Cooking increases the caloric value of meat and starches

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.

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3 Responses to Cooking increases the caloric value of meat and starches

  1. rita says:

    I know this is about raw food diets for pets, but just to keep the record straight, “studies showing that modern humans relying on exclusively raw foods, for ideological reasons, are chronically undernourished as a result” gives a slightly misleading impression: raw foodists, as far as I know, maintain these diets for health &/or weight even “spiritual” reasons , not ideological ones; there is nothing essentially ethical/philosophical about the whole business. That said, by its very nature raw food is often exclusively plant-based because animal food products are generally cooked or processed. This does lead some of the adherents of this type of diet to ethical veganism, for the simple reason that once people find they do not need to proffer excuses for the exploitation of nonhumans (having no personal interest in doing so), they are free to see that current human treatment of nonhumans is not ethically sustainable.

    But many – Gabriel Couzens, to pick an extreme example, make their raw food regimes vegan because eating animal products causes suffering to the animals, so that the human consuming them absorbs “bad energy”: in other words, the system is not designed to reassess humans’ behaviour in the world, but to accumulate health benefits or spiritual brownie points. Science Based Medicine reviewed some of his videos a while back and, again, the confusion with ethical veganism occurred.

    Since the American Association of Dieticians has repeatedly declared that well-planned vegan diets are adequate for human health from cradle to grave, the dubious benefits advertised by raw-foodists have to be seen solely as part of the relentless human tweaking of diet to favour themselves or give themselves some sort of advantage in the race for life. Veganism, on the other hand, is concerned with how humans can and should behave so as to distribute the world’s resources more fairly, without exploitation of the helpless, cruelty and unnecessary killing. This is ideological, raw foodism in its essentials is not.

    It is unfortunate that this confusion occurs, because it perpetuates the myth that vegans are skating on thin ice so far as nutrition is concerned, and that they are inextricably linked with “alternative” nostrums, belief in energy therapies, vitalism and so on, which is emphatically not the case.

  2. skeptvet says:

    I think the confusion here is largely semantic, especially since I referred pretty specifically to the distinction between cooked and uncooked foods, not between meat-based and non-meat-based dets.

    In the broadest sense, of course, any dietary choice is ideological in that it is based on a set of beliefs and values. However, what I was referring to, not so clearly, was the distinction between dietary choices made on the basis of the best scientific understanding of nutrition versus other beliefs not based on nutritional science. Choosing to eat raw or vegan for “spiritual” or ethical reasons is an ideological choice, not a scientific one. There is, of course, nothing wrong with this. I pesonally don’t eat meat for primarily ethical reasons, and that is part of my ideology about what is appropriate treatment of other animals by humans.

    My point was simply that raw foodists often choose not to cook their food for reasons having to do with beliefs about the “energy” of “living food,” the necessity of consuming “enzymes” in unprocessed foods, the nature of a “natural” pre-industrial human diet, and other such concepts that are not based on sound science. These ideological concepts lead to decisions which are, in the case of those practicing pure raw foodism, nutritionally unhealthy in most cases. I also think veganism is as much or more an ideological position rather than one based on nutritional science and health. I agree that it is possible to practice a healthy vegan diet, and there may even be some health advantages to some form of vegetarianism, but that doesn’t make dietary choices based on ethical concerns any less “ideological.”

    So I didn’t mean “ideological” to sound perjorative, I simply wanted to point out that the reasons people make the particular dietary choice not to cook their food is based on considerations other than nutritional science, and in this specific case these choices generally lead to nutritionally inadequate diets. While the ideological nature of the dietary choices leading to various forms of vegetarianism is much the same, this doesn’t imply that these diets are necessarily nutritionally inadequate, and as you point out they can in fact be perfectly healthy if properly formulated.

    Thanks for the comment!

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