How Gut Bacteria Convert Vegetable Nitrate and Plant Iron Into Heart-Protective Molecules: What the New Research Shows

A landmark study published in Cell in August 2026 reveals that gut bacteria can combine two ordinary dietary components — nitrate from vegetables and non-haem iron from plant foods — to synthesise a class of biologically active molecules called dinitrosyl iron complexes (DNICs) that appear to protect the heart, blood vessels, liver, and metabolic system. The research, led by scientists at Karolinska Institutet in Stockholm, offers the most mechanistically detailed explanation yet for why vegetable-rich diets are consistently associated with lower rates of cardiovascular and metabolic disease.

The implications are significant. This is not simply another observational correlation between eating greens and staying healthy. It is a specific biochemical pathway in which identifiable gut microbes act on identifiable food compounds to produce identifiable molecules with measurable physiological effects.

At a Glance: Key Facts About DNICs and the Karolinska Study

Feature	Detail
Molecules produced	Dinitrosyl iron complexes (DNICs)
Dietary precursors	Nitrate (leafy greens, beetroot) + non-haem iron (beans, whole grains, green vegetables)
Who makes them	Gut microbiota — absent entirely in germ-free mice
Primary organs targeted	Liver and kidneys (confirmed tissue detection)
Health effects observed (animal models)	Lower blood pressure, improved vascular function, better blood sugar control, reduced liver fat accumulation
Study design	Multi-model: mice, cell cultures, isolated bacteria, human samples
Published in	Cell, 2026 (DOI: 10.1016/j.cell.2026.07.055)
Lead institution	Karolinska Institutet, Department of Physiology and Pharmacology
Collaborating institutions	University Medical Centre Hamburg-Eppendorf; Johannes Gutenberg University Medical Centre Mainz
Funding sources	Swedish Research Council, Swedish Heart-Lung Foundation, Novo Nordisk Foundation, European Research Council, Knut and Alice Wallenberg Foundation

What Are Dinitrosyl Iron Complexes, and Why Do They Matter?

Dinitrosyl iron complexes are small inorganic molecules formed when nitric oxide (NO) or nitrite binds to iron in a specific two-to-one ratio, creating a stable iron-nitrosyl structure. In biochemistry, DNICs act as carriers and donors of nitric oxide equivalents — a property that gives them considerable physiological reach, since nitric oxide is one of the body's primary signalling molecules for vascular tone, insulin sensitivity, and cellular energy metabolism.

What the Karolinska team discovered is that the gut microbiota is capable of generating DNICs de novo from dietary substrates — specifically, from the nitrate abundant in leafy vegetables and the non-haem iron found in plant-based foods. This is a previously unrecognised biosynthetic route: the gut acting as a molecular factory that upgrades raw dietary inputs into bioactive signalling compounds.

Before this study, DNICs had been studied mainly as synthetic compounds in laboratory settings or as incidental products of nitric oxide chemistry in tissues. The idea that the gut microbiome produces them systematically from food — and that the body then absorbs and distributes them to distant organs — is genuinely novel.

What Exactly Did the Karolinska Researchers Do?

The study, published in Cell and led by first and co-corresponding author Andrei L. Kleschyov, Senior Researcher at Karolinska's Department of Physiology and Pharmacology, used a multi-model experimental approach to establish the DNIC pathway from multiple angles simultaneously.

Germ-free mouse experiments were central to proving microbial necessity. When mice were raised in sterile conditions — meaning their guts contained no bacteria whatsoever — DNIC molecules were completely absent from their tissues. This is a strong causal signal: the absence of microbes meant the absence of DNICs, ruling out the possibility that the body produces these molecules through some independent non-microbial chemistry.

Cell and bacterial cultures allowed the team to probe which types of bacteria are involved and under what conditions DNIC synthesis occurs. Advanced analytical techniques were used to detect and quantify DNICs in several tissue types.

Human samples were incorporated to establish that the pathway is not purely a rodent phenomenon, though the researchers are careful to note that the human data is preliminary and that the bulk of the mechanistic evidence comes from animal and cell models.

