Output all field values into a single unordered list

gistfile1.php

// Prepare a renderable array to hold items.
$variables['planning'] = array(
 '#theme' => 'item_list',
 '#items' => array(),
 );

// Add the term as a new renderable item in the list.
foreach(($variables['field_planning'] + $variables['field_diet'] + $variables['field_healthy']) as $taxon_term_field) {
 $term_name = $taxon_term_field['taxonomy_term']->name;
 $variables['planning']['#items'][] = $term_name;
}