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- [Voiceover] We are the paradoxical ape.
Bipedal, naked, large brain,
long the master of fire, tools, and language,
but still trying to understand ourselves.
Aware that death is inevitable, yet filled with optimism.
We grow up slowly, we hand down knowledge,
we empathize and deceive.
We shape the future from our
shared understanding of the past.
CARTA brings together experts from diverse disciplines
to exchange insights on who we are and how we got here.
An exploration made possible
by the generosity of humans like you.
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- The world loves meat.
Each one of us in the U.S. eats about
200 pounds of meat per year,
which makes us one of the top
meat consuming countries in the world
and it's more than twice the global average.
So we are a nation of meat eaters
living in a world of meat eaters
and global meat consumption is on the rise.
But the question is, are we, as a species,
inherently vegetarian or carnivorous?
The answer is that we are both.
Our species evolved to consume an ommniverous diet
that contains both plant and animal products.
But today, I'll be giving you a very brief history
of our species' relationship with meat
and I have been tasked with the job to outline
the nutritional benefits and costs of eating meat.
Man the hunter.
The statement is a catchphrase of our species.
It conjures bold images that have dominated
academic discourse, the media,
and public opinion for decades.
Here, a popular artist named Banksy plays with this idea
in his piece The Trolley Hunters.
And I urge you to do a search for man the hunter
on the internet and view the type of images that pop up.
There are tens of millions of images
and most of them are a variation on a theme,
as you might imagine.
The individual images and their content
are not what's important.
It's the underlying take-home message.
And that message is that meat made us human.
For well over a century, anthropologists have touted
meat consumption as the catalyst for critical watershed
moments in our evolutionary past.
Things like pair bonding, family formation,
neural expansion, toolmaking, and even cooperation.
While the specific role that meat might have played in the
evolution of human behavior is debated,
one thing is certain.
Meat did change the playing field
for our earliest ancestors.
So our history with meat goes back quite far in our
evolutionary past and how far back continues to be debated.
The image you see here dates to
approximately 20,000 years ago.
This artwork is found on the caves in Lascaux, France
and by the time that the artists were painting these images,
it's possible, and likely, that early members of our genus
had already been eating meat for millions of years.
Hunters living in the paleolithic
did not eat only muscle tissue.
Much like contemporary foragers today,
they consumed all of the animal.
All edible portions of the carcass.
Which would have included organs, bone marrow,
and even, in some instances, the GI tract of the animal,
which is a practice called gastrophagy.
They would've targeted game animals initially
using stone tools with some early, though controversial,
dates putting the first stone tools in Kenya
at 3.3 million years ago.
Hafted, or stone-tipped, spears came on the scene later
with some finds in the archeological record
dating to around 500,000 years ago in South Africa.
Bow and arrow technology later still,
possibly around 70,000 years ago.
The important point here is that
different complex technologies were created, modified,
and used to target animal protein, going very far back
in human evolutionary history.
So the question of when is a bit tricky to pin down
and is something that we'll be talking about today.
The question of why our ancestors turned to meat
is slightly less contested.
This is a photo of women in the population with whom I work,
the Hadza foragers at Tanzania, who live in east Africa
and very rarely do we see or associate
women with big game hunting.
And so I like to show this photo
because it highlights the often very cooperative form
that hunting in human populations can take.
And on this day, a man killed a cape buffalo
and there was so much meat that all hands were needed
on deck to transport this meat
from the butchery site back to the camp.
And I was also conscripted to help.
I am not on camera, I'm taking the photo,
and I'm useless and I was useless that day as well
so my portion had to be carried in a backpack.
It was humiliating, but it was helpful
and I'm not very efficient at carrying anything on my head
so the backpack worked for the day
but when I said all hands on deck,
I meant all hands on deck.
So this begs the question, why all the effort?
Meat is a concentrated nutrient source
that is easy to digest, depending on preparation,
which we will talk about later today also.
