Why the surge in obesity?

By Lane Kenworthy
June 22, 2012

Editor’s note: This post is republished from the author’s blog.

The Weight of the Nation is a four-part series on obesity in America by HBO Films and the Institute of Medicine, with assistance from the Centers for Disease Control (CDC) and the National Institutes of Health (NIH). It’s been showing on HBO and can be viewed online. Each of the four parts is well done and informative.

Obesity is defined as having a body mass index (BMI) of 30 or more. For a person 6 feet tall, that means a weight of more than 220 pounds. For someone 5’6″, the threshold is 185 pounds. People who are obese tend to earn less and are more likely to be depressed. They are at greater risk of diabetes, heart disease, stroke, and some types of cancer, and they tend to die younger. The CDC estimates the direct and indirect medical care costs of obesity to be $150 billion a year, about 1% of our GDP.

The chart below, which appears several times in The Weight of the Nation, shows the trend in obesity among American adults since 1960, the first year for which we have good data. The data are from the National Health and Nutrition Examination Survey (NHANES). They are collected from actual measurements of people’s height and weight, rather than from phone interviews, so they’re quite reliable. After holding constant at about 15% in the 1960s and 1970s, the adult obesity rate shot up beginning in the 1980s, reaching 35% in the mid-2000s.

What caused the surge in obesity? The standard explanation is too much eating and too little physical activity, and The Weight of the Nation sticks with this story. But it shouldn’t, because the evidence suggests one of these two hypothesized culprits has been far more important than the other.

Here is the trend in eating, measured as average calories in the food supply (adjusted for loss and spoilage) according to data from the Department of Agriculture. This chart too is from The Weight of the Nation. The timing of change matches that for obesity; the level is flat through the 1970s and then rises sharply beginning in the 1980s. An alternative series, measuring energy consumption per capita, goes back to 1950 (see figure 6, chart F here); it too shows little or no change until 1980, and then a sharp jump. The rise in food consumption correlates closely with the rise in obesity.

That isn’t true of physical activity. We’re less active now than we were half a century ago, but the timing of the decline in activity doesn’t match up with the shift in obesity.

We don’t have good historical data for a comprehensive measure of activity, such as calories expended, so we have to look instead at individual components. We can begin with the most-often-cited culprit: television. Here too The Weight of the Nation presents data, shown below, with the suggestion that TV watching is a significant cause of rising obesity. But the trend doesn’t support that inference. Time spent watching television has increased steadily since 1950. There was no sudden rise in the 1980s.

What about video games, the internet, and smartphones? The internet and smartphones arrived on the scene too late to account for the rise in obesity in the 1980s and most of the 1990s. The timing doesn’t work for video games either; they’re played mostly by the young, beginning in the 1980s, but obesity rates rose sharply in the 1980s and 1990s among adults of all ages, even among the elderly (see table 2 here).

More Americans now have sedentary jobs and drive to work. Yet as David Cutler, Edward Glaeser, and Jesse Shapiro noted in a paper published nearly a decade ago, these shifts have been going on for a long time, with no acceleration in the 1980s.

Between 1910 and 1970, the share of people employed in jobs that are highly active like farm workers and laborers fell from 68 to 49 percent. Since then, the change has been more modest. Between 1980 and 1990, the share of the population in highly active jobs declined by a mere 3 percentage points, from 45 to 42 percent. Occupation changes are not a major cause of the recent increase in obesity.

Changes in transportation to work are another possible source of reduced energy expenditure — driving a car instead of walking or using public transportation. Over the longer time period, cars have replaced walking and public transportation as a means of commuting. But this change had largely run its course by 1980. In 1980, 84 percent of people drove to work, 6 percent walked, and 6 percent used public transportation. In 2000, 87 percent drove to work, 3 percent walked, and 5 percent used public transportation. Changes of this minor magnitude are much too small to explain the trend in obesity.

Another reason to doubt the importance of declining physical activity is that the elderly probably have become more active over time, rather than less, and yet we observe a rise in obesity among the elderly too, similar in timing and magnitude to that of younger adults (again see table 2 here).

In short, the evidence suggests that reduced physical activity has not been a key cause of the surge in obesity in America (more hereherehereherehere).

