Busting the Great Myths of Fat Burning

By Tony Ryan and Martica Heaner

Your body burns either fat or carbs depending on the intensity of your activity. But when it comes to losing weight, calories are calories. You burn fat even when you're in couch-potato mode. Yet, a lot of misunderstanding prevails.

Get ready to break down some of the myths people have about burning fat:

Myth: The body completely shuts off one fuel source when it turns on the other.

The Truth: What has often been misunderstood by both exercisers and exercise instructors alike is that the body relies on both fat and carbs for energy all the time, albeit in different ratios. In fact, as you sit here reading, you may be burning about 50-60 percent fat and 50-40 percent carbohydrates. 

You're not using much of either, however, because the amount of calories you need probably amounts to about one or two calories a minute. If you were to get up and start jogging in place, your body would need to supply you with some quick energy to do so, so the metabolism ratio might shift to drawing upon more carbohydrates, say 70 percent, and less fat, say 30 percent.

If you were to continue jogging, then, in order to preserve the carbs (which can run out since you have limited stores in the body), your body would gradually shift its metabolism ratio again to say, 60 percent fat and 40 percent carbohydrates. From an energy efficiency point of view, it pays to be fit. The endurance athlete would be able to make the shift sooner, and his fat-burning percentage might be 65-75 percent.

However, in practical terms this is purely technotalk, and these ratios don't make a big difference when it comes to losing weight and decreasing your body fat. For the most part, athletes are often leaner not because they might rely on slightly more fat for fuel, but because they practice their sport two to three, or more, hours a day — this burns a lot of calories.

If you had the time, energy, and fitness level to work out three hours a day, being overweight would probably not be an issue. To lose weight, you need to burn more calories than your body consumes and uses every day. Exercise is one main way to burn a lot of calories. But when it comes to weight loss, what matters is how many calories you burn, not so much whether they are fat or carbohydrate calories.

Myth: Exercise done at a low intensity, such as walking, is better at fat burning than other high-intensity activities, like running or cardio activities where you push yourself very hard.

The Truth: In a strict scientific sense, these claims are true because working at a lower intensity requires less quick energy and a higher percentage of fat is burned. But you'll also burn fewer calories than you would if, for the same amount of time, you work out at a harder intensity (running versus walking). If you're trying to lose weight, even though a higher percentage of fat is being used, a lower total amount of fat is lost.

Whether increased fat burning will result in actual weight loss is dependent upon several variables, including the total calories burned (which include both fat and carbohydrate calories) and the total fat calories burned. If you do work at a low intensity, you need to increase the time spent exercising to burn more calories.

What matters most is the total number of calories burned. If you burned 250 calories every day from a short, fast jog, you'd see a bigger difference in weight and fat loss than if you walked every day for the same amount of time.

The number of fat calories you burn isn't that important, because even if you burn a lot of carb calories, these need to be replaced both by the carbs you eat in your diet and also within your body. Your fat stores will be broken down and transformed into carbohydrates when you need fuel. Even if you're burning lots of carb calories and less fat calories through exercise, your fat still inevitably gets used.

It boils — not burns — down to this: During the same amount of time you don't use more calories at lower exercise intensities. If you're trying to lose weight and you have only 30 minutes to work out, you would burn fewer calories walking at a moderate pace compared to walking at a fast pace.

Working out at higher intensities may cause you to burn a lower percentage of fat, but since you burn more total calories, you still use more fat calories.

Low- to moderate-intensity exercise can burn a significant number of calories over a period of time. If you aren't fit enough to push yourself to work at a high intensity, or you have a physical weakness that prevents you from doing so, you can still burn a lot of calories by doing low-intensity workouts for a longer period of time.

Myth: Running, cycling, or other cardio activities are more fat burning once you've been doing them for more than 15 or 20 minutes.

The Truth: Technically, once you've been exercising for 15 or 20 minutes, your body has made the shift to using a higher percentage of fat for fuel. But again, if you're trying to lose weight, it's about the total number of calories burned, not necessarily the fuel source.

For example, say that at rest you burn up to 60 percent fat. When you enter the initial phases of intense exercise, the ratio changes. You may now burn only 30 percent fat because your body is using quick-energy carbohydrates. Once the exercise is sustained, the body switches back to using a higher percentage of fat to fuel the movement (up to 75 percent fat).

