The following are foods to either feed with caution or to completely avoid feeding your pet rats. The information below is based on my personal experience along with internet research. Please note this is not to be considered an exhaustive list, just a guideline.
Apple Seeds contain a deadly cyanide derivative. The fruit of the apple, however, is fine for rats to eat.
The pit, rind, and skin of Avocados are toxic. The fruit of avocados is fine as long as it’s ripe. However, any part of the fruit in contact with the pit or the rind should not be fed to pet rats. Nutritious but also high in fat, avocado can be helpful for rats who need to gain weight.
Green Bananas can inhibit starch-digesting enzymes. Bananas that have ripened are fine to feed your rats.
Beets are high in oxalic acid which can cause urinary crystals to form. They are also high in nitrates which can result in an increased cancer risk for rats when fed frequently and in large quantities.
Carbonated Beverages should be avoided. Once rats ingest a food, they don’t have the option of vomiting or even burping. Instead the food has to pass through their entire gastrointestinal system which could be very uncomfortable for your rat.
Celery is stringy which can cause choking in rats. It’s also high in nitrates which can increase cancer risks in rats.
Chocolate contains stimulants that can lead to heart failure or neurological poisoning if fed in high quantities. Some say very small bit of chocolate is okay and that it can actually temporarily alleviate respiratory distress. I myself, though, wouldn’t feed chocolate to my rats…..to me, it just doesn’t seem like a good idea!
Citrus Juice can cause kidney damage and kidney cancer in male rats only. Citrus juice is dangerous due to d-limonene, a chemical contained in the oil of the rind, which is extracted into the juice during squeezing. If a male rat consumes too much d-limonene, it causes a specific protein found only in male rat’s kidneys to build up which can then result in tumors. It’s okay for females to consume citrus juice since they don’t have this protein in their kidneys. Male rats can eat pieces of the sections of an orange, just make sure to wash the orange skin oil off after peeling it. Also, to prevent choking, make sure there aren’t any of the stringy fibrous materials attached to the pieces you give a male or a female rat. Some people prefer not to feed male rats oranges at all.
Collard Greens – High in nitrates, cancer risk if fed frequently and in large quantities.
Corn – Dried corn can contain high levels of fungi which have been shown to cause liver, kidney and colon cancer in rats. Corn also contains high levels of both nitrates and amines. These two compounds can combine in the stomach to form nitrosamines which are carcinogenic. Fresh corn is fine, although you’ll probably want to keep it to a minimum. If your rats are being fed lab blocks, it is probably best to avoid brands which have corn as the first ingredient.
Eggplant: High in cancer-causing nitrates for rats if fed frequently and in large quantities.
Fats from Meats: Rats do not have a gall bladder which, in humans, is where the bile acids produced by the liver are stored. Without a gall bladder, the amount of bile acids available for digestion at any given time is greatly reduced.
Iceberg Lettuce: Contains no nutrients and often causes diarrhea due to its high water content
Licorice: Has been thought to contain a neurotoxin. I wouldn’t even think to feed my rats any sort of candy or sugary food anyways. I also avoid feeding them any sort of junk food such as chips or cheetos.
Mangos: Same as Citrus Juice above
Moldy food: Spoiled or moldy food can contain deadly toxins. Never, EVER, feed your rats anything that looks spoiled or smells rotten. I would be hesitant to even feed aged cheese to my rats. If you see mold growing on a food, throw the whole thing away. Don’t attempt to just cut away the moldy section. Once any part of the food is moldy, it’s a good bet the entire thing is contaminated.
Nuts: Every once in awhile as a special treat, roasted nuts are fine. The problem with nuts, however, is they’re extremely high in fat. Rats easily gain weight and can become obese. Being overweight is not only being uncomfortable but also can lead to a host of health problems. Some people like to give their rats nuts inside the shell, thinking it’s a fun game for their rats to crack open the shell. I’ve given my rats walnuts in the shell in the past. I was amazed when I was in the same room while they were trying to break open the walnuts. It sounded like my rats’ teeth were going to crack off since they had to chew so hard on the shells. I wouldn’t recommend that anyone feed their rats walnuts or any other nuts in a shell.
Peanut Butter: It’s okay to spread a very thin layer of peanut butter on a bit of bread or to let your rats lick a small amount thinly smeared on your finger. However, if you were to give your rat a chunk of peanut butter by itself, it could cause your rat to choke.
Plum Pits: The pit of a plum contains cyanogens, which are bound molecules of sugar and cyanide. When this bond is broken, the cyanide becomes viable. Fortunately the cyanogens don’t leak into the flesh of the fruit. In fact, plums are a good source of potassium, Vitamin A and fiber.
Poppy Seeds: Can cause neurological damage, and even death.
Green Potato Skin and Eyes: Contains solanine, a toxin.
The following foods should not be fed Raw:
Radishes are high in nitrates, a cancer risk for rats.
Commercially made Seed and Nut Mixes aren’t good sources of nutrition for pet rats. They definitely don’t work well as a mainstay since most rats will eat only their favorite ingredients, leaving out the rest. Thus, since only some of the ingredients in the mix are consumed, the diet becomes nutritionally incomplete. Even if you feed mostly lab blocks with a little seed and nut mix on the side, I’d still be concerned about ingredients in the mix being rancid and/or moldy.
Spinach: High in nitrates, cancer risk if fed frequently and in large quantities.
Turnip Greens: High in nitrates, cancer risk if fed frequently and in large quantities.
Wild Insects: Can carry diseases and can result in internal parasites.