First of, I would like to just introduce
attractiveness a little bit to you.

Especially thinking about

why should we even bother
thinking about attractiveness?

Well, first, psychological research
has shown that people largely agree

on who is attractive
or who is perhaps, less so.

So I'm pretty sure
most of you in this room would agree

that Angelina Jolie is perhaps
somewhat more attractive than Ugly Betty.

And this perception of attractiveness
even hold universally.

So even if you went
to a very different culture,

people would probably still agree
that Angelina Jolie is more attractive.

In addition to this, work in psychology
over the last two decades or so

has shown that attractiveness
has advantages

over and above perhaps getting bought
a drink in a bar on a night out.

And specifically,
these advantages include things

like being seen as more honest,
more socially competent,

more successful, more trustworthy,
friendlier, and even smarter.

And that last bit is quite important
because even in your career,

your attractiveness levels matter.

And this holds by the way
for men just as much as for women.

If you are more attractive,
you are more likely to have a good career.

Being attractive literally pays.

And we call this the Halo Effect,

which means that simply
because you look a certain way,

people make all sorts of attributions
about what you're like.

And while that might seem
a little bit gloomy for some,

there's actually a flip side to this coin

which is: can you make yourself
more attractive?

I'm not talking about
going and getting plastic surgery,

or going to a salon and paying
for very expensive beauty treatments.

I'm talking ... - oh, not about that! -
I'm talking about changing your health.

With that in mind, I'd like to turn
to the animal kingdom for a moment.

You can see these beautiful birds on here,

and they have something in common
which is that they are all colorful;

and these colours aren't just there
for us to think of them as beautiful

But they're actually signals
that they use to attract mates.

The more colorful these birds are,

the more likely they are
to find another bird

who's willing to mate with them.

And this is important
and relevant for humans,

because the colors in these birds
are not actually something

they produce from their own biology.

This is something they can only produce
following their diet.

They eat something
that makes them colorful.

And this something are carotenoids.

Carotenoids are little pigments;
they are a group of pigments.

There's about 500 or 600 different ones.

But they have something in common,

which is that they are all red,
yellowish, orangey in color,

and they are contained
in almost all fruit and vegetables.

Importantly, they are actually contained

not only in carrots
that are obviously orange

but even in fruit and vegetables
that are perhaps less clearly colorful,

including green vegetables;

and fruit, for that matter.

And these pigments in the birds

signal that these birds are able

to go out and look for a healthy diet

by foraging through perhaps
the forest or the fields,

which they couldn't do
if they were in poor health condition.

So in those birds, being very colorful
suggests to a mate that they are healthy.

Of course, us humans,

don't have to go in to the forest
to get fruit and vegetables,

we can walk in to the supermarket
and buy any food that we desire.

Our problem is more, perhaps,
that we'd choose foods we shouldn't eat.

I'm sure you're all aware
that we are supposed to eat

about a third of our diet
from fruit and vegetables.

This is also often referred to
as the five a day:

you're supposed to at least eat five
portions of fruit and vegetables per day.

So if eating fruit and vegetables

- which have all sorts of health benefits

including getting vitamins, getting fiber,

and getting a whole range
of relevant products into you body -

if that is important for birds,
then what about humans?

Do we perhaps also somehow
signal in our appearance

the fact that we have eaten
lots of fruit and vegetables?

So, to recap how this works:

the carotenoids that we've consumed
with fruit and vegetables

work and function in our immune system.

So if some nasties, some bugs
enter your system,

one thing that the immune system
can do is use carotenoids

that are stored in our system
as antioxidants

that will then fight these nasties
and cause them to disappear.

If there are carotenoids
left over, as it were,

after this immune function has happened,

these carotenoids can then
be layered into our skin.

This happens through a process whereby
carotenoids are entered into the sweat

which is then of course sweated out
through the sweat glands

and are literally layered onto our skin.

And this layering process causes our skin 
to turn somewhat goldenish yellow.

This is just a representation;
it's not accurate.

You're not going to turn
exactly that color,

if you eat more fruit and veg,
but it illustrates the point.

There's a different scenario
that we could imagine

whereby again, we have
plenty of carotenoids,

but this time, there isn't just
four of these nasties but many more;

which should hopefully appear
on screen in a moment.

There we go.

And in this situation, the majority
of our carotenoids stored

might be used up to fight these nasties.

And then, there's very little leftover
to go into our skin,

which then causes our skin

to turn a lighter color again.

This is because the carotenoids

that were originally layered
into our skin get rubbed off,

and our skin of course
rejuvenates all the time.

So if you don't replenish constantly,

then our skin color will change back

to a less attractive version of itself.

That led us to the interesting question

of whether this different skin color
is perhaps found attractive in humans.

