Guinea Pigs are vegetarians, so that means that they eat lettuce carrots and etc. but some foods aren't good for Guinea Pigs to eat them. Guinea Pigs eat lettuce, carrots, spinach, alfalfa (timothy hay), grass hay, fresh fruit and veggies. But you should really stay away from from foods like peanuts, pellets, and things you wouldn't see where they live (they live in mountain terrain, such like in South America). I now, will list the foods that will kill your guinea pigs is you feed them these, these include potatoes,(all potatoes, the skin the plant everything, DO NOT feed them anything to do with potatoes)beans(just stay away from ALL beans, otherwise this list will be way too long)the tomato plant not including the tomato itself because that is fine, all rhubarb, dill, houseplants, anything that was once frozen, not known weeds, and flowers (I would only recommend feeding your guinea pig(s) dandelion, because that's what I feed my guinea pigs all the time and they are fine). Note; Guinea pigs have little medium bowls (look on google), they should be filled 1/3 of the way a day. And their treat (The leaves carrots etc.) should be given once a day and only one a day.