In 16 states, at least 35 percent of adult residents are obese, an increase from nine states two years earlier, according to new data from the Centers for Disease Control and Prevention. In all 50 states, however, more than 20 percent of adults are obese. Although the numbers vary from state to state, the highest prevalence of obesity was found in states in the Midwest and South. Looking at the U.S. population as a whole, about 42 percent of adults are obese, the CDC says. Being obese, a medical term based on a calculation called body mass index, can lead to an array of health problems, including an increased risk for diabetes, high blood pressure, heart disease, liver problems, arthritis, some cancers and depression. Overeating and lack of physical activity are common causes. Obesity also appears to be on the increase among U.S. youths, according to a separate new report from the CDC. It found that 22 percent of youths ages 2 to 19 were obese in August 2020, up from 19 percent a year earlier, with the greatest increase among children 6 to 11. The agency said that pandemic-related circumstances — increased stress, less access to nutritious foods, more screen time and fewer options for physical activity such as recreational sports — were probably contributors to the accelerated weight gain seen in children. Treating obesity usually involves lifestyle changes: eating a healthier diet that reduces caloric intake and increasing exercise. Health experts say that even modest weight loss, 5 to 10 percent, may improve or prevent the health problems linked to obesity.