CARTA: The Role of Hunting in Anthropogeny: Alyssa Crittenden – Nutritional Significance of Meat

CARTA: The Role of Hunting in Anthropogeny: Alyssa Crittenden – Nutritional Significance of Meat

November 1, 2019 6 By Ewald Bahringer


(computer mouse click) (piano music) – [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. (synthesizer music) (upbeat music) – 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) (upbeat music)