Editing Food energy (section)

===The Atwater system===
{{main|Atwater system}}

However, the direct calorimetric method generally overestimates the actual energy that the body can obtain from the food, because it also counts the energy contents of [[dietary fiber]] and other indigestible components, and does not allow for partial absorption and/or incomplete metabolism of certain substances. For this reason, today the energy content of food is instead obtained indirectly, by using chemical analysis to determine the amount of each digestible dietary component (such as protein, carbohydrates, and fats), and adding the respective food energy contents, previously obtained by measurement of metabolic heat released by the body.<ref name=CANH1997/><ref name=SciAm/> In particular, the fibre content is excluded. This method is known as the [[Modified Atwater]] system, after [[Wilbur Atwater]] who pioneered these measurements in the late 19th century.<ref name=marsh2020/><ref name=triv2009/>

The system was later improved by [[Annabel Merrill]] and [[Bernice Watt]] of the [[USDA]], who derived a system whereby specific calorie conversion factors for different foods were proposed.<ref>{{cite book|author1=Annabel Merrill|author2=Bernice Watt|title=Energy Values of Food ... basis and derivation|date=1973|publisher=United States Department of Agriculture|url=https://www.ars.usda.gov/ARSUserFiles/80400525/Data/Classics/ah74.pdf|archiveurl=https://web.archive.org/web/20161122060858/https://www.ars.usda.gov/ARSUserFiles/80400525/Data/Classics/ah74.pdf|archivedate=22 November 2016|url-status=dead}}</ref>