Obesity in the United States is projected to continue its rise over the next 18 years, extending to 42% of Americans by 2030, according to a study released Monday by the Centers for Disease Control and Prevention. 
 
 That expected growth in the proportion of obese Americans -- up from 34% -- contained good news and bad: Obesity's growth has slowed from the record-setting pace that has marked most of the last three decades; at the same time, the numbers of the severely obese -- those carrying 80 or more pounds more than the healthy, normal weight for their height -- is expected to grow by 130%. 
 
 The continued growth in obesity will be expensive, said CDC statisticians: Additional spending on healthcare for Americans who will join the ranks of the obese in the next 18 years was projected to reach $549.5 billion over the next two decades. 
 
 By the most current obesity statistics, 35.7% of American adults -- 78 million people -- and 16.9% of U.S. children and adolescents -- 12.5 million kids -- are obese, meaning their body-mass index is 30 or over. 
 
 The new projections capture several trends in American society: the swelling population of Latino adults, among whom obesity is a growing problem, the transition into adulthood of a population of obese children -- especially African American boys -- who stand a high likelihood of becoming obese adults, and the aging of overweight and obese adults, who are far more likely to take on more weight than to lose as they get older. 
 
 In a bit of good news, the obesity rate among women was flat. Currently, 35.8% of American women are considered obese, and the forecast released Monday does not predict a significant change in that level. 
 
 Still, the projected 33% rise in obesity is rosier than the 51% rise that had been projected by statisticians assuming a continued level of the roaring growth seen in the 1980s, 1990s and early 2000s. "This and other forecasts likely overstate future obesity prevalence given the recent evidence of slower growth," wrote Duke University global health professor Eric A. Finkelstein and co-authors in a forecast of the nation's weight problem close to 20 years out. 
 
 In a news conference that was the centerpiece of a second annual "Weight of the Nation" conference in Washington, D.C., Finkelstein said it was unclear whether the galloping rate of growth has slowed because of public policy initiatives aimed at preventing child obesity, greater societal awareness of obesity's risks, or because Americans have hit the maximum level of fatness a population can sustain. 
 
 "The slope has changed," he said. Statistically, he noted, "it doesn't take much" for obesity prevalence to rise from 34% to 42% in 18 years. 
 
 By the same logic, the authors of the projection noted that even small successes in anti-obesity efforts -- new, more effective weight-loss drugs, communities and campaigns designed to encourage more exercise and healthier eating, work-site health-promotion policies -- could flatten the upward curve. 
 
 "Even small improvements in obesity prevalence ... could result in substantial savings," they added. The projected $549.5-billion healthcare bill represents the difference between providing healthcare for a population with 34% obesity and a population whose obesity prevalence has risen to 42%. 
 
 The CDC forecast took into account a host of factors thought to influence Americans' eating and exercise habits, including the cost of groceries, the density of restaurants, rates of unemployment, Internet access and the price of gas. Most important, however, was the aging of the population, which tends to nudge many overweight adults into the obese category, and to push a growing number of those who are already obese into "severely obese" territory. 
 
 "Long-term, sustained weight loss" in adults who have become obese, said Finkelstein, "is elusive." 
 
 Finkelstein and his co-author, health economist Justin G. Trogdon of RTI International, cautioned that despite their detailed modeling of factors that influence obesity, forecasting fatness in a future population "is tricky business." While tendency to exercise, access to healthy food and convenience of high-calorie fast food all influence a population's propensity to gain weight, such factors stand alongside far more powerful influences, such as genetics. 
 
 "They're estimates, but like any estimates, are they going to be accurate?" Finkelstein asked Monday. "Well, time will tell." ||||| “If we don’t do anything, this is going to really hinder any efforts to contain future health-care costs,” Justin G. Trogdon, an economist and one of the authors of the projection, told experts Monday at the start of the two-day “Weight of the Nation” conference in Washington. 
 
 However, if obesity stays at its current prevalence — 34 percent of adults — and does not increase, the savings in projected health-care costs will be considerable, about $550 billion, the authors said. The most recent evidence, in fact, suggests that obesity rates are plateauing. 
 
 “Regardless which is correct, we still have a very serious problem,” William H. Dietz, head of the Centers for Disease Control and Prevention’s obesity program, said of the scenarios. 
 
 Obesity related ailments — diabetes, heart disease, kidney failure — consume at least 9 percent of health-care spending the United States. Some researchers believe the cost may be twice that estimate. Total health spending is about $2.6 trillion a year. 
 
 The new study, published in the American Journal of Preventive Medicine, used obesity prevalence data from 1990 through 2008 to extrapolate future trends. The information came from the Behavioral Risk Factor Surveillance System, a federally funded telephone survey. People underestimate their weight when asked on the phone; that fact was compensated for in the mathematical model. 
 
 The researchers also incorporated variables, measured in each state, that affect obesity rates. These included the price of gasoline, which discourages walking when it is low; access to the Internet (and other technologies), which encourages sedentary behavior as it increases; and restaurants per 10,000 people, which increases eating out and weight gain when the number goes up. 
 
 In 2030, 42 percent of people are projected to be obese, and 11 percent severely obese. Obesity is a body mass index (BMI) of 30 or more, which is 186 pounds for someone 5 feet, 6 inches tall. Severe obesity is a BMI of 40 or more — 248 pounds for someone that height. 
 
 Cynthia L. Ogden, an epidemiologist at the CDC, told the conference that, in general, obesity rates changed little in the 1960s and 1970s, rose steeply in the 1980s and 1990s, and have been leveling off in the past decade. 
 
 For men, obesity prevalence doubled but has changed little in the past eight years, with no difference between blacks, whites and Mexican Americans (which are the three groups for which there are good data). For white women, the obesity prevalence has not changed in 12 years. It has risen slightly in black women and Mexican American women, although that increase mostly occurred early in that 12-year period. 
 
 There are some exceptions to this general picture of stability. 
 
 Obesity is rising in higher-income men. Severe obesity is increasing in both sexes. It was 6.2 percent in women in 1999 and 8.1 percent in 2010. For men, it was 3.1 percent in 1999 and 4.4 percent in 2010. 
 
 Eric A. Finkelstein, a researcher at Duke University who led the new study, said that just in the past 50 years has it been possible for millions of people to be both sufficiently inactive and to have access to enough food to become severely obese. 
 
 “The world has changed in ways that allow people to be that overweight,” he said. 
 
 The reason for the plateauing of the obesity prevalence is uncertain. It almost certainly reflects many factors, including an approach to a natural limit of the epidemic and the success of efforts to fight it by encouraging exercise and educating people about better eating habits.
– The once-explosive growth in the proportion of Americans who are obese has slowed, but it's still expected to grow to 42% by 2030, according to the latest Centers for Disease Control study. The study found that if the obesity rate stays at the current level—34%—then some $550 billion in health care costs would be saved, reports the Washington Post. Earlier studies predicted that 51% of Americans would be obese by 2030, but no matter which is correct, "we still have a very serious problem," the head of the CDC's obesity program says. The obesity rate among women has stayed flat, but other groups, including higher-income men, are continuing to put on weight, and more obese people are becoming severely obese, according to the study, which predicts that the aging of the population will probably nudge many overweight adults into the obese category, and obese people into severely obese. The study's authors say it's not clear whether the growth in obesity has slowed somewhat because of the success of public policy initiatives, or because the US is nearing the maximum level of obesity that a population can sustain, notes the Los Angeles Times.