What’s In A Calorie?
photo credit: ϟnapshot 19A calorie is actually a measure of energy; scientifically, “the amount of energy it takes to raise one gram of water by one degree Celsius”. What we term “calories” are actually kilocalories (kcals), or 1000 Calories. We use kcal when we talk about how many are in the foods we eat, because if we didn’t, a Three Musketeers Bar would have 285,000 calories and no one would ever eat one!
Calories in food are measured by an apparatus called a Bomb Calorimeter that burns a portion of food and measures the energy that is released. Calories that people burn are measured with an Indirect Calorimeter; a machine that measures the amount of oxygen taken in and carbon dioxide released during certain activities.
In grade school we learned that humans breathe in oxygen and breathe out carbon dioxide (CO2). How does this happen? The oxygen we breathe in combines with carbon from the energy-yielding nutrients in our food (carbohydrate, protein, and fat) during the process of obtaining the energy (calories) from the food, and yields CO2. The other nutrients–vitamins, minerals, and water–do not contain carbon. This means they do not provide calories.
Humans burn most of their calories by their continuous body functions: The beating of your heart, breathing, regenerating new cells, etc. This is called your Basal Energy Expenditure (BEE) and accounts for about 2/3 of the daily calories burned by most people. When you add to this your movements and exercises during the day (even the process of digestion), the result is your total calories expended.
How do we calculate the number of calories in a food? There are a few basics to begin with: Carbohydrates provide 4 calories per gram. Protein provides 4 calories per gram. Fat provides 9 calories per gram. The only other substances that provide calories are drinking alcohol, and sugar alcohols (such as sorbitol, found in sugar-free gums and candies). You can calculate the calories in a food by reading the nutrition facts label that shows grams of carbohydrates, grams of protein, and grams of fat. The gram weight of a food will be more than the total of the carbohydrates, protein, and fat, because of water weight. Water can compose of up to 90% of some foods (fruits in particular) but is present in very small amounts in high fat foods, such as butter.
Here’s an example: A teaspoon of sugar weighs approximately 5 grams. Only about 4 grams are carbohydrate (the rest a little bit of water). If you multiply 4 grams x 4 calories per gram, you’ll find there are 16 calories in a teaspoon of sugar. Now let’s calculate the calories in butter: a teaspoon weighs about 5 grams. There are 9 calories in a gram of butter (fat). Take 9 calories per gram times 5 grams and find that there are 45 calories in a teaspoon of butter. Hmmm, butter sure has more calories than sugar!
Try doing the math on food labels you find around your house: On a label of bread you might find 12 grams of carbohydrate (x 4 = 48 calories) and 3 grams of protein (x 4 = 12 calories) and the total calories in a slice will be near 60 calories. The slice of bread weighs 30 grams, but the rest of the weight is from the water content.
I hope you enjoyed this little nutrition class!
Written by Laurie Beebe
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About The Author: Laurie Beebe has been a registered dietitian for 25 years and is certified in adult weight management. Laurie currently serves as a Related posts:
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