What Happens When Fat Is Burned?

Earlier this week someone in our 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. It's actually quite a complex biochemical process, but I'll explain it as simply as possible, so by the end of this article, you'll be a "fat burning" expert!

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.

The fat is not burned right there in the fat cell,
it must be liberated from the fat cell.

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? 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.

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
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. (learn about your body type) 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 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 "empty out" fat cells.

Take-home lessons:

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. More info: burning fat without burning muscle article.
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!