An Expert Interview With David L. Katz, MD
David L. Katz, MD, MPH, Laurie Scudder, DNP, NPSep 27, 2013
Obesity: How Big Is the Problem?
Medscape: Could you review the epidemiology of obesity, particularly in children, and the impact on type 2 diabetes mellitus (T2DM) over the past 5-10 years? Is the epidemic beginning to abate?
David L. Katz, MD, MPH: For a long time, we have been talking about obesity as epidemic in both adults and children. By definition, that term refers to a condition affecting the population at an unprecedented level, so it doesn't necessarily tell us how many people are affected. It just says it is rising beyond all precedent. Actually, rates in adults have stabilized, and so I think the right way to characterize the prevalence of obesity now is hyperendemic.
It seems to be fixed at a very high level, and there are various sources of information that confirm that, including the National Health and Nutrition Examination Survey and the Behavioral Risk Factor Surveillance System (BRFSS) at the Centers for Disease Control and Prevention (CDC). These various sources of epidemiologic information and population-level surveys suggest that at least two thirds of the adult population is either overweight or obese nationally. Some surveys have suggested it is as high as 80%.
In the case of children, the figure is lower but actually far more worrisome, because the rates of childhood obesity are unprecedented in history. We really don't know what happens when 30% or more kids are overweight or obese over the course of the lifespan. Consider that the adults who are now dealing with hyperendemic obesity were not subject to hyperendemic or epidemic obesity as children. We can anticipate, then, that with a much higher rate of childhood obesity, these kids, when they grow up, will be experiencing an even higher rate of adult obesity.
In terms of the link to diabetes, we have really seen an epidemic of T2DM, and there the term "epidemic" remains appropriate because the rate of T2DM continues to rise. The CDC has projected that should current trends persist, by or about the middle of this century as many as 1 in 3 Americans could be diabetic. Almost all of that will be T2DM. Since that projection was made, on the basis of computer modeling, we are right on course -- a dire course.
The advent of T2CM in children really is a signature event that characterizes the full toll of epidemic obesity. Those of us who trained in medicine less than 100 years ago learned about 2 kinds of diabetes: juvenile onset, now called type 1, and adult onset, now called type 2. Part of the reason it is now called type 2 is because kids get it now, too. That really never should have happened. The advent of T2DM as a condition in children is a direct by-product of epidemic childhood obesity.
Some good news: We have seen some signs of site-specific stabilization in rates of childhood obesity,and even some slight dips in some regions where a lot of work is being done. We have seen stabilization in the overall rate of adult obesity as well. But one other thing to throw in the mix here is that rates of severe obesity in both adults and children continue to rise briskly.
So as we take stock of the obesity epidemic now, it may no longer serve us adequately to keep asking how many people are overweight or obese, because that number may become relatively stable. What we may now need to start asking is how overweight those people are, because the severity of obesity is worsening.
Medscape: Can you briefly review the recent data on obesity rates from the CDC?
Dr. Katz: The CDC is tracking state-by-state prevalence of obesity on an annual basis, and they issue annual color-coded maps depicting obesity prevalence. Many of us in this field have been following the obesity trends for many years, which are based on self-reported data (Figure).
Medscape: Many experts are suggesting that children born after 2000, new millennium kids, are going to be the first generation in history to have a shorter lifespan than their parents. Is it too simplistic to point at obesity as the sole factor in that? Can you discuss that prediction and what led to that conclusion on the part of many experts?
Dr. Katz: Well, in some ways it is too simplistic to even say with any confidence that this is going to happen, although the analysis that set that discussion in motion was certainly robust. There was a study published in the New England Journal of Medicine in 2005 by Jay Olshansky and colleagues.Inputting current data on obesity and its effect on longevity, these authors used computer modeling to forecast that life expectancy would level off and potentially decline in the first half of this century.
We have epidemic childhood obesity. We are seeing the advent of what formerly were adult-onset conditions. In addition to T2DM, there has been a proliferation of ever more cardiovascular risk factors in childhood. All of this would conspire not only against life in years, but years of life lived in vital good condition. To some degree, it makes sense to look at the toll of all of this -- ever more risk for ever more chronic disease at ever younger ages -- and conclude that this means a shorter life expectancy.
The problem with that projection from the start was the fact that one of the things we do best in modern medicine is stave off death. We do a very poor job of preserving true vitality. If you look at the epidemiology of the United States, and increasingly much of the world, as was addressed by The Lancet in their Global Burden of Disease Report 2010, the global burden of chronic disease is huge and rising. We tend to do a fairly poor job of maintaining health, and the epidemiology reflects that we have a lot of chronic disease.
However, we are able to keep people with chronic disease alive. That is where the cutting edge of biomedical advance really comes into play. We have powerful drugs and powerful procedures, and of course, that will only be more so in all probability 10, 20, or 30 years from now, when we might start to see the shortened life expectancy of kids growing up today. We don't know that that will come to pass, but it is still a terrible state of affairs if life expectancy per se is not declining, but health expectancy -- years of life lived in vital good condition -- is on the decline. So I think Dr. Olshansky and the authors involved in that 2005 report would look at what we have learned over the 8 years since then and might not be as sure of that conclusion.
We certainly don't have clear signs of declining life expectancy. It may come to pass, but it may be that medical technology will help us hang on to years of life. What we are clearly losing already is life in years. We are much more confident about that. The basic sentiment in that assertion -- that this is the first generation of kids where we are looking ahead at a shorter life expectancy -- I think is still valid. Whether or not we measure what they are losing in years of life or life in years is what remains to be seen, but clearly there is a lot at stake.