Medicine: Obesity a problem among the affluent

It's not just the poor people packing on the pounds any more:

Money for quality food aside, higher-income people are thought to be better educated and to have better access to health care, so why such a jump among them? In an interview, Robinson said no one yet knows. But she speculated that longer commutes, growing popularity of restaurants and possibly longer work hours since the 1970s are playing a role.

The poor still are the most likely to be fat, said Dr. Adam Drewnowski of the University of Washington, an expert on the problem. Moreover, since the '70s, rates of extreme obesity — being 90 to 100 pounds or more overweight — have ballooned among lower-income groups, something the study doesn't address, he said.

Further complicating attempts to compare income and obesity are cultural factors. Certain racial and ethnic groups positively equate a man's girth with wealth — it's a sign of success, Drewnowski said.

"I would caution against any attempts to interpret these data to say social differences have disappeared," he said. "It just shows that obesity is a general problem and it's now affecting pretty much everybody. ... But it would be very shortsighted to stop paying attention to the people who are most vulnerable."