This doesn’t mean physical activity plays no role in determining which people become obese. And it doesn’t mean an increase in activity won’t help reduce obesity’s prevalence. But it does suggest that a strategy focused on increasing activity — and The Weight of the Nation leans in this direction — may not get us as far as we’d like. To make serious progress in reducing obesity, we need to significantly reduce the number of calories many of us consume.

12 comments

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I just saw this great Taco Bell ad during a baseball game. In slow motion, it said I could be hero if I could manage to hold my taco in one hand, thereby freeing the other hand to catch a ball in the stands.

In a culture that values mindless consumption, excess and decadence are defining values. We can talk personal responsibility all we like but it’s stupid considering we’ve raised alcoholics, sent them to live in a bar and are now telling them they’re solely to blame. Let’s not pretend that marketing and advertising has no effect.

U.S. food lobby fighting hard to defend kid ads

http://www.reuters.com/article/2011/11/0 7/us-advertising-children-idUSTRE7A66OA2 0111107

Special Report: How Washington went soft on childhood obesity

http://www.reuters.com/article/2012/04/2 7/us-usa-foodlobby-idUSBRE83Q0ED20120427

At every level of government, the food and beverage industries won fight after fight during the last decade. They have never lost a significant political battle in the United States despite mounting scientific evidence of the role of unhealthy food and children’s marketing in obesity.

Lobbying records analyzed by Reuters reveal that the industries more than doubled their spending in Washington during the past three years. In the process, they largely dominated policymaking — pledging voluntary action while defeating government proposals aimed at changing the nation’s diet, dozens of interviews show.

In contrast, the Center for Science in the Public Interest, widely regarded as the lead lobbying force for healthier food, spent about $70,000 lobbying last year — roughly what those opposing the stricter guidelines spent every 13 hours, the Reuters analysis showed.

Posted by TheUSofA | Report as abusive

The Center for Science in the Public Interest is a left-wing advocacy group for vegetarians, pure and simple. They started the movie popcorn hysteria. They have no credibility with true scientific minds.

CSPI devoted its mission to “nutrition” in 1977…about the time the obesity epidemic started.

I saw The Weight of the Nation, all four parts. Its “experts” are hardly the examples of healthy eating that their rhetoric advocates. One of them, Kelly Brownell of Yale University is extremely obese. What gives this Ivy League pinhead the right to dictate to us?

Posted by cpps90 | Report as abusive

I would be very curious to see the rise in obesity charted against the decrease in SMOKING. My parents both gained weight when they quit smoking. I think that when people have excess energy or stress they need to do something. For decades, people smoked to relax, and release excess energy. That made them look cool and stay thin. Now, without that release, many eat too much. That is not cool, and makes them fat and unhealthy. I think to think about the body without psychological needs is the part of the problem here.
By the way, I personally do not smoke, and am not obese. I try to exercise to relax.

Posted by Montefuego | Report as abusive

Turn on the television. Luscious looking food is flashed on the screen during commercial after commercial, from pizza, to Mexican food, to seafood, etc. Food ads are even more commonplace than the wash of pharmaceutical ads pushing every kind of unsafe drug there is. So, the big lobbyists have hijacked our airwaves as well as our governing bodies in Washington. Is it any wonder we are becoming obese? Food is about the only ‘comfort’ left to an increasingly powerless, impoverished and oppressed national population. The top corporates and filthy rich 1% has determined that we, as a people, are ‘cockroaches’ for them to step on as they please. We pay the bills they run up for us via joblessness,taxes,oppressive work conditions and low wages. Yet we are told we are to blame for all our own problems. It is never the politically and financially powerful who cause so much of our pain that are to blame, to hear the national media tell it. As Jesus Christ said, “woe to you, scribes and pharisees, hypocrites: for you load men with burdens grievous to be borne, but you yourselves won’t touch them with one of your fingers.”

Posted by allen_osuno | Report as abusive

I would like to see this study paired up with the smoking cessation rates to see if they coincide. I guarantee you’ll have an “Aha” moment.

Posted by MizT | Report as abusive

I don’t have a quarrel with the data presented in this article and will accept the hypothesis that eating more is more important than exercising less in the overall Us obesity problem.

