This is a question that we commonly receive from customers and site visitors! The truth is, most folks who adopt foot-healthy footwear (i.e., shoes that stay out of the way of your feet) in combination with other helpful footgear (e.g., toe spacers, toe socks, metatarsal pads, sole-stimulating insoles, etc.) experience a lengthening of the feet. It's not that the feet are growing after adopting minimalist and foot-shaped footwear, it's just that the feet are realizing their true, innate dimensions after being crammed into shoes that were too short and too constricting (for too many years).
So, a foot that lengthens out necessarily requires a larger shoe size. Just to clarify: Most of the foot lengthening that happens occurs in the toes as they begin to unfurl and straighten out over time. The realignment of all the foot's bones and tissues is another factor at play here. It's also possible to see an increase in foot width, though the increased width mostly occurs at the ends of the toes due to improved toe splay.
Men tend to experience the largest swings in shoe size after adopting foot-healthy footwear. By way of example, Natural Footgear co-founder Dr. Marty Hughes used to wear a men's US size 9.5 shoe before switching to minimalist shoes in 2009, but he now regularly wears a men's US size 11.5 to 12, depending on the brand. Correct Toes inventor Dr. Ray McClanahan has also experienced a similar increase in shoe size over the years.
Most women tend to go up about one-half to one full shoe size with long-term use of footwear that respects normal and natural foot anatomy. For example, Dr. Robyn Hughes, Natural Footgear co-founder, went from wearing a women's US size 7.5 to a women's size 8.
The extent of shoe size increase, for both men and women, also depends on just how affected the feet and toes are by conventional footwear. In our experience, we've noticed that the more significant a person's toe deformities are, the more significant is their shoe size increase.
So, don't be surprised if you someday find your toes bumping up against the ends of your foot-healthy shoes’ toe boxes. This is an indication that progress is occurring and that your feet are becoming rehabilitated. To encourage this process along, consider sizing up as soon as possible. Your feet and toes will thank you!