Addition of slot(s) for nutrient converstion factors

[kaiiam]

At the moment USDA Foundation Foods and SR legacy keeps track of conversion factors used for components. E.g. the values from the Atwater tables, and or Jones' factors (6.25 for nitrogen conversions). At the moment my understanding in SR and FF is that these factors can be specific or general (following literature standards). Additionally this data is kept track of at the Food level e.g. almond's are using a Protein from Nitrogen factor of 5.18.

An open question for me is how best to model this in MIFC. Do we want to keep track of these in the Food table (as per how it is done in SR/FF) or do we want to keep track of it in the component table. The latter would make for potentially duplicative information, however, it would allow for for the factor information used in a final calculated value to be included in the same data "row" as as the component's value in case that's more transparent or we used a different factor for different data that were of the similar type (e.g. if almond butter's protein from Nitrogen factor of 5.18 but for Almond milk we used 6.25). It would be good to get someone with more expertise in food composition data to weight in here.

[KyleMcKillop-USDA]

Regarding Nitrogen Factors in Foundation Foods and Standard Reference: The values for protein are calculated from the amount of total nitrogen in the food using the nitrogen- to-protein conversion factors recommended by Jones (1941) for most food items. The factor applied to each food item is provided in the NFactor field in the Food Description table. If a specific factor is not available, the default value of 6.25 is used for the nitrogen-to-protein conversion factor. Protein values in Foundation Foods are now listed as "calculated." This differs from the approach taken in SR Legacy, which denotes protein as "analytical."

[KyleMcKillop-USDA]

Regarding use of general and specific atwater values: Most energy values are calculated using the Atwater general factors of 4, 9, and 4 for protein, fat, and carbohydrates, respectively. These general calculations are represented in FoodData Central as "Metabolizable Energy (Atwater General Factor)" and is identified in download files and API with nutrient ID: 2047.

Other energy values are calculated using Atwater specific factors per food as outlined in the USDA Handbook 74. These specific calculations are represented in FoodData Central as "Metabolizable Energy (Atwater Specific Factor)" and is identified in download and API with nutrient ID: 2048.