LOS ANGELES, United States — Bryan Johnson, the longevity entrepreneur widely known as the “World’s Healthiest Man,” has disclosed that he has autoimmune gastritis, a chronic disease in which the immune system damages vital cells in the stomach.
Johnson, 48, has built an international following by documenting an intensive programme designed to slow ageing and extend his lifespan.
His routines include tightly controlled meals, frequent medical tests, supplements, exercise and experimental health interventions.
But years of monitoring failed to immediately explain one persistent abnormality: his body was struggling to maintain adequate stores of iron.
“I have an autoimmune disease. My stomach is eating itself,” Johnson wrote on X on Tuesday, June 30, 2026.
The stomach is not literally consuming itself.
Johnson was describing an immune response that attacks acid-producing cells in the stomach lining, gradually interfering with the organ’s ability to support the absorption of iron and vitamin B12.
Johnson responded to the diagnosis in the language that has defined his public campaign against ageing.
“I’m going to try and solve it,” he wrote.
Years of Low Iron Led to the Diagnosis
Johnson said his doctors had repeatedly found low levels of ferritin, a protein that reflects how much iron the body has stored.
His haemoglobin and haematocrit levels remained within normal ranges, meaning he had not developed the blood-test pattern typically used to diagnose anaemia.
That made the abnormal ferritin easier to treat as an isolated finding rather than evidence of an underlying stomach disorder.
Johnson was eventually diagnosed after an upper gastrointestinal examination and stomach biopsies. He said the diagnosis was made in May following years of unexplained low ferritin.
Autoimmune gastritis can progress quietly because its first signs may appear outside the digestive system.
Some patients experience tiredness, weakness or neurological symptoms rather than stomach pain.
The disease is therefore frequently discovered through investigations of iron deficiency, vitamin B12 deficiency or pernicious anaemia.
Autoimmune gastritis “is notoriously insidious and frequently remains silent for decades, with symptoms often presenting outside of the gastrointestinal tract as fatigue, weakness, or neurological issues,” Mimi Chang Tan, an assistant professor of gastroenterology at Baylor College of Medicine, said.
The condition is often missed during routine care. Even an upper endoscopy may not reveal an obvious problem unless doctors take tissue samples from the appropriate parts of the stomach.
“I think gastroenterologists should really be sampling more ‘normal’-appearing stomachs in patients with a history of iron deficiency that’s been treated,” Toby Cornish, a gastrointestinal pathologist and professor at the Medical College of Wisconsin, said, “because many of those patients will actually turn out to have autoimmune gastritis.”
How the Disease Damages the Stomach
In autoimmune gastritis, the body mistakenly targets parietal cells, which are found mainly in the upper and central regions of the stomach.
These cells produce hydrochloric acid, which helps the body release and absorb nutrients from food. They also produce intrinsic factor, a protein required for vitamin B12 absorption.
As the cells are destroyed, stomach-acid production declines. The body may first struggle to absorb iron, causing ferritin levels to fall. Vitamin B12 deficiency can emerge later as the supply of intrinsic factor becomes inadequate.
Untreated vitamin B12 deficiency can lead to anaemia and neurological complications, including numbness, weakness and nerve damage. Medical reviews describe iron deficiency as an early presentation that can precede pernicious anaemia.
The illness does not necessarily produce symptoms at every stage. Some people may have significant tissue damage before recognising that anything is wrong.
Diagnosis usually draws on blood tests, antibody testing and an upper endoscopy with biopsies. Medical guidelines advise clinicians to evaluate patients with atrophic gastritis for both iron and vitamin B12 deficiencies.
The estimated prevalence remains uncertain because diagnostic practices differ and many cases may never be identified. A 2024 clinical review placed estimates in the general population between 0.3 and 2.7 per cent.
Johnson’s Explanation Remains Speculative
Johnson has looked to his personal history for a possible explanation.
He has recalled eating fast food, sugary cereals and soft drinks as a child.
As an adult, he has described periods of stress, depression and weight gain before beginning the highly controlled lifestyle that became his Blueprint programme.
Johnson has raised the possibility that those earlier experiences contributed to his illness.
There is no established evidence connecting a childhood diet of processed foods or a later period of weight gain directly to autoimmune gastritis.
