Guinea pigs kept as pets should be limited to about 1 cup of carrots once or twice a week. The major component of a guinea pig's diet should be fresh timothy hay.
Guinea pigs should have unlimited daily access to timothy hay, because it is good for their digestion and controls the growth of their teeth. As a supplement, they should be allowed 1/8 of a cup of commercial guinea pig food daily. In addition, guinea pigs should receive about 1 cup of leafy vegetables, such as romaine lettuce, spinach, kale or parsley, each day. Along with carrots, zucchini and sweet potato should be weekly treats.