Why so big? In part, it's simple human anatomy.

"If you look at the adolescent growth spurt, the timing starts with feet," said John Himes, who researches childhood growth at the University of Minnesota's School of Public Health.

"Kids grow from the bottom up, which is why they grow out of their shoes before they grow out of their pants. If they have bigger feet, you can rest assured that the rest of their body will catch up."

Foot size stabilizes in adolescence, but many women report that they jump a size or so when pregnant. It's not the baby on board that broadens out the maternal foot.

Dr. Stephen Powless, president of the Minnesota Board of Podiatric Medicine and podiatrist at Park Nicollet Clinics, said hormones create the change.

"The ligament in the arch is sensitive to the same hormones produced at the end of pregnancy that cause the pelvic ligaments to relax to allow for childbirth," he said. "The foot doesn't grow but it effectively gets longer and wider."

Feet are not just getting bigger. They are also getting wider.

"This may have to do with the higher BMI [body mass index]," Powless said. "With increased weight, the arch flattens and the foot splays out."