The raw vs the cooked

April 2nd, 2010  |  Published in Stumpblog  |  10 Comments

I’ve been reviewing a 2009 article on the significance of cooking in human development.

Many folks argue that eating a diet of exclusively raw foods improves health. While it’s certainly true that humans traditionally consumed a lot of food types raw (e.g. fruit, some types of fresh-caught meat), they also cooked many (e.g. starchy roots, many other types of meat). (Interestingly, few raw food advocates suggest eating sashimi or something like the Inuit delicacy of raw organ meats.)

The authors of this study review the evidence that supports or refutes the significance of cooking in human evolution and health. Some key findings:

  • Humans on vegetarian diets gain more weight and exhibit higher reproductive performance when eating cooked food than raw food. Reproductive performance is generally a good proxy for overall health; when sex hormones are happy, everyone is happy.
  • Diets with a high proportion of raw food — even if that includes meat — nevertheless tend to result in lower body weights.
  • Women who eat a high amount of raw food have higher rates of amenorrhea or menstrual irregularities than those eating cooked food. Menstruation was absent in 23% of females of childbearing age who ate at least 70% of their food raw and in 50% of women reporting a 100% raw diet. Fascinatingly, this is not explained by vegetarianism alone, but rather by the proportion of raw food in the diet. As the authors note, “The poor ovarian performance of raw-foodists therefore cannot be attributed to their vegetarianism… [one researcher] concluded that women suffered because of their relatively low net energy gain as a consequence of eating their food raw.”
  • Many raw-foodists apparently do not limit their food intake, since they commonly describe themselves as experiencing persistent hunger despite eating frequently.
  • “We have found no records of individuals tending to gain weight while eating raw diets, even though the plant foods eaten by raw-foodists are mostly high-quality items such as germinated seeds, sprouts, fruits, nuts, and cereals, and tend to include oil. This is especially surprising since raw-foodists are typically members of urban communities, where habitual activity levels are lower than observed in traditional communities of hunter-gatherers or pastoralists. Furthermore, although raw-foodists are averse to cooking, they typically process their foods extensively by such methods as grinding, pounding, sprouting, and pressing, and even heating up to 48°C. A nutritional analysis suggested that on a diet of raw wild foods, which are generally lower in energy value and higher in fibre, energy intake in traditional communities would be so limited as to render survival and reproduction difficult.”
  • Cereals tend to be more digestible raw than tubers and legumes, but raw starches of all three types have important reductions in digestibility compared to cooked starches. In general, few cereals, tubers, or legumes are digestible raw — and many are highly toxic (such as raw kidney beans).
  • Archaeological evidence suggests that fat derived from bone marrow may have been preferred over muscle tissue as a source of energy and nutrients among early Homo. Moreover, it is known that diets deriving more than 50% of calories from lean protein can lead to negative energy balance, so-called “rabbit starvation,” due to the high metabolic costs of protein digestion, as well as a physiological maximum capacity of the liver for urea synthesis.
  • “The ileal [small intestinal] digestibility of raw eggs was found to be 51% in ileostomy patients and 65% in healthy volunteers. By contrast, the ileal digestibility of cooked eggs was 91–94%. These data indicate that cooking increased the digestibility of egg protein by 45–78%. This is a striking result considering that chicken egg proteins are commonly treated as having high biological value for humans whether they are consumed raw or cooked.”
  • “The poor performance of humans eating both raw vegetarian and raw omnivorous diets suggests that our species is biologically adapted to the consumption of cooked food; and importantly, some of the features preventing humans from utilising raw food efficiently include traits recognisable in fossils (i.e., small molars and relatively small total gut volume).”

In short, while we are still not 100% certain about small individual variations in digestibility, the balance of the evidence indicates that when it comes to health, fire is good.

Rachel N. Carmody; Richard W. Wrangham. The energetic significance of cooking. Journal of Human Evolution (October 2009), 57 (4), pg. 379-391

Responses

  1. Elizabeth says:

    April 2nd, 2010at 10:11 pm(#)

    I wonder how reliable the self-reporting is on “eating frequently.” Raw-foodism seems to be a pretty common form of orthorexia, and I don’t know if those following the lifestyle have a good handle on normal eating habits. Were there any numbers on how many calories they were taking in gross?

    Definitely interesting that raw-food advocates don’t talk a lot about sashimi, tartare, carpaccio, and so on. The study says that amenorrhea and low body weight don’t correlate with vegetarianism, but I would guess that meat of any kind still doesn’t play a large part in the raw-foodist’s diet.

    A food blogger I used to read posted once about working as a personal chef for some raw food people — here’s the post — and she balked at a “pizza” involving sprouted grains dried at 110 degrees Fahrenheit for 12 hours, because it would have amounted to the world’s most accommodating petri dish. I wonder if raw foodists generally have trouble with bacterial gastroenteritis, or if that was an isolated incident? A couple bouts of that every month would be enough to keep you from gaining weight, ugh.

  2. Keiko says:

    April 3rd, 2010at 8:20 am(#)

    This post made me realise that although vegetables – especially greens – are eaten daily in Japan, and in astonishing variety, raw vegetables don’t really play a large part in Japanese cuisine (and for the record, sushi and sashimi are not eaten daily in Japan, but rather as special-occasion-type meals. Fish is almost always eaten grilled). Most vegetables are either steamed or pickled before consumption. Fruit is eaten only in small quantities, as a snack or as dessert.

