Get custom fields from users table in global user object
You can implement the hook_user_load() for this purpose 

I have altered the user table with field "fname" , Now you can load this in user object with the help of hook_user_load() func.

function testing_custom_user_load($users) {
  foreach ($users as $record) {
     foreach ($users as $record) {

        $result = db_query("SELECT fname FROM {users} WHERE uid IN ($record-&gt;uid)")-&gt;fetchAssoc(); 

        $users[$record-&gt;uid]-&gt;extra =$result['fname'];
     }
  }

}


Just put this code snippet in any of your custom module file.