It's high in protein, niacin,
essential micronutrients like B-complex vitamins,
iron, and fat.
It has three major types of fats: trans-fatty acids,
cholesterol, and triglycerides that are comprised mostly
of saturated fatty acids, monounsaturated fatty acids,
and polyunsaturated fatty acids, which we often call PUFAs.
Two essential fatty acids found in meat are
linoleic acid, which is an omega-6,
and alpha-linolenic acid, which is an omega-3.
These cannot be synthesized by humans and so we need them.
They are important for brain growth and function
so we must consume them in our diet.
Additional important omega-3 PUFAs
that are found in red meat include docosahexaenoic acid,
or DHA, and eicosapentaenoic acid, or EPA.
These are essential during pregnancy and lactation
and have also been shown to reduce
the risk of some chronic diseases.
Red meat also plays a role in
preventing iron deficiency, or anemia.
And around the world, iron is one the most commonly
deficient nutrients and this might be linked to the fact
that it has low bioavailability,
which can be defined as the ease and speed at which
a nutrient, like iron, makes its way
from the food that we eat to the target tissue.
There are two different types of dietary iron,
as you might have interpreted from this slide,
heme and non-heme iron.
Non-heme iron is found in both plant foods and
animal tissues and this type of iron
is poorly absorbed and has low bioavailability.
Heme iron, on the other hand, comes from hemoglobin
and myoglobin that's found in animals
and this type of iron is very bioavailable.
For example, while it only contributes to a modest 10-15%
of total dietary intake in the diet of red meat eaters,
it accounts for more than 40% of total absorbed iron.
So heme iron is also known to increase the absorption
of non-heme iron, which means that meat really
is the best source of iron that we can consume.
It's important, as delays in global brain function
and motor function have been associated
with chronic iron deficiency.
Heme is also involved in the distinction between red
and white meat, which is largely based
on the myoglobin content.
Myoglobin is the heme iron that contains pigmented proteins,
which make the meat red in color
so the more myoglobin, the redder the meat.
Beef has far more myoglobin when compared to chicken,
which is considered a white meat,
and if you are used to classifying pork as a white meat,
you're probably likely to do so based on a very successful
advertising campaign from the late 1980s.
The slogan, Pork. The Other White Meat, was created
for the National Pork Board in order to boost sales
to compete with chicken and turkey,
and the campaign was very effective.
So although pork is typically classified as a white meat
in culinary contexts, it is most certainly a red meat
when it comes to its nutritional composition.
And this is important, because red meat has certain
characteristics that white meat does not
and these are often associated
with negative health outcomes.
Associations reported with colorectal cancer and other
carcinomas, atherosclerotic cardiovascular disease,
type 2 diabetes, and potentially
other inflammatory processes as well.
There are many proposed explanations for these disease
associations, such as saturated fat, high salt intake,
and environmental pollutants that
may be contaminating red meat.
Another mechanistic explanation is the metabolic
incorporation of a non-human sialic acid called Neu5Gc.
And much of this groundbreaking work is being done
right here at UCSD at the medical school
in Ajit Varki's lab.
Sialic acids are a family of monosaccharides
that are widely distributed in animal tissues
and, to a lesser extent, other organisms.
And they're located at the very distal end of sugar chains
that are connected to the surfaces of cells and proteins.
We lost the enzyme synthesizing Neu5Gc
in our evolutionary past, yet trace amounts
are still found in humans.
So even though it's a foreign molecule to the human body,
we incorporate small amounts
from the red meat that we consume.
Red meat contains very high amounts of Neu5Gc.
I did a postdoc in Ajit's lab and played a very small role
in a very large project that attempted to quantify the
amount of Neu5Gc in commonly consumed foods
in the human diet and Neu5Gc is in all animal products
so anything associated with red meat,
which would include dairy products as well,
eating red meat, or the products of red meat,
allows for the metabolic incorporation
of this Neu5Gc into human tissues.
So the immune system recognizes it as a foreign threat
and then produces antibodies to counter it.
