Add body classes in Omega subtheme

function YOURTHEMENAME_alpha_preprocess_html(&$vars) {
  $sidebar_count = 0;
  $sidebars = array('sidebar_first', 'sidebar_second');
  $body_sidebar_classes = array();
  foreach ($sidebars as $sidebar) {
    if (isset($vars['page']['content']['content'][$sidebar])) {
      $sidebar_count ++;
      $body_sidebar_classes[] = str_replace('_', '-', $sidebar);
    }
  }
  switch ($sidebar_count) {
    case 0:
      $body_sidebar_classes[] = 'no-sidebars';
      break;
    case 1:
      $body_sidebar_classes[] = 'one-sidebar';
      break;
    case 2:
      $body_sidebar_classes[] = 'two-sidebars';
      break;
  }
  foreach ($body_sidebar_classes as $body_sidebar_class) {
    $vars['attributes_array']['class'][] = $body_sidebar_class;
  }
}