The fat burning process is a complex biochemical process.

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”. 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 high.

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/enzymatic 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? 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.

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 billion!

The average size (weight) of an adult fat cell is about 0.6 micrograms, but they can vary in size from 0.2 micrograms 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 a reserve source of energy and fat cells operate like reserve 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.

FAT is not merely an inert storage tank for surplus calories. Fat cells don’t just store fat, the fat tissue is actually very much part of the body. Fat is an active organ than sends chemical signals to other parts of the body. The adipose tissue (FAT), occupies the niche of an endocrine organ, along with the pancreas, thyroid and adrenal gland.

The more traditional organs typically produce one or two hormones. However, fat cells, spit out a huge array of chemicals - at least 80 different substances. Among these hormones is leptin, which controls appetite, and adiponectin, which makes the body more sensitive to insulin and controls blood sugar levels. However, little is known about most of the proteins produced by the billions of fat cells in the adult body. Scientists have identified 80 different proteins produced by fat cells. These include new proteins and 20 proteins that have not been previously detected in human fat cells.

Many of the fat chemicals are not unique to fat cells, but a handful, such as leptin and adiponectin, are only made by fat cells. Scientists are trying to figure out what all these chemicals do, but many of them are involved in inflammation. The official term for all these chemicals being produced by fat cells (adipocytes) is adipokines.

Important Lessons:

Calories count. The signal that triggers your body to release adipose from fat cells is an energy deficit… you have to take in less energy from eating or drinking food than the amount of energy that your body uses ("burns") to sustain all of its ongoing activities.  Most of the body's activities are involuntary (such as breathing, cell repair, pumping blood etc.) which would continue even in a coma.  Voluntary activity, such as normal physical movement - which includes additional exercise/fitness activities - normally accounts for only about 16% to 20% (sedentary) to 25% (physically active) of all of the energy used by the body.

Eating food and fat burning are inter-related. You cannot lose weight without cutting calories, but when you cut calories, your body decreases many of its automatic functions, including the activity of fat burning enzymes that release fat from the cells.

After weight-loss, you must be forever diligent. Your fat cells are not gone, they have merely “shrunk” or “emptied out.” Weight-loss maintenance requires continuing a lower-calorie lifestyle forever.

Genetics and Life-History are factors. You can’t control the number of fat cells you currently have, but you CAN achieve control over SOME of the factors that determine how much fat you store. Reducing and limiting your food intake, through portion controlled eating, is the most important helpful factor in weight-control.

                               
Fat people have the right to exist in fat bodies without shaming, stigmatizing, bullying, or oppression.  "Well-meaning" expressions of your "concern" about their health etc. fall into these categories.

It doesn't matter why a person is fat, what being fat means, or if a person could be thin.

There are no other valid opinions on this. It is not up for debate. Fat people have the right to exist.

I agree with the sentiments expressed in the following article.

Striking A Balance, Or Not
               by Ragen Chastain of Dancing with Fat

Articles in mainstream media commonly indicate that while Size Acceptance is ok, we need to “strike a balance between body acceptance and health”.

There are many issues here but the first and most important is that body acceptance and health are two very separate things.

The idea that health should be linked to Size Acceptance or self-worth is incredibly dangerous and completely fucked up.  Health is not an obligation, barometer of worthiness, or completely within our control.  Often issues around this happen when people confuse the concepts of Health at Every Size with Size Acceptance.

The bottom line is that Health at Every Size is a paradigm from which to approach health and healthcare, but Size Acceptance is a Civil Rights Movement.  There is absolutely NO health or behavior requirement Size Acceptance. Nobody owes anybody else “health” or “healthy habits” by any definition. You do deserve, and have the right to demand, respect and the rights to life, liberty and the pursuit of happiness in the body you have right this minute – whatever your size, health, habits and disability.  This is a civil rights issue, plain and simple, it is vitally important that we not confuse Size Acceptance with health or disability in any way.

There are more issues with this idea of “striking a balance between Size Acceptance and Health”.  The logic-defying idea here is that liking and appreciating our bodies will somehow preclude health. That idea is precisely as ludicrous as it sounds. Of course when people are talking about “health” in this context they typically mean thinness, which is absolutely NOT the same thing. What they are often saying is that if you allow yourself to completely like your body, you won’t hate it enough to try dieting again and again when, like almost everyone, you fail repeatedly at long term weight loss. Or perhaps they think that in the multi-dimensionality, no guarantees, concept of health, self-loathing is a positive force.

Often if you scratch just below the surface you’ll find that this “strike a balance” idea is just diet industry manipulation for profit – it’s a way to give lip service to the myriad health professionals, experts, evidence, and heaping helping of common sense that points out that liking and appreciating our bodies is a good thing. 

By “striking a balance” they mean that it’s ok to like our bodies as long as we’re actively working to change them, preferably buying their product (or services) to do it. People like this see Size Acceptance as something for fat people to do until we become thin.  This idea then gets repeated by people who either didn’t think it through, or who actually believe that the key to “health” [thinness] is juuuust enough self-hatred.

We can consciously opt out of this system.  I do not think that hating myself does any good at all – and trust me when I tell you that I gave it the old college try. Hating myself never inspired me to take care of my body or led to a single positive outcome.  In fact, I got so caught up in hating my body for how it looked that I forgot to have even a second’s appreciation for what it did and that was no way for me to live.  Like everyone’s experience, mine is just for me – it can’t be extrapolated to anybody else so I’m neither trying to tell you what to do or trying to tell you that your experience will be the same as mine. I’m just trying to give an option.

So one option is to say “Screw striking a balance” and fully appreciate the body you have now – total, 100% body acceptance.  Not because your body is “perfect” (as if there is such a thing) but because it’s your body, the only one you have.  You get to decide for you, but for me, my body is amazing and deserves nothing less than my love, respect, and full-throated support, and anything less than that is way out of balance.

Article's Author is Ragen Chastain.
Speaker, Writer, Dancer, Choreographer, Marathoner, Soon to be IRONMAN,
Fat Person, Activist. blogging at www. dances with fat.