Intervention experiments tested what happened when DNIC levels were deliberately raised — either by giving animals dietary supplements containing both nitrate and iron, or by administering synthetically produced DNIC directly. Both approaches produced measurable improvements in cardiovascular and metabolic markers.

Which Vegetables Provide the Necessary Precursors?

The two dietary inputs required for DNIC synthesis are nitrate and non-haem iron, both readily available from ordinary plant foods.

Nitrate is an inorganic anion (NO₃⁻) found naturally and in high concentrations in certain vegetables. Beetroot is among the richest sources, which is why beetroot juice has been extensively studied as a blood pressure intervention. Leafy greens — spinach, rocket (arugula), and lettuce — are also high-nitrate foods. A related ScienceDaily report from July 2026 noted that chewing gum after eating nitrate-rich vegetables or drinking beetroot juice helped the body produce more beneficial nitrite, temporarily lowering blood pressure — a finding that now fits neatly into the broader DNIC framework.

Where nitrate comes from matters far more than how much you consume. A large long-term study of more than 54,000 adults published in June 2026 found that people who obtained nitrate from vegetables showed protective effects against dementia, while those who got it from drinking water did not. The Karolinska DNIC research may help explain this discrepancy — vegetable nitrate arrives alongside plant iron and a food matrix that supports the gut bacteria needed to complete the conversion.

Non-haem iron is the form of iron found exclusively in plant-based foods, as opposed to haem iron, which is bound to haemoglobin or myoglobin in meat. Non-haem iron sources include beans, lentils, whole grains, tofu, and green vegetables like broccoli and kale. It is generally less bioavailable than haem iron — a fact that has historically been framed as a limitation of plant-based diets. The DNIC discovery reframes this: non-haem iron may be less available for direct absorption precisely because gut bacteria are using it as a substrate for DNIC synthesis, which may be a more valuable metabolic fate.

How Does the Gut Microbiota Actually Make DNICs?

The precise bacterial species and enzymatic steps involved are not yet fully characterised, and the researchers acknowledge this as a key area for future work. What the study establishes is the following sequence:

Dietary nitrate is ingested and reaches the large intestine, where gut bacteria reduce it to nitrite (NO₂⁻) and then to nitric oxide (NO) or related reactive nitrogen species.
Non-haem iron from plant foods is also present in the gut lumen.
Gut bacteria facilitate the combination of these nitrogen and iron species into DNICs — the stable iron-nitrosyl complexes.
DNICs are absorbed through the gut wall into systemic circulation.
They are transported to and detected in organs including the liver and kidneys, where they exert their physiological effects.

The requirement for both substrates to be present simultaneously is implied by the experimental design: supplements containing both nitrate and iron raised DNIC levels, while the pathway requires the microbial machinery to be intact (as shown by the germ-free mouse data).

This is a meaningful mechanistic detail for anyone thinking about diet. Eating spinach — high in both nitrate and non-haem iron — may be more effective at generating DNICs than eating a nitrate-rich food alongside a separate iron source, because co-localisation in the gut matters. Whether timing and food combinations significantly alter DNIC output in humans is one of the open questions the researchers intend to pursue.

What Health Benefits Were Observed, and How Strong Is the Evidence?

The animal model results, as reported by Karolinska Institutet, showed four distinct improvements when DNIC levels were elevated.

Lower blood pressure and improved vascular function is the most mechanistically expected finding, given that DNICs act as nitric oxide donors and nitric oxide is a potent vasodilator. Reduced vascular resistance leads directly to lower blood pressure. The vascular function improvements go beyond simple blood pressure reduction — they suggest better endothelial responsiveness, which is relevant to atherosclerosis risk.

Better blood sugar control followed as well. Nitric oxide signalling plays a role in insulin sensitivity and glucose uptake in muscle and fat tissue. DNIC-mediated NO delivery to peripheral tissues could plausibly improve insulin signalling, which would explain the blood sugar findings and connects to a broader body of literature on nitric oxide and metabolic syndrome.