What I’d like to see is more analysis of what it is that we’re eating and where we’re eating it. I would contend that both processed food provided by big corporate food and food provided in the big corporate restaurant industry is long on satiety and short on nutrition and elements that would reduce obesity. Added sugars, salt and unhealthy fats dominate both prepared foods and chain restaurant food, because it’s cheaper and easier to provide. If we took out most all of the added sugars and overabundance of salt and saturated and Omega-6 fats and instead gave people the fiber, Omega-3 fats and nutrients they need, upping the glycemic index of meals, I think we’d start to see some changes.

This would have to start with better labeling, which is going to require better laws and regulations. Then a tax on junk foods or a tax structure that rewards producers of nutritious foods . . .

Posted by royjohn | Report as abusive

The incredible recent surge of highly morbidly obese cannot come from simply “eating too much” and “exercising too little” of our former frames of reference. People would have to stay bed-ridden gobbling boxes of bon-bons and mashed potatoes to explain the phenomenon.

It has to be deriving from “something” we are eating that wasn’t there 30-40 years ago, e.g., High Fructose Corn Syrup – not accusing, just an example, that is faking some people’s bodies into hoarding calories and bulk in the belief that the body is ‘starving to death’.

@cpps90 wrote, “What gives this Ivy League pinhead the right to dictate to us?”

The professionals do not “dictate”, but inform. They have the “right” to the platform because they are the highly knowledgeable professionals in the field, not you.

Posted by Whittier5 | Report as abusive

The world is complex, with lots of variables shifting. Trying to isolate one variable among hundreds of variables is difficult.

Clearly, both sugar and HFCS intake has soared dramatically.

Taubes suggests that it’s basic dietary shifts. The USDA documents that the standard American diet is 69% processed carbs. This means more sugar and fewer nutrients. http://www.nytimes.com/2010/12/28/health  /28zuger.html He also suggests a generational cascade effect; fat parents have fat babies who grow up to be fat parents, etc.

There are significant family and cultural changes. In terms of families: 34% of kids live in a single parent family. The share of children in one-parent families has nearly tripled since 1970, when the rate was 11 percent. Over the last two decades, the rate of nonmarital childbearing rose substantially—from 22 percent in 1985 to 39 percent in 2006. This statistic reflects a decline in the likelihood of marriage in every age group. Researchers report not only a rise in the divorce rate, but also an increase in the number of women who postpone marriage or never marry. The share of married-couple families where both parents worked was 58.5 percent in 2011. Most kids are bussed to school (90%). Students spend an average of an hour and a half in a school bus each day.

Centralized schools, decentralized communities, use of antibiotics, farm subsidy priorities, etc. all contribute. Even medical treatment changes the equation (use a pill to change the lab results but don’t change the behavior).

You do realize that BMI is not a direct BF measure? And that a BMI-to-DEXA comparison shows that BMI significantly underestimates obesity rates?

http://www.scribd.com/doc/37081820/Obesi ty-Will-All-Americans-Become-Overweight- or-Obese

http://www.scribd.com/doc/37488514/Obesi ty

http://www.scribd.com/doc/71740870/Chron ic-Dis-Trends

Posted by Cwolf88 | Report as abusive

I am surprised that they did not attempt to correlate the “social emphasis on food” to the obesity numbers. I would venture to guess that it was in around 80′s when government mandated calorie counts started, the sale of cookbooks rose, the media attention to diet fads started building, and an entire society became focused on food.
Maybe if we go back to ignoring the issue, our appetites will diminish?

Posted by z0rr0 | Report as abusive

Increased consumption has to be a part of the story.

there are likely also epigenetic effects.

But you have to reduce consumption to have any serious impact.

Tax on Restaurants. Tax on take away food. Tax on sugar. Tax on fat.

Help with the deficit too!

Posted by Dafydd | Report as abusive

The rapid rise in obesity after 1980 coincides remarkably with national dietary recommendations to reduce our intake of meat, eggs, whole milk and butter–food that had traditionally been considered valuable sources of our most important nutrient, protein–and to increase our intake of grains and cereals–food that had traditionally been considered poor sources of nutrition in general (that’s why we fortify and enrich them). Lots more information here: http://wp.me/p29Lnc-1g

Posted by ahhite | Report as abusive