Written by: Sarah Strange
An Intro to the Ideas of Richard Wrangham
“ Nowadays we need fire wherever we are. Survival manuals tell us that if we are lost in the wild, one of our first actions should be to make a fire. In addition to warmth and light, fire gives us hot food, safe water, dry clothes, protection from dangerous animals, a signal to friends, and even a sense of inner comfort. In modern society, fire might be hidden from our view, tidied away in the basement broiler, trapped in the engine block of a car, or confined in the power station that drives the electrical grid, but we still completely depend on it.”
Richard Wrangham is the Ruth Moore Professor of Biological Anthropology at Harvard University and the author of the book and source of this excerpt, Catching Fire: How Cooking Made Us Human. His theory picks up where Man the Hunter leaves off, explaining the major transition of our species from the apelike ancestors to the manly ones. He explains how mastering the use of fire affected us in every aspect of our lives, from being able to live without the protection of the trees, to the structure of our digestive systems adapting to the inclusion of cooked foods, and with greater digestibility and a less-expensive digestive system, the bonus of increased brain size. As you read his explanation, even within the first few pages, you realize that his theory is genius and you can’t help but shake your head at how obvious it seems.
Ditch That Fur Coat and Come out of the Tree House
Most primates sleep in trees. This is a handy insurance policy against being snatched away in the night by a crafty predator. Why would we start sleeping on the ground? This would have illustrated a decrease in brain size, unless there is some factor we weren’t thinking of… like fires. Nighttime predators would have cautiously avoided fire and the chances that we would be better able to see them coming or hold watch in the night by firelight, and would have enabled us to live farther from the trees and forest. And how did we lose all of our body hair without a greater source of nighttime heat? At some point, somewhere, somebody must have dropped food into a fire or discovered a cooked something or other… it must have been almost as earth shattering as the invention of ice cream. Barbecued lizards!
Adapted to Cooking
To me, this is where it really gets interesting. So we start scavenging a little, add brains and marrow to the menu, get a little brain boost out of it, start making knives. Cool. We do this for a while, a few million years, no big deal, then suddenly we go from zoo creature to the Geico commercial guy? It’s clear that Homo erectus was a much better hunter than the hairy little habiline butchers, but the common sense concepts of evolution go a little wacky when we learn that erectus’ jaw and teeth shrank. This is not a structural improvement if you’re going to be eating a lot of raw meat or raw plant matter, and successful adaptations rarely suck.
Not only did we show up with smaller jaws and teeth, accompanied by much weaker jaw muscles, we also showed up with shorter digestive tracts, small stomachs and small colons. Our boss should have fired us on the spot for incompetence. These changes to our “outfit” make it impossible for us to extract the same amount of energy from raw plant matter as our ape ancestors, and impossible to tear through and masticate raw meat as well as our carnivore acquaintances. We don’t keep food in our stomachs as long as carnivores do, which is what enables them to break down raw meat. We don’t keep food in our colons as long as other primates do, which allows the fibers to ferment long enough to derive a lot of calories from them. Apes keep food everywhere longer than we do. In their giant mouths, giant stomachs, not-so-small intestines, and of course, their giant colons. Great apes eat at least twice as much by weight as we do, and fiber composes 30% of their diets as opposed to 5-10% of ours. Humans also have a reduced physiological tolerance for raw vegetation high in toxins and tannins that apes and monkeys can clean through pounds of in a sitting. We can’t even hang in long enough to chew some of their favorite foods because the chemicals are either extremely bitter or severely agitating- some can even numb our mouths like novocaine. We are food wusses. If our guts are inflamed, handling fiber at all is a pain.
However, our digestive system is highly proficient at digesting cooked food. Digestion is a costly process in terms of how much energy is needed to carry it out, and just like greater muscle mass being more energetically expensive to maintain, so is a giant digestive tract. The adaptations of the human digestive system are less efficient at digesting raw plant matter and raw meat, but highly efficient when the food has been partially broken down and processed prior to consumption. Interestingly, the adaptation of smaller teeth can be produced independent of genetic evolution, just by weaning an animal on soft, cooked foods.
The Energy Theory of Cooking
Wrangham’s energy theory of cooking states that the more digestible a food is made by thermal processing, the more access you would have to it’s calories. A food that has been softened by cooking (some of it’s starches gelatinized and it’s proteins denatured) will be moved along much easier, and your gut will appreciate it’s decreased workload. Pre-processing is the same reason we chew our food, so this really isn’t an abstract concept. Some types of cooking can make portions of food less digestible, like searing a steak- that outside part of the steak, while delicious, is less-digestible. Some nutrients can be lost in run-off juices not added back to the food before eating, but all in all, cooking greatly helps us out. Typically the minor amount of nutrient loss does not account for the even greater amount of nutrients lost in undigested food that winds up in our septic tanks.
In the 1990’s, Belgian gastroenterologists tested the digestibility of raw vs cooked egg by examining the contents of the ileum, the end bit of the small intestine. Ileostomy patients were digesting around 51% of the raw egg as opposed to 91% of the cooked. Healthy subjects digested 65% of the raw egg and 94% of the cooked. Wrangham and two of his colleagues tested the effect of thermal and nonthermal processing of meat and starch in 2011, and demonstrated that the energy gain from the thermally processed food was greater than nonthermally processed food. Observational evidence shows us that most animals will prefer cooked food if it’s offered to them, and they will gain more weight on cooked diets over raw diets. This is why the raw diets we put our fat dogs on work so well.
