How Calories are Measured

• What we call a "calorie" when it comes to food is technically a "kilocalorie" (kcal). A kcal is the unit of energy that is required to raise a single mL of water by 1 degree celsius.
• Historically, calories in food were measured with a calorimeter. The food would be dehydrated to remove all water, then placed in a sealed container surrounded by water and ignited. Then, calories were calculated based on how much impact the process had on the temperature of the water.
• The calorimeter process was flawed in that some components of food, including fiber, will burn and create heat, but cannot be absorbed into the bloodstream and therefore are not processed as calories by the body.
• The more common method for calculating calories today is called the "Atwater indirect system," which identifies the grams of carbohydrates, fats, proteins and alcohols in food and calculates the calorie content based on the average calories per gram of these three nutrients. The averages used are 4 calories per gram for carbohydrates and proteins, 7 calories per gram for alcohol and 9 calories per gram for fats.
• Using the atwater method, it is necessary to subtract the grams of fiber in food from the carbohydrates prior to calculating the calories.

Impact of Calories on Weight

• The basic premise that our weight is dependent on how many calories we take in vs how many we expend has dominated thinking about weight and weight loss for decades.
• However, even with a focus on reducing the number of calories we take in and increasing the number we burn, the obesity epidemic continues to worsen.
• An alternative model, called the carbohydrate-insulin model, focuses on how the types of foods we eat impacts hormones in the body, which impact how those foods are stored and used in the body and therefore impacts weight.