"In the past year, obesity rates have continued to rise in 31 states. Eighty-five percent of Americans believe that obesity is an epidemic," the Trust for America's Health (TFAH) said in its fourth annual "F as in Fat" report.
The rate of adult obesity more than doubled in percentage terms in the past 25 years across the United States, growing from 15 percent in 1978-80 to 32 percent in 2003-04, the report said.
In the same period, childhood obesity increased more than three-fold.
Poor nutrition and physical inactivity were putting Americans at greater risk for developing diseases such as diabetes, heart disease and stroke, and even some forms of cancer.
"Today's children are likely to be the first generation to live shorter, less healthy lives than their parents. Approximately 25 million children are already obese or overweight," the report said.
The report urged "new, grand scale changes" across the country to stop the obesity epidemic from impacting negatively on workforce productivity.
"US economic competitiveness is hurting as our workforce becomes less healthy and productive. Obesity-related health care costs are draining dollars from the bottom line of businesses."
Poorer southern states were particularly affected by the epidemic.
In Mississippi, which has one of the highest rates of poverty in the United States, nearly every third adult -- 30.6 percent -- was obese, and slightly more said they engaged in no physical activity, the report said.
Washington DC, which was ranked equally with Mississippi in terms of poverty, last year had the highest rate of overweight children, at 22.8 percent.
In all but three of the 50 states -- the western state of Colorado, and Massachusetts and Vermont in the northeast -- adult obesity rates exceeded 20 percent last year.
New York City was singled out for praise in the report for making it mandatory for restaurants to provide detailed nutrition and calorie information to patrons and for banning trans fats, which help to raise so-called bad cholesterol levels and increase the risk of heart disease.
Trans fats are made when hydrogen is added to vegetable oil, to increase the shelf life and flavor of foods.
As the report was released Monday, fast-food chain Dunkin' Donuts announced that all items on its menus -- including its calorie-rich doughtnuts -- will soon be free of trans fats.
The Massachusetts-based company, which sells doughnuts in 30 countries around the world, said the move was a first among fast food providers.