When germ-free mice, animals raised without any microorganisms in their digestive systems, consumed nitrate and iron through their food, no protective compounds formed. DNICs were completely absent, providing strong evidence that intestinal microbes are necessary for this conversion. That experiment, conducted by researchers at Karolinska Institutet, points to something that nutritional science has not previously documented: gut bacteria appear to manufacture a class of protective molecules from nutrients found in ordinary vegetables, and those molecules may influence blood pressure, blood sugar, and liver fat accumulation.
The study was published in Cell on August 19, 2026, with collaborators from University Medical Centre Hamburg-Eppendorf and Johannes Gutenberg University Medical Centre Mainz. The research focused on two nutrients that commonly appear together in plant-based diets: dietary nitrate and nonheme iron. Both have familiar nutritional roles, but their interaction with gut bacteria appears to produce something additional.
What Gut Bacteria Are Actually Making
Nitrate occurs naturally in many vegetables, particularly beetroot and leafy greens such as spinach, arugula, and lettuce. Nonheme iron, the form of iron found in plant-based foods such as beans, lentils, whole grains, and green vegetables, is the main type of iron in plant-based diets. Both nutrients are familiar components of a healthy plate. What the Karolinska team found is that when these two compounds arrive in the gut together, certain bacteria combine them into something new.
The researchers showed that gut bacteria can convert nitrate and nonheme iron into dinitrosyl iron complexes (DNICs), signaling molecules that are absorbed by the body and transported to various organs, with particularly noticeable levels detected in the liver and kidneys. The process relies on nitrate-reducing bacteria, which first convert dietary nitrate to nitrite. That nitrite then interacts with nonheme iron present in the gut environment to form DNICs.
Human fecal bacteria generated DNICs when exposed to nitrate and iron in laboratory experiments, giving the pathway relevance beyond animal models. The study incorporated experiments involving mice, cells, bacteria, and human samples.
The Germ-Free Mouse Test
DNICs were completely absent from germ-free mice, even when those animals consumed nitrate and iron through their food. This ruled out the possibility that the gut lining or some other bodily mechanism was responsible for DNIC production, providing strong evidence that intestinal microbes are necessary for this pathway.
The Karolinska findings suggest that certain vegetables supply specific raw materials that the existing microbial community can convert into active biological compounds.
What Happened When DNIC Levels Rose
The researchers increased DNIC levels in animals showing features of cardiovascular and metabolic disease using two approaches: dietary supplements containing nitrate and iron, and laboratory-made DNICs administered directly. Both produced improvements across multiple health markers.
Higher DNIC levels were associated with lower blood pressure and improved vascular function in these animal models. The animals also controlled blood sugar more effectively and accumulated less fat in their livers. These findings connect to a well-established body of research: vegetable nitrate intake is inversely associated with cardiovascular disease risk, an effect that appears to be mediated in part by reductions in systolic blood pressure.
The liver findings are particularly relevant to metabolic disease. Fatty liver involves excess fat accumulating in liver cells and is closely tied to insulin resistance, obesity, and type 2 diabetes, often developing without noticeable symptoms. Reduced fat accumulation in the liver under elevated DNIC conditions suggests the molecules may interact with the metabolic machinery governing how the body handles energy and fat storage, not only with blood pressure regulation.
The Connection to Vegetable Nitrate Research
Large population studies have repeatedly linked diets containing plenty of vegetables with lower rates of cardiovascular disease and chronic illness. Researchers have typically attributed these benefits to fiber, potassium, antioxidants, and specific vitamins. The DNIC pathway adds another candidate explanation: some of those benefits may depend on what gut bacteria do with food after it reaches the intestine.
Two people can eat identical diets and experience different health outcomes, partly because their gut bacteria differ. If an individual’s microbiome lacks adequate nitrate-reducing bacteria, eating more spinach or beetroot may not produce the same DNIC-related effects. This remains speculative; the research has not yet mapped which specific bacterial species are the key players, but it represents a plausible and testable hypothesis that could help explain variability in dietary responses.
Building a Plate That Covers Both Substrates
Both nitrate and nonheme iron need to be present for DNIC production to occur, and many vegetables naturally supply both. Spinach delivers meaningful amounts of nitrate, while lentils are among the most iron-dense plant foods available, providing 6–7 mg of iron per cooked cup. Combining lentils with arugula or adding beet greens to a grain bowl puts both substrates on the same plate.
Read More: Studies Report Chayote Consumption Linked to Key Digestive and Cardiovascular Health Benefits
What This Means for You
The Karolinska study does not recommend any specific supplement protocol. The health implications remain preliminary, the disease-related benefits were demonstrated in animal models, and larger human trials are needed before conclusions can be drawn about effects in people. The team’s next steps involve developing methods for measuring DNIC levels in humans and investigating how these molecules are produced and transported through the body.
The study offers a mechanistic explanation for a long-standing epidemiological observation: vegetable-heavy diets consistently correlate with lower rates of heart disease, better blood pressure, and more stable metabolic health. The earlier explanation pointed to fiber, vitamins, and antioxidants. This research identifies an additional pathway: gut bacteria actively manufacturing protective compounds from two nutrients that routinely coexist in plant-based foods, with those compounds traveling through the bloodstream to organs well beyond the digestive tract.
Eating a variety of vegetables, including legumes regularly for their iron content, and supporting gut microbiome diversity through dietary variety aligns with what this research describes, whatever an individual’s particular microbial composition happens to be.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.