question: How are calories calculated in food?
comment: You are probably asking about how they are measured, but they are calculated by adding up protein (4kcal per gram), carbohydrates (4kcal per gram), and fats (9kcal per gram). Alcohol is 7kcal per gram. Try it out on a packaged food and see if you get the total
passages: Section::::Measurement of energy content of food.
  
  In the past, a bomb calorimeter was used to determine the energy content of food by burning a sample and measuring a temperature change in the surrounding water. Today, this method is not commonly used in the USA and has been succeeded by calculating the energy content indirectly from adding up the energy provided by energy-containing nutrients of food (such as protein, carbohydrates, and fats). The fibre content is also subtracted to account for the fact that fibre is not digested by the body.
  
  Section::::See also.
  
  BULLET::::- Basal metabolic rate
  
  BULLET::::- Caloric theory
   Section::::Chemical analysis.
   In addition to its web site, the company also produces personal computer software and several popular books. Many of its products are based on the CalorieKing food database, which claims to contain over 100,000 foods in the American version and 20,000 foods in the Australian version.
  
  Section::::History.
   BULLET::::- calorie – a basic measure of energy that has been replaced by the SI unit the joule; in physics it approximates the energy needed to increase the temperature of 1 gram of water by 1 °C which is about 4.184 joules. The Calories in food ratings (spelled with a capital C) and nutrition are ‘big C’ Calories or kcal.
  
  BULLET::::- calorific value – the energy content of a fuel measured as the heat released on complete combustion.
   The calorie equals the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, from a temperature of 14.5 degrees Celsius, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J. Food energy is measured in large calories or kilocalories, often simply written capitalized as "Calories" (= 10 calories).
  
  Section::::Atom physics and chemistry.
   Section::::Relationship to other works.
   Calorie amounts found on food labels are based on the Atwater system. The accuracy of the system is disputed, despite no real proposed alternatives. For example, a 2012 study by a USDA scientist concluded that the measured energy content of a sample of almonds was 32% lower than the estimated Atwater value. Furthermore, it is known that some calories are lost in waste, without ever having been chemically converted or stored. The driving mechanism behind caloric intake is absorption, which occurs largely in the small intestine and distributes nutrients to the circulatory and lymphatic capillaries by means of osmosis, diffusion and active transport. Fat, in particular is emulsified by bile produced by the liver and stored in the gallbladder where it is released to the small intestine via the bile duct. A relatively lesser amount of absorption, composed primarily of water, occurs in the large intestine.
   To facilitate comparison, specific energy or energy density figures are often quoted as "calories per serving" or "kilocalories per 100 g". A nutritional requirement or consumption is often expressed in calories per day. One gram of fat in food contains nine calories, while a gram of either a carbohydrate or a protein contains approximately four calories. Alcohol in a food contains seven calories per gram.
  
  Section::::Chemistry.
   BULLET::::- Estimating values from other sources, including manufacturers food labels, scientific literature and FCDBs from other countries.
  
  Section::::Food composition dataset.:History.
  
  Some of the earliest work related to detecting adulterated foods and finding the active components of medicinal herbs.
   Nutritional rating systems
  
  Nutritional rating systems are methods of ranking or rating food products or food categories to communicate the nutritional value of food in a simplified manner to a target audience. Rating systems are developed by governments, nonprofit organizations, or private institutions and companies.
  
  The methods may use point systems to rank or rate foods for general nutritional value or they may rate specific food attributes such as cholesterol content. Graphics or other symbols may be used to communicate the ratings to the target audience.
   One of Foodporn’s most popular blogs titled ‘"a photographic representation of what 200 calories looked like in different foods"’ was shared extensively across the internet, with one website generating over 900,000 views for the article.
  
  Section::::Controversy and rating system.
   The code above shows ""Porridge, made with low fat milk"" from Irish published ""Irish Food Composition database 2009""
  
  Section::::Examples.:US15.15083.
  
  The code above shows ""Fish, salmon, pink, raw"" from US published ""United State Department of Agriculture, SR28 2015""
  
  Section::::Use on Barcodes and numeric systems.
   Estimated dietary fibre by various AOAC methods such as 985.29,
  
  Sodium (and thereby Salt) either by flame photometry, AA or ICP-OES,
  
  Total sugars, normally by a liquid chromatography technique, such as IC-HPAED or HPLC-RI,
  
  Fatty acids by GC-FID,
  
  Carbohydrates and energy values are normally calculated from these analytical values.
  
  Section::::Methods.:Software.
  
  Software is available as an alternative to laboratory nutrition analysis. This software typically utilizes a database of ingredients that have previously been laboratory tested. The user can input ingredient data by matching their ingredients to ingredients found in the database; the analysis can then be calculated.
  
