What's one of the things about body fat that most people believe is true? How about this one: Muscle burns more calories than fat. While yes, our skeletal muscle does burn more calories every day than our body fat does, it's not as notable as you may think. It's really a surprisingly negligible difference when you're talking about how many calories are consumed for energy while you're just sitting around. The calories the body needs just to take care of its survival is called our resting energy expenditure, and when you're not exercising or expending your energy, your fat tissue burns two calories for every pound of your total body weight — but your skeletal muscle burns just six calories per pound [source: McClave].
What does consume the most energy every day is the brain. It gobbles up about 20 percent of the calories you burn, which is amazing when you consider the brain accounts for only about 2 percent of your body's total weight [source: Ray.] And despite the fact that they make up only 5 percent of the body's weight, the heart, liver and lungs combined consume the most energy, about 50 percent [sources: McClave, Ray]. So while muscle tissue burns more calories than fat, it's still a relatively small percentage of the body's overall calorie consumption.
What are other common beliefs about body fat? That muscle weighs more than fat? That, inevitably, the mid-life spread will get us all? As the majority of Americans, 69 percent, are overweight, and more than 35 percent are considered obese, maybe it's time to bust some myths about body fat — from its relationship with our hormones to the best way to lose it.
All Fat Is the Same
It's long been thought that adults have just one type of fat: the white/yellow, lumpy fat that gets blamed for spare tires. White fat stores any extra calories you eat for your future energy needs, but if you have too much of it, it's also associated with health problems such as insulin resistance and heart disease. As it turns out, though, it's not the only kind of fat in our bodies.
Humans also have brown fat, located in deposits in the neck and around collarbones. Although people have an abundance of it when they're kids, we have far less as adults, and some of us don't have any at all — studies have found that thin people are more likely to have brown fat than people who are overweight or obese, but no one is sure why that is, at least not without further investigation [source: Doheny].
Brown fat doesn't behave the same way as white fat. Brown fat gets its color and name from its iron-rich mitochondria, and scientists describe its function as more similar to muscle than how we've always thought fat behaved. For instance, brown fat is a good insulator because it burns white fat for energy. Burns? Yes. While white fat stores energy and is associated with weight gain, brown fat is thermogenic. It burns energy for heat and may play a role in weight loss. Under the right circumstances, an average healthy person at a healthy weight could burn as many as 250 calories in a single day just because of their brown fat stores, and as it turns out, all that's needed is a cold environment to activate brown fat. The bigger our brown fat stores, the bigger the benefit; just 2 ounces (56 grams) of brown fat activity could burn as many as 8 to 9 pounds per year [sources: Cypress, Raloff].
Cellulite Is Caused by Impurities and Toxins
Cellulite is that dimpled skin that develops usually around our thighs and butts, and maybe our hips and knees, and although many of us may think it's unsightly, it's harmless. It's not caused by toxins or impurities, and despite all the claims about solutions from lymphatic drainage to caffeine cream treatments, there is no cure for it because it's really nothing more than fat.
Everyone has the potential to develop cellulite — overweight, thin, young, old, men, women — although it mainly affects women. As many as 90 percent of women (and only 10 percent of men) develop cellulite, which is thought to be caused, at least partly, by genetic predisposition and declining estrogen levels. Diet and a sedentary lifestyle also play a factor in whether a person will develop cellulite, as does the structure of the connective tissue below the surface of the skin [source: Harmon]. This connective tissue is a framework of fibers made of collagen that connects skin and muscle. Cellulite appears when the fat deposits accumulating below the skin bulge through that framework.
Restricting Calories for Weight Loss is Good; Drastically Restricting Them Is Even Better
Drastically cutting the number of calories you eat may sound like a fast way to lose a few pounds, and it can be, but in the long run, it's bad news. In fact, there's a high likelihood that crash dieters who restrict the number of calories they consume to 800 or fewer per day will, in addition to being hungry, regain the weight they've lost within the first six months after giving up the diet.
Eating too few calories, less than 1,200 per day, doesn't just cause fat loss; it also causes muscle loss. And in the long term, severe calorie restriction can cause anemia, dizziness, headaches, low blood sugar, liver and kidney problems, and a host of other complications. It also triggers the body to conserve its potential energy (that means it hoards calories and uses them slowly). Crash dieters often find that their body fat percentage ratio is worse after dieting than before they started cutting calories [sources: Hensrud, Zelman].
Your Body Fat Can't Be Too Low
Your body fat conserves your energy, keeps you warm, cushions your organs and allows the body to maintain the basic functions that keep you alive. Your ideal body fat percentage will be different from that of other people. How much each person has depends on some things that can't be changed including age, bone structure, biological sex and genes, in addition to things we can change, such as whether we lead an active or sedentary lifestyle.
Too much body fat is associated with chronic disease such as type 2 diabetes, cardiovascular disease and some cancers. But the pendulum can swing too far in the other direction. You can have too little body fat, which poses a different set of health issues.
A body needs to have a certain percentage of fat in order for it to be able to function: Women need about 13 percent body fat and men about 3 percent. This is your essential body fat and doesn't include any fat stores. In addition to essential body fat, a body also needs storage fat. On average, 15 percent of a woman's body weight should reflect her storage fat, and that number is about 12 percent for men.
When body fat drops lower than 14 percent for women and 8 percent for men, health risks increase, including everything from reproductive dysfunction (such as amenorrhea in women), dehydration, starvation, loss of muscle tissue and premature osteoporosis, in addition to complications such as organ and nerve damage [source: UPDR].
