It's no secret that Americans have grown accustomed to convenience, where cheap 700-calorie cheeseburgers are only a 10-minute drive away.

But this lifestyle is literally killing us.

That's because our eating habits contribute to our ill health. According to the Centers for Disease Control, obesity is associated with 112,000 deaths each year in the United States, and contributes to an increased risk of contracting chronic illnesses, including heart disease, diabetes, and some cancers.

In Pictures: Most Sedentary Cities

What's also to blame? Lack of exercise and sloth.

We set out to discover which cities were the worst offenders when it came to leading a sedentary lifestyle. Our list of 20 cities is topped by Memphis and New Orleans. It also includes surprising entries, such as Miami and San Diego.

Behind The Numbers

We created our list by collecting data on body mass index (BMI), physical inactivity and TV watching habits for the country's 50 largest metropolitan statistical areas. For information on BMI and physical inactivity, we turned to 2006 data from the Centers for Disease Control and its comprehensive Behavioral Risk Factor Surveillance System, which surveys metropolitan areas annually on a range of health issues. For BMI, we added the percentage of obese or overweight people and ranked cities based on the combined number. When measuring frequency of exercise we looked at the survey's sole indicator: the percentage of people who had not engaged in any physical activity in the past 30 days. To determine TV watching habits, we used Nielsen data on the average number of hours of TV watched per week by metropolitan area.

After establishing where cities ranked in each category -- 1 for the heaviest city and 43 for the lightest, for example -- we then added the three for a final score. Memphis earned the lowest score with 10, and San Francisco claimed last place with 123. Some metropolitan areas, like Sacramento, Calif., or Columbus, Ohio, could not be included due to insufficient data from either the CDC or Nielsen. In total, we ranked 43 cities out of the original 50.

The Findings

We learned that many cities on our list were aware of public health challenges, such as obesity and inactivity. They were also working to improve access to amenities like parks, while also mounting advertising campaigns on the dangers of leading a sedentary life.

While obvious trends plague most cities -- sprawl was mentioned consistently -- it also became clear that each city battles very specific problems. In post-Katrina New Orleans, for example, the slow rebuilding of supermarkets and a growing reliance on corner stores stocked with junk food posed a unique predicament. Over the years, Oklahoma City, Okla., has become a prime breeding ground for fast-food franchises when developers capitalized on cheap land and minimal traffic congestion.

Though the debate over how to solve this nationwide crisis is still under way, experts talk of 'reshaping the environment' to foster increased physical activity, while cities experiment with new approaches to promote public health. The end goal is to shrink waistlines, decrease chronic health diseases caused by obesity and inactivity, and encourage a fitter populace.

Reshaping The Environment

Memphis, the most sedentary city on our list, landed at the top for scoring high on every indicator. In terms of BMI, 65 percent of the population is overweight or obese. Though the city is slightly behind the national rate at 66 percent, about 30 percent of its residents neglect to exercise regularly. Combined with the 41 hours of TV watched per week -- the national average is 30 assuming that patterns remain relatively constant -- the numbers revealed the extent of Memphis' problem.

"We have heavily invested in a sedentary, sprawling lifestyle," says Tom Jones, a Memphis-based consultant for Smart City Consulting.

Jones' former colleague, Carol Coletta, president of the nonprofit organization CEOs for Cities, also points out that the economically bifurcated population, lack of transit options, unwalkable neighborhoods, and favored Southern cuisine are a "deadly formula" for the city.

To combat worsening public health, Smart City recently worked in conjunction with local grassroots organizations to lobby Memphis officials to dedicate more funding to outdoor recreation and parks. According to Smart City, the city provides 16.1 acres of parkland per 1,000 residents whereas Austin, Texas, for example, offers 35.4.

Focusing on such public amenities as parks is just one strategy of an urban planning movement that emphasizes "built environment" as the answer to obesity and inactivity.

Dr. Thomas Glass, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, says that further studies of cities' physical characteristics, like neighborhood walkability and street connectivity, will improve understanding of how the sedentary lifestyle wins out over the active one.

"It's a very interesting puzzle," Glass says. "Suburban sprawl is a major player. There are very different scales of urban density and finding the best ones could be a prescription for reducing inactivity." He is also careful to clarify that rates of obesity and inactivity vary according to the availability of healthy food and perceptions of neighborhood safety.

A study published last year in the American Journal of Preventive Medicine, which Glass did not write, identified 10 components of an "activity-friendly" community, including access to exercise facilities, transportation environment, aesthetics and land-use economics. A similar study funded by the National Institutes of Health is currently under way in El Paso, Texas, a city in which 65 percent of residents are obese or overweight.

Changing Course

The wealth of such research on what causes physical inactivity in major metropolitan areas has prompted some cities to explore different approaches. For Houston, Texas, no stranger to the label of "unhealthiest" city, the answer came partly in the form of convincing businesses to create healthier workplaces. Houston ranked 11th on our list, given that 59 percent of residents are obese or overweight and 31 percent forego regular exercise.

Herb Lipsman, chairman of Houston's Mayor's Wellness Council, says that the city has reached out to 400 business leaders with the aim of promoting wellness policies in the workplace. The goal? Lipsman hopes that capturing the attention of employees and providing tools for healthier living at work will have a significant effect on obesity levels.

It's unclear whether this approach might work in New Orleans, a city where 63 percent of the population is overweight or obese, 31 percent don't exercise regularly, and residents watch 42 hours of TV a week. In the wake of Hurricane Katrina, city officials found one of their greatest public health challenges in the paucity of grocery stores.

According to the city's health department, the area lost 21 of 36 major supermarkets, and local residents turned to corner stores stocked with calorie-rich but nutrient-deficient junk food to meet their shopping needs. As a remedy, the city recently spearheaded an initiative to stock and promote 13 corner stores with fresh fruits, vegetables, and low-fat dairy and whole grain products.

Beth Branley, communications manager for the city's department of health, said that the initiative is also combined with long-term efforts to provide more bike and walking paths and exercise classes.

It's initiatives like these, says Dr. Thomas Glass, at the Johns Hopkins Bloomberg School of Public Health, that residents will most benefit from. People, he says, should be "sucked outdoors to the spirit and energy in the street and then there's no reason not to participate."

In Pictures: Most Sedentary Cities