I feed Nature's Gold® hamster food, made by Hartz® , that I buy at K-Mart. There are many hamster seed mixes out on the market. Hamster food consists of a mixture of corn, barley, peanuts, rabbit pellets, oats, sunflower seeds, bird seed, and sometimes other treats. This mix should be the hamsters main diet.
Hamsters also like fruits and vegetables, but they should be fed in small amounts, as treats. I usually feed my hamsters apples, carrots, kale, and green-leaf lettuce. Some other fruits and vegetables that can be fed to hamsters are: parsely, broccoli, peas, cucumber, grapes, spinach, chicory, bananas, pear, and many, many others. It is not recommended to feed iceberg lettuce (head lettuce) as it is bad for any small animals digestive system and it can cause diarrhea. In fact, all fruits and vegetables should be introduced to a hamster's diet slowly, to prevent diarrhea.