A Syrian Hamster's diet in the wild would consist of Grains, Seeds, Roots, and Insects.
In captivity, a Hamsters common Diet is a pre-made muesli that contains corn, peas, hay based pellets, seeds and various other things.
In an ideal world, a Hamster's diet should be the closest possible to it's natural diet, but this is not possible the majority of the time.
The ideal diet for main food in Captivity should be a Mix of Muesli and fresh things like meal worms, small quantaties of veggies and herbs, etc.
The usual go to food for the muesli is "Harry Hamster" unfortunately while it does have brilliant Protein and Fat levels it does contain a lot of colourants and "filler" so things like Hay Based pellets which hamsters don't need and won't eat.
My Hamsters are fed on a mix of Harry Hamster with extra bits added in. The reason for this is because Harry Hamster is the most popular diet in the UK and due to the protein and fat levels, one of the healthier options despite the colourants, because it is the most popular diet the chances are that if someone was to switch one of our babies diets, it'd be to Harry Hamster. This makes the transition a lot easier on their tummies seeing as they are already used to it.
In addition to that, they also get fresh Kale once a week, fruits like Bananas and Apples, Fresh Carrots, Cooked Pasta, and other things.