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A Scientific Look at Fat I decided I would put my years of college biology and chemistry to good use by explaining exactly how the body uses fat. The Joy of Fat We always tend to look at fat as a bad thing, but it actually is hanging on our bodies for a good reason. Fat is our primary energy source. It's slow burning, so it lasts a long time. It's easy to store; your body can stick it just about anywhere. It's easy to make, too; our bodies can take a protein or carbohydrate molecule and turn it into fat. (Can you imagine being able to take some apples and turn them into a stick of grease? It's pretty amazing.) Our bodies need protein to build and repair tissue. They need carbohydrates to give our cells quick boosts of energy and to act as kindling to burn fat (keep reading and I'll explain this). If, however, we eat more proteins or carbohydrates that we can use or if you eat fat, our body sticks them in the reserve pile for later use as fat. This way, we don't waste our precious calories. Fat is great when you're working out in the fields for your food, running from wild beasts, or trying to last through a hard winter. Fat has helped our species to evolve. So, the next time you're mad at your body for being so fat, just remember it's just doing its job and trying to help you the way it has helped your ancestors for thousands of years. Unfortunately, today we just don't need it the way we once did. We sit a lot for various purposes. We eat a lot for various reasons. Plus, we really would rather have a life of convenience and leisure over a life of hard labor. Our body still keeps making fat like it always did, but we just don't burn it like we used to. It all comes down to metabolism. The Story of Metabolism Once upon a time, there was a little muscle cell. It was a smart little muscle cell. It knew that the best way to create energy was to burn fat and sugar together. It was also a conservative little cell and only used as much fat and sugar as it needed, so it wouldn't be wasteful because it knew that one day it may need to use that excess energy. So the great body stored that extra energy as fat. Fat burns in our muscle cells like a big old log in a fireplace. The fireplace that our cells use is called mitochondria. A mitochondria is a small organelle inside of the cell. Every cell has at least one, but the ones we really want to focus on our the ones in our muscle cells. When our muscle cells don't use much energy, they don't need very many mitochondria. (Why would you light every fireplace in your home if it wasn't very cold?) Now as those your with fireplaces know, you can't just light a log on fire. You need to have some kindling to start that log burning (i.e. newspapers, twigs, wood chips, and the like). Our bodies use sugar as kindling. To make sure that we always have a supply of kindling available, our muscle cells store the sugars as glycogen which gets broken down into glucose. When a muscle cell needs some energy it says to the body, "Hey, give me one of those fatty acid (fat) molecules floating around in the blood stream, and I'll mix it with one of my glucose (sugar) molecules." Then it sticks the two in the mitochondria and lights the fire. If the human starts to exercise, the muscle cell suddenly needs more energy to keep going. It screams out to the body, "Hey, I think we need some more fatty acid molecules to burn down here." Of course, the body, being stingy with its fat reserves, doesn't want to give up its precious fatty acids, so the muscle cell is forced to continue to work without it's primary source of fuel. After all of the muscle cell's fatty acids supply is used up, it needs to find something else to burn, but all it can find is kindling (sugar), so it burns that. Unfortunately, sugar doesn't burn as efficiently as fat. When sugar burns all by itself, it only burns partially. What's left over is lactic acid. (Lactic acid is the stuff that makes your muscles burn when you're lifting weights and leaves you sore the day after a big workout.) After awhile, the muscle cell starts nagging the body again, "We really need some fatty acids here!" Eventually the body gives in and says, "Fine you want fatty acids? Here's your fatty acids." The body releases a huge flood of fatty acids, and the muscle cell quickly grabs onto them (just as every other cell that needs them gets a hold of them ). The muscle starts burning fat and sugar together again (eliminating the terrible lactic acid), and they all lived happily every after. The Story of Metabolism Part 2: The Exercise Continues The happy little muscle cell is just doing its thing one day, when the human starts exercising again. The whole process repeats, but today they all get a bit smarter. After the human exercises, the muscle cell and the body have a meeting. They decide that if this ordeal happens again, the body should release that flood of fatty acids a bit sooner than it did before because they don't want to go through that whole lactic acid deal again. They also decide to build up some extra blood vessels near the muscle, so the cells can have better access to the fatty acid molecules when they are released. On the third day, the human exercises again! Their plan works, but not well enough. They decide to release the flood in even less time and add a few more blood vessels. The muscle cell has another idea though. it decides that it can burn more fatty acids to make more energy if it has more fireplaces to burn the fatty acids in, so it orders up some extra mitochondria. The process repeats every time the human exercises. Eventually, the muscles are just filled with blood vessels, ensuring that all the cells will have excellent access to the fatty acids. The body releases the fatty acid flood sooner and sooner until finally it just releases it when the human even thinks about getting ready to exercise. The extra little mitochondria keep burning fat and sugar even when the human isn't exercising. The human becomes a 24 hour fat burning machine. (So remember, when you exercise, you're goal isn't to burn fat, it's to become a fat burning machine!)
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Copyright © 2001 Kristen Helmer |