A few weeks ago Eleanore shared with me this gem of a paper. It’s a case study of a 456 lb man who fasted for 382 days, eating nothing but a multivitamin with “no ill effects”. It’s content possibly only rivals this one in terms of uniqueness in the diet literature: an 88-yr old man who eats 25 eggs per day and has normal cholesterol levels in the New England Journal of Medicine.
The question of why we eat what we eat has a lot of proximate answers. We eat the foods we eat because the taste and textures appeal to us, or some combination of appeal and availability, price or season. Presumably, the 88-yr-old egg eater really likes eggs. But that doesn’t explain why all humans don’t like eggs this much. And why certain foods that appeal to me seem less appealing to others. Shouldn’t we all need to eat the same things? What does an “optimal” diet look like and why might there be variation in what we eat or want to eat?
It’s a question my grandmother was wondering the year my mom made tofurky for Thanksgiving and one I’m often asking with mosquitoes. In both systems, taste preferences seem to lack ultimate answers. We (and mosquitoes) don’t always prefer to eat things that are “healthiest” for us. If I could increase my fitness by eating watercress, why can’t watercress taste a bit better? If mosquitoes can lay more eggs off of eating mice than eating me, why don’t they eat more mice?
A few weeks ago I was chatting with an insect mass-rearer named David. David said that even if we could provide a perfect, optimal diet with all the nutrients an insect needs to live long and make lots of insect babies, it would only be a good diet if the insects wanted to eat it.
“Imagine,” he said, “that a bunch of insects were developing an artificial human diet and they watched us for a while and said ‘Hmm’ humans eat this hamburger stuff. Live cows have the same nutrients. Let’s feed humans the live ones, it’s less work.”
A live cow diet to rear humans would likely fail because most humans wouldn’t take a bite of raw cow if they were put in the same pen. I don’t think this is because we couldn’t survive a long time eating steak tartar, but because much of what we eat might be learned behavior rather than instinct (as a non-anthropologist, I have no idea if this is true). It’s strange to me that the cravings of our sensory system may be out of sync with what our other bodily systems crave. If my digestive system wants fiber and my vascular system wants iron and my skin wants fats and my teeth want calcium are my cravings for different foods loosely reflecting the needs of various systems? Or are we all captives to vestigial cravings to seek efficient high calorie foods that led to fitness optimums in scarce resource environments of the past? Optimal foraging theory in humans suggests that cravings derive from reducing risk of energy-depletion but that one other way we can reduce risks of having too little food is a strategy called sharing — a holiday-appropriate result.
Happy Thanksgiving everyone! And happy foraging to an optimal micronutrient intake.