Analysis shows ancient people and nonindustrial societies today have about the same gut bacteria; industrial populations have different biomes, and meanwhile, some bacteria seem to have gone extinct

We are what we eat, they say. Or as Hippocrates wrote 2,500 years ago, “Let thy food be thy medicine and medicine be thy food,” resulting in 2,500 years of arguing over how our diet impacts our health.

Indeed, the science of diet and nutrition is bewildering, characterized by contradictory evidence and uninformed anecdotal reports. What works for some doesn’t work for others. One reason for this frustrating inconsistency involves change to the bacteria in our digestive systems.