Leafy greens and other vegetables are often praised for fibre and vitamins. A 2026 study from Karolinska Institutet, published in Cell, points to another pathway: gut bacteria can take two common plant nutrients—nitrate (high in beetroot, spinach, rocket, and lettuce) and non-haem iron (from beans, whole grains, and greens)—and combine them into molecules called dinitrosyl iron complexes, or DNICs.
In experimental models of cardiometabolic disease, higher DNIC levels were associated with lower blood pressure, improved blood-vessel function, better blood-sugar control, and less fat in the liver. The researchers describe this as a previously under-appreciated way the microbiota may turn everyday plant foods into bioactive compounds. That helps explain, they argue, why vegetable-rich patterns are repeatedly linked with lower disease risk—not only because of fibre or a single vitamin, but because microbes and micronutrients work together.
The finding is still early (animal and experimental systems, not a human diet trial that “proves” DNICs prevent disease). It does line up with a broader 2026 picture: large diet–microbiome maps, such as the Human Phenotype Project analysis of more than 10,000 people, show that specific foods and overall dietary patterns predict many gut species and metabolic pathways. Isolated fibre supplements often fail to copy the effects of mixed whole-food diets. Tracking the foods you already eat—and the nutrients they actually contain, including iron and the plant foods that supply nitrate—is a more honest starting point than treating any single number as an oracle.
Sources
- Karolinska Institutet / ScienceDaily: Gut bacteria may unlock a hidden benefit of vegetables (22 Aug 2026)
- Hu et al., “Gut microbiota generate dinitrosyl iron complexes with cardiometabolic benefits,” Cell, 2026. DOI: 10.1016/j.cell.2026.07.055
- Shoer et al., Diet–microbiome associations in 10,068 individuals from the Human Phenotype Project, Nature Medicine (2026)
- GMFH World Summit 2026 notes on whole-food fibre vs isolated fibre