Sure, it may not be the sweet stuff you're thinking of. But there is a sugar molecule hidden in the leaves of green vegetables such as spinach and kale that is lapped up by your good gut bacteria, which use it as a source of energy to fuel their growth. And for that, your body will thank you.

Researchers from Melbourne and the United Kingdom have established how the bacteria extract the sugar from leafy green vegetables and turn it into energy.

The gut bacteria's ability to grow and colonise the large intestine is good news for the health of the host human. The more good gut bacteria, the less room there is to accommodate bad gut bacteria.

"It's bums on seats basically," said Ethan Goddard-Borger from the Walter and Eliza Hall Institute of Medical Research. "The good bacteria fills the auditorium so none of the bad eggs can get a foothold."

The unusual sugar molecule called sulfoquinovose, or SQ for short, is produced by all green plants for photosynthesis, though it is indigestible by humans. However despite being produced on a huge scale by plants, SQ has long been overlooked by science.

"No one had any idea where it went or what happened to it when the plant died," Dr Goddard-Borger said. "But it is actually being used by bugs that live in the gut to promote their growth, which is a good thing for you."

The SQ sugar is also found in herbs and other green vegetables such as broccoli – the greener the plant, the better the SQ sugar content. But SQ is a different class of sugar to glucose and sucrose.

"It's a related molecule, nonetheless it has different properties," he said.

Dr Goddard-Borger, a chemical biologist who led the research, said the good gut bacteria such as protective strains of E. coli, needed the SQ sugar in leafy greens to thrive.

Published in the journal Nature Chemical Biology on Tuesday, the findings could have implications for the development of new types of antibiotics.

The sugar has the potential to be used as a pathway to deliver antibiotics directly to bad bacteria in the gut – meaning drugs of the future could be attached to the SQ sugar which travels to the large intestine.

"Bacteria that metabolise SQ actively import it, so if you put an antibiotic on an SQ a bug will actively import it thinking it is a tasty treat," he said.

The research was a collaboration between Dr Goddard-Borger at the Walter and Eliza Hall Institute, Spencer Williams from Melbourne University's Bio21 Institute and Gideon Davies from the University of York.