Glycerin

Its source is not always clear on the label, and some glycerin is a by-product of biodiesel production.

Glycerin, also called glycerol, is a sweet, syrupy compound that keeps soft foods and treats moist. FDA includes glycerin on its GRAS list for animal feed, for use at levels consistent with good manufacturing practice. It adds calories but no other nutrition. If your cat has diabetes or another medical condition, ask your veterinarian about foods and treats that contain it.

Source: ecfr.gov

Glycerin is a humectant, which means it holds water. Makers add it to semi-moist foods and treats to keep them soft and chewy and to slow drying out. It also has a mild sweet taste. It appears in some dry foods with soft pieces mixed into the kibble.

Both are humectants that keep food soft, but FDA treats them differently for cats. Glycerin appears on FDA's GRAS list for animal feed. Propylene glycol is prohibited in or on cat food under 21 CFR 589.1001, though it is still allowed in dog food. So a cat food may list glycerin, but it should not list propylene glycol.

Source: ecfr.gov

Yes. Glycerin is a carbohydrate-like compound that the body can use for energy, so it adds calories. It does not add protein or micronutrients. In treats and semi-moist foods that use a lot of it, those calories can add up, which is worth keeping in mind for a cat on a weight plan.

Pettings gives glycerin 2 out of 5 and lists it as a humectant. It appears on 9 of the 149 dry cat foods we list. It scores in the middle because it adds calories without other nutrition, and its source is not always clear. Each food's page shows how it scores overall.