As you all well know, look at any food product and there is a list of the calories per serving, along with fat grams, sodium milligrams, total carbohydrate grams, sugar grams and protein grams. The FDA requires that companies put that information on each food and drink product but the FDA does not state how they should gather that information. So this leads to the question of how are these factors determined?
According to an article on Slate by Sam Schechner: “one calorie is defined as 1,000 times the energy it takes to heat a gram of water from 14.5 to 15.5 degrees Celsius. But instead of burning anything, food laboratories often freeze their samples in liquid nitrogen and then blend them into a fine, monochromatic powder that can be used in a variety of chemical analyses. In a Kjeldahl analysis, for example, lab techs remove nitrogen from the food powder and then use it to calculate the amount of protein the sample contains. A hexane extraction can gauge the amount of fat. Carbohydrates are usually measured by difference – they’re what is left over when you remove everything else.”
As to how calories are determined, again from the article by Sam Schechner, “food labs rely on conversion factors first assembled more than 100 years ago by the agricultural chemist Wilbur O. Atwater, who literally did burn things like beef and corn in a device called the bomb calorimeter. The idea is that burning, say, a hamburger shows the total energy that hamburger contains, but it doesn’t account for what the human body cannot absorb, nor what is used in the digestive process. So Atwater derived a set of tables that specify the practical energy values of different foods, distinguishing, for example, among different sources of protein. The most recent update to the conversion tables was published by the U.S. Department of Agriculture in 1973.”
So now you know how the nutrition facts of foods and drinks are determined!
