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Your income and social status are written all over your body, Adam Drewnowski says.

Drewnowski is an epidemiologist. He directs the Center for Obesity Research at the University of Washington in Seattle, and he lectures frequently. "I can pretty much guess the income of an audience by the number of obese women in the room," he says.

"If one-third of my audience is obese, I don't think, 'Oh, my God, these are people with weak willpower or who made bad choices.' I say, 'These are women who do not make more than $40,000 a year.'"

Poor women pack on pounds

Several studies, including Drewnowski's, show that poorer Americans are more likely to be obese than those who are wealthier. But when you look deeper into these studies, University of California, Davis, nutritionist Marilyn Townsend says, the difference is mostly among women: Poor women are much, much more prone to obesity than their wealthier counterparts.

The discrepancy between men and women isn't well understood. The drive for status may be what keeps wealthier women thinner, suggests Townsend, who specializes in behavioral change and works with other researchers, including Drewnowski.

Often, the obese are blamed for being morally weak, says a 2010 study in the International Journal of Obesity.

"People say things like, 'Why don't they just make a cheap pot of lentil soup and live on it for a week?'" Drewnowski scoffs. "Obesity is not the result of excessive indulgence; it's a symptom of lower socioeconomic standing in this country."

Lower-cost diets that are high in fat and sugar and lower in nutrients are more often consumed by people with lower education and incomes, Drewnowski says in research published last year in the American Journal of Clinical Nutrition.

In smaller studies in Seattle, Drewnowski has found obesity as low as 6% in wealthy neighborhoods and as high as 30% in poor areas. (Obesity is a body mass index over 30; you can calculate your own body mass here.)

Drewnowski has even linked obesity to grocery stores: Customers of lower-cost Seattle supermarkets were up to 10 times more likely to be obese. As much as 40% of shoppers at cheaper grocery stores, such as Safeway, were overweight, compared with as little as 4% at stores such as Whole Foods.

"The minute you move to an area served by Wal-Mart -- because they place themselves in lower-income areas -- you will be surrounded by obesity," Drewnowski says.

The point is not that a particular store makes you fat or thin but that people who eat cheaply are prone to getting fat. Those who spend more generally are thinner.

There's "almost a straight-line correlation between wealth of the neighborhood and obesity among women," Drewnowski says. The 2012 federal poverty line for a family of four in the Lower 48 states is $22,050; that takes in nearly one in six Americans.

A spreading epidemic

Five years ago, only one state -- Mississippi -- had an obesity rate of more than 30%. But by 2010, 12 states had joined that club, according to a report published last year by the Robert Wood Johnson Foundation and Trust for America's Health, two nonprofit health advocacy organizations.

America's obesity problem is worst in the South. It's least bad in the Northeast and West. But here's how fast it's growing: The leanest state in 2011, Colorado, with an adult obesity rate of 19.8%, would have been the fattest in 1995. Two decades ago, not one state had a rate above 15%.

The two health advocacy organizations, among others, also link the problem with poverty. Their report says 33% of American adults earning less than $15,000 per year are obese, compared with 24.6% making more than $50,000.

Mississippi, with an obesity rate of 34.4%, is the poorest state in the union. Its poverty rate was 22.4% in 2010, the Census Bureau reported recently.

Causes of rising obesity

Although the connection isn't a simple straight line, Drewnowski see roots in three changes:

  • Rising costs and stagnant wages. Salaries haven't kept up; single salaries rarely can support families as they commonly did 50 years ago.
  • Changing jobs. The switch from manufacturing to a service economy reduced the number of stable, well-paid 9-to-5 jobs. Lower-paid shift work, now prevalent, pays less and makes it hard to schedule regular mealtimes.
  • Working women. Fast-food restaurants are blamed a lot for obesity; the huge change in U.S. households stemming from the large-scale entry of women into the workforce in the past 50 years gets less attention.

Not everyone who is at risk is obese. There are other factors -- including genetics, emotions, psychology and metabolism -- although they appear to play smaller parts.

Townsend is interested in the minority who stay lean on tight food budgets. Immigrants from Asian countries, for example, largely resist obesity despite low incomes. In subsequent generations, however, Asian-Americans have joined the epidemic.

How to stay thin on a lean budget

The immigrants' secret? It's basic, says Townsend: They cook from scratch.

You can eat well without cooking at home. But it's expensive. Americans consume about a third of our calories away from home, according to University of Washington epidemiologist Barbara Bruemmer.

People trying to eat healthy on a low budget have no choice but to cook from scratch, Townsend says. But for many, it's not easy -- or even possible. Cooking from basic ingredients is nearly a lost art among large numbers of Americans because of a lack of training, time and organizational skills, she says.

When Townsend interviews people, she asks if they cook meals at home. Sure they do, many say. But it turns out that what they mean is that they're combining boxed ingredients or reheating processed food in a microwave.

"Changing is so much work," says Townsend. Taste buds attuned to fatty, salty, sugary fast foods and processed foods must be retrained. Processed foods combine cheap ingredients -- corn syrup, refined grains and fats -- and sophisticated chemical research for addictive eating experiences.

A bowl of homemade soup filled with vegetables and subtler flavors has trouble competing. It's often not realistic to expect people stuck in difficult lives with few good solutions to become enthusiastic about changing their diets.

Fast food isn't just nutrition; it's also cheap, satisfying entertainment. "And it's one of the few things that less-well-off people have: They don't have to cook," Julie Guthman, an associate professor of community studies at the University of California, Santa Cruz, told The New York Times. She's the author of "Weighing In: Obesity, Food Justice, and the Limits of Capitalism."

The federal food stamp program, now called SNAP (Supplemental Nutrition Assistance Program), is trying a $20 million pilot program in Hampton County, Mass., to see if incentives can entice users to buy fruits, vegetables and other healthful foods.

Townsend's solution is simpler and more radical: Revamp SNAP so it can be used to purchase only ingredients -- no prepared foods, prepared ingredients, snacks or soda pop.

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"The intent of the (food stamp) program, when it was established in the 1930s, was to help people buy ingredients that they would in turn use to cook at home," she says.

Drewnowski has another solution: Bring home-economics classes back to schools. "It would do more for obesity prevention than any other thing," he believes.

While the experts wrestle with big-picture solutions, you can start here: