The Washington Post

Burn, baby, burn those calories by staying active

By John Briley
April 10, 2005
 
This week we take up the question we hear more than any other, with the sole exception of "Do you fitness guys really do all this stuff yourself?" Since we've learned to dodge that one, we'll take No. 2: How do I figure out how many calories I burn?

This is an area loaded with misinformation. Let's take it from the top.

In a typical day, you burn calories four ways:
1. Basal metabolic rate (BMR), or calories used when sedentary.
2. Thermal effect of feeding (TEF), or calories burned digesting food.
3. Physical activity (anything you do besides sitting: walking, piano playing, shadow boxing).
4. Excess post-exercise oxygen consumption (EPOC), that oft-hyped afterburn from a workout.

To see how these might add up, let's say hi to Ms. Example Given, a 5-foot-5-inch, 45-year-old who weighs 135 pounds and consumes 2,100 calories worth of food and drink a day. (Caveat: The figures below are approximate, vary widely between individuals and are subject to debate in the field.)

First: You can do little to change your basal metabolic rate, despite what some dietary supplement makers say. Worse, BMR declines with age.

As for the talk that muscle burns more calories than fat: Muscles burn six calories per pound per day while fat burns two calories per pound per day. So, yes, muscle is more industrious than fat. But even if Ms. Given converted 2 pounds of fat into 2 pounds of muscle -- no mean feat -- she would burn only an extra eight -- eight! -- calories a day through BMR.

Using a generic calculation for BMR (trust us, it's too messy to get into), we derive a burn of slightly more than 57 calories per hour while sedentary. Assume Ms. Given sleeps for eight hours and is basically inert (sitting at some kind of screen, talking on the phone, driving, doing a crossword) for 11 more hours. She'd burn 1,090 calories in those 19 hours. Add another eight (!) calories to account for her buffness, and we can round up to 1,100 calories.

TEF -- the number of calories burned digesting food -- is estimated at 10 percent of daily caloric intake. Because the body works a little harder digesting protein than other nutrients, you can nudge up this number by eating more protein and fewer fats (carbs fall in the middle). But not much, said Darlene Sedlock, associate professor of exercise physiology at Purdue University.

Because Ms. Given's diet is protein-rich, she "might burn another 20 or 25 calories" beyond the 210 a standard 2,100-calorie diet would consume, Sedlock said.

Now, the fun: Ms. Given found time for a 30-minute, three-mile run, which burned 306 calories. If you've bought the hype on afterburn, you'd think her body would devour calories well above her BMR for hours. Wrong. Given's EPOC "is probably less than 30 calories" after her run, Sedlock said. So: 335 calories for the run and its resulting EPOC.

Luckily, Ms. Given spent the other 41/2 hours of her day doing a variety of mild physical activities -- walking to the printer, carrying groceries, practicing guitar, cleaning her apartment. These incinerated another 700 calories (for data: www.caloriesperhour.com).

The total? For the day, she burned 2,370 calories and consumed 2,100 -- a modest deficit that could, if sustained, support weight loss. But if she halves her activity calories, if she doesn't run every day and if she adds an afternoon latte with 2 percent milk . . . she's suddenly running a surplus. Love-handle alert!

More important, Ms. Given has taught us two key things: Exercise is the only significant calorie-burning method you can control -- and little episodes of activity really add up.