I guess I should have Googled it BEFORE I started this topic. I found this answer at the Mayo Clinic website:
Quote:
When you consume fewer calories than your body needs, your body turns to fat for energy. Your fat cells (triglycerides) provide the fuel for this energy.
Through a series of complex metabolic processes, triglycerides are broken down into two different components — glycerol and fatty acids — which are absorbed into your liver, kidney and muscle. Here, these components are further broken down by chemical processes that ultimately produce energy for your body.
The heat generated through these activities is used to help maintain your body temperature. The waste products that result are water and carbon dioxide. You excrete water primarily in urine and sweat and carbon dioxide in air exhaled from your lungs.
Though that's kind of confusing.
Last edited by goldferris; 01-31-2010 at 02:52 PM.
Every pound of fat on our bodies is made up of 3500 calories of stored fat. The fat is stored in fat cells and under a microscope, it looks an awful lot like liquid Crisco oil.
When we create a calorie deficit in our bodies by eating fewer calories than we burn off through exercise and daily activity, our bodies are forced to go into their supply of stored fat and use those calories to make up the calorie deficit. Those stored fat calories are metabolized for energy, just the way your car burns gas and your body uses the food you eat for energy.
So in a nutshell, when we eat fewer calories than we burn in our day, our body uses its fat reserves for energy. Does that make sense?
Yeah, that makes more sense than what the Mayo Clinic said. Thanks Meg! It's just weird to think that my body can essentially liquify and use-for-energy 5 (or more) pounds of icky fat in one week.
Mother Nature actually created a pretty clever system to keep us from starving by letting our bodies store fat for times of famine. Too bad that the world we live in today has way too much food, not too little!
When and if you take physics class, all these questions start answering themselves. Before I took physics, there's no way you could explain to me about the energy from the sun being used to power up your electric tooth brush or how the energy of footsteps could be harnessed and reused to power a car.
Basically, everything you do requires energy. Moving your fingers to type, your heart beating to push blood around your body, sweat dripping our your pores, blinking, breathing, laughing, digesting, seeing, hearing, feeling, day dreaming... everything your body does can only be done if it's supplied with a source of energy. (Un)Luckily for us, our bodies are so good at storing energy to keep us from running out of gas.
So the pounds get out of storage and are put to work to keep your body running smoothly. Remember what Newton said: Energy is neither created nor destroyed. So the calories from the food (calories are a source of energy) are transferred into you running, and then the energy that your body makes is released into the sound of your feet hitting the ground, your body working up a sweat, and getting hot.
Gas is for cars as calories are for people. Just as your car loses gas through the energy of driving, heating the vehicle, wiping the windshields and all of that, we lose our energy source the same way.
Physics is one of the few things I could never wrap my head around. I am a math person and love algebra, and of the sciences I like chemistry the best. But physics? All of that flies right over my head.
Thanks for explaining, Wild. You are a smarty, that's for sure.
Think of our bodies as steam engines which are powered by energy in the form of steam. Where did they get the steam? By burning coal. Now think of fat as our coal. We need energy to do EVERYthing, and we get that energy from burning fat. If you have a big pile of coal and burn it, it "disappears." If you burn a pound of fat, it disappears. It's not technically disappearing, really, it's just a chemical reaction which changes the form and releases energy.
Everything in your body is bound to water, so a good deal of the weight you lose will always, technically, be "water weight."
I've read that, in "normally lean" people, the body will actually up the calorie expenditure to match the calorie input, in the form of simple heat. This could explain those people who can eat 5,000 calories a day and never gain a pound (like my husband). Supposedly, these people's bodies will just "burn" all the excess off.
There's also a theory that some "normally obese" individuals don't have a mechanisms even close to this one. In fact, again supposedly, their bodies show a preference for fat storage rather than metabolism. The really brutal implication of this (which has been shown in lab rats) is while the body "loses weight" it eats away at the organs and other tissues in order to sock away more energy in the fat cells.
Yuck. Anyway, fat metabolism isn't always as cut and dry as "eat fewer calories," as there are so many biochemical reactions that go into fat storage and metabolism. Insulin causes fat storage, while adrenalin (among others) causes fat metabolism. As your blood sugar gets lower, your cells will tap into fat stores to keep energy constant. Blood sugar goes up, though, and the insulin is released, fat stores are put on lock down and the circulating glucose is trapped wherever possible.
If your blood sugar is low, your cells will release their fat stores, in the form of triglycerides, for use elsewhere. These are broken down into fatty acids and are taken up by other cells. As soon as your blood sugar goes back up, though, the fatty acids are reassembled into triglycerides, which can't be absorbed into non-fat cells, and either float around your blood stream (bad) or are sent back to fat cells. Since the newly packaged triglycerides can't fit into the cells, they have to rely on the circulating glucose, probably because glucose will do more damage to cells in the short term than triglycerides.
As to where it specifically goes, most is simply burned off as energy (heat) once it's used as fuel for the cells. It's broken down into particles, pieces are used to run the cells and the rest is either metabolically incinerated, recycled or expelled.
Thats a smart question! It's been a while since biochem but the way overly simplified answer is that everything interacts chemically to produce a derivative of glucose which then reacts with the oxygen we breathe to produce water (which is thenexcreted in urine/sweat etc), carbon dioxide (which is exhaled), and heat/energy to fuel your daily activities. In other words, your body breaks down its' fat cells, turns them into glucose which then reacts with O2 to turn into water and CO2 and heat.
I guess that's confusing. it doesnt officially turn fats into glucose...just into a derivative of glucose... that then gets fed into the same metabolic "machine" that breaks down glucose.
It's a complex process and also explains the idea that just because you have a calorie deficit one day doesn't mean that the fat is gone instantaneously. It may take a little while for the engine to chug along, need the fuel and burn it.
And as others have said, when you lose 1 or 2 pounds in a week, you aren't only losing the fat you want to lose. You're losing lots of water as part of the process and some lean muscle mass too (another good reason to try to build that back up with weight training!)
My nutritionist told me that our fat cells never actually leave our bodies, they just shrink. Once you have a fat cell, it is always there. You can develop new ones, and they can shrink but will still be there. That is why an overweight person that loses weight is more apt to gain it back... the cells are already there.
Where Does it Go?
Anyway, fat metabolism isn't always as cut and dry as "eat fewer calories," as there are so many biochemical reactions that go into fat storage and metabolism. Insulin causes fat storage, while adrenalin (among others) causes fat metabolism. As your blood sugar gets lower, your cells will tap into fat stores to keep energy constant. Blood sugar goes up, though, and the insulin is released, fat stores are put on lock down and the circulating glucose is trapped wherever possible.
