/**
 * Add {new_column} field to {my_table} table.
 */
function MY_MODULE_update_7100() {
    $table = 'my_table';
  $spec = array(
    'type' => 'int',
    'description' => "blah blah",
    'size'=> 'tiny',
    'default' => NULL,
  );
  db_add_field($table, 'new_column', $spec);
}

$get_entity = entity_load('{my_table}', array(184));
dpm($get_entity) // showing all columns, except the new_column