Not sure if this allowed. sorry if it isn't but I'm just really confused about what they are.
As it turns out, waist beads were very popular in Africa a few hundred years ago. It was used as a symbol of maturity and for cultural purposes as well. It could have also been used to maintain a woman's shape. Today, not many wear waist beads, but those who do, do so for beautification purposes. This makes perfect sense, as Nessa is a model, and also of African decent.
This isn't totally related to Pokémon, but interest was shown in the comments, so I thought I would answer.
All the information can be found here.