    Salads are never featured as a main dish, only as a small side serving.

    In fact, the first time my grandmother here saw me fix up a lovely, huge green salad she stared and asked repeatedly, “are you really going to eat that stuff raw?” She’d never seen anyone do that before. She never ate raw vegetables, ate only one piece of fruit a day, and lived to the ripe old age of 96. Some of her friends lived even longer.

  3. Dean J says:

    April 4th, 2010at 11:16 am(#)

    There’s one strong exception to “fire is good”, and that is charring/burning/etc is pretty bad for you, and deep frying is pretty bad for you.

    In both cases, fat of the deep fryer aside, it’s the temperature. Google for “Advanced glycation end-products”, or AGE compounds. The temperature of a deep fryer turns the outside of potatoes into something toxic that accelerates aging. Which sucks, because I love french fries.

  4. Ginger Baker says:

    April 7th, 2010at 11:40 am(#)

    I am a fan of raw foods, definitely, but I am FAR from a vegan. There are some of us out there who enjoy raw meat and fish (and I am not opposed to cooked meat too but I’ve always enjoyed my steak bloody LOL). I’ve been leaning lately towards a seasonal approach – I am very drawn to salads and fruit and “light” foods in the summer, and more into cooked foods in the winter.

    I don’t know if I will ever be 100% raw, all of the time, but I do find it very beneficial to do for a few months at a time. It just *feels* good. And I need less sleep, which is really a nifty effect – it freaked me out at first! Mostly though I eat a high percentage of raw because it’s yummy. :-)

  5. Great links for the weekend! says:

    April 16th, 2010at 2:34 pm(#)

    [...] the book, this BBC article summarises it nicely.  Alternatively, Mistress Krista at Stumptuous has looked in detail at a paper published in the Journal of Human Evolution that Richard Wrangham has [...]

  6. Travis says:

    May 31st, 2010at 4:09 pm(#)

    Very interesting article. I’m not huge on tons of raw foods, but do eat raw eggs regularly. I’m surprised by the findings on eggs, since I’ve always heard that egg proteins are supposed to be MORE bioavailable raw, not less.

    I *thought* my previous sources were solid, looks like I’ll need to go back and review them. What’s your opinion on raw eggs?

  7. Mistress Krista says:

    June 1st, 2010at 6:24 am(#)

    Travis: Raw egg white contains a protein called avidin that can bind with biotin in the body and create a biotin deficiency. Apparently this is a big problem in some countries where eggs are often eaten raw or undercooked. When cooked, this protein can no longer bind. I am told that we need egg yolk protein to digest egg white protein properly, but I am not sure whether this applies to cooked eggs as well. Raw eggs in general always carry some salmonella risk, although I believe that this risk varies from country to country; I believe the risk is higher in the US than in Canada simply because of differences in food regulation etc.

  8. Travis says:

    June 1st, 2010at 12:32 pm(#)

    Oooh, I got a response! As long as we’re talking eggs, the salmonella risk in the US is about 1 in 10,000, and that’s largely due to factory eggs. I make sure to buy cage free or free range eggs, check them before I eat and I’ve never had a problem.

    I don’t consider the biotin thing an issue either. There IS that protein in raw egg whites. But the yolk also happens to be a rich source of biotin itself, which supposedly compensates for the decreased absorption. Of course, this is from the same source that claimed higher protein bio-availability in raw eggs. Looks like I need to find more literature.

  9. Simma says:

    June 1st, 2010at 9:32 pm(#)

    Travis, animal protein is almost always easier for the body to use when it is cooked. I imagine it’s the same for plant protein, but I don’t know. Re: eggs, specifically, here is an ileal digestibility study:

    http://jn.nutrition.org/cgi/content/full/128/10/1716

    I don’t worry about salmonella from eggs, either. I use eggs raw in recipes that call for it, and I like the yolks still runny when I eat them fried or boiled.

    If you just like raw eggs and otherwise consume plenty of protein, I wouldn’t worry too much about digestibility issues. But if you’re relying on them for protein, then you might consider cooking them or eating more than you’re currently eating.

    As for biotin/avidin, I’ve always been told it’s only an issue if you’re consuming raw whites without the yolks (cooking denatures avidin, so cooked whites don’t pose this problem), as the yolks have more than enough biotin to compensate. Still, if your interest is in getting the full nutritional value out of the egg, it seems that you would be better off cooking them.

    I eat raw seafood and raw or nearly raw beef on occasion and don’t worry about digestibility, since I get plenty of protein otherwise. But if I had limited access to protein, I would cook it all more thoroughly to get as much out of it as I could.

    As Krista mentions, there are theories that the final stages of evolution of the human brain and social structure were able to happen because of advent of the ability to cook foods, and that we adapted physically as a species to a cooked diet. So I tend to take any assertion that raw food is more “natural” to humans with a pinch of salt and a liberal application of fire.

  10. Starlight says:

    March 15th, 2011at 4:57 pm(#)

    i found eating cooked egg whites without yolks to be quite toxic but i dont get any toxicity from eating cooked whole eggs (whites and yolks together)Could anyone explain this?


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