What the heck is a calorie?

We hear so much about calories when it comes to our body weight and how much food we should have. The importance of calories is underscored by the amount being prominently displayed just under the serving size at the top of the Nutrition Facts label on food packages.

Simply put, a calorie is a unit of measure of energy. Purely scientifically, a calorie is the amount of energy it takes to raise one cubic centimeter (think of a little box with half-inch sides all around) of water one degree Celsius.


Why we need calories

Our bodies are essentially an internal combustion engine. The greatest majority of our calorie needs come from just being alive, otherwise known as our basal metabolism. Remember, we are warm blooded, and need calories to keep our bodies at a normal temperature of about 98.6° F, for our hearts to pump blood and for our lungs to breathe.

Two more reasons we need calories

The second is called the Specific Dynamic Effect (SDE) of food or the calories needed to digest the foods that we eat. Yes, we do burn some calories just by eating!

The third component of our calorie needs depends upon how much physical activity we get and how regular that activity is. I say regular because a person who is physically active on a regular basis usually has more lean muscle mass than someone of the same height and age that is not regularly active.

Lean muscle mass is more metabolically active (needs more calories) than fat mass. This is one of the reasons it is so important to be physically active, it gives us a body that needs more calories to maintain body weight than that same body would if it were not physically active. The ability to consume more calories gives us the opportunity to get more health benefit and enjoyment from foods.

I really want to make a point here regarding burning calories and physical activity. Yes, you can walk longer and harder to ‘burn’ off that dessert you just ate with your meal. But, I believe we’ve got this calorie burning stuff all backwards when we look at it on an individual food (or indulgence) basis.

The exercise and weight loss industry provides educational tools and products that will measure how many calories we need to ‘burn’ or what we need to do for exercise and for how long to equal the calories contained in particular foods and beverages that we have just recently consumed. It is a way to entice us to use those products. We somehow need an immediate result for our efforts. The way to think about it holistically is a body that is exercising regularly has a composition that consists of more lean muscle mass to fat mass and this body is more metabolically active, thus requiring more calories from food. Pretty good news, if you like food.

Back to the calories from foods… The table below shows how many calories are provided by each macronutrient per gram (1 gram = 1/5 of a teaspoon), what is recommended for a percent of calories each day from each macronutrient and an 1,800 calorie per day example broken down by the calories needed from the macronutrients.

Carbohydrate455 percent calories from carbohydrates990 calories each day

Calories from Foods
Macronutrient Calories per gram Percent of calories each day 1,800 cal/day example
Protein 4 20 percent calories from proteins 360 calories each day
Fat 9 25 percent calories from fats 450 calories each day


To find out your daily calorie needs, the amount of each food group you need each day, and to receive a customized food guide, go to MyPyramid Plan. Have fun! Next week we’ll get the whole truth about simple, then complex carbohydrates.

About our Nutrition Expert

Lori Kaley MS, RD, LD, MSB is a member of the Guiding Stars Scientific Advisory Panel. Lori has 30 years of combined experience working in healthcare and public health creating policies and environments to help families and children have access to healthy foods and beverages. She is currently Policy Associate at the University of Southern Maine’s Muskie School of Public Service.

Lori’s greatest achievement and joy has been in raising her three daughters to be healthy and productive young adults, each with their own particular love of food, cooking and being physically active. Lori’s passion for nutritional community outreach has been a cornerstone of the Guiding Stars Scientific Advisory Panel. Lori regularly contributes to the Guiding Stars blog.