According to "F as in Fat: How Obesity Policies Are Failing America, 2006," there are now 13 states where more than a quarter of the adult population is obese.

Nevada is the only state that saw a decrease in the percentage of obese adults compared to last year's report.

Obesity rates remained the same in the18 remaining states and in Washington DC.

Overall, adult obesity rose from 15 percent in 1980 to 32 percent in 2004. Taken together, individuals who are either overweight or obese comprise a whopping 64 percent of the US adult population.

Obesity among children is increasing at an even more alarming pace, having more than tripled between 1980 and 2004 -- from 5 percent to 17 percent, according to the report.

The report notes that obesity can lead to potentially fatal health problems including diabetes, stroke and cancer.

"The most important news in this report is that the obesity epidemic in America is getting worse," Jeff Levi, executive director of Trust for America's Health, told reporters.

The report is based on data from telephone interviews with a random sampling of adults. The rates are based on averages calculated over a three-year period, from 2003 to 2005.

Mississippi has the dubious distinction of coming in heaviest, with more than 29 percent of that state's adults considered obese -- an increase of 1.1 percent from last year's report. Alabama came in second, and West Virginia third. Louisiana, Kentucky, Tennessee, Arkansas, Indiana, South Carolina and Texas round out the top 10.

Five states among the top 10 -- Mississippi, Alabama, West Virginia, Louisiana and Kentucky -- are also among the most impoverished in the country.

Colorado has the lowest obesity rate, at 16.9 percent of its adult population. Hawaii is second leanest, while Massachusetts ranked third. Rhode Island, Vermont, Connecticut, Montana, Arizona, Utah and Nevada complete the list of the 10 trimmest states.

The five leanest states -- Colorado, Hawaii, Massachusetts, Rhode Island and Vermont -- are also among the most well off.

However, despite lower rates in some areas, the general trend toward obesity is on the rise almost everywhere, affecting all ethnic and socioeconomic groups, according to Dr. Jeffrey P. Koplan, vice president for academic affairs at Emory University's Woodruff Health Science Center, and chairman of the Institute of Medicine Committee on Progress in Preventing Childhood Obesity.

Poor nutrition and lack of exercise are at the root of America's obesity epidemic, the report suggests. The report criticizes governments for doing too little to combat obesity and offers a 20-step action plan.

Among its recommendations are improving nutritional labeling on foods; supporting community-driven efforts to increase access to healthy foods in low-income areas; improving the nutritional content of foods and beverages served and sold in schools; providing communities with more and better sidewalks, parks and bike paths; offering better physical fitness programs in schools; and promoting employer-sponsored programs to increase physical activity and to provide better insurance coverage for obesity prevention.

A national health objective for the US is to reduce the prevalence of obesity among adults to less than 15 percent by the year 2010, according to the Centers for Disease Control and Prevention.

However, unless Americans are willing to change their lifestyles, that goal may be impossible to reach.

Many people live sedentary lives, the CDC notes. In fact, 40 percent of adults in the US do not participate in any leisure-time physical activity.

Less than one-third of adults engage in the recommended amount of physical activity -- at least 30 minutes most days -- according to the CDC.