Cardio Is the Only Way to Lose Fat
Doing cardiovascular (aerobic) exercise such as walking, biking or — everyone's favorite — the Stairmaster is good for you. It reduces heart disease risk by keeping the heart and lungs in shape, helps meet weight loss goals and keeps your whole body healthier.
But if your focus is to burn the most fat, it's not actually the best choice.
You may think of weight training (also called strength or resistance training) as the way to build muscle mass, which it is, but weight-bearing exercises have also been found to be better at burning abdominal fat than cardio exercise alone. Two 15- to 20-minute resistance training sessions every week have positive effects on everything from your resting metabolic rate to your blood pressure and how well your body handles insulin — and it's been found to be better at keeping the waistline from expanding than cardio alone. Combine the two for the best results [sources: ACSM, Winett].
Spot Reducing Can Happen
Unlike building muscle by targeting different muscle groups, such as abs or glutes, when you lose fat you lose it systemically — that means you lose it all over, not just in one place. Crunches may tighten the abdominal muscles, but those crunches won't specifically reduce your abdominal fat. The reason? Incompatible fuel. Fat cells store triglycerides. But when your body calls upon its energy reserves to be used as fuel, those triglycerides need to be converted into a fuel that your muscles are able to use — glycerol and fatty acids — and those can enter the bloodstream from anywhere fat is stored in the body, mid-section or otherwise [source: Perry].
As You Age, Fat Gain Is Inevitable
Age-related weight gain is typically centered around our mid-section; it's abdominal fat (called visceral fat), and it begins to settle in around the time you turn 40 [source: Melone]. It's true that as people age, metabolism slows down and the amount of fat in the body increases, but gaining weight because of those changes isn't inevitable. You do need to kick things up a notch to stave it off, though. The trick? Weights.
Aside from a sensible diet, adding weight training to a cardio-centric exercise routine will help combat age-related loss of muscle mass, called sarcopenia. Combining weight training with cardiovascular exercise also increases bone density, balance and flexibility. And weight training has been found to be better at burning stubborn abdominal fat than aerobic exercise, especially as you age. Plus, the more muscle mass you maintain as the years go by, the lower your chances of dying prematurely [source: Srikanthan].
Fat Cells Only Store Fat
Body fat has two primary functions. It will come as little surprise that our fat cells store lipids for future energy needs, but did you know that body fat, which is adipose tissue, is considered an endocrine organ? Fat cells are biologically active, and they produce hormones such as leptin, which influences our appetite, and adiponectin, which controls how well the body regulates glucose and breaks down fats.
There's a bit of a chicken-and-egg scenario when it comes to our body fat, though, as we know that an excess or lack of certain hormones can cause us to gain or lose weight, but our weight also directly affects the amounts of these hormones in the body. If the wrong messages are sent throughout the body, there's a risk of insulin resistance, elevated levels of lipids in our blood (hyperlipidemia) and vascular inflammation.
Turn Fat Into Muscle, Muscle Into Fat
You've probably heard that if you don't exercise or work out, your muscle will turn to fat. If that was a concern, stop worrying about it; it's not possible. Nor can fat turn into muscle. Fat and muscle are different types of body tissues — fat is adipose tissue, and muscle is protein — and you can't change one type of tissue into another. While it may appear that you're turning fat into muscle or muscle into fat when you get slack or get serious about exercise, that appearance is only because fat is less dense than muscle, which means an ounce of fat takes up more space inside the body than an ounce of muscle does.
So if fat doesn't turn into muscle, where does it go when you lose weight? Does it just shrink? Does it melt into energy that you burn off? Researchers studying this biochemical process tracked fat molecules to figure out exactly where fat goes when you lose it, and they use a chemical formula to calculate the process: C55H104O6 + 78O2 → 55CO2 + 52H2O + energy. As it turns out, mostly, we just exhale it. If you were to lose 22 pounds (10 kilograms) of body fat, 20 pounds (9.4 kilograms) would be released as carbon dioxide (CO2) when you breathe; the remainder would become water that is excreted in our urine, sweat or tears [source: Meerman].
Eating Fat Makes You Fat
While it's true that some fats are worse for us than others — we're looking at you, LDL cholesterol-raising, man-made trans fats — it's not true that eating dietary fat makes us fat. Calories are what make us fat. You gain weight when you eat more calories than you burn, whether those calories come from fat, carbohydrates or protein.
Regardless of whether a fat is saturated or unsaturated, healthy or unhealthy, all dietary fats contain about the same amount of calories. Fats give you the most energy when you eat them because they're more calorically dense than protein and carbohydrates, ounce per ounce. While there are about 112 calories in one ounce of protein or carbohydrates, one ounce of fat contains about 252 calories [source: Youdim].
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Author's Note: 10 Myths About Body Fat
I didn't end up using this in my final draft, but it's cool, so I'm going to share it here. Did you know that the average adult brain consumes about 12 watts each day, just one-fifth of the power a standard 60-watt bulb needs? That's right: 12 watts. That's the same wattage your iPad power adapter uses.
Let's look at how that math works out. We're going to assume that your body's resting metabolic rate — that's the energy your body needs to take care of just the vitals while you lounge about — is 1,300 kilocalories. That's just about 15 small calories (also called gram calories) every second in a 24 hour day. But we can't convert small calories straight to watts, so let's first turn them into joules: 1 small calorie is roughly 4 joules, which then means that 15 small calories per second equals 60 joules per second. And 60 joules per second is the equivalent of 60 watts. Knowing that the brain consumes 20 percent of our total resting energy, 20 percent of 60 watts equals 12 watts.
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