“I would call that highly speculative,” Cornish said.
Scientists have not identified a single cause. The disease is believed to involve immune dysfunction, genetic susceptibility and possible environmental triggers.
Autoimmune gastritis is also associated with other autoimmune illnesses, particularly autoimmune thyroid disease. Johnson has said he was previously diagnosed with an autoimmune thyroid condition.
The presence of both conditions does not establish that one caused the other. It does, however, fit a recognised pattern in which people with one autoimmune disorder face an increased likelihood of developing another.
Long-Term Risks Require Medical Surveillance
Autoimmune gastritis is not ordinarily considered an immediately fatal illness. Its consequences can nevertheless become serious when the disease is undiagnosed or poorly monitored.
Beyond iron and vitamin B12 deficiencies, the damaged stomach lining can create a higher risk of type 1 gastric neuroendocrine tumours.
The loss of acid-producing cells causes the body to release more gastrin, a hormone intended to stimulate acid production.
Because the damaged cells cannot respond normally, gastrin levels may remain high and encourage abnormal growth in other stomach cells.
Patients may also face an increased risk of gastric adenocarcinoma, although studies have produced differing estimates of that risk and researchers continue to examine the role of other factors, including previous Helicobacter pylori infection.
The disease is therefore managed through regular medical assessment, replacement of missing nutrients and endoscopic surveillance intended to identify abnormal growths early.
Small neuroendocrine tumours can sometimes be removed during an endoscopy when they are found before they grow or spread.
No Established Treatment Reverses the Damage
Current treatment does not ordinarily restore the stomach cells already destroyed by the immune system.
Doctors instead address the disease’s consequences. Patients may receive oral or intravenous iron and vitamin B12 supplementation. They may also undergo periodic endoscopies to monitor the stomach lining.
“We don’t really have good treatments for it,” Cornish said.
Johnson has presented conventional management as inadequate because it replaces nutrients and watches for complications without curing the underlying immune disorder.
His team is considering experimental interventions, including chimeric antigen receptor T-cell therapy, commonly called CAR-T.
CAR-T modifies a patient’s immune cells and has been used primarily to treat certain blood cancers. Researchers are also investigating whether it could help people with severe autoimmune diseases by targeting immune cells responsible for damaging antibodies.
The therapy has not been adequately studied as a treatment for autoimmune gastritis.
“It’s probably the best line of investigation for finding a cure in autoimmune gastritis. However, it’s still very early,” Cornish said.
He added: “It’s encouraging to know that people are exploring CAR-T for this because, honestly, there’s not a lot you can do to help these patients.”
CAR-T can carry substantial medical risks and is not an approved routine treatment for autoimmune gastritis.
Johnson’s interest in the therapy does not demonstrate that it will be safe or effective for his condition.
A Disease That Escaped Extreme Health Monitoring
Johnson’s diagnosis has attracted attention partly because it appears to contradict the image around which he has built his public life.
The technology multimillionaire has described himself as one of the most closely measured people in the world.
His Blueprint company sells supplements and other products connected to longevity, while his Don’t Die movement promotes the pursuit of longer life as a guiding philosophy.
He has spent heavily on physicians, testing and procedures intended to measure and improve the condition of his organs.
His more controversial experiments have included receiving blood plasma from his teenage son.
Yet autoimmune gastritis advanced without producing an early, definitive diagnosis.
Jennifer Dowd, a professor of demography and population health at the University of Oxford, said Johnson’s experience demonstrated that health optimisation has limits.
“You really can’t biohack your way completely out of disease or death,” she said.
Johnson also acknowledged that he was overdue for a routine colonoscopy despite the scale of his health programme.
United States preventive guidelines generally recommend colorectal cancer screening for adults beginning at 45.
A colonoscopy examines the large intestine and does not diagnose autoimmune gastritis. But the admission reinforced a broader point: extraordinary medical monitoring does not eliminate the possibility of missed routine screening or diseases that require particular diagnostic procedures.
For Johnson, finally identifying the illness was preferable to continuing without an explanation for his low iron levels.
“You want to know if there is a problem with your body,” he wrote. “Ignoring it doesn’t make it better. Delay just makes it harder, costlier, and riskier.”
