In a startling discovery, researchers have found that bone marrow stem cells, which can travel to the stomach to help heal inflammation or injury (such as the infection that starts ulcers), may also play a part in the origins of stomach cancer. In the experiment, the “rescue” bone marrow stem cells became infected themselves and eventually turned into stomach cancer.

This research belies the long-held belief that cancerous tumors originate from the cells that surround the site of the tumor–in this case, it would have been stomach cells. So in another dramatic case of what’s good for us can also be bad for us, the incredible power of stem cells to heal is turned around into a destructive force.

What is the message of finding that so many substances are both good and bad for us? Seems like it might simply be a vivid illustration of the old adage… moderation in all things.