Your saliva enzymes and your stomach acid can't touch the butyl in the gum base, but that doesn't mean it just hangs out.
你身体中的唾液酶和胃酸不会接触到口香糖原料中的丁基橡胶，但这并不表示口香糖会直接被排出体外。
英语百科
Gum base
Gum base is the non-nutritive, non-digestible, water-insoluble masticatory delivery system used to carry sweeteners, flavors, and any other substances in chewing gum and bubble gum. It provides all the basic textural and masticatory properties of gum.