Researchers have made an important discovery about the health benefits of eating leafy greens: they contain an unusual sugar sought by beneficial bacteria in the gut that helps them grow and thus crowd out bad bacteria.

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The researchers suggest that consumption of the sugar molecule SQ within leafy greens will prove to be an important factor in improving and maintaining healthy gut bacteria and good digestive health.
Image credit: Walter and Eliza Hall Institute

The team – from Australia and the UK – reports the finding in the journal Nature Chemical Biology.

The sugar is called sulfoquinovose (SQ) and is made in green leaves by photosynthesis – the process by which plants use energy from the sun to make chemical energy in the form of sugars. Bacteria use SQ as a source of carbon and sulfur.

Sulfur is important for building proteins – the essential building blocks of all living organisms – explain the authors, who point out that SQ is the only sugar molecule that contains sulfur.

Senior author Dr. Ethan Goddard-Borger, of the Walter and Eliza Hall Institute of Medical Research in Parkville, Victoria, Australia, says:

“Every time we eat leafy green vegetables we consume significant amounts of SQ sugars, which are used as an energy source by good gut bacteria.”

He goes on to explain that there are crucial and protective strains of Escherichia coli and other beneficial bacteria in the gut that use SQ as a source of energy.

These bacteria provide a protective barrier that “prevents growth and colonization by bad bacteria, because the good bugs are taking up all the habitable real estate,” Dr. Goddard-Borger adds.

The team discovered that the bacteria extract SQ to fuel their growth using the enzyme YihQ. The enzyme breaks down the sugar so the bacteria can absorb and metabolize the sulfur and other components.

The study resolves a mystery that has puzzled scientists for 50 years: how sulfur – an element that is essential for life – is used and recycled by living organisms.

Coauthor Prof. Spencer Williams, from the Bio21 Institute at the University of Melbourne, Australia, says:

“What is remarkable is that the YihQ enzyme was hiding in plain sight and is produced by the humble bacterium E. coli, present in nearly every biologist’s laboratory.”

Dr. Goddard-Borger sums up an important conclusion of the study:

E. coli is a key bacterial colonizer needed by our gut. We speculate that consumption of this specific molecule within leafy greens will prove to be an important factor in improving and maintaining healthy gut bacteria and good digestive health.”

He says the study may also offer vital clues for developing a completely new type of antibiotic to meet the desperate need for new ways to fight drug-resistant superbugs.

The team thinks it may be possible to use enzymes like YihQ to deliver highly specific antibiotics that target harmful forms of E. coli and other bacteria, such as the food-poisoning bacteria Salmonella, while leaving the good bacteria alone.

When bacteria break down SQ from plants, they release sulfur into the environment, where it re-enters the global sulfur cycle and is used again by the other organisms.

Every year, the huge amount of SQ produced around the world by leafy green vegetables – such as spinach, kale, watercress and many others – is comparable to the total annual global production of iron ore.

Meanwhile, Medical News Today recently reported a study that shows solid food is the main driver of gut bacteria development by the time a child reaches 9 months of age.