Thursday, October 11, 2007
The brain of an adult human uses 25 percent of the body’s total energy expenditure. That’s a lot of resources devoted to brainpower, but it seems to have paid off. Apes, who only allocate 8 percent of their energy budget toward thinking, are either in the zoo or backed into dwindling crumbs of habitat in Africa, while humans have invented things like mayonnaise.
This high-input, high-performance brainpower presents a riddle to evolutionary scientists. Building, operating and maintaining these amazing brains could only have come about with some kind of increasing energy supply. So where did this extra energy come from?
One widely accepted idea, the “swapping guts for brains” hypothesis, is that our ancestors’ switch from a plant-based to a meat-heavy diet provided this energy. Since meat generally contains a greater density of protein and calories than vegetables do, this digestive shift allowed our ancestors to utilize a more efficient form of energy, while helping them develop the brainpower to hunt it. Evidence from many corners of the animal kingdom consistently suggests that meat eaters – hunters – are smarter.
But according to Richard Wrangham, a Harvard University primatologist, there’s more to the solution of this energy riddle than just hunting and meat.
“Cooking produces soft, energy-rich foods,” he says, in an article in Science last June. This, he explains, increases the efficiency with which the food’s energy is extracted. Fewer calories are spent in digestive efforts, which leaves a higher margin of caloric recovery, he says.
Conducting research on Burmese pythons, Wrangham and a colleague, Stephen Secor, determined that the pythons spent 12.7 percent less energy digesting meat that was cooked. “By eating cooked meat, less energy is spent on digestion; more energy can be used for activities and growth,” suggests Secor.
The advent of cooking would also have increased access to calories in both hunted meat and gathered plants. As heat from cooking gelatinizes the matrix of collagen in animal flesh, it open up tightly woven carbohydrate molecules in plants to make them easier to absorb.
Subsequent experiments on mice showed that raw food eaters weighed less than mice that ate cooked food – even though the raw food diet had more total calories. This suggests that our ancestors would have received rapid benefits out of cooking, in terms of energy recovery, Wrangham says.
But wait a minute. Maximal caloric absorption may have been useful back in the day, but now we have too many fat people. Following Wrangham’s line of reasoning, food processing, like cooking, also makes calories more available, as sugar. Perhaps today’s over-processed food is contributing to obesity.
So it’s worth considering that even if cooked meat helped us evolve to who we are today, tomorrow’s dietary breakthrough might come from elsewhere.
To that end I’ve noticed a growing community of “raw-foodists” who seem quite happy and healthy, with no meat or heat in their diet, and very bright eyes.
The other week I ran into some raw-foodists while traveling. The raw food market stand of Colorado’s nonprofit Turtle Lake Refuge (turtlelakerefuge.org) is vibrant and fun. Flanked by a bicycle-powered juicer, the table was laid out with some interesting and tasty items like cabbage rolls, purslane kim-chi and acorn chocolate brownie.
“We’re into getting life out of food closer to when it’s alive,” says Katrina Blair, a founding member of Turtle Lake Refuge. Technically, raw food has not been heated above 118 degrees, she explains, because enzymes start to break down at 120 degrees. She says that the abundance of living enzymes in raw food can provide energy sources and nutrients unavailable in cooked food.
“Every other creature eats 100 percent raw,” says Katrina.
But while cooking may have been an important part of our past, it may be less of a factor in the future.
It almost goes without saying that the raw-foodists are hardly obese. They were definitely on the lean side – like the mice who ate raw food.
Maybe in times of scarcity it was good to maximize calories. But in times of first-world abundance and obesity, there is a growing body of scientific data – finding support in every animal, large and small, that has been studied in this way – suggesting animals that eat less live longer. There are many possible explanations floating around, but few refute the basic statistical premise that, assuming you meet basic nutritional requirements, you live longer by living leaner.
So while the evolution of our brain may have been dependent on cooked meat, maybe the next step will be about cultivating a different kind of sensor, one that factors in compassion, a sense of place, long life, and who knows, maybe some light spilling from your eyes.