Calories: Feel the Burn

This week we take up a question we hear often: How do I figure out how many calories I burn?

This is an area loaded with hooey and misinformation. Let's take it from the top. In a typical day, you burn calories four ways: Basal metabolic rate, or calories used when sedentary; Thermal effect of feeding, or calories burned digesting food; Physical activity (anything besides sitting: walking, piano playing, shadowboxing); and Excess post-exercise oxygen consumption, that oft-hyped afterburn from a workout.

Say hi to Example Given, a 5-foot-5, 45-year-old woman who weighs 135 pounds and consumes 2,100 calories a day. (Figures are approximate, vary widely between individuals and are subject to debate in the field.)

Basal Metabolic Rate (BMR)

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

Physical Activity

As for 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. But even if our example, Given, converted two pounds of fat into two pounds of muscle (no mean feat) she would burn only an extra eight calories a day through BMR.

Using a generic calculation for BMR, we derive a burn of slightly more than 57 calories per hour while sedentary. Assume Given sleeps for eight hours and is basically inert (sitting, talking on the phone, driving) 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.

Thermal Effect of Feeding (TEF)

TEF, or 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 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. OK, 235 calories for TEF.

Excess Post-Exercise Oxygen Consumption (EPOC)

Now, the fun: 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.

Given spent the other 4 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, visit online).

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, doesn't run every day and adds an afternoon latte with two percent milk, she's suddenly running a surplus. Love-handle alert!

Exercise is the Key

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

Check your basal metabolic rate using our BMR Calculator

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