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Obesity, The Facts of the Case (Or Why Obesity Pushes Our Buttons) - Tom Glass

Course video 2 of 30

Obesity, the facts of the case, and human populations through a systems science lens.

Systems science has been instrumental in breaking new scientific ground in diverse fields such as meteorology, engineering and decision analysis. However, it is just beginning to impact public health. This seminar is designed to introduce students to basic tools of theory building and data analysis in systems science and to apply those tools to better understand the obesity epidemic in human populations. There will also be a lab in which students will use a simple demonstration model of food acquisition behavior using agent-based modeling on standard (free) software (netlogo). The central organizing idea of the course is to examine the obesity epidemic at a population level as an emergent properties of complex, nested systems, with attention to feedback processes, multilevel interactions, and the phenomenon of emergence. While the emphasis will be on obesity, the goal will be to explore ways in which the systems approach can be applied to other non-communicable diseases both nationally and internationally. Topics will include: a) the epidemiology of obesity across time and place, b) theories to explain population obesity, c) the role of environments and economic resources in obesity c) basic concepts and tools of systems science, d) modeling energy-balance related behaviors in context, e) agent-based models, systems dynamic models, and social network models

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Ministrado por

Jessica Jones-Smith
Assistant Professor
Rahmatollah Beheshti
Postdoctoral Fellow
Daniel Taber
Assistant Professor
Kayla de la Haye
Assistant Professor of Preventative Medicine
Thomas Glass
Professor

Transcrição

[MUSIC]

Hello, my name is Thomas Glass.

I'm a professor of Epidemiology here at Johns Hopkins Bloomberg School of

Public Health, and I'm with the Global Center on Obesity Prevention.

The title of this lecture is obesity, the facts of the case or

why obesity pushes our buttons?

Today in this lecture, I'll be covering three main topics.

The first part A, the obesity epidemic, the facts of the case.

Here I'm going to talk a little bit about how we should be thinking about

obesity as a population level problem, requiring population level solutions.

I'm going to talk a little bit about basic features of the obesity epidemic.

What are the most important things we have to keep in mind when thinking about

obesity from a systems science viewpoint?

And the most important piece

of this section will be the critical importance of location.

How obesity rates vary dramatically in space and time, and

why this is important for understanding the epidemic and addressing it.

The second part of this talk will be beyond the usual suspects.

Why this care is hard to crack?

And here we'll be discussing why exactly obesity is a particularly

challenging problem for epidemiology in public health.

Why when we take a close look at the usual suspects,

the factors that have been mostly relied upon for explanations

of the obesity epidemic come up short in terms of a complete explanation and

why we have a limited set of cause or risk factors that we have established?

Part three is moving toward potential explanations with a focus on

the food supply, taking a what will begin to be a systems viewpoint of this problem.

It's clear that the obesity epidemic is in part about people eating more

across the full range of population scales.

But the question is why and what can we do to address this?

And how is it that the food system delivers calories in a way that

facilitate surplus consumption in ways that have led to this obesity epidemic.

So let's get started with part A,

the obesity epidemic, the facts of the case.

Now in order to begin, I want to suggest

that what's critical about thinking about the obesity

epidemic is to think in terms of population explanations.

And to illustrate this, I begin with a famous paper and

a famous quote from Jeffery Rose,

a cardiovascular epidemiologist who is one of my personal heroes who

wrote very important paper in 1985 called Sick Individuals in Sick Populations.

And in this paper, he argued that

in order to understand the roots of a problem like obesity, we have to

think separately about the question of what causes an individual

to become obese versus what causes an entire population to become obese.

Now it seems in a sense almost

counterintuitive that these questions would not be the same.

But it's a basic and

critical insight that underlies a lot of what we do in epidemiology and

public health, to think about these kinds of questions as being separate.

And here's an example in the figure below.

These are distributions of blood pressure in two populations,

London Civil Servants and Kenyan Nomads.

What's interesting about these distributions is not that each

has a certain percentage of individuals who by themselves are hypertensive.

And in fact in both Kenya and

in London, the risk factors at the individual level that determine who is

going to be hypertensive versus not are quite likely the same.

What is really different about the two populations is the shape and

the actual mean value of the entire distribution.

In London civil service, the entire distribution

of systolic blood pressure has been shifted to the right.

So what Rose tells us is, in order the understand

why the rates of hypertension are different in these two places.

We need not to look at characteristics of the individuals who live there, but

what he calls mass influences, or

characteristics of the entire society that characterize these two populations.

Here's a second example.

Looking at homicide rates in Chicago versus England.

And what you see is the distribution of age of perpetrators for

males and females in both contexts.

In Chicago and England you see that it is quite consistent that the peak age for

perpetrators is about the same.

What is important is that individual factors that explain

who becomes a perpetrator of violence, maybe the same in these two contents.

However what is dramatically different in Chicago versus England are the rates.

The hot sides per unit of population so

you can see on the vertical axis here,

that the scale of rates on these two populations is dramatically different.

So that if we super imposed the two distributions, the entire distribution

in England would simply be a tiny bump at the bottom of the distribution in Chicago.

This is a very clear demonstration of how when we think

about explaining differences in rates we have to think about characteristics

at the population level that may explain population

factors differently than factors that explain individual risk.