Reduced fat accumulation in the liver was another notable outcome. Non-alcoholic fatty liver disease (NAFLD) is closely linked to insulin resistance and metabolic syndrome. The liver is one of the organs where DNICs were directly detected in tissue samples, making it a primary target. Reduced hepatic fat accumulation in the animal model is a clinically meaningful endpoint given the rising global prevalence of NAFLD.

Taken together, these effects in a single animal model of cardiovascular and metabolic disease suggest that DNICs may act as a broad cardiometabolic modulator rather than a single-target drug.

It is essential to state clearly: these findings are from experimental models, primarily mice. The researchers themselves emphasise that additional research is necessary to determine exactly how the process operates in humans. The human samples included in the study establish biological plausibility but do not constitute clinical trial evidence. Effect sizes, dose-response relationships, and inter-individual variability in humans are all unknown at this stage.

Why Does the Source of Nitrate Matter So Much?

One of the most practically important implications of the DNIC research is that it reinforces the idea that food matrix and co-nutrients matter enormously — not just the isolated compound.

Nitrate from drinking water, processed meats, or synthetic supplements does not arrive with the plant iron, the fibre, the polyphenols, or the food-matrix factors that accompany vegetable nitrate. The 54,000-person dementia study found protective effects only for vegetable-sourced nitrate, not water-sourced nitrate. The DNIC pathway offers a mechanistic explanation: without the co-presence of non-haem iron and the right gut bacterial environment, nitrate alone cannot complete the conversion to DNICs.

This also has implications for how we think about nitrate supplementation. Beetroot juice supplements and isolated nitrate capsules have been studied for athletic performance and blood pressure. They may raise nitrite and NO levels through the salivary nitrate-nitrite-NO pathway, but whether they generate DNICs at the same rate as whole vegetables — with their iron content and fibre intact — is an open question.

For people following plant-based diets, this research is particularly relevant. Non-haem iron has often been discussed primarily as a nutritional challenge — harder to absorb, requiring vitamin C for optimal uptake. The DNIC finding suggests that some of the non-haem iron that does not get absorbed in the traditional sense may be doing something more valuable: serving as a substrate for gut microbial synthesis of cardiometabolic signalling molecules.

What Role Does the Gut Microbiome Play, and Can It Be Modified?

The germ-free mouse data establishes that gut microbes are not merely helpful but essential for DNIC production. Without them, the pathway does not operate at all. This makes the gut microbiome a critical variable in determining how much cardiovascular and metabolic benefit any individual extracts from a vegetable-rich diet.

This is consistent with a growing body of research showing that the gut microbiome mediates many of the health effects previously attributed directly to dietary compounds. A February 2026 ScienceDaily report described a gut compound that helps protect the liver, and a September 2025 study identified D-lactate — a molecule made by gut bacteria — as a hidden trigger of high blood sugar and liver disease. The DNIC story fits into this broader picture: the gut microbiome as a biochemical intermediary between diet and systemic health.

The Karolinska researchers have identified this as a major open question: whether diet or deliberate changes to the gut microbiota could be used to alter DNIC levels and help prevent disease. Practically, this could mean dietary interventions that simultaneously increase nitrate and non-haem iron intake while supporting the bacterial species that perform the conversion; probiotic or prebiotic strategies targeting the specific bacteria responsible for DNIC synthesis, once those species are identified; or combination supplements containing both nitrate and iron in forms that reach the colon intact, where the relevant bacteria reside.

None of these interventions have been tested in humans yet. The researchers' immediate next step is to develop reliable methods for measuring DNIC levels in people — a prerequisite for any clinical trial.

How Does This Fit Into the Broader Science of Nitrate, Nitric Oxide, and Heart Health?

The nitrate-nitrite-nitric oxide pathway has been studied for decades. The classical understanding is that dietary nitrate is reduced to nitrite by bacteria in the mouth and on the tongue, and nitrite is then reduced to nitric oxide in the stomach and tissues — a process that lowers blood pressure and improves exercise performance. This is the mechanism behind beetroot juice's well-documented effects on athletic endurance and blood pressure.

