Hey Jessica,
It depends what you mean by healthy- if you mean super healthy like no oil/ carbs/ salt then I think you would find it hard, but if you mean just a normal healthy balanced diet then I think you will have no problem.
Since moving to Chengdu I am eating more vegetables than I have ever eaten in my life, and generally the dishes here are heavier on veg content than meat, which for guys is probably a bad thing but for women I think its pretty healthy. There are many supermarkets selling western products so you can always cook western food at home if you prefer. I eat a lot of fruit here and what is great is the sheer variety of fruti available. Also its a lot cheaper than back home. Not sure you should worry too much about the pesticides on the fruit- I eat all my fruit after a quick rinse under the tap and I have NEVER got sick from it.
Finally, it is pretty healthy in terms of the low usage of dairy- something which I had a lot of before I came here. I have found some low fat milk in Hong Qi supermarkets, and to me it tastes fine, a lot better than the full fat version that is readily available.
I think people worry about the food here but at the end of the day Chinese people are on the whole slim and active, and I believe have the longest lifespan ?! so i’m sure the food can’t be all bad!