Gut Bacteria Turn Vegetable Nitrate and Iron Into Heart-Protective Molecules

Researchers at Karolinska Institutet in Sweden have found that gut bacteria can transform nitrate and iron from vegetables into molecules that may help protect the heart and metabolism, according to a study published in the journal Cell. Nitrate occurs naturally in vegetables such as beetroot, spinach, rocket and lettuce, while non-haem iron -- the form of iron in plant foods like beans, whole grains and green vegetables -- is also common in the diet. Gut microbes combine the two into compounds called dinitrosyl iron complexes (DNICs), absorbed into the body and carried mainly to the liver and kidneys.

Using mice, cells, bacteria and human samples, the researchers detected DNIC in several tissue types, but found it absent in germ-free mice, raised without gut bacteria -- showing gut microbes are essential for producing DNIC. "Our results show that gut bacteria can convert components in food into biologically active molecules that influence important bodily functions," said Andrei L. Kleschyov, senior researcher at Karolinska Institutet and the study's first and co-corresponding author.

The team then raised DNIC levels in an animal model of cardiovascular and metabolic disease, either with dietary supplements containing nitrate and iron or by giving synthetic DNIC. Higher DNIC levels were associated with lower blood pressure, improved blood vessel function, better blood sugar control and reduced fat buildup in the liver. Professor Mattias Carlström of Karolinska Institutet, a shared last author with professor Jon Lundberg, said this helps explain why vegetable-rich diets, which contain both nitrate and iron, are linked to a lower risk of several diseases.

The researchers caution most of the work was done in experimental models, so further research is needed to confirm how it works in humans. The study, done with the University Medical Centre Hamburg-Eppendorf and the Johannes Gutenberg University Medical Centre Mainz in Germany, will next aim to measure DNIC levels in people and test whether diet or gut microbiota changes can alter them.