A human grade dog food must provide documentation that every ingredient must be edible for humans and the food must meet federal manufacturing and packaging regulations. Most dog foods don't meet these standards and many human grade ingredients may not be automatically safe or healthy for an animal.
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Human food is much more highly regulated and has very strict standards on quality, ingredients, and nutritional profiles. FDA and AAFCO have loose guidelines for dog foods that contain filler ingredients like cornmeal and soybean hulls which add no nutritional value to the food. They are also why many dog food companies use animal-byproducts which can contain highly processed disease or rotten meat or the excess materials from industrial meat production like beaks, feathers, and fat
Some companies may tell you that they can't classify as "human grade", but don't buy what they are telling you. The company should be able to tell you that their ingredients they use are human grade!