Gut bacteria turn plant nutrients into protective compounds in mice

A plate of spinach, beets or other plant foods may be supplying more than raw nutrients. Researchers at Karolinska Institutet have found that gut bacteria can convert dietary nitrate and plant-based, or nonheme, iron into dinitrosyl iron complexes, known as DNICs—molecules that may influence cardiovascular and metabolic health. The health effects were observed in mice, not yet in people.

The team identified DNICs in tissues using experiments with mice, cells, bacteria and human samples. The molecules were absorbed by the body and transported mainly to the liver and kidneys. In germ-free mice, they were completely absent, suggesting that the gut microbiota is crucial for making them. The finding adds a specific biological mechanism to the broader link between vegetable-rich diets and health.

When the researchers raised DNIC levels with dietary supplements containing nitrate and iron, or by administering synthetic DNIC, several markers improved in an animal model of cardiovascular and metabolic disease. The study reported lower blood pressure, better vascular function, improved blood sugar control and reduced fat accumulation in the liver. Andrei L. Kleschyov, the study's first and co-corresponding author, said the results show how gut bacteria can turn food components into biologically active molecules.

For people, the immediate takeaway is not a new supplement or a proven treatment. It is a clearer hypothesis: what the gut microbiota does with nutrients may matter alongside the nutrients themselves. That could eventually help researchers investigate diet-based ways to influence cardiometabolic disease, but the relevant DNIC levels, transport and effects still need to be measured in humans.

The study was published in Cell by researchers from Karolinska Institutet, University Medical Centre Hamburg-Eppendorf and Johannes Gutenberg University Medical Centre Mainz. Its evidence is largely based on experimental models, and the researchers say further work is needed before the pathway can be assessed as a human health intervention.