More than 72 million U.S. adults, or 26.7 percent, are obese, up 1 percent in two years, the U.S. government reported on Tuesday.
Obesity has become "a major public health threat" and is steadily worsening, the U.S. Centers for Disease Control and Prevention reported.
"We need intensive, comprehensive and ongoing efforts to address obesity," CDC director Dr. Thomas Frieden said in a statement.
"If we don't more people will get sick and die from obesity-related conditions such as heart disease, stroke, type 2 diabetes and certain types of cancer, some of the leading causes of death."
The CDC examined data from the national Behavioral Risk Factor Surveillance System, which surveys 400,000 people and asks about height and weight, among other things.
Looking state-by-state, the CDC found that 30 percent of adults in nine states are now obese. In 2000, no states reported obesity rates of 30 percent or more.
Height and weight are used to calculate body mass index or BMI, the medically accepted way to measure obesity.
A BMI of 25 or more makes someone overweight and obesity begins at a BMI of 30.
A 5-foot-4 inch tall person who weighs 174 pounds (79 kg) or more or a 5-foot-10 inch (1.8 meter) tall person who weighs 209 pounds (95 kg) or more has a BMI of 30, and is considered obese.
The survey found 2.4 million more people admitted to being obese in 2009 than in 2007, a 1.1 percent increase. And the CDC said this is almost certainly an underestimate, as people often say they are taller and weigh less than they actually do.
"Recent estimates of the annual medical costs of obesity are as high as $147 billion. On average, persons who are obese have medical costs that are $1,429 more than persons of normal weight," the report reads.
Blacks were the most likely to be obese, with 36.8 percent of U.S. black adults having a BMI of 30 or more — more than 41 percent of black women.
More than 30 percent of Hispanic adults were obese.
As in previous surveys, Mississippi had the most obese people and Colorado the fewest.
The federal government and some states have been moving toward using legislation to help people to exercise and eat healthier foods.
New York and California have been considering a tax on sweetened soft drinks to defray the cost of treating obesity-related diseases. President Barack Obama has made reducing obesity a priority, assigning his wife Michelle Obama and cabinet secretaries to tackle childhood obesity in particular.
"People in all communities should be able to make healthy choices, but in order to make those choices there must be healthy choices to make," the CDC's Dr. William Dietz said.
"We need to change our communities into places where healthy eating and active living are the easiest path."