Now, moving to the problem of obesity,

we see from this fairly simple graph that similar to

the distributional shift that was shown for blood pressure.

In the US we have seen a shift to the right in the entire distribution

of body mass index the entire US population has shifted.

This is a very important insight, because it tells us that the obesity problem,

the obesity epidemic in the United States is not just

about those individuals who have become heavier.

It is about a shift in the entire distribution.

As Jeffrey Rose famously used to say,

no population can divorce itself from its tail.

So not only has the tail moved but the entire

center of the population distribution has moved, and this alerts us to

the fact that there is something complex and going on at a population level.

Now this next slide shows most clearly and in simplest terms,

I love this slide because it is so simple to get the message,

what we've observed in the United States is that obesity rates.

Have been were fairly uniform and

consistent in the United States between world war two and sometime around 1980.

In 1980, something happened some important set of changes took place.

Is it a single factor?

Probably not.

But something happened that led to an inflection

in the distribution of obesity in the United States in both.

Both men and women also in children, we see that

evidence of 1980 popping up again as a crucial turning point in the epidemic.

What happened in 1980, we're still not sure.

That's partly what the journey of this course and

our discussion is about, is unraveling that mystery.

Now in addition to the United States,

we see dramatic variability in obesity rates across country.

Here is some work that demonstrates that almost

every possible prevalence of obesity is seen somewhere.

From India to the island of Nauru,

the variability across populations, across contexts in obesity rates is so

high that it suggests that environment is what matters.

It suggests that no simple genetic explanation

is likely to capture this variability, and that's an important lesson.

Not only are there dramatic differences in obesity rates by country, but

the speed at which the epidemic is occurring is also dramatically

different across countries, across nations.

This tells us that there's something that nations are doing or

not doing that must be terribly important in driving the speed of the epidemic.

This slide shows the actual change in rates of obesity across countries.

Reflecting dramatic differences in the speed or rate.

So the epidemic is going on globally, but

it is going on at different speeds in different places.

And this provides us with important clues to try to understand

what is it about the environment that's driving these trends?

Now this slide shows how obesity

rates have changed across OECD countries.

And again it shows that the United States has the most dramatic rise

and the highest starting point in terms of obesity rate of any OECD the countries.

The United States like a variety of countries,

has seen a doubling in rates of obesity from in the first

20 years of the epidemic with continued evidence

of increasing rates of obesity after that.

What's interesting is if you look across a variety of countries you'll see

that there is a tendency towards a doubling of obesity rates.

Across a variety of countries in the first couple decades of the epidemic.

But what's particularly interesting is how much variability there is

in how the epidemic is moving through different countries.

We have some countries where the epidemic starts and stops.

We have some epidemics that appear to flatten out.

Great Britain for example,

had a dramatic rise in obesity rates and in the last couple decades,

it appears that the epidemic has slowed down, almost to a stop.

So this suggest that some things happening in that context that we should be paying

attention to.

This is a slide that shows exactly how unusual United States is or

how far ahead we are in the epidemic if you like.

In comparison to Spain for example right now, Spain is

about where the United States was in 1990, which means that we are more

that 20 years ahead in terms of the pace of the epidemic compared to Spain.

And in Spain as a another country there's a lot of worry about the obesity epidemic,

but just to give some context for how the speed and

extent of the epidemic is occurring across different countries.

One important thing to say is that obesity is tightly connected to

other epidemics of great public health concern.

Obesity is a package deal and where we see obesity,

we see the concurrent rise in related conditions such as diabetes,

cardiovascular disease, renal disease,

even stroke and cognitive impairment.

So there are interactions and cenergies where in fact,

the pressure's created by high rates of

obesity lead to a variety of complications that

dramatically increase healthcare costs and

threaten quality of life and well being.

Because of the co-occurrence in space and

time of obesity with other diseases of interest.

So in summary, here are five important

facts about the obesity epidemic that we need to always keep in mind.

Number one, that there has been a temporal patterning.

Something happened around 1980.

What was it?

What lead to the inflection.

We still don't have a clear answer.

It's probably not a single factor.

It's probably a co-occurence of

a complex a pattern of changes that led

to the initiation of the epidemic.

We're still struggling to figure out what those are.

Location, location, location, this is a population level phenomenon.

There's tremendous variability across countries.

These suggest that aspects of the context matter a lot.

When we look at for example studies of migrants, we see that when people

move from countries with low obesity rates such as Japan to places in like

the United States where obesity rates are much higher that migrants quickly adopt

the obesity risk profile of their new home.

This suggests that environments matter, but

exactly how is it that location context matters?

Well this remains something of a mystery.

The epidemic is about the shift in the entire population,

not just about the tail of the distribution.

We can't blame this epidemic entirely on those who are overweight and obese.

This is all of our problem as a society, and

it's going to require societal level commitment and

recognition to address it from a public health point of view.

Number four, population factors.

Appear to shape the speed of the epidemic and this provides really important clues

as to how we might come up with strategies to address the obesity epidemic

in a way that is going to be more effective than we've done so far.

And finally obesity, diabetes, heart disease are all chained together.

These are spatial [INAUDIBLE] co-working epidemics.

They create a package deal that is going to be responsible for

dramatic reductions in the quality of life of Americans and

others worldwide unless we come up with a better public health solution.

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