Was it solely based on his weight of 550g that he was considered overweight? I only ask because a healthy hog can range anywhere from 300-800g, so mass alone isn’t necessarily a good Hague as to whether they’re overweight. If they have fat rolls around their legs/can’t completely curl up into a ball/are more rounded shape rather than a teardrop shape; that’s a good indication of being overweight. Nonetheless, you should start by finding the fat % of the kibble you’re feeding currently. If it’s any higher than 18-20%, that’s a good guess as to why he might be overweight. As already mentioned, you could find another kibble with a low fat content and create a mix of the two to balance it out. You can also try using insects as a main part of their daily diet. Being insectivores, they’re built to process insects the best, so that’s another option.
Hope this helps 🙂