Translator: Tanya Cushman Reviewer: Rhonda Jacobs
Imagine you're in a rainforest.
It's hot. It's humid. You can taste the air.
There's green all around you
and so many kinds of trees you can't count them all.
Some have red fruits;
some have tiny purple flowers.
And the animals - birds and bats and squirrels and monkeys.
Mosquitoes buzzing in your ear.
A giant Goliath beetle quietly searching for a mate.
The sheer diversity is overwhelming,
and it's almost impossible to describe how all these living things are connected.
Now imagine that same rainforest, but inside of you.
It's still hot and humid,
but instead of plants and animals and insects,
you have microbes,
tiny creatures that all look the same under a microscope,
but are just as different from each other
as birds and bats and squirrels and monkeys,
if not more.
These are bacteria, archaea and eukaryotes.
It's a diverse, interconnected, relatively unexplored place.
Welcome to your gut.
It's one of the most complex ecosystems on the face of the planet,
and like other complex ecosystems,
we're just barely beginning to understand it.
And that's where I come in.
As a microbial ecologist,
my job is to find these tiny creatures
that we can't see
and find out what they're doing
and how it affects our lives without us ever even knowing.
Now, over the past couple of decades, thanks to technology advancements,
researchers have made some amazing discoveries
about gut microbes.
They give us energy,
they help make our immune system strong,
and they can even put us in a good mood.
These are huge discoveries,
but I'm here to tell you today I think we can do better
if we change the way we do our research.
You see, what interests most of us about gut microbes
is how they affect our health and how we can use them to treat disease,
and that's a good, important goal to have.
But the problem is, as a result,
a lot of the studies we do right now on gut microbes
are based on humans,
particularly Western humans,
and model animals that we use to portray humans, like mice.
And that's a pretty narrow perspective.
You see, microbes affect our lives today,
but gut microbes in humans
have been rubbing elbows for a much, much longer time:
we co-evolved together.
At least that's what we like to say.
But evolution implies certain things.
It implies changing environment, adaption and survival of the fittest.
And Western humans and lab rats
are just about as far away as you can get from survival of the fittest.
Using only them to try to understand our relationship with gut microbes
is like trying to use a greenhouse
to understand how the entire Amazon rainforest works.
You'll probably figure some things out,
and you might even discover something that you wouldn't have seen in the wild,
but you're never going to get the whole picture.
Likewise, to understand our relationship with our gut microbes,
we need to go out into the unpredictable environments that they evolved in,
or at least something similar.
Imagine what we could learn if we studied these microbes in the wild.
So these are the things I was thinking about
when I started by PhD.
You see, gut microbes are considered mutualists.
That means that they benefit the hosts that they live inside of
and also receive benefits.
And I wanted to know how this might work in the wild.
For example,
we know that some gut microbes contribute to obesity in some people
by producing extra energy that doesn't get used.
But what if you were a wild animal
trying to survive a season with low food availability?
Maybe that extra energy would come in handy.
I wanted to figure this out.
So I went to the rain forest, and I found these guys:
(Howler monkey howling)
howler monkeys.
Howler monkeys are common
throughout southeastern Mexico, Central America and South America.
But their diet is special.
See, howler monkeys love fruit,
but when there's no fruit around,
they can actually survive on a diet of almost entirely leaves.
And this is impressive because leaves have high amounts of fiber and toxins,
which make them hard to digest.
This means there's not a lot of energy in them.
If we ate a completely leaf diet,
we'd be lying on the couch, asleep all day.
And while anybody that's studied howler monkeys will tell you
that they spend lots of time sleeping during the day,
they do pretty well on a leafy diet.
And we thought for a long time that this is because of their gut microbes,
but we didn't have the technology to go look at it,
and that's what I decided to do.
So I went to Palenque National Park, Mexico, and I spent a year there,
following the monkeys around every day, all day, from dawn until dusk,
watching what they were eating
and picking up their poop to analyze for microbes.
Yep. That's what I said.
I had a fridge full of monkey poop.
And I had to fight more than a few dung beetles to get it.
So once I successfully got that poop back to the lab in the United States,
here's what I found.
Howler monkeys have different gut microbes during different seasons.
So when they're eating more fruit, they have more of some types of microbes,
and when they're eating more leaves, they have more of other types of microbes.
And when they're consuming less energy,
the gut microbes are actually producing more energy.
They're compensating for the howler monkeys,
which is a huge benefit,
and it's the first evidence I've given you today
of a mutualism between gut microbes and their hosts in the wild.
So that's great for howler monkeys,
but we're not very closely related to them,
and most of us don't live in the rainforest.
At least we haven't for about a million years.
But here's where using a wider perspective to understand humans comes in.
You see, our ancestors probably depended on our gut microbes
to survive seasons like droughts or harsh winters
when there wasn't a lot of food,
just like the howler monkeys depend on their gut microbes.
That's probably why we have our gut microbes.
We gave them a place to live, and they helped us not to starve.
But today we're ruining that relationship.
At least Western humans are.
Look at our diet.
It's high in energy, it's easy to digest, and we get a lot of it -
sometimes too much of it.