Unfortunately, this has not at all been widely tested, and the National Nutrient database does not factor for digestibility. Not everyone is on the same page yet. The current system used to determine the caloric value of foods is the Atwater system, which determines how much protein, carbohydrate, fat, and alcohol are in a given food, then counts up the values assigned to 1 gram of each of these nutrients. One of Wrangham’s research partners, Rachel Carmody, explains the failings of the current system:
“The system is based on principles that don’t reflect actual energy availability,” Carmody said. “First, the human gastrointestinal tract includes a whole host of bacteria, and those bacteria metabolize some of our food for their own benefit. Atwater doesn’t discriminate between food that is digested by the human versus the bacteria. Second, it doesn’t account for the energy spent digesting food, which can be substantial. In both cases, processing increases the energy accrued to the human. Such evidence suggests that food labels do not properly account for the effects of food processing.” 
Yet another reason why OCD attempts at calorie counting fall short of their attempted accuracy.
The Raw Deal
The cooking theory makes absolute sense, but it still has to tackle the myth that most of us have been operating under, that raw, unadulterated foods are “better” for us. Well, define “better”. In a world where calories are scarce, like the one our species grew up in, making energy more available by cooking would have been “better”. Could we have survived and would we have evolved to the very expression of the species that created Facebook on a raw diet? We’d have to make that one look pretty good to sufficiently deflate the cooking theory. Let’s take a quick look at the raw camp and see if it seems plausible that we evolved to eat raw, that we could really thrive on raw back in the day and not wind up with 4’ long torsos and a yap that would put Mick Jagger to shame.
Raw foodist theory points out that our genes are 99% chimp, chimps were pretty much vegetarians, and they were raw foodists, so therefore that’s how we should eat. Nevermind the 5 or so million years of evolution between us, and the subtle differences, like they’re in zoos and we’re in condos.
In 2006, the Brits conducted an experiment on 9 unhealthy individuals over the course of 12 days, known as the Evo Diet. They put them in their own plot in the zoo, and fed them a raw diet, under the supposition that this is the diet we were evolved to eat. Go ahead and chuckle, I just did. What does being in a zoo have to do with a diet supposedly evolved for humans? Anyway, the diet they were fed for 12 days consisted of a variety of raw fruits and vegetables, nuts, and seeds, and in the second week they were fed a little cooked oily fish. The people ate until they were full, taking in up to 10 pounds of food a day with about 2500 calories. The people running the experiment were happy with the improvements in health, but shocked by the weight loss averaging .8 of a pound a day, since they were consuming enough calories to maintain weight, according to their calculations.
There are only three studies conducted on the body weight of raw foodists, according to Wrangham’s book. The most comprehensive of them was the Geissen study, which questioned and examined 513 raw foodists. This isn’t quite as legit as confining people to a zoo for 30 years, but what was shown was that the higher the percentage of raw food in the diet, irrespective of whether or not they consumed meat, the lower their BMI. One third of those who ate purely raw had body weights that categorized them as being in a state of chronic energy deficiency. The Geissen study also found that 82% of long term raw foodists included some cooked food in their diets. The study also showed that the more raw food women ate, the less likely they were to have regular periods, many of whom had completely ceased to menstruate. This equates to being infertile and losing bone mass. Some raw foodists (and I did hear this one at a raw food guru talk I attended once upon a time in Boulder) claim that menstruation and ejaculation are just a body’s way of eliminating toxins and once you become truly clean, ejaculating and menstruating is no longer necessary. Facepalm! Seriously, I remember the promises of menstrual cycles practically becoming “unnecessary”, provided you really stuck to it. While this does sound like an upshot, it’s kind of like promoting the loss of your legs by saying you’ll never have to run 400m repeats. Locomotion: just for the overachievers!
The last sort-of nail in the coffin for the theory that raw foods are our evolved diet, is that they would never work in the wild. Wrangham found no reports of long term survival in the wild on a raw diet. Most commonly, rapid starvation is the biggest threat to survival in the wild on raw foods, even with intimate knowledge of edible forage, just ask Robb and the I Cavemen cast. What makes a modern raw foods diet livable is that we now have unlimited access to food processing, making nutrients a little more available. Blenders, dehydrators, grinders, sprouting, and grocery stores that can provide year-round access to produce and nut butter that clearly would be hard to scrounge up in the wild. Also keep in mind that these domesticates are a wee bit more energy dense than they were in the wild. The German team also found that 30% of the raw foodists’ calories came from lipids that would have been inaccessible to any hunter gatherer.
So without these modern conveniences, how well do you think they would do? Anybody really wanna try? And judging by the fact that many of them cease to be reproductively functional, how well do you think we’d do if this was our evolutionary strategy?
I think the cooking theory just won. Maybe for some of you this was like watching a dance battle, and you’re not so sure. And so what is he saying? That no one should ever eat raw food? Taking a look at the waistlines in our country, including more raw foods in our diets, provided they aren’t teeming with parasites, could be a great way to reduce the energy load of our meals… or, if you’re trying to get jacked to holy hell and need as much help as you can get, then cook it up! If your dog’s a fat ass, give him some raw kibble. The temperature at which you should cook your food is a whole other exciting discussion, but low and slow seems to be the winner.
It’s compelling to think that the use of fire and cooking created the shape of our faces, hairless (more or less) bodies, and short torsos. Our shortened digestive tracts are adapted to including cooked food. Now ponder all the other ways we’re all hooked on fire, and Wrangham’s theory that cooking made us human seems more than natural.
1. Energetic consequences of thermal and nonthermal foodprocessing
Human adaptation to the control of fire
Sarah is a resident of Denver, Colorado and co-owner of a gym where she coaches, heads up the nutrition seminars and counseling, and organizes the local foodshares program. Her athletic background includes 13 years as a ballet dancer, martial arts, yoga, Pilates, triathlon, and currently focuses on Olympic weightlifting.