/**
 * Implements hook_user_load().
 */
function {{ machine_name }}_user_load($users) {
  $result = db_query('SELECT uid, foo FROM {my_table} WHERE uid IN (:uids)', array(':uids' => array_keys($users)));
  foreach ($result as $record) {
    $users[$record->uid]->foo = $record->foo;
  }
}