How Calories Work

written by runnergirl training

Ever wonder what a calorie means? We all seem to either counting, watching & burning them. But what is it that we are really talking about when we mention calories?


A calorie is the amount of heat/energy it takes to increase the temperature of 1 gram of water by 1 degree Celsius. When talking about food a calorie is actually called a kilocalorie. Did you know 1,000 calories = 1 kilocalorie? If we said it takes about 100 calories spent by walking/running/cycling we would be meaning kilocalories. 

Food has different calorie components based on its type of nutrition. Protein and carbohydrates both have 4 calories each per 1 gram. Fat has 9 calories per 1 gram. You can see how if you are trying to lose weight a low fat diet is helpful when reducing calories. Fat (per gram) has over twice the calories as protein and carbohydrates (per gram)! That means fat is more calorie dense than protein and carbohydrates. 

Since food is fuel, after it is eaten digestive enzymes break it down into useable or stored components. Carbohydrates are broken down into sugars including glucose to be used as immediate energy. Fat is broken down into fatty acids and glycerol. Protein is broken into amino acids. The body decides what to do with all of the broken down pieces. They are used for energy (as glucose in the blood stream or glycogen in muscles) or stored as fat. 

If you ate a snack and then worked out some of the snack would be used for energy. This is especially true if the snack was primarily carbohydrates. If you ate a meal and worked out 6 hours later then you would be drawing upon stored energy as fuel.

I hope you now have a little bit better understanding of what a calorie is and how is is used by the body!