Remember, in birds,
the high-carotenoid coloration

was something they use to attract mates,

which is similar
to attractiveness in humans.

And given this is a cue of somehow health,
so you have a lot of disease burden,

you might not be able to create
this lovely skin color,

this might actually be a cue
of your appearance.

So, for this, we conducted an experiment.

We first measured empirically

the axis of color change in skin
associated with carotenoids.

To do this, we had a group of students

that eat a lot of fruit and vegetables
in their regular diet,

and we measured their skin color;

we also had a group of students

that didn't eat
very many fruit and vegetables

- It was more easy to recruit
in that group unsurprisingly -

and we match these groups
on their sex, on their age,

and on other lifestyle characteristics

so that we could be relatively certain

that the only consistent difference
between these groups

was their fruit and vegetable consumption.

After we measured
each individual's skin color,

we averaged this skin colors,
and could then calculate

the difference between the color
of the high carotenoid intake group

and the low carotenoid intake group.

We could derive this kind of color axis.

This allows us to take a photograph
of anybody, for example this girl,

or anybody in this room,

and we are then able 
to transform this image

to become either higher
or lower in carotenoid color.

We then asked people, in an experiment

which color they think is more attractive.

So let's try this here:
you see the two versions of her face.

Who thinks the girl on the left
is more attractive?

One … not many, good.

Who thinks the girl on the right
is more attractive?

That's a vast majority,

and this is consistent
with what we found in our experiments

where of course we wouldn't present
people with only this one girl

but with a large range of faces
that we have manipulated in this way.

We find that in fact,
nine out of ten people approximately

chose the higher carotenoid version
of faces as more attractive.

So this is a really good indication

that there is something about this color
that makes people more attractive.

We also looked at other cultures

and found that in Asian
and African cultures the same holds:

people who had
a more carotenoid-linked skin color

were seen as more attractive.

And even some people were still
arguing back at us and saying,

"Oh, this is just about sun-tanning."

We all like a suntan, so you all know
you like to go out in the sun,

you like to go to the beach,

and it leads to of course a somewhat sort
of brownish yellowish color on your skin.

This color is caused
by a pigment called melanin,

which is activated by UV rays

and it's meant to protect your skin
to some degree from a sunburn.

A lot of research in the past has shown

that a suntan is thought of as attractive
at least in our societies.

People argued with us, that perhaps,

what is going on is
that carotenoid coloration

looks somewhat similar to a suntan;
it's also a little bit yellow,

so perhaps people like a tan.

And because they like a tan,

they also like this color
which looks somewhat similar.

So we investigated this question.

We investigated it by asking people

which face they prefer

out of a high carotenoid face
and a high suntanned face.

So we manipulated the tan in the same way
I showed you before for the carotenoids.

And now, let's do this again: who thinks
the face on the left is more attractive?

OK, and who thinks the face
on the right is more attractive?

Fewer. Interesting.

Right, I'm sure you all now want to know

which of these is the tan
and which of these is the carotenoids.

Well, this one if the carotenoid face;
and the majority of you prefer this face.

We find the same pattern
of results in our research

with eight out of ten people on average

preferring the carotenoid face
over a suntan.

That really means
that there's something specific

about this color that people like,

even when we compare it to another color

which is normally liked
by people in this culture.

This also might actually mean

that the reason or part
of the reason we like a tan

is because it mimics to some degree
this healthy color of carotenoids.

We've seen that eating
fruit and vegetables

makes your skin change color,

and that this new color
is seen as attractive.

But remember, at the start, I told you
attractiveness isn't the end of the story,

but other traits such as being perceived
as more trustworthy or smarter

are also associated with attractive faces.

So we were interested to assess
whether these traits

might also be associated
with a carotenoid skin color.

We've conducted two studies to date:

we once looked
at trustworthiness judgments,

and we also looked
at leadership judgments,

so how good a leader
people thought a person was.

And in both cases, we found that having
a high carotenoid coloration in your skin

influenced these judgments
quite dramatically.

People really thought the people
with the healthy carotenoid coloration

were more trustworthy
and would be much better leaders.

So that should give you
some food for thought hopefully.

But to finish off,

there is one important question
to answer, isn't there?

How much do you actually need
to eat of the stuff?

Do you need to eat
25 carrots every day to get this effect

which might be rather unmanageable?

Well, colleagues
at the University of St. Andrews

have conducted a study into this

and found that actually eating
only two more portions a day,

this might be for example eating an apple
and drinking a glass of orange juice,

or eating a portion
of vegetables twice a day,

is enough to change
your skin color within six weeks

to be perceived as more attractive.

the difficulty is though,
as you might recall,

that if you don't keep it up,
your skin color will go back down.

So really what this means 
is you have to eat

more fruit and veg
for the rest of your life.

Thank you very much.

(Applause)