Custom fields

Hi, I have 2 questions 🙂
first one is: is it possible to make different templates for single post displaying?
second and most important one: I was editing a ready made theme and I had to create custom fields for nutritional facts, in my test I created only 3 fields and as I saw I should declare each one in my code like that:

<div>
        <span class="item">Protein</span>
        <span class="value"><?php echo get_post_meta($post->ID, 'Protein',true); ?></span>
    </div>
    <div>
        <span class="item">Sodium</span>
        <span class="value"><?php echo get_post_meta($post->ID, 'Sodium',true); ?></span>
    </div>
    <div>
        <span class="item">Sugars</span>
        <span class="value"><?php echo get_post_meta($post->ID, 'Sugars',true); ?></span>
    </div>

but what if the admin wanted to add an extra field, say Cholesterol?
how can I make it responsive to each field the admin add? how to make it able to add every new field automatically?
I though there might be a loop which loops through these meta data and echo them out automatically without having to declare each one of them, it is possible?
thanks in advance..