Our Weight: It’s Gaining On Us

Since the late 1980s, America’s average Body Mass Index, or BMI, has been climbing rapidly. As a result, we’re losing life expectancy relative to people in other rich countries.

Americans of all ages, all education levels, and all income levels have been packing on lots of pounds over the past 25 years. That’s apparently why, even though as a nation we’re smoking less, our average lifespans haven’t grown as much as those of people in other advanced nations.

The numbers are startling: As many as half of all adult Americans will be obese by 2040, and half of the obese women will be “morbidly” obese. And it’s not just the poor and uneducated who getting huskier. Since the late 1980s, the prevalence of obesity has grown most sharply among higher-income, college-educated men.

Along with sporadic governmental responses—like Mayor Bloomberg’s war on Big Gulp containers—this trend has attracted considerable scholarly attention. A new paper from the National Bureau of Economic Research, for instance, tries to measure the effects of two behavioral factors, smoking and obesity, on life expectancy.

The paper, “Projecting the Changes in Smoking and Obesity on Future Life Expectancy in the United States,” was written by Samuel H. Preston, Andrew Stokes and Bochen Cao, all of the Population Studies Center of the University of Pennsylvania, and by Neil K. Mehta of Emory University.  

In short, the researchers suggested that the combination of reduced smoking and rising obesity will by 2040 have added 0.92 years to male life expectancy at age 40 and 0.26 years to female life expectancy at age 40. By itself, the decline in smoking would have added 1.52 years to male and 0.85 years to female life expectancy, the paper said; obesity accounts for the difference. Those numbers, in turn, are embedded in the Social Security Administration’s recent prediction that life expectancy at age 40 will grow by 2.55 years for men and 2.17 years for women between 2010 and 2040. 

Weight gain from 1988 to 2040

“Obesity” has a specific definition. The CDC considers a person to “obese” if he or she has a Body Mass Index (BMI) of 30.0 or higher. A person who stands 5’10” tall would be obese if he or she weighed 215 pounds or more. They would need to lose more than 50 pounds to achieve the normal BMI range of 18.5 to 24.9.

U.S. obesity rates have especially risen sharply over the last quarter century, for reasons that researchers have guessed at but not proven. Over the next quarter century, they’re expected to rise another 10 to 15 percentage points. Today, 37.5% of American adults are obese. “By 2040, 47% of men and 51% of women are projected to be obese,” the authors of the NBER study wrote.   

Even before then, many people will have to lose weight just to call themselves merely obese. “Alarmingly,” the researchers added, “the morbidly obese (BMI>35.0) increase as a proportion of the obese for both males and females, to the point where they constitute a majority of obese women by 2020 and thereafter,” the paper said.

Preston estimated that “US life expectancy at age 50 in 2006 was reduced by 1.54 years for women and by 1.85 years for men as a result of obesity. Relative to higher life expectancy countries, allowance for obesity reduces the U.S. shortfall in life expectancy by 42% (36%-48%) for women and 67% (57%-76%) for men.”  

Cross-demographic impact

One of the biggest increases in obesity in the last quarter-century occurred among demographic groups that once had the lowest rates of obesity. The obesity rates of men with higher incomes rose to 32.9% in 2007-09 from 18% in 1988-94—an 83% increase. The obesity rates of men with college degrees rose to 27.4% from 15.6%–a 76% increase. Indeed, men with high education and income levels had higher obesity rates in 2007-2008 than did men with low incomes and less than a high school degree in 1988-1994, according to CDC data. (The CDC chart below shows the rising prevalence of obesity among men and women over age 20 since 1988. For additional data, click here.)

The data show that our stereotypes about obesity, like most stereotypes, are exaggerations. “Although obesity is frequently associated with poverty, recent increases in obesity may not occur disproportionately among the poor… Over the course of three decades, obesity has increased at all levels of income,” wrote Virginia W. Chang and Diane S. Lauderdale in a 2010 article in the Archives of Internal Medicine.

Although minority groups have higher rates of obesity, “It is typically not the poor who have experienced the largest gains,” Chang and Lauderdale found. “Among black women, the absolute increase in obesity is 27.0% for those at middle incomes, but only 14.5% for the poor. Among black men, the increase in obesity is 21.1% for those at the highest level of income, but only 4.5% for the near poor and 5.4% for the poor.”

Fast food versus statins

In a statistical irony, the NBER paper noted that mortality rates for the obese have been falling as obesity increases, while mortality rates for smokers has been rising as smoking becomes less prevalent. That’s because so many young people, who naturally have lower mortality rates, have been entering the ranks of the obese, and because so many smokers are reaching retirement age, when their mortality rates naturally increase.  

In short, obesity is a more recent phenomenon than smoking, so the obese are younger, on average, than smokers. “Smokers today have been smoking for a longer period, on average, than smokers in the past,” Preston told RIJ in a telephone interview.

“But obese people today haven’t been obese for as long, on average, as obese people were in past,” he added. “That’s one reason why the mortality risks associated with obesity have declined. It also appears that statins and other blood pressure drugs, which have been used disproportionately by obese people, have been effective in reducing mortality.”

For his part, Preston doesn’t know exactly why obesity began to snowball in America 25 years ago—at the sunset of the Cold War and the dawn of the Internet Age.  “Government efforts to discourage smoking and tax increases on cigarettes were effective by the late 1980s,” he speculated. And, while smokers might tend to eat more after they stop smoking, Preston blames other factors for rising obesity since the late 1980s. “The rise of fast food is certainly part of the issue,” he said. “The price of calories in general has declined dramatically.” 

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