In this aerobic phase of exercise, a higher percentage of fat is being used for energy. But if you aren't working out for a very long period, you may still burn more total calories and, therefore, more fat calories working out harder.

Put another way, if burning as many calories as you can is the best way to lose weight, even a dummy can figure out which activity of the following is going to give the best results (answer: jogging and sprinting), even though their fat-burning quota is on the low end of the ratio.

Activity	Calories Burned	Fat Percentage	Calories from Fat
Watching TV for 20 minutes	40 calories	60 percent	24 calories
Walking for 20 minutes	100 calories	65 percent	65 calories
Jogging & sprinting for 20 minutes	250 calories	40 percent	100 calories

How to Measure Your Body Fat Percentage

When assessing your level of fitness, it is helpful to determine your body composition — how much of your body is composed of fat and how much is composed of everything else. Your body composition is also called your body-fat percentage. If you score a 25 percent on a body fat test, this means that 25 percent of your weight is composed of fat.

You should consider your body-fat percentage in context with other health measures, such as your cholesterol levels, blood pressure, resting heart rate, and other gauges of fitness.

Although body fat testing has its limits, your results can give you great insight into how your fat-loss and exercise program is coming along. For example, a body-fat test can tell you that a 7-pound weight loss means that you lost 10 pounds of fat and gained 3 pounds of muscle.

Here’s a look at some methods of measuring your body fat:

• Pinching an inch: This body-fat test uses the skinfold caliper that pinches your skin, pulling your fat away from your muscles and bones. Typically, the tester pinches three to seven different sites on your body, such as your abdomen, the back of your arm, and the back of your shoulder. The thickness of each pinch is plugged into a formula to determine your body-fat percentage.
  Your tester should pinch each site two or three times to verify the measurement.
  
  
  • Taking your measurements: You don’t get a body fat percentage by taking your measurements, but you can use the numbers to keep track of inches lost (or gained, if you’re trying to pack on muscle), which can be motivating in and of itself. If you’re losing inches, chances are, you’re dropping body fat.
    Some common places to measure include across the middle of your chest, the center of your upper arm, the smallest part of your waist, the widest part of your hips, the widest part of your thigh, and the widest part of your ankle.
  • Getting dunked (underwater weighing): Underwater weighing is the most cumbersome method of body-fat testing, but it’s also the most accurate method that’s anywhere near affordable. You sit on a scale in a tank of warm water about the size of a Jacuzzi.
    Then you blow all the air out of your lungs and bend forward until you’re completely submerged. You stay submerged for about five seconds while your underwater weight registers on a digital scale. The result is then plugged into a mathematical equation.
  • Bioelectrical Impedance Analysis (BIA): For this method, you lie on your back while a signal travels from an electrode on your foot to an electrode on your hand. The slower the signal, the more fat you have.
    This is because fat impedes, or blocks, the signal. The signal travels quickly through muscle because muscle is 70 percent water and water conducts electricity. Fat, on the other hand, is just 5 to 13 percent water. Similar technology is used in body-fat scales and handheld gadgets that are less accurate than BIA.
  • Dual-Energy X-ray Absorptiometry (DEXA): Not only does this method measure how much fat you have, but it also determines where the fat is located on your body, a more relevant health indicator.
    Originally developed to scan bone density, DEXA is available at hospitals and in doctors’ offices; it usually requires a physician’s referral. You lie on a bed while low doses of two different X-ray energies scan your body from head to toe.
    
    

    How to Calculate Your Body Mass Index

    
    

    
    
    Your body mass index (BMI) is a way of relating your height and weight to estimate how fat you are. You can use a simple formula to determine your BMI.
    
    
    If you’re in the mood to pull out your calculator, follow these steps to determine your BMI:
    
    
    Multiply your height in inches times your height in inches.
    
    
    Divide your weight by the number you arrived at in Step 1.
    
    
    Multiply the number you came up with in Step 2 by 705.
    
    
    The result is your BMI.
    
    
    So what does your BMI mean? The National Institutes of Health (NIH) has issued the following BMI guidelines:
    
    
    BMI of 19 or below: You’re considered underweight.
    
    
    BMI between 19 and 24.9: You’re in the healthy range.
    
    
    BMI between 25 and 29.9: You’re considered overweight.
    
