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Body fat, or the more technical term adipocytes (adipo means fat and cyte means cell), is found in many places around the human body and mostly underneath your skin, what we call subcutaneous fat. There is also some on top of your kidneys, inside your liver, and a small amount in your muscle tissue, which we call visceral fat.
An adult male often tends to carry his body fat in his chest, abdomen, and buttocks. An adult female tends to carry her fat in the breasts, hips, waist, and buttocks.
The main role of body fat is to serve as a type of energy storage facility. Up until the mid-nineties, it was thought of strictly as a passive place for us to store energy for the hard times, the times when our ancestors’ hunt didn’t go well (or the weather was poor) and there wasn’t enough food available. This turned out to be incorrect and it does have other uses but it is exceedingly good at storing energy.
A single pound of fat contains roughly 3,500 calories of stored energy.
A single pound of fat contains roughly 3,500 calories of stored energy. Assuming you could burn 100% body fat as fuel, this is enough energy for a 150-pound person to trudge about 35 miles. And that is only one pound of fat and most of us have a lot more than that to spare.
So how does the body use fat and what else is it for? Let’s take a look.
What burns the most energy?
Even though it just sits there, on top of our sinuses, our brain uses about 20 percent of the calories we burn in a day, despite the fact that it only makes up about two percent of the body’s total weight. Now, I know what just crossed your mind: Yes, making yourself think harder, or solving a really complicated math problem, does indeed increase the glucose uptake of the brain, but not for very long. So thinking hard is not your best weight loss plan and mathletes may need to do more than math to stay fit.
Interestingly, the average adult brain consumes about 12 watts of energy in a single day. That is about one-fifth of the power a standard light bulb needs or the same amount of wattage that your iPad uses. So it turns out we have more in common with our devices than we thought.
Your organs, like your heart, lungs, and liver make up five percent of the body’s weight but together consume about 50 percent of your daily calories. Now, we know how to give our heart and lungs a good workout but if you can devise a way to exercise your liver, let me know. That is a million dollar exercise craze right there!
We’ve all heard that muscle burns more calories than fat and yes, that is true, but sadly it is not as exciting and impactful as you may think according to a paper on the energy needs of the body.
Your fat tissue burns two calories for every pound of your total body weight and your skeletal muscle burns six calories per pound. Three times as much isn’t anything to sneeze at. Still, relying on your biceps to burn off that extra piece of pie may be a better weight loss strategy than cracking a Sudoku puzzle, but not by much.
But there is some good news. We have more than one kind of fat in our body. We have white fat and brown fat. The primary type of fat cell in our body is called white adipose tissue (WAT), so named because it is a milky yellow. The other type of fat is called brown adipose tissue (BAT) which is actually reddish orange, and turns out to be a lot more interesting than WAT.
What is brown fat?
Brown fat, which is generally located in the neck, shoulders, and around collarbones, doesn’t behave the same way white fat does. We are born with a bunch of it and we tend to keep it while we are children but we lose more and more of it as we age. Interestingly, studies have found that thin people are more likely to have brown fat than people who are overweight or obese, but the researchers don’t know why that is.
What is known is that 50 grams of this metabolically-active brown fat can burn 300 to 500 calories a day. That is roughly the equivalent of jogging for 30 minutes or swimming for 45.
Brown fat gets the color from its iron-rich mitochondria, and scientists believe that it behaves much more like muscle than it does like fat. Brown fat actually burns white fat for energy. So, while white fat stores energy and is associated with weight gain, brown fat is thermogenic (increases the heat in the body) and burns white fat’s energy for heat.
In a cold environment, which activates the brown fat, an average person with a healthy BMI could burn up to 250 calories per day because of brown fat. The bigger the brown fat stores, the bigger the white fat thermogenesis.
How much fat do we need?
It is important to remember that your ideal body fat percentage will be very different than your friends.
It is important to remember that your ideal body fat percentage will be very different than your friends. How much body fat we each have depends greatly on things that are beyond our control. Age, bone mass, gender, and genes play a large role in how much or how little body fat we will carry.
