This week, the FTC also released some new guidelines, the first changes it has made to its green marketing guidelines since 1998.

FORBES: Gang Green: Rules Are Tightening. Don't Say Green If You Don't Mean Green.

"We need to understand better what the normal microbiome is like and what happens to it when it changes to cause or influence disease, " Dr. Green said.

WSJ: Gene Map of Body's Microbes Is New Health Tool