I'm trying to add product_type to my Magento Google Base output based on the product's categories, but I seem to be unable to. I have the following code:

// Get categories from  product to include as product_type
$categoryIds = $object->getCategoryIds();
foreach($categoryIds as $categoryId) {
    $category = Mage::getModel('catalog/category')->load($categoryId);
    $this->_setAttribute('product_type', $category->getName(), 'text' );
}

The issue is that it returns all of the categories, not just the ones the product is in. Anyone have a solution?