Think of body fat as “potential energy.” Calories, which you consume through the food you eat, are fuel. Once these calories make it into your bloodstream, your body burns the calories. Your muscles, digestion, breathing, brain function, growing hair, etc. Basic being-alive stuff. Now, sometimes we consume more calories than our bodies are prepared to burn. When that happens our bodies say, “I don’t need all this energy right now. I’d better save it, in case I need it later.” And so the miracle of fat begins.
Your body then takes these free calories and packages them into cells of fat. So, if calories are car fuel, think of fat cells as rubber balloons filled with car fuel. They expand as they collect more fuel, and they shrink when you use some of the fuel.
It undergoes a chemical conversion so that it stores the energy more efficiently. It’s kinda like a .ZIP file; it makes the energy more compact and storable, but makes the content itself harder to access. When it’s time to pull some energy out of the cells, another chemical conversion takes place to turn it back into usable energy.
So, when you lose fat, where does it go? Most people don’t really know. Just like your car’s engine turns fuel into heat and exhaust, your body utilizes a similar process.
The mitochondria (cellular energy centers) in your muscle or liver cells pull some of the fat (stored as triglycerides) from within your fat cells and put it through a metabolic process. This converts the fat into heat, carbon dioxide, water, and ATP (adenosine triphosphate). Let’s break those down.
Heat: You know how you, being a warm-blooded mammal, keep your body temperature right around 36.5 degrees Celsius pretty much all the time? Your body does this by burning calories. When you’re cold, you burn more calories to keep yourself warm.
ATP: We need ATP for muscle function. Our primary source of immediate energy is produced when we break a phosphate molecule off the ATP. It makes a little explosion of available power in your muscles. Then it becomes ADP, and it can’t be used again until it picks up another phosphate molecule. It carries fuel to your muscles.
Carbon Dioxide: Whenever you burn anything (see heat, above), it gives off carbon dioxide. It’s true with fuel, and it’s true with body fat. The carbon dioxide will travel through your bloodstream until it returns to your lungs to be exhaled out.
Water: Fat typically feels kinda wet to the touch, right? That’s because there’s some water in it. You’ll pee it out.
So that’s where the weight actually goes when you lose it.
Remember how we said fat cells were like balloons? When you lose weight, you are letting some of the stuff out of the inflated balloons, thus shrinking the fat cells. You can shrink them until they’re practically empty, but they will always be there—waiting to be refilled.
More bad news: Fat loves to hang out with more fat. Because fat and muscle are enemies (we’ll get to that in a minute), your fat cells are trying to erode your muscle cells. Worse, while most fat resides under your skin, the more dangerous fat actually accumulates around your internal organs (this is why belly fat is more medically problematic than fat in other areas). This fat, called visceral fat, is metabolically active, and it secretes biochemicals that increase your risk of heart attack, stroke, liver failure, diabetes, and high blood pressure. Additionally, visceral fat inhibits a very important hormone called adiponectin, which regulates metabolism in your body. In other words, the more visceral fat you take on, the slower your metabolism will be, and so the more easily you take on more fat. It’s a tough cycle to break
What do fat cells store?
If cells were personified, each fat cell would be an overbearing grandparent who hoards. They’re constantly trying to make you eat another serving of potatoes, and have cabinets stacked with vitamins they never take.
Like that grandparent, your fat cells are always trying to store stuff. Fats, Vitamins, Hormones? You bet. Random pollutants and toxins? Sure. Adipose tissue will soak all that up like an oily little sponge and keep it safe until you need it again. That’s the whole point of body fat—to store energy for you. When you lose weight, your fat cells start shrinking, releasing lipids and other fats into your bloodstream. These get broken down, and the smaller molecules exit via your urine or breath.
But adipose cells release all the other molecules they’ve hoarded, too. Including key hormones like estrogen, along with fat-soluble vitamins and any organic pollutants, that found their way into your bloodstream as you gained weight.
Adipose tissue’s tendency to store things is an unfortunate side-effect, because often we need those things to be circulating, not sitting around. Take hormones, for instance. Female body fat actually produces some of its own estrogens in addition to storing it. The more adipose tissue a person has, the more estrogen they’re exposed to. This is why being overweight puts you at an increased risk of getting breast cancer. Many types of breast cancer are caused by malfunctions in estrogen receptors, which are more likely to go haywire when more estrogen is around to stimulate them.
