[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.
