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By Bonnie Taub-Dix

Many people are concerned about counting calories, but may not understand what a calorie is or how many they really need.

What is a calorie?

Basically a calorie is a unit of energy; it measures how much energy a food provides to the body.

Here are a few points to help clear up calorie confusion:

How many calories are in a pound?

It has been believed that there are 3,500 calories in a pound, so therefore it would seem that if you reduce your diet by 500 calories a day, or exercise and burn off 500 calories a day (or any combo of the two), that you would lose a pound a week.

This is not, however, an exact science. When it comes to weight loss, there are many different variables to take into consideration including one’s metabolism.

All calories are not the same

For example, a gram of carbohydrate has 4 calories and the same goes for a gram of protein. A gram of fat provides 9 calories. Carbohydrates generally digest the fastest, then protein and fat digest more slowly. Because each of these food groups impact metabolism differently helps to support that all calories are not alike.

It’s best to not just look at the number of calories you take in, but instead, focus on the kind of calories you’re consuming. A balance of the three is optimal.

Label calorie counts are a guide, not gospel

Calorie counts on labels are permitted to have a 20 percent swing. It’s important to remember that the Percent Daily Values on the Nutrition Facts Panel is based upon a 2,000 calorie diet.

This amount is more calories than many of us need (those who are trying to lose weight) and not enough for others (young athletes).

It’s also important to point out that the calories listed on the food label indicates how many calories are in one serving of that particular food. If you’re watching your weight, you’ll need to be mindful of portion sizes you actually eat, multiplying the numbers on the package by the number of servings you consume.

TODAY contributor Bonnie Taub-Dix, R.D. is the author of "Read it Before You Eat it". For more, go to http://www.bonnietaubdix.com