We = (what we eat) – (what they eat)

The sound track for yesterday’s run was a talk by primatologist Richard Wrangham1, author of Catching fire: how cooking made us human. Cooking, he says, has long been thought to be an optional cultural practice, like wearing jewelry. But really, he argues, cooking was the essential technological innovation that enabled us to produce the metabolic energy we needed to become human.

How? Cooked food is more digestible than raw food. And not just by a little, but by a lot. Learn how to control fire, use it to cook your food, and you free up extra energy — plus time that would otherwise be spent masticating. Spend that time hunting, and your metabolic equation gets even better.

Wrangham has fascinating things to say about how this surplus time and energy explains such cultural universals (or former universals) as marriage, sexual division of labor, and the family dinner. Whether you agree or disagree with this analysis, though, it’s supported by an attention-grabbing claim. Everything we thought we knew about absorption of energy from food is wrong.

To this day, Wrangham says, the USDA website2 publishes tables that make no distinction between the nutritional value of cooked and raw food. On this page, for example, the energy content of one large raw egg is given as 75 kcal. The value for one large hard-boiled egg is almost the same: 78 kcal.

This is wrong, Wrangham says. A cooked egg delivers way more energy than a raw egg. How could this be? And how could we not know it?3

Here’s the explanation. We have traditionally measured the energy content of food by comparing input (the food we eat) and output (the feces we excrete). Burn both in a calorimeter, subtract, and the difference is the energy that was extracted from the food.

Yes, but extracted by whom? Or rather, by what? The energy that we humans take from our food has almost all been extracted by the time it reaches the end of the small intestine. But it has a long way to go yet. It must also pass through the large intestine, where dwell a myriad of gut flora. And they, Wrangham says, are hungry. If you eat a raw banana you only get some of its energy, and they get most of the remainder. If you eat a cooked banana, though, you get a lot more of its energy and leave less for them. The end result looks the same, but the internal distribution is quite different.

So you need to compare the energy in food entering the mouth to the energy remaining in the digestive products leaving the small intestine.4 Only then does the dramatic difference between the energies we get from raw versus cooked food become evident.

This is a great parable about instrumentation, measurement, knowledge, and epistemology. What other profound errors of basic understanding arise from misplaced instrumentation? And what might we learn by making simple — and in retrospect obvious — adjustments?

1 Yet another podcast from KUOW’s Speakers’ Forum, which has become one of my most reliable sources of audio brain food.

2 A sad reminder that government website and chamber of horrors are still, too often, synonymous.

3 The error, if it is indeed an error, propagates to WolframAlpha, which sources the USDA data. Compare 100 g of raw egg to 100 g of cooked egg.

4 How do you tap in at that point? Recruit people who have had ileostomies.

21 thoughts on “We = (what we eat) – (what they eat)

  1. “explains such cultural universals”

    He has become my favorite example of that pattern were people take an perfectly valid interesting insight and then run out of control until it explains _everything_.

    cooked carrots v.s. feminism

  2. This is a fascinating topic. One of my undergraduate biology books stated that up to 10% of our caloric intake comes from otherwise-inedible food digested by our gut flora. I did some quick googling and couldn’t find a reference to that particular figure, but I did find this paper, The microbiome and obesity: Is obesity linked to our gut flora? (http://www.springerlink.com/content/f478905k8606g5m4/) which presents research suggesting the microbiome (the total community of microbes living in our gut) can predispose or protect the host from obesity.

    I would ask Dr. Wrangham if perhaps prehistoric humans had different gut flora optimized to liberate energy for the host from a non-cooked diet.

  3. I would ask Dr. Wrangham if perhaps prehistoric humans had different gut flora optimized to liberate energy for the host from a non-cooked diet.

    As I understand the argument, they extract energy perfectly well from raw food — but for themselves, not us, since by the time most of them get hold of it the train has left the station w/respect to human metabolism.

    Regarding the microbiome/obesity connection, I actually traced that meme a while back.

    It started here:


    (or, rather, in the article that press release refers to, which itself may still be unavailable online)

    and went here:


    I reflected on the disconnect between scientific and mainstream literature in a few posts:



  4. I’ve heard a different Pollan presentation about that book. Since you mention it, though, I’ve been looking for a convenient way to rip audio tracks out of YouTube videos for offline listening. (I know what Michael Pollan looks like, after all, and don’t need to be glued to the computer for yet another hour to listen to what he has to say.)

    There are various services that will take a YouTube URL and return an MP3. But the Cadillac solution for me would be:

    1. Favorite a video
    2. Subscribe to favorites
    3. Receive MP3s as enclosures in the subscribed RSS feed

    If anyone knows about (or has created) that, please do let me know.

