securing vsftp nopriv_user

[sigix]

read from vsftp documentation.
"The nopriv_user option allows us to specify the user that vsftpd will run as. We have specified the ftp_nopriv user that we created as part of the installation process. This causes vsftpd to run as a non-privileged user and enhances the security of the daemon. This mitigates the risk of an attacker gaining root privileges through the daemon."

nopriv_user=some_ftp_user
on change this option in vsftpd.conf file I get the same result
vsftpd is run as root but not as some_ftp_user
any clue what's wrong/missing?