Think of a calorie as a way to measure one unit of energy. Energy, in this case, in the form of food and drink, can be neither created nor destroyed. Because of this, digestion transforms the calories into a new form of energy, according to The American Journal of Clinical Nutrition. Calories vary by the amount of nutrients they provide the body, which means all calories are not created equal. They derive from macronutrients in the form of carbohydrates, protein, or fat, which are broken down on the back of any nutrition label found within the United States.

Each macronutrient is measured with grams, and according to Greatist's "Complete Guide To Calories" healthy adults should consume calories with calculated effort. However, there are a different amount of calories in each gram of carb, protein, and fat. One gram of carbohydrates adds up to four calories, which means if there are 10 grams of carbohydrates in your granola bar, there are 40 calories' worth of carbohydrates in your bar.

Protein is measured with the same equation. However, carbohydrates and proteins fuel the body differently; protein sustains energy for longer, giving it a low glycemic index. Carbohydrates provide shorter bursts of energy, therefore a higher glycemic index. As for fat, one gram equals to nine calories. Although alcohol isn’t considered a macronutrient, because it isn’t a necessary fuel source for the body, it’s still useful to know one gram adds up to seven calories.

It’s not just about what types of food sources you’re eating, but also how much. Losing, gaining, or even maintaining weight requires an understanding of how many calories are burned or used up throughout the day, and how many are fed back into the body to re-fuel. In order to maintain weight, the calories in must equal the calories out, while burning weight will require you to burn more calories than you consume. Weight gain occurs when too many calories are consumed but not enough are burned, forcing the body to store extra calories in the form of fat.

“Calories (noun) - Tiny creatures that live in your closet and sew your clothes a little bit tighter every night.”

Calorie counting is a popular way to keep a person on track when it comes to calories in and calories out, and the type of energy that’s being processed into the body. The Department of Health and Human Services recommends setting calorie goals after calculating your body mass index, and assessing how many calories you need in order to maintain, lose, or gain weight in accordance to your level of physical activity. When it comes to health, it’s important to make sure you’re not underweight and especially not overweight or obese like the 160 million Americans living today.

The Complete Guide to Calories