Gastritis

The stomach has its own microbiome, and gastritis disrupts it

Gastritis is inflammation of the stomach lining, most often caused by H. pylori infection, though it can happen without it too. A population study of 316 people, comparing normal stomach tissue against different stages of gastritis using genetic sequencing, found the stomach's own bacterial community became progressively more disrupted, or dysbiotic, as tissue changes advanced from normal, to inflamed, to atrophic gastritis, a more advanced, precancerous stage.

Source: Gastric Microbiota in a Low-Helicobacter pylori Prevalence General Population and Their Associations With Gastric Lesions

A stomach that can no longer defend itself

As gastritis progresses, the stomach often produces less acid. Lower acid makes it easier for bacteria that don't normally belong there, including several species from the mouth, to colonise the stomach. Some of these bacteria, including species called Actinomyces oris, Rothia dentocariosa, and Rothia mucilaginosa, can convert nitrate from food into compounds called nitrosamines, a group of chemicals known to cause cancer in animal studies. Researchers isolating these bacteria found that strains taken from people with gastric cancer produced far more of these nitrate-converting compounds than strains taken from people with gastritis alone. Researchers found that even in a population with relatively low H. pylori infection rates, this non-H. pylori bacterial disruption alone was linked to more advanced gastric lesions.

Source: Effects of Helicobacter pylori and Nitrate-Reducing Bacteria Coculture on Cells

A second type of gastritis, driven by the immune system

Not all gastritis comes from H. pylori. In autoimmune gastritis, the body's own immune system attacks the cells that produce stomach acid. Over time, this leads to low acid levels, vitamin B12 deficiency, and a higher risk of stomach cancer. Researchers have found this type has its own distinct bacterial pattern too.

In a study of 19 people with autoimmune gastritis, compared with 12 people without H. pylori infection or autoimmune gastritis, the autoimmune gastritis group had significantly less bacterial diversity in their stomach lining. The bacterial pattern also differed depending on whether early tumour changes were present, suggesting the gastric microbiome may track with how far the condition has progressed, not just whether someone has it.

Source: Journal of Gastroenterology, Development of gastric mucosa-associated microbiota in autoimmune gastritis with neuroendocrine tumors

The pattern shows up in children too

A study of 154 children compared three groups: 50 with H. pylori-related gastritis, 42 with gastritis but no H. pylori, and 62 healthy children with neither. In the H. pylori-infected group, the Helicobacter genus made up 66.3% of their gut bacteria, compared with just 0.45% in children without the infection. The infected children also had lower overall bacterial diversity in their gut. Researchers also found that certain other bacteria, including Lactobacillus and Streptococcus, seemed to interact with H. pylori in ways that increased inflammation and pushed the stomach lining further toward disease.

Source: Helicobacter pylori Infection Aggravates Dysbiosis of Gut Microbiome in Children With Gastritis

What this means for you

Persistent stomach pain, indigestion, or unexplained weight loss should be assessed by a doctor, since gastritis needs a proper diagnosis, usually through endoscopy and tissue sampling, and treatment depends on the exact underlying cause. Where H. pylori is present, that needs specific antibiotic treatment, not diet changes alone. Alongside medical care, a varied, plant-rich diet supports a more diverse gut and stomach bacterial community generally. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.