"What’s the “Natural” Human Diet?"
There are three broad theories about evolution and food.
One is that humans have become adapted to the
products of the agricultural revolution
over the last 10,000 years.
Two is the paleo view
that 10,000 years is a blink of an evolutionary eye,
and that humans are adapted to paleolithic diets
with lots of lean meat.
But why stop there?
The last 200,000 years as mostly stone age humans
represents just the last 1% of 20 or so million years
we've been evolving since our common great ape ancestor.
During our truly formative years,
the first 90% of our existence
one might say, our nutritional requirements
reflect an ancestral past
in which we ate mostly leaves, flowers, and fruits,
with some bugs thrown in
thanks to wormy apples to get our vitamin B12.
For this reason, another approach
that might improve our understanding
of the best dietary practices for modern humans
is to focus attention not on the past,
but rather on the here and now;
that is, on the study of the foods eaten
by our closest living relatives
given the bulk of our ancestral diets
and the lack of evidence supporting any notable diet-related changes
in human nutrient requirements, metabolism, or physiology
compared to our fellow great apes.
This could explain why fruits and vegetables
are not only just so good for us,
but vital to our survival.
We’re actually one of the few species
so adapted to a plant-based diet,
that we can actually die from not eating fruits and vegetables,
from the vitamin C deficiency disease scurvy.
Most other animals just make their own vitamin C.
But why would our body waste all that effort making vitamin C,
when we evolved hanging out in the trees
just eating fruits and veggies all day long?
It’s presumably not a coincidence that the few other mammals
unable to synthesize their own vitamin C
(like guinea pigs, some bunny rabbits, and fruit bats)
are all, like us great apes, strongly herbivorous.
Even during the stone age,
we may have been getting up to ten times more vitamin C
than we get today.
And ten times more dietary fiber,
based on essentially rehydrated human fossilized feces.
The question is, are these incredibly high nutrient intakes
simply an unavoidable by-product
of eating whole plant foods all the time
or might they actually be serving some important function
like antioxidant defense?
Plants create antioxidants to defend their own structures
against free radicals.
The human body must defend itself
against the same types of pro-oxidants,
and so we have also evolved an array
of amazing antioxidant enzymes,
which is effective, but not infallible.
Free radicals can breach our defenses,
cause damage that accumulates with age,
leading to a variety of disease,
causing ultimately fatal changes.
That’s where plants may come in.
Plant-based, antioxidant-rich foods
traditionally formed the major part of our diet,
and so we didn’t have to evolve
that great of an antioxidant system.
We could just let the plants in our diet
pull some of the weight,
like the not-bothering- to-make-vitamin C thing—
let the fruit do it.
Using plants as a crutch
may well have relieved the pressure
for further evolutionary development of our own defenses,
meaning we’ve become dependent
on getting lots of plant foods in our diet,
and when we don’t,
we may suffer adverse health consequences.
Even during the stone age
this may not have been a problem.
Only in recent history
did we start giving up on whole plant foods.
Even modern-day paleo and low carb advocates
may be eating more vegetables
than those on standard western diets.
There’s this perception that low carbers are chowing down
on the three B’s: beef, bacon, and butter,
but that’s just a small minority.
What they are eating more of is salad.
The #1 thing an internet low carb community said
they were eating more of was vegetables—great!
If people want to cut their carb intake
by swapping junk food for vegetables,
that’s not the problem.
The concern is the shift to animal sourced foods.
Greater adherence to a low carb diet
high in animal sources of fat and protein
was associated with higher mortality
for example, after a heart attack,
meaning they cut their lives short.
If there’s one takeaway from our studies of ancestral diets,
perhaps it’s that diets based largely on plant foods
promote health and longevity.