By Donna Feldman, MS, RD

Dieters think of calories as the enemy--the part of food that prevents weight loss and sneaks onto the thighs. Food packages list calorie content per serving. Diets with one-size-fits-all calorie limits are promoted for weight loss. You can track your calorie intake with computer software. Calorie information overload can turn eating into a numbers game instead of a pleasurable part of daily life. We are calorie-obsessed!

The truth is, everyone needs some calories every day. Unless you are a highly trained athlete, your biggest daily calorie cost is something called resting metabolic rate (RMR), or the calories you need just to exist. Breathing, heart beat, cell metabolism, kidney function, and even thinking and dreaming uses calories. Muscle cells use calories even when at rest. Eating and digesting food, standing, sitting, talking, and surfing the Internet all burn calories beyond the basic RMR requirement.

What Is a calorie?

Calorie is a term for the energy content of food. Some foods are very dense in energy, like butter and vegetable oil.

Others, like celery and cucumbers, have much less. It is a bit like comparing octane in gasoline. Higher octane fuel will make your car go a bit further for every gallon burned. Likewise, a tablespoon of canola oil, with 100 calories, will get you further than a tablespoon of chopped celery, with maybe 1 calorie. Unlike cars, humans do not have limited fuel tanks. We have expandable fuel tanks called fat cells. Also unlike cars, we can ramp up our daily calorie use by adding physical activity.

 

What is the recommended daily calorie intake?

It is not easy to come up with an accurate number for your calorie requirement. Accurate measurement of calorie requirements is limited to research settings. Subjects sit in a closed chamber for hours, while researchers measure the amount of oxygen used. Calculations based on oxygen use give the number of calories burned in a day. This procedure is not practical for widespread use. There are mathematical equations that attempt to estimate calorie needs based on simple body measurements, such as gender, age, height, and weight. But equations have limitations. Research shows that most equations are off by anywhere from 5% to 25% when used to predict a person's basic calorie requirement. If you are trying to plan a reduced calorie diet, it is not helpful if the equation overestimates your basic needs by 25%.

Recently, small portable calorie measuring devices have been developed. Some health clubs, medical offices, and wellness clinics use these to help clients plan weight loss diets. The procedure usually involves wearing a nose clip and breathing by mouth into a small, hand-held device for several minutes. This is an attractive concept for dieters, but there are many complications. Exercise, caffeine, nicotine, alcohol, and eating too soon before the test can throw off results. In addition, anxiety or fidgeting will result in erroneously high results. If you decide to have a measurement done, be sure to carefully follow all the instructions for pre-test preparation.

How many calories do I need?

If you do not have access to a metabolic measurement, you can use an equation to estimate your basic calories. The most accurate one is the Mifflin-St. Joer equation. Weight in pounds must be converted to kilograms by dividing weight in pounds by 2.2. Height must be changed to centimeters by multiplying inches by 2.54. Plug your height and weight into the basic equation:

9.99 x weight + 6.25 x height - 4.92 x age.

Men then add 5; women subtract 161.

The total is your approximate calories per day for resting metabolic rate. The RMR for a 40-year-old man who weighs 190 lbs and is 6'1" is 1800 calories per day. A 25-year-old woman who is 5'6" and 140 pounds has a basic calorie requirement of 1380. Because the equation is not completely accurate, real RMR may be slightly lower or higher.

In addition to the RMR calories, each person needs additional calories for daily activities and exercise. A sedentary person will need fewer calories than an active person.

Burn more calories: physical activity

Physical activity not only burns calories, but helps you burn extra calories all day, even when you're not exercising. Active people have more muscle than sedentary people. Muscle tissue has higher calorie needs even at rest than fat tissue. This is an excellent reason to include exercise in your daily routine.

Conclusion: if you are eating the right amount of calories your weight remains stable

In the future, when the technology improves, fast accurate metabolic measurements might be part of the bathroom scale. Until then, the one true, but indirect, way to know your calorie intake is to monitor your weight. If your weight is stable, you are eating the same amount of calories you burn. If you want to lose weight, you have to eat less than that amount or burn more with exercise.