Gut bacteria transform vegetables into heart-protective molecules, study finds

Your grandmother always said to eat your greens. She didn't know why, exactly—just that they were good for you. Scientists at the Karolinska Institutet in Sweden may have finally found part of the answer, and it turns out the mechanism is far stranger and more elegant than anyone expected. The vegetables themselves aren't the whole story. What matters is what happens to them inside your gut.

When you eat a bowl of spinach or a beetroot, you're consuming nitrate—a compound that sits quietly in leafy greens and root vegetables. You're also getting non-haem iron, the plant-based form found in beans, whole grains, and dark leafy vegetables. For years, nutritionists knew these foods were protective. People who ate more vegetables had lower rates of heart disease, better blood sugar control, healthier blood vessels. But the precise mechanism remained obscure. Now researchers have identified a missing link: your gut bacteria.

The bacteria living in your intestines can perform a kind of molecular alchemy. They take the nitrate and the plant iron from your food and combine them into compounds called dinitrosyl iron complexes, or DNICs. Once formed, these molecules are absorbed into the bloodstream and distributed throughout the body, accumulating particularly in the liver and kidneys. The discovery emerged from a series of experiments involving mice, human cell cultures, bacterial samples, and tissue analysis. When researchers examined germ-free mice—animals raised without any gut microbiota—they found no DNICs at all. The absence was total and telling. Without bacteria, the transformation simply doesn't happen.

To understand what these molecules actually do, the research team then tested what occurred when DNIC levels were artificially elevated. They did this in two ways: by giving animals dietary supplements containing both nitrate and iron, or by directly administering synthetic DNICs. The results were striking. In animal models of cardiovascular and metabolic disease, higher DNIC concentrations correlated with measurable improvements across multiple health markers. Blood pressure dropped. Blood vessel function improved. Blood sugar control became more stable. Fat accumulation in the liver decreased. Each of these changes represents a meaningful shift away from disease.

Andrei Kleschyov, the study's first author at Karolinska Institutet, framed the finding in straightforward terms: gut bacteria can convert food components into biologically active molecules that influence fundamental bodily functions. Mattias Carlström, a professor of cardiorenal physiology at the same institution, went further, suggesting the work explains something long observed but never fully understood—why diets rich in vegetables correlate so strongly with protection against cardiovascular and metabolic disease. The connection between what you eat and what your microbiota produces turns out to be a conversation, not a one-way street.

But the researchers are careful about the limits of their findings. Most of the work was conducted in experimental models—mice, cells, tissue samples. The leap from laboratory conditions to the human body is substantial. No one yet knows exactly how efficiently human gut bacteria perform this transformation, whether the process varies between individuals, or whether the DNICs produced in a living person circulate and function the way they do in controlled experiments. The next phase of research will focus on developing reliable methods to measure DNIC levels in people, understanding how the molecules move through the body, and determining whether dietary changes or microbiota modifications could be used to boost DNIC production as a disease-prevention strategy.

The work was a collaboration between Swedish institutions and research centers in Germany, funded by the Swedish Research Council, the Swedish Heart-Lung Foundation, the Novo Nordisk Foundation, and several other organizations. What emerges is a portrait of health that is neither purely genetic nor purely dietary, but rather a three-way conversation between the food you choose, the bacteria you harbor, and the molecules your body produces as a result. Your grandmother's intuition about greens may have been closer to the truth than she knew.