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 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, 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, Frieden said. If the numbers keep going up, he said, 'more people will get sick and die from the complications of obesity, such as heart disease, stroke, diabetes and cancer.' The report estimates the medical costs of obesity to be as high as $147 billion a year and notes that 'past efforts and investments to prevent and control obesity have not been adequate.' Researchers blame the usual suspects: too little exercise and too much of the wrong kind of food, which means not enough fruits and vegetables and too many high-calorie meals full of sugar and fat, like french fries, soda and other sweet drinks. Children do not get enough exercise during the school day; Frieden noted that even in gym classes, students are active for only about a third of the time. A 5-foot-4-inch woman is obese if she weighs 174 pounds, as is a 5-foot-10-inch man who weights 209 or more, according to the disease centers. Both would have a body-mass index, or BMI, of 30; that index is calculated from height and weight, and scores of 30 or over are defined as obese. The nine states with obesity rates of 30 percent or more are Alabama, Arkansas, Kentucky, Louisiana, Mississippi, Missouri, Oklahoma, Tennessee and West Virginia. The highest rate, 34.4 percent, was in Mississippi. People older than 50 had higher rates of obesity than those who were younger. The aging of the population may account for some of the general increase in obesity, but not all of it, said Dr. Heidi Blanck, chief of the disease centers' obesity branch of the division of nutrition, physical activity and obesity. Non-Hispanic black women had the highest obesity rate, 41.9 percent. Overall, blacks and Hispanics were more likely than whites to be obese, and the more education people had, the less likely they were to be heavy. Only Colorado and Washington, D.C., had obesity rates under 20 percent. Researchers are not sure why. Dr. William Dietz, director of the nutrition, physical activity and obesity division, said that Colorado had spent money from a state lottery on biking and walking trails and that many people were using them. The state seems to have 'a culture of physical activity,' he said. Dietz said the relatively low prevalence of obesity in Washington was harder to explain, particularly because the area has a large black population. He said one explanation may be that many residents ride the subway; studies have shown that compared with people who drive, those who use public transportation tend to be thinner because it involves more walking. In addition, Dietz said, there is evidence of above-average fruit and vegetable consumption, and higher rates of breast-feeding, both of which are linked to lower rates of obesity. 