The percentage of Aiken County residents with a body mass index greater than 30 expanded to 31.2 percent in 2007, according to new data from the Centers for Disease Control and Prevention.
But the county is still slimmer than its Georgia neighbor, Richmond County, where 32.6 percent of residents are obese.
The South as a whole leads the country in populations with excessive body fat.
The Palmetto State had an obesity rate of 25.1 percent in 2004 but hit 30.7 percent last year, cracking a list of the six fattest states.
The others with 30-percent-or-higher obesity, according to the CDC, are Alabama, Mississippi, Oklahoma, Tennessee and West Virginia.
"There are so many variables in play in that equation," said Nick Davidson, a spokesman for the South Carolina Department of Health and Environmental Control. "It's really hard to point to any one thing."
He said people's genetics contribute to their chances of becoming obese, as do their environment and personal habits, including nutrition.
Obesity, which afflicts nearly 26 percent of Americans, is also more common among some minority populations.
Compared with whites, blacks had a 51 percent higher prevalence of obesity, and Hispanics were 21 percent more obese than whites, according to the CDC data.
Obesity is a risk factor for cardiovascular disease, some cancers and type 2 diabetes, which tends to affect adults and is associated with older age, a family history of diabetes, a history of gestational diabetes, impaired glucose metabolism, physical inactivity, and race and ethnicity, according to the CDC.
Aiken County's obesity rate has increased:
2007: 31.2 percent
2006: 30.0 percent
2005: 28.2 percent
2004: 27.3 percent
In 2007, the most recent year available, some neighboring counties had higher obesity rates:
BARNWELL: 35.8 percent
EDGEFIELD: 32.8 percent
ORANGEBURG: 38.5 percent
SALUDA: 28.2 percent
LEXINGTON: 26.8 percent
Source: Centers for Disease Control and Prevention