Biohacker Bryan Johnson, who spends millions on optimising his health for longevity, has revealed he's battling Autoimmune Gastritis, a chronic inflammatory disease which results from antibodies attacking stomach cells. In a lengthy X post on July 1, he wrote: "I have an autoimmune disease. My stomach is eating itself. 2–5% of people have this, too. Likely more, because it hides." The good news, he said, was that he would try and solve it.Bryan Johnson was diagnosed with Autoimmune Gastritis in May 2026. (Instagram)What is Autoimmune Gastritis?Autoimmune Gastritis is a chronic disease, whereby the body's immune system incorrectly identifies the stomach lining and specifically the cells responsible for producing gastric acid as a threat to the body. This leads to damage to the lining of the stomach and eventually leads to a reduction in the production of gastric acid. This further affects the absorption of key nutrients like vitamin B12 and iron, resulting in anaemia among other possible complications, if left untreated, explains Dr Ronak Tate, Consultant Gastroenterology, Fortis Hiranandani Hospital, Navi Mumbai."It is important that the patient is aware of the symptoms of the disease since the initial signs are mild and could be related to other medical conditions like bloating and fatigue," he adds.Johnson, 48, who has had hypothyroidism since he was 21 years old, was diagnosed with AIG only in May, after over a decade of fighting unexplained low ferritin levels. His diagnosis was confirmed following multiple blood tests, which revealed elevated levels of anti-parietal cell antibodies, and stomach biopsies.For details, check out his full X post on the condition.Symptoms of Autoimmune GastritisAccording to Gastroenterologist Dr Rajdeep More, key symptoms of AIG include a burning sensation in the upper abdomen, nausea, bloating, a feeling of discomfort after eating, as well as lethargy and weakness.However, Johnson shared he had no clear symptoms. He said the condition is usually silent for years until the damage is enough to cause iron deficiency, B12 deficiency, anemia and an increased stomach cancer risk.Can aggressive biohacking worsen autoimmune gastritis?Johnson's latest revelation about his health has left people curious about how someone so invested in his health can suffer this condition, which can only be managed, not resolved."While there is no evidence that biohacking directly causes autoimmune gastritis, extreme dietary restrictions, excessive supplementation, prolonged fasting, or unmonitored use of supplements may aggravate nutritional deficiencies or gastrointestinal symptoms. Any intensive health regimen should ideally be undertaken with medical supervision, especially in people with known autoimmune conditions," says Gastroenterologist Dr Rajdeep More.A healthy lifestyle overall also doesn't guarantee preventing autoimmune diseases. "Good nutrition, avoiding smoking, limiting alcohol, and regular medical follow-ups can only help manage the condition and reduce complications," adds the doctor.Bryan Johnson's health adviceThe absence of symptoms is not the presence of health, Johnson asserted."You too may have a lurking health issue that is undiagnosed and could increase in severity from unhealthy life choices, without your knowing. A gentle nudge that minding your health, no matter your situation in life, is good decision making," he added in his X post.