So repeated consumption of red meat can cause
chronic inflammation, which has been known to
increase risks of tumor formation.
Neu5Gc has been linked to cancer as well as
cardiovascular and other inflammatory diseases.
And all available evidence supports this,
including studies that have been done with mice,
with humanized sialic acids.
So despite these disease risks,
red meat consumption around the world is on the rise.
As much of the world is protein deficient,
red meat is a good source of protein
and not only protein but also iron,
which we've talked about.
So perhaps the solution then, according to many
nutritionists, is just to eat less meat.
The American Institute for Cancer Research recommends
that we don't eat more than about
18 ounces of red meat per week.
If the world does continue its upward trajectory however,
how will we feed an expected global population
of 9.7 billion by 2050?
According to the Food and Agriculture Organization
of the United Nations, about 60% of the world's
ice-free land surface is currently dedicated to raising
crops and providing grazing land
for the animals that we eat.
So this is supporting around 360 million cattle
and 600 million sheep and goats.
About 788 million acres are used
almost exclusively for livestock.
A recent census of agriculture by the USDA estimates
that this totals up to about 40% of all of the tillable land
in the U.S. and many food scientists argue
that this level of production is unsustainable.
So sustainable alternative feeds for cattle are now being
introduced like microalgae, sugar cane, or brewers grains,
which are the solid residue that are the product
of germinated and dried cereal grains used to make beer.
Diets are also switching to alfalfa,
which reduces methane emissions in cattle.
So in addition to coming up with more sustainable feed
for livestock, people are trying to come up with ways
to make the entire food system more sustainable.
And some estimates suggest that in order to produce
one billion kilograms of beef today, we're only using about
88% of the water that we did in 1970
and only about, approximately, 67% of the land.
In addition to coming up with this more sustainable feed
for livestock, people are trying to come up with ways
to just make the entire system more efficient
and this effort extends to reducing waste outputs as well.
So the amount of manure, for example, has been reduced
by 18% compared to 1977, and in addition, the overall
carbon footprint per billion kilos of beef produced in 2017
was reduced by over 16% compared to
the same footprint from the late 1970s.
But while they might be down,
livestock still contribute to greenhouse gas emissions.
As of last year in 2017, the FAO estimated that, globally,
livestock contributes to about 14.5% of all anthropogenic,
or man-made, greenhouse gas emissions
due to enteric fermentation and manure.
Some estimates suggest that emissions may be similar
to those produced by the transportation industry,
although this figure is very controversial suggesting
that cows might emit as much gas on earth as vehicles.
So some in the agricultural industry caution
that these are not easy comparisons to make
and other factors are, of course, at play.
But one thing that conservationists and agricultural
industry agree on is that livestock does contribute to
a substantial percentage of greenhouse gases in the world.
The agricultural industry is making strides, however,
to reduce gas output by introducing feeds that create
less belching in cows, improving breeding in a way
that animal health interventions are done differently,
and the FAO argues that if herd sizes were to shrink
based on these best practices,
that would mean fewer, yet more productive, livestock.
So in addition to belching and passing gas,
cows also produce a lot of manure.
It's the end point of their digestion
and it also produces nitrous oxide.
So there are many fascinating new practices being developed
that are turning manure into electricity.
Electricity which is then being sold back to the grid.
So the costs of meat production are high.
And beyond the environmental costs,
there's a segment of nutrition science,
as well as animal rights activists, that are
arguing for the elimination of meat consumption altogether.
But given the global rise in consumption patterns,
this doesn't seem to be the most likely future outcome.
So despite the nutritional benefits of consuming meat,
there are significant health and environmental
costs of consumption as well.
That being said, as we'll hear about today,
our species has a very long relationship with red meat.
It is one of the hallmarks of human evolution.
So the question I leave you with, and one that I borrowed
from Ajit Varki, has meat in human evolution
gone from a blessing to a curse?
Thank you.
(audience applauds)
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