Richard Wrangham
“Every day, humans in every global society devote time and energy to processing food--cooking it, grinding, slicing it, pounding it--yet we don’t understand what effect these efforts have on the energy we extract from food and the role these might have played in our evolution. It is astonishing, since energy gain is the primary reason we eat it.” (Rachel Carmody, student and colleague of Richard Wrangham, Harvard Gazette, 2011)
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Kenneth Heaton’s interpretation of the word “overnutrition” changed my way of thinking about food. It made me wonder whether my body might have as little need for a surfeit of nutrients as it does for a surfeit of calories. After all, living as I do amidst a smörgåsbord of plenty, the chances of my becoming nutritionally deficient are minimal as long as I eat a rounded variety of foods. So I have changed my selection and preparation of food to favour a less nutrient-dense intake. As I ponder the gastrointestinal literature, the words which now interest me most are “digestible” and “indigestible”--because I see that the degree of digestibility of a food predicts the degree of calorie absorption available from it. In a nutshell, the less digestible a food, the less fattening it will be.
To switch from eating food in as digestible a form as I can--a natural human instinct--to eating it in the least digestible form I can is a quantum leap for me. It is also one most people wouldn't understand–my sister the nurse, for example--which is why I call it “nutritionally incorrect” (by analogy with the term “politically incorrect”: the saying of something that contravenes an official moral code. The doctrine of nutritional maximisation--five a day, and all that--is surely a moral imperative: do what nanny says or you deserve all you get.)
Many of our assumptions about health derive from official propaganda aimed originally, and with the best of intentions, at sparing sections of the populace from malnutrition. It was a numbers game: if we all max up on nutrients, fewer will suffer and die--who can argue with an equation like that? But the aspiration towards basic nutrition for the uneducated masses has turned into an aspiration towards maximal nutrition for the educated elite. Rare is the health guru who fails to recommend us a cartload of supplements. In fact, such gurus often set themselves up on the side as commercial dispensers, flogging us nutritional supplements more expensive than those on the supermarket shelf, which they implicitly mock us for buying. The aura of nutritional morality pervades even the scientific vocabulary, where terms such as “malabsorption” and “inefficiency” are used to describe the passing of superfluous calories in the stools, as if the body were some sick and recalcitrant child unable to polish off what was provided for its own good.
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One day, while surfing, as one does, the topic of monkey nutrition, I stumbled on the thoughts of the British primatologist Richard Wrangham, a Harvard University professor specialising in the study of chimpanzees. As a young man, Wrangham carried out a somewhat eccentric experiment on himself, in which he tried living on a diet of chimpanzee food. He found he could just about sustain himself on the diet but only with great effort, because the food was so much less calorie-dense than what he was used to.
“I learned that nothing they ate was so poisonous it would make you ill, but nothing was so palatable that one could easily fill one’s stomach." (Wrangham, Interview in Discovery Magazine, 2011)
To absorb the nutrients you need from a chimp diet, it seems you would have to eat for much of the day, as monkeys themselves do. Wrangham hypothesised that as we evolved from wild apes something radical happened to our nutrition, something that helped us extract more nutrients, and more quickly, from our food and conferred on us an evolutionary advantage. He proposed that the revolution occurred when we began to process and cook our food, thus enabling us to absorb more calories from it than had we eaten it raw. To his surprise, Wrangham, a relative interloper in the field of nutritional studies, found his theory rejected by the food-science establishment, and not so much for its evolutionary hypothesis as for its nutritional science. Many peer commentaries simply dismissed the notion that cooked food provides more energy than raw. To test his theory, therefore, Wrangham (with his colleagues) recently carried out experiments on differences in calorie absorption rates between raw food and pounded or cooked food. Here is an extract from the summary of one of those studies:
“Using mice as a model, we show that cooking substantially increases the energy gained from meat, leading to elevations in body mass that are not attributable to differences in food intake or activity levels […] Our results indicate significant contributions from cooking to both modern and ancestral human energy budgets. They also illuminate a weakness in current food labeling practices, which systematically overestimate the caloric potential of poorly processed foods.” (Carmody, Weintraub, & Wrangham, Energetic consequences of thermal and nonthermal food processing, 2011)
This finding did not surprise me, of course, for I’d read Heaton and the classic school of British gastroenterology; but that adverb “substantially” leaped out at me. Scientists don't use such words lightly. All I’d seen to this point were estimates of between 5% and 20% of calorie savings from eating whole foods. Those are impressive enough figures, and worth taking advantage of, but I’d forgive any reader of this thread for not finding them much to get excited about (and anyway, as dietary pessimists, most of us would probably assume it our luck to calorie-save at the 5% end of things). Yet, as I mentioned in earlier posts, my experience with nuts told me unequivocally that I was excreting a considerably larger proportion of the calories in them than 20%, perhaps even the majority of the calories listed on their packets. Did Wrangham’s “substantially” encompass what had happened to me?
In another study, Wrangham’s team, under Rachel Carmody, compared mice given raw sweet potatoes and beef at certain times and cooked sweet potatoes and beef at other times.
“For both meat and sweet potato, [Carmody] found that when the food was cooked the mice gained more weight (or lost less weight) than when it was raw.” (Wrangham, Interview in Discovery Magazine, 2011)
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What then are the implications for weight loss and maintenance? I’ve no intention of becoming a raw foodist, by which I mean someone who never cooks food and would voluntarily nibble a parsnip. In Britain, we mostly don’t cook nuts, so I don’t think of eating uncooked nuts as different from eating uncooked fruit; but both are raw, and they retain their internal architecture till they enter the mouth, at least when unchopped. If the difference in available calories between uncooked and cooked food were only small, maybe there’s little I can do (by way of food preparation) to reduce potential calorie absorption from my diet. But if, as I suspect--and as Wrangham believes--the differing potential calorific effects of cooked and raw food are “substantial”, then the degree of calorie availability should vary according to how broken up or well cooked a food is. To this end, I chop and grind my food as little as possible before cooking it, and I cook it as lightly as I may for it to be tasty. It’s too early for me to tell whether this makes a difference; but I find these days I can eat many more calories a day than I used to, without putting on weight. Of course, the reason could be something else entirely--time will tell.
As I’ve mentioned before, many studies find that food has less calorific effect the less it is processed. But, unfortunately, apart from Wrangham’s studies, little research has been done on the calorific differences between cooked and raw food, as such. Food labels that mark a difference (for example on rice) do so on the basis of calculations from calorimetric tables rather than on the basis of digestive tests. This is particularly true of meat–the meat industry doesn't fund research into the matter, because there's no profit angle. Nevertheless, I find myself choosing types of meat that can be cooked lightly, such as rump steak, chicken breast, and liver. I try to avoid overcooking meat, as so easily happens in the oven or slow cooker.
Every variety of food on the market would have to be studied at different cooking levels for a picture of what is at stake to emerge . For the moment, we have Wrangham’s estimate of what is at stake, and it is mind-boggling:
“The next wave of research will decide how profound the effects of cooking are. My best guess, based on studies of specific foods, is that the increase in net calorie gain from cooking will prove to be in the region of 25%–50%. That is only a guess, but I am confident it will be much higher than 10%.” (Wrangham, Interview in Discovery Magazine, 2011)
Wow. If anything deserves reading twice on this thread, surely that is it.
Last edited by Plinge : Sat, Jun-09-12 at 09:50.
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