  5. Wow, fascinating and profund! I’ve heard of the expensive tissue hypothesis regarding humans, meat consumption, and brain size versus intestinal size … but if cooking can give you 20-50% better absorption of a food, then that would give the first animal to master fire a huge boost over the other primates.

    I broke out my slow cooker after listening to that and put a kangaroo stew on the go :)

  6. While I agree that the body breaks down food much more easily when it has been cooked, you do lose quite a lot of nutrients and live enzymes. Live enzymes (that help break down and digest food) are found only in raw foods. If you were to juice fruits and vegetables, removing the fiber allows the food to practically digest itself as it is no longer slowed down by the fiber. This also allows your body to extract the nutrients from the juice instantaneously. A balance of cooked and raw foods is the best way to keep from overtaxing your digestive system.

  7. Tanya – Wrangham’s point is that we have substantially less digestive track compared to other animals. His argues that we have moved much of the digestive function out and into the kitchen. So in his model the juicer is a substitute for what other animals do with their small intestine.

    We have a saying at my house: “Any food that is unusual will have health claims made for it.” I suspect that extends to any dietary pattern.

  8. His argues that we have moved much of the digestive function out and into the kitchen. So in his model the juicer is a substitute for what other animals do with their small intestine.

    That’s a /great/ analogy!

  9. If you can be satisfied with viewing YouTube offline

    I don’t actually want to view, I want to listen to the audio tracks. Many, many videos of lectures — and I listen to a lot of lectures — work quite well as audio.

    I know various ways to download the video and convert to audio, but it’s just not very convenient. I want to point a podcatcher at service that take a set of YouTube URLs and emits an RSS feed with MP3 enclosures.

  10. Interesting topic. But, call me a skeptic on this. When something in my gut digests food it certainly would steal some portion of the energy available to me, but wouldn’t that organism also generate excess heat that my body would be able to use? (My body wouldn’t have to generate as much heat as a result).
    It’s not clear to me that the delta is that significant.

    Also, I recall from my days at Penn State that original calorie work was done by locking the subject in a room for a period of time and measuring the intake & outflow of energy. This type of closed system measurement would include the little guys in the subject’s gut.


  11. When something in my gut digests food it certainly would steal some portion of the energy available to me

    The assertion is that beyond your small intestine the energy wasn’t going to be available to you anyway.

    Your point about a possible reduction in the need for heat production is interesting, though.

    Anyway the real point here, for me, is about instrumentation, measurement, and scientific method. The closed system you describe does account for everything at a macro level. But it wouldn’t reveal a (possibly) significant variance in the distribution of energy within the system.

    If the variance is significant, and if in fact our definitive tables on the nutritive value of foods don’t account for that, it would be a pretty big failure of scientific method, and an important thing to correct.

    On an even more meta level, I’m viewing this whole thing as another test of whether online communication can actually enhance rather than preclude rational discourse.

    Along those lines, this caught my eye:


    The thread begins:

    My boyfriend sent this to me and said essentially “See? Raw food isn’t the right way to eat.” This article (blog?) is so dumb. First of all, the only concrete example of getting more energy from the cooked food than from its raw form is an EGG. Come on! Who is going around eating raw eggs thinking they are the right way to eat an egg? The rest of the info just seems unfounded. I’d be interested to see the study. Nevertheless, there’s no way I would eat a cooked banana over a raw banana, or any other fruit/veg. Seems like boolsheet.

    And I thought, sigh, it’s hopeless. But then, farther on:

    Roughly the same idea about cooking and calories with citations. Your boyfriend is misinterpreting it, but I don’t see why the blog post itself is dumb. It’s not making any claims about what we should currently be eating and there’s a link to the podcast the author is talking about. If you were interested in reducing your caloric intake without eating smaller portions, for instance, you’d want to be eating more raw food, not less.

    And finally:

    Yeah you are right, I posted without looking into it more and while I was still mad from my bf’s comments. Sorry all!

    Believe it or not, that made my day.

  12. I have heard from someone who would know (a researcher in food tech) that the Glycaemic Index is a bit dodgy for the same reason.
    The GI value of foods depends on not only raw vs cooked but even cold vs warm. It is also affected to a small extent by other foods eaten at the same time.
    For those who don’t recall: GI is a measure of the change in blood sugar after eating. Blood sugar level being a good measure of the energy immediately available to a body (fat being stored energy which must be converted prior to use).

  13. Jon, thanks for steering me to KUOW Speaker’s Forum. Some interesting topics there. Question – have you found an RSS feed for the archive? The feed with enclosures only seems to go back 10 shows.


    1. I just noticed that myself recently. I guess it’s one of those deals where you don’t get to reach back into the archive.

  14. Jon, have you seen huffduffer? It allows you to gather audio files as you browse the web. It apparently builds a podcast feed for all you’ve collected. Thought of you when I heard this on this week in google


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