Now, on to other issues.
In researching the the idea that not all proteins are created equal, (e.g. is a diet of beef, venison, chicken, duck, etc. as good for cats vs. what they would naturally hunt, those prey items being lower fat naturally) I did wind up finding some very interesting information on the cooked vs. raw issue (although it wasn't what I was searching for at the time.
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The bottom line is that there is a LOT more research that needs to be done. (Yeah, that's news LOL!) There is also conflicting information, based on what or how the issue is studied.
The only "definitive" in the cooked vs. raw debate (and not specifically as it relates to cats) is that nutrients/energy in starches and most plant-based proteins are more available if cooked.
And while there does appear to be some question on the work done on the impact of cooking on enzymes, even if we accept that enzymes are destroyed in animal protein when cooked, initial research into "cooked vs raw" in meat indicates that the process of cooking functions as a form of "pre-digesting," increasing the energy available in the protein (meaning the loss of enzymes is not critical to the use of the protein).
Certainly, some amino acids are affected by light, oxidation, and temperature. But this appears to be more the exception than the norm, taurine and B12 being the most sensitive.
For those interested in the topic, the references are:
Easy start at BBC News:
Did the discovery of cooking make us human?
The study referenced in the news story:
Boback et. al 2007, "Cooking and grinding reduces the cost of meat digestion," Comp Biochem Physiol A Mol Integr Physiol. 2007 Nov; 148(3):651-656. (
http://www.ncbi.nlm.nih.gov/pubmed/17827047)
Abstract
The cooking of food is hypothesized to have played a major role in human evolution partly by providing an increase in net energy gain. For meat, cooking compromises the structural integrity of the tissue by gelatinizing the collagen. Hence, cooked meat should take less effort to digest compared to raw meat. Likewise, less energy would be expended digesting ground meat compared to intact meat. We tested these hypotheses by assessing how the cooking and/or grinding of meat influences the energy expended on its digestion, absorption, and assimilation (i.e., specific dynamic action, SDA) using the Burmese python, Python molurus. Pythons were fed one of four experimental diets each weighing 25% of the snake's body mass: intact raw beef, intact cooked beef, ground raw beef, and ground cooked beef. We measured oxygen consumption rates of snakes prior to and up to 14 days following feeding and calculated SDA from the extra oxygen consumed above standard metabolic rate. Postprandial peak in oxygen consumption, the scope of peak rates, and SDA varied significantly among meal treatments. Pythons digesting raw or intact meals exhibited significantly larger postprandial metabolic responses than snakes digesting the cooked ground meals. We found cooking to decrease SDA by 12.7%, grinding to decrease SDA by 12.4%, and the combination of the two (cooking and grinding) to have an additive effect, decreasing SDA by 23.4%. These results support the hypothesis that the consumption of cooked meat provides an energetic benefit over the consumption of raw meat.
Of course, this only addresses the energetic aspects of cooked meat. But it's a start.
For more information and details, there is a study published by several Harvard professors (and available online).
http://www.anthro.utah.edu/PDFs/Carm...okingHumEv.pdf
Carmody and Wrangham 2009. "The energetic significance of cooking," Jour Human Evol 57: 379-391.
Abstract
While cooking has long been argued to improve the diet, the nature of the improvement has not been well defined. As a result, the evolutionary significance of cooking has variously been proposed as being substantial or relatively trivial. In this paper, we evaluate the hypothesis that an important and consistent effect of cooking food is a rise in its net energy value. The pathways by which cooking influences net energy value differ for starch, protein, and lipid, and we therefore consider plant and animal foods separately. Evidence of compromised physiological performance among individuals on raw diets supports the hypothesis that cooked diets tend to provide energy. Mechanisms contributing to energy being gained from cooking include increased digestibility of starch and protein, reduced costs of digestion for cooked versus raw meat, and reduced energetic costs of detoxification and defence against pathogens. If cooking consistently improves the energetic value of foods through such mechanisms, its evolutionary impact depends partly on the relative energetic benefits of non-thermal processing methods used prior to cooking. We suggest that if non-thermal processing methods such as pounding were used by Lower Palaeolithic Homo, they likely provided an important increase in energy gain over unprocessed raw diets.
However, cooking has critical effects not easily achievable by non-thermal processing, including the relatively complete gelatinisation of starch, efficient denaturing of proteins, and killing of food borne pathogens. This means that however sophisticated the non-thermal processing methods were, cooking would have conferred incremental energetic benefits. While much remains to be discovered, we conclude that the adoption of cooking would have led to an important rise in energy availability. For this reason, we predict that cooking had substantial evolutionary significance.
Italics my emphasis.
The paper is an excellent review piece, with tables that cover the literature on proposed consequences of cooking, calories per gram of dry matter for selected meats (raw and cooked), and comparison tables of the annual energetic cost of foodborne illness from meat given cooking vs. consumption of raw meat (applicable to humans, but with relevence to pets, given the commercial nature of the meat processing industry and the fact that dogs and cats may be more resistant to illness by ingested bacteria and parasites, they certainly can and do get sick from them).
Finally, for those interested in the topic, this is a more thorough discussion of the impact of cooking on numerous vitamins and minerals. It is not a piece published in a scientific peer-review journal, but it is very well researched and referenced:
http://www.beyondveg.com/tu-j-l/raw-...ooked-2h.shtml
"Does cooking render minerals "inorganic" or less assimilable?"
For those who don't want to read the whole thing, the primary conclusions of relevence to this discussion are:
"Considering trade-offs rather than spurious black-and-white divisions. We see from the many considerations above that there is no clear-cut conclusion that can be stated with confidence about the question of raw vs. cooked foods as a whole. However, if we break the question down into simpler aspects, there are several general observations that can be made. First, the two major overarching considerations are:
Amount of nutrients in a food (the potential "benefit"). First, virtually all foods contain more nutrients in the raw state. On the other hand, the differences are not very great: ranging from approximately 10-25% in the case of most vitamins, while the difference is negligible (almost zero) with respect to minerals.
"Cost" to obtain the nutrients. However, there are also digestibility, antinutrients/toxicity, and bioavailability to take into consideration when assessing how many nutrients can actually be assimiliated from a particular food. Cooking can affect these considerations positively or negatively, depending on the circumstance.
"Net value" of a food depends on assessing the cost/benefit trade-offs. Putting the two above points together means that one must consider the cost/benefit trade-offs--that is, the nutrients present vs. the "cost" to get them--the latter determined by both absorbability and antinutrient concerns."
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