If you're going to go through the trouble of using bind variables, why not move the second prepare outside the while? That way you avoid needless re-prepareing of the same statement on every iteration of the loop...

my $sth_news = $dbh->prepare("
  SELECT id, body 
  FROM   news
");
$sth_news->execute;
$sth_news->bind_columns(\my $news_id,\my $news_body);

my $sth_comments = $dbh->prepare("
  SELECT COUNT(id) 
  FROM   comments 
  WHERE  id = ?
");

while ($sth_news->fetch) {
    $sth_comments->execute($news_id);
    $sth_comments->bind_columns(\my $comments);
    $sth_comments->fetch;
    print "$news_id, $news_body, $comments";
}
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    --k.