Obesity and Age among Women

I was looking through some data on how people's weight has changed over time in this CDC publication.  I have been curious how researchers calculate age adjusted measures, so I wanted to delve into it a bit myself.  

Here is an excerpt of the data for women from Table 6 in the CDC report.

It is apparent that weight has increased in every age range from the 1960-1962 time period (which I've called 1960) to 1999-2002 (which I've called 2000).  It is also apparent that the age distribution has shifted, with a larger share of older women in 2000 than in 1960 (I'm assuming the sample sizes in these data are consistent with population statistics on age).  So far, none of that is news.  So, let's dig a little deeper.

The mean body weight of women in the US in 1960 can be calculated by multiplying the weight of women in each age range by the % of women in each age range and summing across all age ranges.  When I do that, I find that the average weight of women in 1960 was 140.05 lbs.  

Now, for a little thought thought experiment.  What if we took the body weights by age observed in 1960 but instead assumed that we had the (older) age distribution that existed in 2000.   ​To calculate this "strange" age-adjusted average, I multiply the weight of women in each age range in 1960 by the % in each age range in 2000 and sum across all age ranges.  The result is 141.2 lbs.  The difference is 1.15 lbs.

What does this mean?  If the female population were, as a whole, older in 1960 - as it is today - then the average weight for women back then would have been 1.15 lbs higher.  ​As a result, a small part of the weight gain from 1960 to 2000 (about 1.15 lbs worth) is due to changing age structure rather than weight gain per se.  

The other thing I noticed is that it matters how you do the age adjustment.  If I use the 1960 age distribution as the "base" then the age-adjusted weight gain from 1960-2000 is 24.1 lbs.  However, if I use the 2000 age distribution as the "base" then the age-adjusted weight gain from 1960-2000 is "only" 23.1 lbs.  Thus, we can push our weight gain figure up or down a pound simply by choosing which base we wish to use.  

It is interesting to note that weight gains have been highest among the youngest females and lowest among the oldest.  The gain in weight from 1960 to 2000 for 20-29 year olds was 28.8 lbs but the gain for 60-74 year olds was only 17.4 lbs.  Also, the variation across years has changed a lot.  In 1960, the difference in 20-29 year olds and 60-74 year olds was 19.6 lbs.  Today, that same difference is only 8.2 lbs.  So, we are fatter but more equal?    

Regardless of what has happened to weight, I can't help but think that it is a very good thing that we have more older women in 2000 than 1960.  Sure, they're a little fatter, but probably thankful to still be kicking.  ​

P.S.  It is important to note that the gains from 1960 to 2000 have, in the recent decade, leveled off and there does not appear to be much change in obesity prevalence among women in the past 10 years (see this paper in the Journal of the American Medical Association or my previous blog post).​

How the Poor Spend on Food

About a week ago, Derek Thompson put up a post at The Atlantic ​with a lot of really interesting graphics on how we spend our money on food and how it has changed over time.

​He shows that we spend a lower share of our income on food than ever before and less than anywhere else in the world.  I know there are some who would bemoan his development and wish we were more like the Europeans.  But for real, life flesh-and-blood consumers it has been a boon.  

My family lived in Paris during much of 2011 and we literally spend twice as much on food there as at home.  Yes, we had access to many things in Paris that we don't in Stillwater, Oklahoma but I think I can pretty honestly say that we didn't eat twice as well in Paris as we do in Stillwater.  You have to remember that living in Paris is not the same as vacationing in Paris - you can't eat at 5 star restaurants every night with two kids and still afford to pay the bills.  So, a lot of what we ate - from cereal to salads to baked chicken - was virtually identical to what we'd have at home; only much more expensive. (I will give the French their bread and wine - the two things that were much tastier and less expensive than at home).   

But, I digress.  The issue I want to point out relates to the focus of the Atlantic piece on how the poor spend their money on food relative to the rich.  The author shows that from 1984 to 2011, the lowest 20% of families spent 16.1% of their income food and that figure remain unchanged over the time period, but for the highest 20% of income earners, in 1982 13.2% of income was spent on food and it fell to 11.6% by 2011.  He says:

In the last three decades, food's share of the family budget has fallen for all but the poorest families, where it's stayed the same

​The first thing to note is that the observation that the poor spend a larger share of their income on food is very old news.  In fact it is something of an economic "law" - Engel's Law - postulated by Ernst Engel in the mid 1800s.  Moreover, because the economic gains at the bottom 20% haven't been terribly pronounced over this time period, it probably isn't that surprising to see that the % they spend on food hasn't much changed either.  However, it is important to note that these are not the same families being compared in 1984 and 2011.  I would suspect the bottom 20% include a lot of really young people and a lot of really old people in 1984 who today are in better paying jobs (or no longer living).  

Not only are these not the same people, it is not the same food being eaten in 2011 as in 1984.  In the conclusion, the author notes:

we can't rule out that the lowest-income households only spend one-sixth of their money on food, not only because real food prices are falling, but also because they're forced to consume less, as mortgages and gas prices eat into the budget.

​Yes, but we also can't rule out that the poor are getting more for their money today then they did in 1984.  The author shows some interesting graphs of total spending on food at home and away from home by the relatively poor and rich in (I assume) 2011 but what isn't shown is how that has changed over time. 

Has total spending among the poor gone up or down in real terms?  Are the poor eating out more than they once did?  I'm not at all surprised to see that the rich eat out more than the poor in 2011, but the better question is whether the poor in 2011 are eating out more than the poor in 1984.  ​

I wasn't even yet a teenager in 1984 but if memory serves me right, it was about that time we got our first microwave (and our first dishwasher I believe).  Over the intervening years, the grocery store has grown and the available flavors, brands, and variety has grown enormously.  In short, the quality of food (including taste, convenience, etc.) has changed a lot from 1984 to 2011.  

As a result, I'm not nearly as worried by statistics showing that the percent of income spent on food by the poor hasn't changed over time as I am about statistics showing potential increases in hunger among the poor.  ​

Moreover, if we really want to worry about the poor and hungry, we should look outside the U.S.​

Our Future?

Assorted Links

• The Economist on GMOs and the environment

• ​Great editorial in the New York Times on genetically engineered animals

• Are plant-based diets really better for the environment?

• Does a food appear healthier if the calorie label appears in green​?

• Never eat again?

Is Food Addictive?

The Neurosceptic at Discovermagazine.com took on that question in a recent blog post. The author discusses a recent article arguing that dopamine release in response to food is evidence of food-related addition.  Here are the problems with that thinking:

If you view addiction as essentially about reward (pleasure), surely that means that anything pleasurable could also be addictive? Or to put it another way, if you’re saying that addiction is the direct consequence of over-indulgence in a reward, then aren’t you saying that reward itself is ultimately what’s addictive?

and

If everything from food to friends to music are rewarding because they trigger dopamine release, then surely all of those things could be ‘addictive’. If ‘reward’ is essentially monolithic, and the various kinds of rewards differ only in how powerful they are, then everything’s addictive to a degree. The more fun, the more (potentially) addictive. The better something is, the worse it is.

This seems to me to be the logical conclusion of this approach to addiction. Let’s call this (very widespread) approach neuropuritanism.

The funny thing is that this idea – for all its medical, neurobiological, scientific language – actually undermines the concept of addiction as a ‘disease’ and reduces it to what amounts to a moral failing – it casts addiction as over-indulgence. The Sin of Gluttony, if you will.