Ten years into her practice as a board-certified plastic surgeon in Austin, Texas, Dr. Ashley Gordon noticed something unexpected about certain liposuction patients she’d “inherited” from older, retiring colleagues: They were slim overall, save for rock-hard belly fat.

“These were women who would have liposuction every couple of years,” she recalls. After repeatedly having fat removed from their arms, thighs, and flanks, these sexagenarians and septuagenarians were anything but flabby—yet their abdomens told another story. “They could barely pinch the skin on their belly—it was tense [and] firm and felt hard,” Dr. Gordon says. “I’d have to explain that it wasn’t fat on the outside, it was fat on the inside.”