Bacteria is meant to stay inside the gut NICOLLE R. FULLER / SCIENCE PHOTO LIBRARY

Bacterial DNA has been found in the blood, liver and fat of people who are obese, showing that either fragments of bacteria or entire live bacteria are leaking into their bodies from their guts, which shouldn’t be happening.

“Even fragments of bacteria can trigger an immune response,” says André Marette at the Québec Heart and Lung Research Institute in Canada.

In people who are obese the intestinal barrier is more fragile, Marette says, allowing bacterial fragments or live bacteria to get inside their body. …