    
    BMI of 30 or greater: You’re considered obese.
    
    
    People with a BMI of 25 or above are considered at higher risk for heart disease, stroke, hypertension, diabetes, gallbladder disease, cancer, and death. But these guidelines are controversial.
    
    
    Even members of the government panel that issued the guidelines believe that setting the low point for overweight at a BMI of 25 is somewhat arbitrary. Keep in mind that BMI, like body-fat percentage, is only one factor in assessing your health. Also know that BMI measurements for extremely muscular athletes and pregnant women are not very accurate.
    
    
    You may wonder: If BMI has so many limitations, why mention it? Because it’s the simplest way — no fees, no equipment, and no schlepping to the health club — of estimating whether you may be in the overweight ballpark.
    
    
    To calculate your BMI, multiply your height in inches times your height in inches. Then, divide your weight by that number. Finally, multiply that result by 705. People with a BMI of 25 or above are considered at higher risk for many health issues.
    
    

    Ten Strategies for Cutting Calories

    
    

    
    
    Whether your goal is to lose a lot of weight or just a few pounds, cutting your calorie intake will help you achieve your goal. Eating low-fat food important, but cutting calories is more important. Here are some strategies to make cutting calories easier:
    • Read nutrition labels: Healthy foods can contain plenty of calories and fat. A container of ramen noodles, for example, packs 15 grams of fat and 400 calories; a bran muffin can top 10 grams of fat and 250 calories. Portion sizes can be deceptively small, too. A serving of sugar-sweetened iced tea contains 60 calories, but each bottle often contains two servings.
      
      
      • Limit alcohol: Alcohol, although fat-free, delivers 7 calories per gram or about 70 calories per ounce (2 tablespoons). The higher the proof, the more calories alcohol has: 80-proof alcohol averages 65 calories per ounce, and 100-proof alcohol comes in at 85 calories per ounce. The average light beer or 5-ounce glass of wine contains about 100 calories. A typical beer has about 150 calories.
      • Use smaller plates: Serve yourself on a salad-size plate, about 8 inches in diameter, rather than on a dinner plate, which is larger. Your portion sizes will be closer to those suggested in the USDA Food Guide Pyramid.
      • Ask for the kid size: Kid-size popcorn at most movie theaters contains 150 calories, but a large size can top 1,000 without the butter-flavored topping. A child-size soda (8 ounces) has about 95 calories; a large soda measuring 36 ounces or more contains at least 400.
      • Eat proper portion sizes: Nibbling from packages of crackers or eating forkfuls of cake from the platter can add up. Portion out everything you eat onto a small plate or bowl.
        Use measuring cups and spoons to portion out a serving onto your dinnerware.
      • Eat in the dining room: When you bring plates to the table already filled, you won’t be tempted to pick from serving bowls and platters in front of you.
      • Eat slowly: Your brain takes a full 20 minutes to register the fact that your stomach is full. Try putting your fork down and taking a sip of water between bites. Chew your food well and don’t load up your fork or spoon until you swallow what’s in your mouth.
      • Fill up on plant food: Fruits, vegetables, and whole grains without butter, dressings, or sauces take up stomach space, leaving less room for denser, high-calorie foods. They also take more time to chew and eat.
        Consider the fact that a teeny little pat of butter has as many calories as 3 cups of broccoli or that a 1-inch cube (1 ounce) of cheddar cheese has the same number of calories as 1 cup of bran flakes.
      • Switch to low-fat dairy products: An 8-ounce glass of whole milk contains 150 calories, but the same amount of fat-free (skim) milk has only 85. One ounce of regular cheddar cheese has 114 calories, but reduced-fat and low-fat varieties contain 80 and 49 calories, respectively.
        Dairy products, such as ice cream and flavored yogurt that are marketed as reduced-fat, low-fat, or fat-free often contain added sugar to make up for the loss of flavor and texture that fat provides. Don’t be fooled into thinking that they provide fewer calories.
      • Cook meats with methods that start with the letter B: Broil, barbecue, bake (on a rack), or braise meats, and you save many calories over frying, sautéing, and stewing, because the fat (and therefore its calories) has a chance to drip away from the meat.
        Cooking chicken and other poultry with the skin on and removing it after it’s been cooked is fine, because the meat absorbs little of the fat but stays moist.