Hamsters/ gerbils = bad news. Don't do it. If he's refusing food stop handling immediately only handle when absolutely necessary. Check your husbandry. If it's not a shed then stress sounds like your culprit for refusing food. These guys won't starve to death but stress will cause him to refuse food. Try adult mice only offer 1 every 5 days. If he doesn't eat it try again in 5 days. Don't offer him to much as it will cause him to get stressed.