On a daily basis, John Jakicic sees progress.
The obesity expert at the University of Pittsburgh sees riverfront trails packed with runners, lively public discussions about bicyclists on city streets and 300-calorie menus at McDonald's.
But still, more than a quarter of Pennsylvanians are obese, according to data released Monday from the U.S. Centers for Disease Control and Prevention.
The state ranks 20th in the nation, with an obesity rate of 28.6 percent. West Virginia ranked third in the country, with 32.4 percent of its residents considered obese.
Mississippi has the highest obesity rate in the country, at 34.9 percent, and Colorado had the lowest, at 20.7 percent.
"Some of it is cultural and some of it is tied to economic factors," said Jeff Levi, executive director of the Trust for America's Health, which analyzed the CDC figures. "Poorer states tend to have higher rates of obesity."
An obese person is defined as one whose body mass index -- their weight, in kilograms, divided by the square of their height, in meters -- is greater than 30. Obesity has been linked to a litany of health problems, from type 2 diabetes to heart disease to some cancers.
The good news, Mr. Levi said, is that obesity rates seem to be leveling off -- though at an "unacceptably high level."
Last year, Pennsylvania's obesity rate was 28.5 percent -- 19th in the country, though Mr. Levi advised against comparing year-to-year because of a slight change in the CDC's methodology.
Other data have also started to show rates holding steady after decades of vast increases. In 1995, Pennsylvania's obesity rate was 16.2 percent.
"We're starting to see progress," said Mr. Jakicic, chair of the department of health and physical activity at Pitt. "It took us decades to get these obesity rates where they are. It will take us decades to get them back in the other direction."
The skyrocketing rates have come in large part because of cultural changes, he said, from the loss of manufacturing jobs to the dominance of the automobile to the easy accessibility of fast food.
Mr. Jakicic, who is also the director of the physical activity and weight loss management research center at Pitt, believes that obesity is both more complicated and more simple than people tend to think.
Losing weight should be simpler, he said. Rather than complicated calorie counting or diets, he recommends that people put food on their plate as they normally would, fill it up only once, and leave 20 to 25 percent of the food on the plate. Combine that with exercise and most people will start losing weight.
But the actual mechanism behind weight loss is more complicated, he said.
"If it was all about willpower, this would be an easy fix, but it's not," Mr. Jakicic said. "What we're learning is that it's much more complicated than that."
For example, he said, brain chemistry in the obese can work differently than in people at healthy weights.
Mr. Jakicic stressed the benefits of physical activity on health even if exercise doesn't have a dramatic effect on initial weight loss. His own grandfather, he said, was obese but lived until age 91. He credits that longevity to the fact that he was active every day.