I wouldn't always trust what folk tell you though (especially not for something as nutritionally void as a doner kebab! )

I remember asking a similar kind of place where I grew up if the vegetarian stuff was fully vegetarian (ie cooked nowhere near meat, etc), and they assured me 100% that it was. I was sick every time I ate from there though... and finally worked out why when I watched them cook my food in the same pan as the burgers etc.

Alas kebab shops by their very nature are more likely to be concerned with their profits than your health/waistline.