Heribert Watzke isn’t a real popular guy with the raw foods crowd, I suspect. He theorizes that humans aren’t omnivores, but coctivors – we are the animals that eat cooked food.
He asks us to smile at each other, and asks us to look at each other’s canine teeth. They’re pretty pathetic, not really useful for ripping meat off bones. Our teeth are now evolved to eat soft, easily digestible, cooked food – our behavior has changed our body over time.
We’ve had to cook food because big brains are expensive. The human brain is 2-3% of body mass, but takes up 20% or more of energy. We can’t get that energy from raw food, he tells us. Cooked food allowed us to be a migrant species, because every time we encountered new food, we could transform it and make it edible. We do this by roasting or burying it in the ground to ferment it. Over the same time our brain has grown, the gut has shrunk 60% from its previous size due to cooked food.
Our bodies make decisions about food based on taste, reward and energy. Three tastes sustain us – sweet (energy), umami (protein), salty (which we need). The other two – sour and bitterness – ward us off from dangerous, spoiled and poisonous foods.
But for feedback on whether this food is good for us, we rely less on taste and more on the reaction of our gut. Watzke tells us that our guts have a full-fledged brain, and he’s not speaking metaphorically. The gut – the stomach, small intestine, colon – has two layers of muscle with lots of nervous tissue between them, which penetrate muscle layers. These nerves also penetrate the mucosa, the layer actually touching the food. If we stretched the gut to its full length, it’s 14 meters, the length of a tennis court. It’s got as many nerve cells as a cat’s brain.
This second brain has 20 different neuron types that sense food. Based on sensing it, it instigates chemical and mechanical processes to digest it. This second brain controls mechanical actions like our gag reflext and the secretion of chemicals to igest the food.
This lower brain can be inhibited by the higher brain. We can ignore the signals we get that tell us we’re full or that we’re hungry. If the brain ignores the healthy hunger signal, this can manifest as anorexia. He tells us, pointing to his own belly, that the more usual case is overeating.
We learned to talk to the big brain about food based on reward. He wonders, “how do we talk to the gut brain so that signals are so strong we can’t ignore it” so we can generate a balance between hunger and fullness. We see an experiment with the digestion of a bubble of oil in the intestine – is it possible that we can change structures so that they trigger different reactions and send different signals to the brain? Watzke believes we can, and that we can even do this by cooking. He asks us to consider this possibility, “I cook therefore I am.”