In 2005, 23.9 percent of adults in the United States were obese, or had a body mass index greater than 30, while in 2007, the percentage had grown to 25.6 percent, data issued by the Centers for Disease Control (CDC) showed.
Body mass index is calculated by dividing a person's weight in kilos by his or her height squared in meters.
In three states -- Alabama, Mississippi and Tennessee -- nearly one in three adults was obese.
Mississippi, which is also the poorest US state, had the highest rate of obesity in the United States, at 32 percent. Colorado had the lowest rate of obesity at 18.7 percent and was the only state in which obesity was running at less than 19 percent.
No state has achieved the official target to bring obesity down to 15 percent of the adult population by 2010, the report showed.
Obesity was highest for non-Hispanic black women, nearly four in 10 of whom were obese.
University graduates were the least likely to be obese -- around 22 percent compared with 29 percent of people who only obtained a high school diploma.
A report issued last year by the Trust for America's Health (TFAH) said the percentage of obsese adults more than doubled in the past 25 years across the United States, growing from 15 percent in 1978-80 to 32 percent in 2003-04.