American Idol alum Mandisa’s official cause of death has been revealed to be “complications of class III obesity,” according to a newly released autopsy report. Her manner of death is listed as natural and a toxicology report found nothing abnormal, RadarOnline.com has learned. TMZ noted the medical examiner stated she weighed 488 pounds at the time of her death. Class III is also categorized as “severe” obesity, according to Web MD, which explains that it is a serious health condition that is diagnosed when someone has a BMI greater than 40, a BMI of greater than 35 with at least one serious …