Filler sugar – definitely not healthy!
But unfortunately, that's exactly why the cats love it and don't want anything else anymore. Since I adopted two cats from a foster home, I now have to buy it for the time being until they've settled in and I can switch their food. My old tomcat also goes crazy for it, even though he hardly ate any wet food after his sister died. I'm happy about that, but I'd still prefer a higher-quality wet food :D