrophy) and in number (hyperplasia) and that
they are more likely to increase in number at
certain times and under certain circumstances, such
as 1) during late childhood and early puberty, 2)
During pregnancy, and 3) During adulthood when
extreme amounts of weight are gained
Some people are genetically predisposed to have more
fat cells than others and women have more fat cells
than men. An infant usually has about 5 - 6 billion
fat cells. This number increases during early
childhood and puberty, and a healthy adult with
normal body composition has about 25 to 30 billion
fat cells. A typical overweight adult has around 75
billion fat cells. But in the case of severe
obesity, this number can be as high as 250 to 300
The average size (weight) of an adult fat cell is
about 0.6 micrograms, but they can vary in size from
0.2 micograms to 0.9 micrograms. An overweight
person's fat cells can be up to three times larger
than a person with ideal body composition.
Remember, body fat is basically just a reserve
source of energy and fat cells are the like the
storage tanks. Unlike a gas tank in your car which
is fixed in size, however, fat cells can expand or
shrink in size depending on how "filled" they are.
Picture a balloon that is not inflated: It's tiny
when not filled with air - maybe the size of your
thumb. When you blow it up with air, it can expand
10 or 12 times it's normal size, because it simply
fills up. That's what happens to fat cells: They
start as nearly empty fat storage "tanks" (when you
are lean), and when energy intake exceeds your
needs, your fat cells "fill up" and "stretch out"
like balloons filling up with jelly (not a pretty
picture, is it?)
So you don't actually "lose" fat cells, you "shrink"
or "empty out" fat cells.
1. Calories count!The signal that triggers your body
to release adipose from fat cells is an energy
deficit... you have to burn more than you eat.
2. Cut calories conservatively. Starving yourself
may cause quick weightloss at first, but never works
long term because it actually decreases the activity
of fat burning enzymes that release fat from the
cells. to avoid this "starvation mode" use exercise
to BURN THE FAT, not very low calorie crash diets.
3. Get control of your weight now. If you are
gaining weight, and especially if your weight is
climbing upwards out of control, make a decision to
STOP RIGHT NOW. Your fat cells might be multiplying,
making it more difficult to burn fat in the future.
NOW is the time!
4. If you've already lost weight, you must be
forever diligent. Your fat cells are not gone, they
have merely "shrunk" or "emptied out." Fitness is
not a 12 week program, its a lifestyle. To stay lean
you have to eat clean and stay active
5. Genetics are only a minor factor. You may not
have control over how many fat cells you were born
with, but you do control the major factors that
determine how much fat you store: lifestyle,
exercise, nutrition, mental attitude.
Genetics are not an excuse. The past is not an
excuse. Your present condition is not an excuse. You
can either make excuses or get results, but you
can't do both.
So keep educating yourself about the science, read
these newsletters, take action every day and go out
there and make it happen!
If you need more help, Burn The Fat is the eating
plan that turned it all around for thousands of
others... why not you? visit:
About Tom Venuto
Tom Venuto is a lifetime natural bodybuilder, an NSCA-certified personal trainer, a certified strength & conditioning specialist (CSCS), and author of the #1 best selling diet e-book in Internet history, "Burn The Fat, Feed The Muscle.Ē Tom has written hundreds of articles and been featured in IRONMAN, Australian IRONMAN, Natural Bodybuilding, Muscular Development, Exercise for Men and Menís Exercise. For information on Tom's Burn The Fat e-book, visit
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