Vitamins pose the opposite problem. Adipose sucks up available fat-soluble vitamins—A, D, E, and K—and often doesn’t leave enough for the rest of your body. Studies suggest that obese people tend to suffer from vitamin D deficiencies because it’s all lurking in their adipose tissue. These vitamins can come back out as you lose weight, and as you decrease your body fat, you also allow more of your new vitamin D to stay in your bloodstream.
Fat is also a safe space to store pollutants and other organic chemicals that might otherwise pose a threat. Organochlorine pesticides build up in fat. So do the polychlorinated biphenyls in coolant fluids and other chemicals of environmental contaminants. These banned chemicals can get into your food supply in small quantities. They are stored in your fat, possibly because your body wants to sequester them away from your organs. Bodies don’t seem to store enough of these to become toxic, but the constant build-up leaves you vulnerable to exposure. And they do start to re-emerge when you lose weight.
Since you’re not eliminating all your body fat at once, this doesn’t seem to pose a problem for most people. You’re dumping toxins into your bloodstream, but you’re also eliminating them through your pee. There’s some evidence that certain pollutants can stick around in your body fat for years. So far it seems that natural toxin-elimination methods (also known as peeing) work well enough to get rid of them.
Safe or not, it’s best not to give your body a spot to stash all the hormones and vitamins it can hoard. Our bodies aren’t designed to hold onto excess body fat and stay healthy—that’s why obesity is a risk factor for so many diseases. Getting rid of fat storage is just another reason to try and cut down on your own adiposity this year. Letting someone shame you into thinking you don’t look the way you should is not a wise reason to lose weight, but doing it to be healthier usually is.
Just think every time you lose a kilogram of fat, you’ve also detoxed yourself without ever having to do one of those terrible juice cleanses (which, by the way, do not work). You’ve used the power of your own body’s filtration systems to get rid of them—and it will thank you for it.
Calories In vs Calories Out?
Body fat is stored calories, so, the widely-known broad-stroke method for losing weight is this: Make sure you are burning more calories than you are taking in. Do that and your body will begin to pull those calories out of your fat reserves. There’s a significant amount of nuance, but for the most part, that’s true. But how exactly are those calories burned?
There are three categories of processes responsible for you metabolic burn. 60 to 70 percent of the calories you burn in a given day are burnt just by being alive. That’s with no movement at all. It’s called basal metabolic rate (BMR). Another 10 to 15 percent is accomplished by the simple act of digesting your food. That’s between 70 and 85 percent—without so much as lifting a finger. That last 15 to 30 percent comes from physical activity.
What’s the takeaway? 60 to 70 percent of your caloric burn comes from your resting metabolism. Doesn’t it make sense to start with the biggest piece of the puzzle? It does!
How can we turn up the internal flame of our metabolism?
The simplest answer is by adding muscle. Muscle tissue, at rest, burns two to three times more calories than fat tissue does. If fat burning is your goal, then weight-bearing, muscle-building exercises will likely yield better results than cardio. Not because it burns more calories while you’re working out. Because it turns up your metabolic flame so that it burns more calories all the time.
Remember, 10 to 15 percent of your metabolic burn comes just from digesting food. If you want to push that higher you can add more lean protein to the mix. Digesting protein burns two to three times as many calories as digesting carbohydrates or fat. Any calories consumed (be they from protein, carbohydrate, or fats) can be stored as fat. The body more readily stores fat taken in from fat consumed, rather than carbs or protein consumed. A balanced diet is important to keeping you healthy, and again—if you want to shed fat, keep the calories coming in lower that the calories you burn.
Lastly, there’s the exercise component (15 to 30 percent of your metabolism). So, that whole fat-burning zone and cardio zone on your treadmill? Technically, it isn’t wrong. When you exercise at a lower intensity, you are burning more calories that are pulled from fat. When you exercise at high intensities, more of the calories you burn come from more-readily available carbs.
You can burn your own fat if you can create a caloric deficit. You can create a caloric deficit much, much faster by engaging in high-intensity, interval-type exercise. It simply burns far more calories, so you’re getting a lot more bang (fat loss) for your workout buck. To say it another way: The slower, “fat-burning zone” pulls more calories out of the fat while you’re doing it. High-intensity stuff will burn more calories overall, which will result in more calories extracted out of your fat reserves over time, which will shrink them more. That, and high-intensity exercise, builds muscle better—just look at sprinters versus marathoners. And again, more muscle equates to a higher metabolism, and that equates to faster fat burning.