From day to day,
at least in terms of energy and nutrients,
we do not depend on our gut microbes to survive.
We've decoupled that relationship.
Now, don't get me wrong:
that doesn't mean that we don't have the gut microbes,
and it doesn't mean that they're not changing and affecting our bodies.
So studies have shown that a Western diet
will actually affect your gut microbial community,
whether you're consuming it for months or even for a few days.
So we have different microbes that are doing different things
and producing different compounds
that affect our digestive system, our immune system and even our brain.
They are affecting everything about us,
and we're oblivious.
Think about it.
Western humans have higher rates of obesity, metabolic disorders,
allergies, autoimmune diseases, stress, anxiety, depression -
all of these things have been linked to gut microbes.
We have a lot to do to figure out the mechanisms still,
but the point is
these differences in our gut microbes that come from our diet
are affecting everything,
and the consequences are greater than we can even imagine.
And so this brings me back to biomedical research.
We're frantically trying to figure out what's going on and how to fix it.
We're doing tests of humans
with different diets, different diseases, different weights,
and taking microbes from humans
and putting them into mice that don't have microbes of their own
to see what happens to the mice.
And we're even starting to do studies of primates.
But here's where that trick about a narrow perspective comes in again.
You see, you would assume that because primates are our closest relatives,
that our gut microbes behave similarly to theirs.
And you'd be right.
They're similar in some ways.
But it turns out there's a few key differences,
and no one thought to look.
I was lucky enough, recently, to get some samples from collaborators
from vervet monkeys,
comparing the gut microbes of vervets in the wild,
consuming fruits and leaves,
to vervets in captivity being fed a Western diet.
Now, don't get me wrong, we're not talking about burgers and fries here.
They're refed monkey chow
that was designed to look like a Western diet,
so high in fat and low in fiber.
And no surprise here,
the vervets on different diets had different gut microbes.
But where it gets interesting
is when we look at how they compare to humans.
It turns out that vervets look more like non-Western humans
in terms of the composition of their gut microbes
no matter what diet you give them.
And Western humans show changes in their gut microbes
that are different than the changes we saw in the vervets.
So, for example,
in Western humans, we see an increased relative abundance of Firmicutes bacteria
and a decreased relative abundance of Prevotella bacteria
on a Western diet.
In vervets, we saw the exact opposite.
And in humans on a Western diet, there's reduced gut microbial diversity.
In vervets, there was no effect on gut microbial diversity.
And the vervets on a Western diet didn't gain weight during this study.
So not only are the gut microbes responding differently to a Western diet,
but it looks like those differences
could be related to a non-human primate resistance to obesity,
So this got me thinking about evolution.
Humans and chimpanzees
are about 96% similar in terms of their DNA -
at least that much -
but we're very different.
What is it that makes humans so special?
This is the million-dollar question
that anthropologists have been asking for years.
And the answer always comes down to the same thing: our brain.
And I don't think this is any different.
I think the reason that human and primate gut microbes are different
has to do with our brains.
Let me explain why.
Human brains are large,
which means that they require a lot of energy to grow and to run.
And researchers have come up with a lot of explanations
as to why this might be so.
These include improved food-processing techniques,
increased energy intake
and even changes in digestive physiology.
But what about gut microbes?
What if they were playing a role?
What if the most unhuman thing about us
actually helped to make us human in the first place?
This isn't that far-fetched.
You see, gut microbes have been shown to modulate our metabolism
and to affect fat storage in humans.
And my data suggests that humans might be a little bit better at doing that
in terms of their gut microbes
than primates.
If this is true,
that means that our gut microbes were producing and storing energy
during periods of unreliable food availability
and allowing our ancestors to keep these big brains
even when there wasn't a lot of food.
And if this is true,
that also means that hyperactive energy-producing-and-storing gut microbes
may be the reason
why we have problems when we're eating a high-energy Western diet.
Primates, on the other hand, don't have that problem.
They don't have the supermicrobes they needed to develop a big brain,
but they also don't face the same problems as us on a Western diet.
They're less sensitive.
So science is about understanding the world around us,
and it's also about understanding who we are.
And I hope that I've convinced you today
that our gut microbes are absolutely a part of who we are.
Even though our bodies are more than 90% non-human,
there's something uniquely human about that microbial part of us,
and this has the power to transform gut microbiome research
in the context of health.
Imagine if we could figure out what it is about human microbes
that make us susceptible to obesity
and change it to make them less human.
What would the consequences of that be for our health?
But what would the other consequences be?
It'll take us a long time to figure this out,
but in the meantime, I want to leave you with this.
What's in here matters;
it matters a whole lot actually.
And we found, with research, that the rainforest outside of us,
just like the rainforest inside of us,
they have similarities.
It's much easier to disrupt the rainforest inside of us, especially for humans,
than it is to restore it.
And by not paying attention, we're actually disrupting it.
So I challenge you
the next time you're at the grocery story:
use that big brain those microbes gave you
and think about protecting your inner rainforest.
And maybe, just maybe, start in the vegetable aisle.
(Applause)