A Calorie (or more precisely – a kilocalorie) is a unit of heat. We associate a unit of heat energy to our foods because it approximates the capacity within the human body to create heat via metabolism (i.e., the breakdown of food into energy). The mathematical formula used to define 1 Calorie is that 1 Calorie is the heat energy required to raise 1 Liter of water by 1 degree Celsius. In order to determine how much Caloric energy food contains, scientists use a device known as a bomb calorimeter. This device works by placing a set weight of food (for instance, 1 gram of fat) into a container that is surrounded by a set volume of water (for instance, 1 Liter of water), and then setting the food on fire to see how much of an influence the heat has on the surrounding water. Scientists have measured the caloric values of different types of food with bomb calorimeters, which we see represented on our food labels as the Calories associated with fat, carbohydrates and protein.

• 1 gram of fat would increase 1 Liter of water by approximately 9 degrees Celsius, thus 1 gram of fat has 9 Calories.
• 1 gram of carbohydrate in a bomb calorimeter raises 1 Liter of water by about 4 degrees Celsius so we say that 1 gram of carbohydrate has 4 Calories.
• Protein is a bit trickier in a bomb calorimeter, because about 20% of protein (by weight) is nitrogen, which cannot be used by the human body for energy production. After accounting for nitrogen, it is determined that 1 gram of protein raises 1 Liter of water by about 4 degrees; thus we associate 1 gram of protein has 4 Calories.

The human relationship to food ranges from what is culturally defining to the memorable and tastes from childhood, but the most important reason behind eating food is its biological purpose to fuel everything happening inside our bodies. If you cut back on your Calories too much, then you are essentially cutting back on your body’s ability to produce energy via metabolism. If you consume too many Calories, then, in your body’s efficient wisdom, you will store what you don’t immediately use for energy production into the ultimate-fuel-storage-depot – adipose, or body fat. The goal for optimal health is to aim for nutrient-dense foods to provide adequate Calories, paired with healthy physical activity. The physical activity serves as the metabolic drive to use the foods you eat for energy production, keeping your body strong, well fueled, and satisfied.

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