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As far back as the 1970s, there were studies indicating the human body had more bacterial cells than human cells. While bacteria in and on humans is "essential to your health," according to microbial ecologist Ruth Ley from the Max Planck Institute, it was determined that, in the words of UC San Diego's Rob Knight, "you're more microbe than you are human." Researchers in the 2010s sought to quantify just how much of a difference there was in terms of human versus bacteria.
At its highest estimations, the ratio between bacterial and human cells was 10:1. That has since been lowered, with scientists like Ron Sender, Shai Fuchs, and Rob Milo offering a 1:1 ratio instead. The revised numbers allow researchers (and anyone who wants to drop a surprising fact at a dinner party) "a better estimate to quote" without losing sight of the symbiosis between humans and bacteria.
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