Two numbers: yield and retention
Weight yield tells you how much a product weighs after processing compared with the raw product. Meat usually loses water and some fat, so the finished portion weighs less.
Retention tells you what part of a specific nutrient remains after processing. It is not the same as the content per 100 g of finished product: after water loss, a nutrient may look more concentrated even though its total amount has fallen.
Together, they show the composition of the finished portion.
Bognár’s tables
Antal Bognár collected yield and retention factors for many products and processing methods, including boiling in water and steaming [1]. These are averaged data, but they are much better than calculating by eye.
What changes most easily
The nutrients that change most are those sensitive to temperature or those that move easily into water. This especially applies to some B vitamins, including thiamine, and to folates. USDA retention tables use a similar logic [2].
Minerals do not “disappear” from heat itself as easily as some vitamins, but they can move into water, sauce, or meat juices. If you pour that liquid away, some nutrients go with it. If you use it in the meal, some of those nutrients return to the bowl.
In cats, taurine is especially important. It dissolves well in water, so during cooking some of it may move into the liquid. Larger losses are possible especially when the product is surrounded by water for a long time and the broth is not included in the meal [3]. In cooked diets for cats, taurine should be calculated deliberately [4].
Steam is gentler than water
The method matters. Boiling in water encourages nutrients to leach into the broth. Steaming limits the product’s contact with water, so it is usually gentler in that respect.
That is why it matters not only whether something is cooked, but also how it is cooked and whether the cooking liquid returns to the meal [1].
What to remember
If you serve a cooked or steamed diet, calculate it in that form. Changing the gram amount alone is not enough, because nutrients are lost unevenly.
That is why in BARFLAB the preparation method is part of the calculation, not just a note for the caregiver.
Sources
- Bognár, A. (2002). Tables of weight yield of food and retention factors of food constituents for the calculation of nutrient composition of cooked foods (dishes). Berichte der Bundesforschungsanstalt für Ernährung, BFE-R-02-03. Karlsruhe. https://www.fao.org/uploads/media/bognar_bfe-r-02-03.pdf
- USDA Agricultural Research Service (2007). USDA Table of Nutrient Retention Factors, Release 6. https://www.ars.usda.gov/arsuserfiles/80400530/pdf/retn06.pdf
- Spitze, A. R., Wong, D. L., Rogers, Q. R., Fascetti, A. J. (2003). Taurine concentrations in animal feed ingredients; cooking influences taurine content. Journal of Animal Physiology and Animal Nutrition, 87(7-8), 251-262. https://www.vetmed.ucdavis.edu/sites/g/files/dgvnsk491/files/aal/pdfs/spitze.pdf
- National Research Council (2006). Nutrient Requirements of Dogs and Cats. The National Academies Press. https://doi.org/10.17226/10668