"By Susan Heavey WASHINGTON (Reuters) - Obesity levels among adults appear to be holding steady across the United States, adding to recent evidence that the growth rate for U.S. waistlines is slowing, according to an analysis released on Friday. But within the holding pattern there is a dramatic rise in "extreme" obesity among adults and children. The annual "F as in Fat" report from the Trust for America's Health and the Robert Wood Johnson Foundation found that the proportion of adults who are extremely obese - at least 100 pounds (45.4 kilograms) overweight - has risen over the last three decades from 1.4 percent in the late 1970s to 6.3 percent in 2009-2010. That is about a 350 percent increase, researchers for the health nonprofit groups said. About 5 percent of children and teenagers are also now severely obese, they added. Rates of extreme obesity were nearly twice as high for women as for men, and were also particularly high for Hispanic boys and black girls. Overall, the report found obesity rates stabilizing across the United States, though at historically high levels with nearly 36 percent of all U.S. adults obese as of 2010. Only one state, Arkansas, had an increase in obesity levels. The findings follow signs of progress earlier this month after U.S. officials announced small but promising declines in the obesity rate among low-income children between the ages of 2 and 4, after 30 years of increases. "After decades of bad news, we're finally seeing signs of progress," researchers for the two health groups wrote in Friday's report. Their analysis, also based on data from the Centers for Disease Control and Prevention, however, underscored America's continuing battle with weight. "While stable rates of adult obesity may signal prevention efforts are starting to yield some results, the rates remain extremely high," Trust for America's Health Executive Director Jeffrey Levi said in a statement. Obesity rates were highest in the South and Midwest in states including Louisiana, Mississippi and Oklahoma. In addition to geographic differences, rates were higher for people with less education and lower incomes, it found. Rates for those ages 45 to 64, the bulk of the so-called Baby Boomer generation, were also a concern as their obesity rates were 30 percent or higher in 41 states. In Alabama and Louisiana, their rate reached 40 percent. Increasingly heavy men also narrowed the obesity gender gap. "Ten years ago, the obesity rate for women was significantly higher than the rate for men," 33.4 percent compared to 27.5 percent, researchers wrote. Now, their "rates are essentially the same" at nearly 36 percent, they said. Obesity is commonly measured by body mass index (BMI), a measure of one's height to weight. A BMI score of 30 or more is defined as obese, while extreme obesity is a score of 40 or higher. A score of 25 to 29 is considered overweight. (Reporting by Susan Heavey; Additional reporting by Barbara Goldberg; Editing by Michele Gershberg and Vicki Allen)"