What You Need to Know About Calories

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In science, a calorie is a unit for measuring energy. It's equal to the amount of heat needed to raise one liter of water one degree. What we call "calories" in nutrition and fitness are actually kilocalories, which are equal to 1,000 calories. We use them to represent the amount of energy available in food and beverages. You use that energy to fuel the various physiological processes that occur inside your body and for physically moving around. When you consume more calories than your body needs, the extra is stored as fat. 

How Many Calories Do You Need?

The number of calories you need depends on your age, body size, and activity levels—most teens and adults need somewhere around 1,500 to 2,500 calories per day. The bigger you are, the more calories you need to maintain that weight. If you want to gain weight, you'll need to take in more calories, and if you want to lose weight, you'll need to consume few calories or burn more. You can determine your caloric need by using the Harris-Benedict formula.

Calories and Weight

A pound of fat is roughly equal to 3,500 calories, so if you do the math, you can see you need to burn 3,500 extra calories to lose a pound of fat. Decreasing your typical daily calorie intake by 500 calories per day should result in losing a pound every week. At least for awhile—as your weight drops, your daily calorie need will also decrease.

What Are Physical Activities' Effect on Calories?

Moving around and lifting or doing various things require energy, so the more you move around and the more things you lift, push or pull, the more calories of energy you burn. Also, resistance training that builds muscle increases your metabolism, meaning your body requires more calories—even when you're not doing much. So, building muscle is a good way to help you reach a healthy weight.

How Accurate Are Calorie Calculators?

Close—maybe not 100 percent accurate, though. Most of them are based on the Harris-Benedict formula, which determines your basal metabolic rate—that's essentially the number of calories you need just to be alive and awake. The calculators also need to factor in your typical daily activity levels, which might be a bit more of an estimate. It's difficult to know exactly how many calories you burn with physical activity and it probably differs every day.

These calculators are a good way to start, but if you feel your weight isn't changing enough, then you may need to adjust your caloric intake or output accordingly. 

What's the Best Way to Track Calories?​

You can use a notebook or a paper food diary, look up the calorie counts and do the calculations. But these days, the best way is to use a calorie tracking website that can help you track calories, such as myfitnesspal. You pick out the foods you eat, the beverages you drink, and the site will count the calories and give you a daily nutrition grade. Also, you can track the calories your body burns every day. And it's free.

What Does All Calories Are Not Equal Mean? 

All calories are equal energy-wise. Each gram of carbohydrate has four calories, each gram of protein has four calories, and each gram of fat has nine calories. That doesn't change. The phrase "all calories are not equal" means that some calorie sources are better than others. In short, you should get most of your calories from nutrient-dense foods. So while 250 calories from a candy bar are utilized the same as the combined 250 calories from a banana, an apple, and a pear, the fruit is obviously much better for you.

By Shereen Lehman, MS
Shereen Lehman, MS, is a former writer for Verywell Fit and Reuters Health. She's a healthcare journalist who writes about healthy eating and offers evidence-based advice for regular people.