Americans are continuing to get fatter and fatter, with obesity rates reaching 30 percent or more in nine states last year, as opposed to only three states in 2007, health officials reported on Tuesday.

The increases mean that 2.4 million more people became obese from 2007 to 2009, bringing the total to 72.5 million, or 26.7 percent of the population. The numbers are part of a continuing and ominous trend.

But the rates are probably underestimates because they are based on a phone survey in which 400,000 participants were asked their weight and height instead of having it measured by someone else, and people have a notorious tendency to describe themselves as taller and lighter than they really are.

“Over the past several decades, obesity has increased faster than anyone could have imagined it would,” said Dr. Thomas Frieden, the director of the Centers for Disease Control and Prevention, which issued a report on the prevalence of obesity. Obesity rates have doubled in adults and tripled in children in recent decades, Dr. Frieden said.