Well, there are many things that happen when you lose weight.

The process, of eating less food, sometimes means less potassium and magnesium consumed.

Also, some people believe that toxins are stored in fat, and when you lose weight they are released. I believe that mercury has been shown to do this.

I would also examine your exercise routine and the shoes you wear. Even tying them too tightly over your instep, can cause nerves to react.
This link shows how to tie shoes for better comfort:
http://neurotalk.psychcentral.com/sh...ghlight=instep

If your toe box is too small, it will also compress nerves. Getting one size wider will help the toes quite a bit!

There is a condition called slimmer's paralysis...where if low fat food is used to lose alot of weight, then nerves can be damaged.
So make sure you consume Omega-3s to keep your nerve sheaths from being damaged. This is a rather dramatic thing and shows up more during fast large losses.