If you can cook and know what/how to eat, you’ll do find in Chengdu as soon as you piece together a few pretty simple things. Like Ray said, food in Sichuan restaurants is delicious but filled with salt, simple carbohydrates, and doesn’t have much protein. It’s best to cook at home at least a few times a week if you have the means. I cook a lot of chicken and it seems to be working fine for me, I also buy large quantities of steak, bacon, and salmon regularly.
I’ve been getting that on Taobao, too. Low prices, good stuff. Search for 无糖花生酱 but make sure you don’t get the kind that’s intended for use as a hotpot dip.
Watson’s has these, but otherwise they’re difficult to find. It’s best to find a trusted Taobao seller, in my experience. I take daily vitamin D, creatine, whey, and fish oil supplements and have been experimenting with some others. Co-Q10, glutamine, piracetam, etc. I’ve been taking a handful of supplements with breakfast on and off since high school, basically.