Found this:
As Sunflower seeds are a favourite, you can give these as treats - however they are high in fat, so perhaps they are best kept as a treat rather than part of their main diet. I usually take out any sun flower seeds, keep them in a jar and offer them as treats. Pumpkin seeds are another, as well as peanuts and for the same reason are best kept as treats rather than part of their main diet.
Fresh fruits and veggies are very good and you can give your Gerbils almost anything. If they don't like one type of fruit or veg, just try another. Most of mine like Lettuce, Banana, Broccoli, and Tomato. Some like others more than the next, it's just all personal taste, just like with us. You have to be careful with fresh fruit and veg though, as too much can cause them to have diarrhoea, and also check the cage once they are done for any left overs, as you don't want them going moldy inside the nest.
Rice and pasta can be given, some claim that they will expand in the stomach though so be sure to cook first, this I don't know if it is true or not.
Below are the foods that I add into my gerbils' diet, either by giving them the food by hand or by mixing it in with the rest of their food.
Apple ? dried or fresh
Carrot
Banana ? dried or fresh
Cucumber
Dried bread
Cheese (very small doses and as a treat!)
Cooked pasta/rice
Grapes
Tomato
Cereals (low sugar, so shredded wheat is ok, all bran, porridge)
Wild birdseed
Dandelion leaves
Grass (make sure no toxins on it)
Dried Dog biscuits - for extra protein and variety in their food
Millet seeds
Walnuts
Hazelnuts
Almonds
Broccoli
NB: only feed in moderation, as with humans a balanced diet is best