Welcome to e-con talk brought to you by the Library of Economics and Liberty. I'm your host Russ Roberts of George Mason University.

My guest today is Darius Lackawalla, an economist at the RAND Corporation in Santa Monica, California.

He is also a faculty research fellow at the National Bureau of Economic Research and an associate professor of economics at the Party RAND Graduate School of Public Policy.

Hi Russ, thanks for having me on.

Oh great to have you Darius. You've done a lot of work on obesity and health and I'd like to talk about that today. A lot of people see obesity as a big social problem.

We might talk about that later but I want you to talk about the scope of the problem, the so-called problem, the nature of it.

Are people getting fatter? Is it true that somehow in the last few years Americans are bigger? That's what we hear, is it true?

It's definitely true that Americans are getting fatter. People all over the world are getting fatter for that matter and it's been happening for centuries.

The weights have been going up for a long time and back in the 18th and 19th centuries that was regarded as a good thing because people were moving from underweight and undernutrition to healthier weights and healthier nutritional status.

But as we've gone farther and farther along down the road, we've now begun to encounter people entering overweight status.

So really this is a continuation of longstanding trends throughout the world that we're seeing in America which is kind of a leading edge of this problem.

What are the magnitudes of those increase? You say people have gotten fatter? Let's stick with say America. How much fatter are we then we were say a century ago or two centuries ago?

Well the century ago it's a little hard to answer quite precisely but I'll do my best in a minute. I can say precisely over the last 30 to 40 years the rates of obesity among Americans which is defined typically as severe unhealthy overweight.

Rates of obesity have tripled over the last 25 to 30 years which is really an enormous increase.

Is that severe unhealthy overweight definition been constant over that time period?

It has, yes. So how do you measure that? How's that defined?

There's something that doctors call the body mass index which is a way of measuring height adjusted weight.

So what it really is is simply your weight and kilograms divided by your height and meters squared.

And that's typically used as the reason that this index is used is it was found about a century ago to be well correlated with people's survival experiences.

So people with really low body mass index tend to have higher mortality risk from being underweight. People who are kind of in the middle have the best experience and then people with very high body mass index tend to be also have elevated mortality risk from the problems associated with being overweight.

So you say it's tripled and give me some, if it tripled from a half of one percent to one and a half percent it wouldn't be so serious a problem but what are the measures?

It tripled from approximately seven to eight percent to around between 20 and 25 percent depending on the group of Americans that you look at.

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