Gutloading is a term that technically only refers to feeding the prey item a high calcium diet to adjust it calcium to phosphorus ratio (and is still used this way in the literature) but to the hobbyist community has become to mean any diet fed to the prey item with the intent to try and modify its nutritional content. As most people do not investigate the nutritional content of the animal before feeding the items, the impact of the "gutloading" diet is unknown.
If you are using commercially aquired live invertebrates, then they should be fed a diet for at least 48 hours before feeding them out to allow for the replacement of minerals, protiens and fats lost in shipment and while they were held at the pet store.
Ed