How Does Your Body Burn Fat?



Burn Two


Digestive metabolism, or thermic effect of food (TEF): Simply digesting food—turning carbs into sugar and turning protein into amino acids—typically burns 10 to 15 percent of your daily calories. Digesting protein burns more calories than digesting carbohydrates or fat—about 25 calories for every 100 consumed. Digesting carbohydrates and fat burns about 10 to 15 calories for every 100 consumed.

So pause a moment to think about this: Between 70 and 85 percent of the calories you burn every day come from either eating or just hanging around doing nothing.

So, what about the other 15 to 30 percent?

Burn Three

Exercise and movement metabolism: This part of your metabolism includes both workouts at the gym and other more enjoyable physical activities (we call this exercise-activity thermogenesis, or EAT) along with countless incidental movements throughout the day, like turning the pages of this book and twiddling your thumbs (that's called non-exercise-activity thermogenesis, or NEAT).

So, here's an interesting question: Why is it so hard to lose weight just by exercising? Why are there so many fat people in the gym? The answer is simple. Exercise only targets 15 to 30 percent of your fat burn. Up to 85 percent of the calories you burn in a given day have nothing to do with moving your body!

So, skip the gym, right? Not quite.

Why the Fatter You Get, the Fatter You'll Get


Fat doesn't just show up at your door one day, rent a room, and live alone quietly. Fat loves company. Fat's organizing a cocktail party where nobody ever goes home and everyone hangs out around your midsection. The more fat you open the door to, the harder it will be to stop even more fat from inviting itself in. Here's why:

Your BMR, or resting metabolism—the body system that eats up the majority of your daily calorie burn—is determined by two things: your parents, and the amount of fat versus muscle in your body. And while you can't choose who your parents are (if you could, there would be no children on The Real Housewives of New Jersey), you can improve the other part of the equation and turn your resting metabolism up a few notches.

Problem is, fat plays its own role in the metabolic game, and it's literally working to slow down your calorie burn. See, the term "fat and lazy" is pretty accurate from a scientific standpoint. Fat is lazy, on a metabolic level. It barely burns any calories at all. For your body to support a pound of fat, it needs to burn a mere 2 calories a day. Muscle, on the other hand, is very metabolically active.

This is key (and why muscle is your BFF): At rest, 1 pound of muscle burns three times as many calories every day just to sustain itself—and a lot of those calories that muscle burns off come from fat's storage units. That's why fat hates muscle (and why you should love muscle), because muscle is constantly burning fat off.

So fat actually fights back, trying to erode muscle and fit more of its fat friends into your body. The real villain in this internal battle happening right now, in your body, is a nasty character called visceral fat. Visceral fat is the kind that resides behind the abdominal muscles, surrounding your internal organs (viscera).

And visceral fat works its mischief by releasing a number of substances, collectively called adipokines. Adipokines include compounds that raise your risk of high blood pressure, diabetes, inflammation, and heart disease. Visceral fat also messes with an important hormone called adiponectin, which regulates metabolism. The more visceral fat you have, the less adiponectin you have, and the lower your metabolism. So fat literally begets more fat.

A study published in the Journal of Applied Physiology showed that those biologically active molecules that are released from visceral fat can actually degrade muscle quality—which, again, leads to more fat. The solution?

More Muscle


After age 25 we all start to lose muscle mass—a fifth of a pound of muscle a year, from ages 25 to 50, and then up to a pound of muscle a year after that—if we don't do anything to stop the decline. And on top of a slumping metabolic rate, loss of muscle strength and mass are empirically linked to declines in the immune system, not to mention weaker bones, stiffer joints, and slumping postures. Muscle mass also plays a central role in the response to stress. And further research is expected to show measurable links between diminished muscle mass and cancer mortality.

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