315 tells us a principle: ordinary people should just eat cheap fruits, cheap vegetables, and cheap grains. Because no one is going to add high-tech tricks or shady practices to cabbage that costs a few cents, because adding those would increase costs and they'd lose money.

On the contrary, the more expensive something is, the more out-of-season it is, the more unusual it is, the more high-tech additives will be in it. Because they're afraid it will go bad, afraid it will spoil, afraid they won't be able to sell it quickly enough and suffer losses.