  Section::::Methods.:Online nutrition analysis.
   In the European Union, along the "old" rules (Directive 90/496, amended), the information (usually in panel format) is most often labelled "Nutrition Information" (or equivalent in other EU languages). An example is shown on the right. The panel is optional, but if provided, the prescribed content and format must be followed. It will always give values for a set quantity — or of the product — and often also for a defined "serving", as an option. First will come the energy values, in both kilocalories and kilojoules.
   Section::::Detection of phase transitions.
   Section::::Government guides.:Sweden.
  
  Sweden's Food Agency uses the Plate Model (), which divides a plate into approximately 40 percent potatoes, rice, pasta and bread; 40 percent vegetables and fruit; and 20 percent meat, fish, eggs and legumes. People requiring more energy are allowed a larger share of carbohydrates, while people who are overweight can make up to half their plate vegetables and fruit.
  
  Previously, Sweden used the Dietary Circle created in 1963, while Swedish consumer cooperative KF created the world's first food pyramid in 1974.
  
  Section::::Government guides.:Switzerland.
   Nutrition analysis
  
  Nutrition analysis refers to the process of determining the nutritional content of foods and food products. The process can be performed through a variety of certified methods.
  
  Section::::Methods.
  
  Section::::Methods.:Laboratory analysis.
  
  Traditionally, food companies would send food samples to laboratories for physical testing. 
  
  Typical analysis includes:
  
  Moisture (water) by loss of mass at 102 °C,
  
  Protein by analysis of total nitrogen, either by Dumas or Kjeldahl methods,
  
  Total fat, traditionally by a solvent extraction, but often now by secondary methods such as NMR,
  
  Crude ash (total inorganic matter) by combustion at 550C,
   The measurement of heat changes is performed using calorimetry, usually an enclosed chamber within which the change to be examined occurs. The temperature of the chamber is monitored either using a thermometer or thermocouple, and the temperature plotted against time to give a graph from which fundamental quantities can be calculated. Modern calorimeters are frequently supplied with automatic devices to provide a quick read-out of information, one example being the differential scanning calorimeter (DSC).
  
  Section::::Systems.
   Developed by Adam Drewnowski, University of Washington, NNR "is based on mean percentage daily values (DVs) for 14 nutrients in 2000 kcal food, can be used to assign nutrient density values to foods within and across food groups. Use of the NNR score allows consumers to identify and select nutrient-dense foods while permitting some flexibility where the discretionary calories are concerned."
  
  Section::::Systems in use today.:ReViVer Score.
   However, good human nutrition measures foods for other values than just energy in calories.
  
  Section::::History.
   In the UK, FCD are listed in tables known as The Chemical Composition of Foods, McCance and Widdowson (1940). FCDBs have become available online on the internet, for example, the USDA Dataset in the States, the Japanese food composition dataset and a number of European food composition datasets. Foods from these national FCDBs can be identified by International Food Code (IFC).
   Section::::Food composition dataset.
  
  Food composition datasets (FCDBs) or food composition tables are resources that provide detailed food composition data (FCD) on the nutritionally important components of foods. FCDBs provide values for energy and nutrients including protein, carbohydrates, fat, vitamins and minerals and for other important food components such as fibre.
  
  Before computer technology, these resources existed in printed tables with the oldest tables dating back to the early 19th century.
   The United Kingdom's Department of Health published Dietary Reference Values. These are equivalent to the easier to understand Eatwell plate used by the National Health Service. This consists of roughly one-third fruit and vegetables ("at least 5 portions"); one-third bread, rice, potatoes and pasta ("plenty"); a smaller amount of milk and dairy ("some"); meat, fish, eggs and beans in the same proportion as dairy ("some"); and a small wedge of fatty and sugary foods.
  
  Section::::Government guides.:United States.
   With processed foods that are made of many different ingredients, it is very complicated, though not impossible, to calculate the CO2 emissions from transport by multiplying the distance travelled of each ingredient, by the carbon intensity of the mode of transport (air, road or rail). However, as both Prof. Lang and the original Food Miles report noted, the resulting number – although interesting, cannot give the whole picture of how sustainable – or not – a food product is.
   Typically grammage is measured in paper mill on-line by a quality control system and verified by laboratory measurement.
  
  Section::::Basis weight.
  
presuppositions: Calories are calculated in food. Calories are calculated in food. Calories are calculated in food. Calories are calculated in food. Calories are calculated in food.
corrections: Calories are measured in food. Calories are measured in food. Calories are measured in food. Calories are measured in food. Calories are measured in food.
raw_presuppositions: Calories are calculated in food. Calories are calculated in food. Calories are calculated in food. Calories are calculated in food. Calories are calculated in food. Calories are calculated in food.
raw_corrections: Calories are measured in food. Calories are measured in food. Calories are measured in food. Calories are measured in food. Calories are measured in food. Calories are measured in food.