The DNIC pathway is a parallel and previously unrecognised branch of this chemistry, operating in the gut rather than the mouth, and requiring iron as an additional co-substrate. Where the classical pathway produces free nitric oxide (a gas with a very short half-life), the DNIC pathway produces a stable iron-bound complex that can be transported in the bloodstream and delivered to distant organs. This stability is a significant advantage: DNICs may be able to deliver NO-equivalent signalling to the liver and kidneys in ways that free NO cannot, because free NO is scavenged rapidly in the bloodstream.

A January 2023 ScienceDaily report on dietary nitrate significantly increasing muscle force during exercise documented the classical pathway's effects. The DNIC research suggests that the full picture of how dietary nitrate benefits the body is considerably more complex and organ-specific than previously understood.

What Are the Limitations and What Comes Next?

The researchers are transparent about the limitations of the current work. The mechanistic evidence is strongest in animal models and cell cultures. Human samples were included, but the study is not a human clinical trial. Key unknowns include:

Which specific gut bacterial species are responsible for DNIC synthesis.
The precise enzymatic steps in the conversion pathway.
How much DNIC a typical human produces from a typical vegetable-rich meal.
How DNIC levels vary between individuals with different gut microbiome compositions.
Whether DNIC levels are measurably lower in people with cardiovascular or metabolic disease.
Whether dietary or microbiome interventions can raise DNIC levels in humans and whether that translates to clinical benefit.

The research team's stated next priorities are: developing validated methods to measure DNIC in human blood and tissues; conducting studies in humans to map DNIC levels against diet, microbiome composition, and health outcomes; and exploring whether targeted interventions can modulate the pathway therapeutically.

The study was conducted in collaboration with the University Medical Centre Hamburg-Eppendorf and the Johannes Gutenberg University Medical Centre Mainz, and was funded by the Swedish Research Council, the Swedish Heart-Lung Foundation, the Novo Nordisk Foundation, the European Research Council, the Knut and Alice Wallenberg Foundation, and Diabetes Wellness Sweden — a funding profile that suggests sustained institutional commitment to following this line of research into human trials.

What Does This Mean for People Who Want to Eat for Heart Health Now?

While human clinical evidence is not yet available, the mechanistic findings support several dietary principles that are already well-grounded in epidemiology.

Eating a variety of vegetables high in both nitrate and non-haem iron — spinach, rocket, beetroot, kale, broccoli, and lentils — provides both substrates the DNIC pathway requires. This is consistent with longstanding dietary guidance, but the DNIC research gives it a more specific molecular rationale. Supporting gut microbiome diversity through fibre-rich, minimally processed diets is likely to support the bacterial populations that perform DNIC synthesis, though the specific species have not yet been identified. And the source of nitrate matters: vegetable nitrate arrives with iron, fibre, and a food matrix that supports microbial conversion in ways that isolated nitrate supplements may not replicate.

For those interested in the broader space of evidence-based cardiovascular nutrition, the DNIC findings complement research on other plant-derived compounds. Our coverage of berberine for insulin resistance and blood sugar and Arjuna for heart health explores other mechanistic pathways through which plant compounds influence cardiometabolic function — pathways that may interact with the gut microbiome in ways that are only beginning to be understood.

The DNIC discovery is a reminder that the health benefits of vegetables are almost certainly not reducible to any single compound or mechanism. Fibre, polyphenols, vitamins, minerals, and now gut-microbially synthesised DNICs all appear to play roles. The practical implication is the same as it has always been — eat a variety of vegetables — but the scientific story behind that advice is becoming considerably richer.

Summary

Karolinska Institutet researchers have identified a previously unknown biochemical pathway in which gut bacteria combine dietary nitrate from vegetables and non-haem iron from plant foods to produce dinitrosyl iron complexes (DNICs). These molecules are absorbed into the body and transported to organs including the liver and kidneys. In animal models of cardiovascular and metabolic disease, higher DNIC levels were associated with lower blood pressure, better vascular function, improved blood sugar control, and reduced liver fat. The pathway is entirely dependent on gut microbes — germ-free animals produce no DNICs at all. The findings, published in Cell in August 2026, provide a plausible molecular mechanism for the well-established epidemiological association between vegetable-rich diets and lower cardiovascular and metabolic disease risk. Human clinical research is the essential next step.