Some 42.4 percent of U.S. adults now qualify as obese, according to a new report from the Centers for Disease Control and Prevention, with no real difference in prevalence between men and women. People who are obese have a body mass index (BMI) — which is an indicator of body fatness calculated from a person’s height and weight — of 30 or higher. Those with a BMI of 40 or higher, described as having extreme obesity, represent 9.2 percent of the adult population, with women outnumbering men. Both obesity and severe obesity are most common among middle-aged adults (those ages 40 to 59), according to the CDC. Data show that since the start of the 21st century, obesity has become increasingly common, rising from about 30 percent to more than 40 percent of adults, while the prevalence of severe obesity has increased from about 5 percent to just over 9 percent in that time. In addition to its effect on overall quality of life, the negative health effects of obesity start with the stress that excessive pounds put on muscles, bones and joints. Obesity also has been linked to an increased risk for numerous diseases and medical issues, including diabetes, heart disease and some cancers, as well as depression, asthma, obstructive sleep apnea, osteoarthritis and back pain. Health experts say that losing just 5 to 10 percent of body weight can help obese people rein in their health risks. As weight falls, so does BMI. A BMI indicating normal weight would be from 18.5 to 24.9, and 25 to 29.9 is considered overweight. A simple and quick way to determine your BMI is to plug your height and weight into an online BMI calculator.