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Measuring Calories

At the turn of the 20th century, a scientist for the U.S. Department of Agriculture (USDA) by the name of Wilbur Atwater was the first to accurately measure the number of usable calories in foods. The measurements he discovered have formed the basis of the present-day Atwater values, which include:
  • Four calories per gram for proteins and carbohydrates
  • Nine calories per gram for fats.
 
These are the basis of calorie levels in USDA food tables, food packaging labels, and restaurant menus. While the estimates for most foods that are based on Atwater values are fairly accurate, certain foods retain some of their calories as they pass through the digestive system.
 
For example, in a 2012 study, USDA scientist Janet Novotny discovered that the measured energy content of a 28-gram serving of almonds was actually 32 percent less than the Atwater value's estimate. This study showed that a single caloric value that is based on the assumption of how much of that food would be digested is not completely accurate for all foods.
 
For some time now, nutritionists have tried to determine the proportion of the food energy we waste versus what our bodies use for physiological functions, such as physical activity, body heat, and fat storage. The body uses different amounts of energy to digest, metabolize, and absorb the energy in food. 
 
In general, more energy is needed to process protein than carbohydrates, and more energy is required to process carbohydrates than fat. While this can be a complicated process, in its most basic sense, this means that even if the calories consumed are equal, a high-protein diet will add fewer calories to the body than a high-carb diet, and a high-carb diet will add fewer calories to the body than a high-fat diet.
 
However, just meeting your energy needs is not enough. To just eat 2,000 calories a day in chocolate (which would meet your energy needs) would deprive your body of many essential nutrients it needs to grow and function properly. For example, the following nutrients are important for specific functions in the body:
 
  • Proteins form important parts of muscles, bone, blood, and enzymes
  • Carbohydrates supply energy to cells in the brain, nervous system, muscles, and blood
  • Fat supplies energy and insulates, supports, and cushions organs
  • Vitamins promote specific chemical reactions within cells
  • Minerals help regulate body functions, while also helping in growth and maintenance of body tissues
  • Water provides a medium for chemical reactions, regulates temperature, and helps remove waste products.
 
So although eating chocolate all day might sound nice (for a while), your body still wouldn't get the nutrients it needs to function properly, which may lead to numerous medical problems down the line.
 
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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