I have reviewed the claimed benefits of raw pet diets previously, as well as the potential risks of these diets (1,2,3). The bottom line is that there is no credible evidence that these diets have any health benefits or that they are safer or more nutritious than conventional commercial diets or properly formulated cooked homemade diets. Given they have small but clear risks, there is reason to avoid them. There is now a small bit of additional evidence arguing that, in fact, the nutritional value of cooked meat is actually greater than that of raw meat.
Carmody, RN. Weintraub GS. Wrangham, RW. Energetic consequences of thermal and nonthermal food processing. Proceedings of the National Academy of Sciences. 2011 [EPub ahead of print)
One of the authors, Richard Wrangham, is an ecologist who has studied the impact of food on the evolution of humans and other primate species. Last year, in his book Catching Fire: How cooking made us human, Dr. Wrangham presented the thesis that a key event in human evolution, the rapid development of a large brain, was made possible by the discovery of cooking, which not only made food safer by destroying parasites and infectious microorganisms, but also increased the energy available in the food. He was able to cite extensive evidence that the difficulty finding adequate calories is a key constraint on the health and reproduction of animals in the wild, including early humans, and that cooking made dramatically more energy available from plant foods. As the authors of the current study put it, “Energy availability is a routine constraint on metabolic processes, including growth, disease suppression, and reproduction, and therefore, it is a key variable for human nutrition and evolutionary fitness.’ The same is, of course, also true for other animals.
In his book, Dr. Wrangham was also able to report studies showing that modern humans relying on exclusively raw foods, for ideological reasons, are chronically undernourished as a result. A missing piece in his argument for the value of cooking, however, was evidence that cooking increases the caloric value of meat, which was suggested by a number of indirect studies but which hadn’t ever been clearly demonstrated. This new study supplies this missing piece.
The study compares the energy intake and weight gain of mice fed either sweet potato or beef. Different groups were fed these foods unprocessed, pounded but not cooked, cooked but not pounded, or pounded and cooked. The results for both sweet potato and beef showed that the mice gained more energy from the cooked foods than from raw or pounded foods, and that cooked foods were preferred.
Of course, dogs and cats are not mice, and they are not fed individual ingredient diets. The point of this study is not to evaluate the issue of the benefits and risks of raw pet diets, which is a much more complex subject. However, it does challenge one common claim made in support of raw diets, which is that raw foods have greater nutritive value. While cooking does reduce the levels of some nutrients, it makes others more available. One crucial nutritive component of food is the energy it provides, measured in calories. And this study demonstrates that the energetic value of both starches and meat are increased by cooking.
Since many of our pets are overweight, one could argue that we shouldn’t care about the greater calorie value of cooked foods since calories are not a limiting resource for domestic animals, as they are for wild animals. Clearly, we need to limit the caloric intake of our pets to maintain a healthy body condition. However, there is still no reason to think that raw diets are superior to cooked diets for this purpose, since the best way to ensure appropriate calorie intake in our pets is to feed them an appropriate quantity of nutritionally balanced food and monitor their body condition. The notion, often advanced by proponents of raw diets, that cooking is an entirely destructive process in nutritional terms is clearly not supported by this study, which reinforces the fact that cooking has been universally practiced by human populations for tens of thousands of years because it improves the nutritional value and safety of food.