While carrying too much body fat is often associated with health issues like Type 2 diabetes, cardiovascular disease and even some types of cancer, carrying too little body fat can also be an issue.
The human body actually needs to have a certain percentage of body fat for it to be able to function properly. For women, 14 percent body fat seems to be the low end of healthy and for men that number can be as low as eight percent based on several epidemiological studies of the general population. Body fat percentages for optimal fitness and for athletes tend to be lower than optimal health values because excess fat may hinder physical performance and activity.
When body fat drops lower than 14 percent for women and eight percent for men, health risks increase, including everything from reproductive dysfunction (such as amenorrhea in women), chronic dehydration, sarcopenia (loss of muscle tissue), osteoporosis (loss of bone density), and potentially even organ and nerve damage.
Essential body fat is often referred to as the amount of fat considered necessary to keep your body functioning efficiently. It’s stored in small amounts in your organs, muscles, bone marrow, and central nervous system. Along with your essential body fat, your body also needs storage fat. This is the adipose tissues that accumulates where we want it the least.
Fat cells store lipids for future energy needs, but it is also considered an endocrine organ, according to The Journal of Clinical Endocrinology & Metabolism. That means your fat cells are biologically active and besides adipocytes, adipose tissue contains connective tissue matrix, nerve tissue, stromovascular cells, and immune cells.
Adipose tissue not only responds to afferent signals from traditional hormone systems and the central nervous system but it also expresses and secretes factors with important endocrine functions. These factors include leptin (which control appetite), other cytokines, adiponectin (which regulates glucose and breaks down fats), complement components, plasminogen activator inhibitor-1, proteins of the renin-angiotensin system, and resistin.
What is the best way to burn fat?
Doing what is commonly known as cardio or aerobic exercise (walking, biking, jogging) is good for you because it reduces heart disease risk, but it’s not the best choice if your focus is to burn the body fat. Sure we have all heard of the “fat burning zone” but it is confusingly named and poorly understood.
You may think of weight training as a way to build muscle mass but it has also been found to burn fat more effectively than cardio.
You may think of weight, strength, or resistance training as simply a way to build muscle mass, but weight-bearing exercises have also been found to burn abdominal fat more effectively than cardio exercise.
In just two 15-20 minute heavy lifting sessions per week you can have positive effects on your resting metabolic rate, your blood pressure, and insulin sensitivity. Which all adds up to being a better way to keep that body fat weight off.
My advice would be to combine the two and get the best of both worlds and also throw in this little morning routine. I know it has been mentioned in a previous Get-Fit Guy post but this three-fold combination can really speed things up:
- Consuming 100-150mg of caffeine from green tea or black coffee on an empty stomach.
- A 30-minute morning, aerobic, fasted, conversational workout with the caffeine in the system (the caffeine mobilizes fatty acids from adipose tissue).
- Followed by a hot-cold contrast shower by alternating between 10 seconds of warm water and 20 seconds of cold water, 10 times through (to activate that brown fat’s thermogenesis).
Where does fat go?
When you go on vacation or take a break from working out you probably worry that your muscle will turn into fat. Well, good news—that is not possible. But sadly, on the other hand, fat also can’t turn into muscle. The truth is that fat and muscle are different types of body tissues (fat is adipose tissue, and muscle is protein) and one can’t change into the other.
When you slack off on your workouts and let your diet fall apart it may look like your muscle is turning to fat but that is only because fat is less dense than muscle. An gram of fat takes up more space inside the body than a gram of muscle does.
So where does fat go when we lose it? Well, researchers studying this biochemical process followed fat molecules through the body to hone in on where fat goes when you lose it. Surprisingly we exhale the majority of 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 (hopefully not) tears. So all that hot yoga, it turns out, is not burning as much body fat as we had hoped. You are better off breathing heavy than sweating heavy but I don’t advocate doing that in a small room full of people in tight pants.
I hope you enjoyed this body fat adventure and have a newly found respect for how your body makes, uses, stores and exhales your adipose tissue. It’s easy to write body fat off as evil or at least unwanted but it does play some interesting roles in our life and health and who knows, it could keep you alive one day or perhaps even power your iPad.