'My stomach is eating itself': Biohacker Bryan Johnson reveals he has autoimmune disease

American tech entrepreneur Bryan Johnson, who is known for spending around US$2 million (S$2.7 million) a year on longevity treatments, has revealed that he has been diagnosed with autoimmune gastritis (AIG), saying that "my stomach is eating itself."

The 48-year-old, who has publicly said he hopes to live until the year 2140, shared the diagnosis in an Instagram post on Thursday (Jul 2), revealing that he discovered the condition in May after months of medical tests to investigate the cause of his iron deficiency.

Johnson has gained international attention in recent years for his extreme anti-ageing regimen, which includes maintaining a strict daily routine, undergoing regular medical testing and working with a team of more than 30 doctors. He has also previously undergone plasma exchange with his son and explored experimental gene therapies as part of his longevity project.

Reflecting on his health, Johnson wrote on Instagram that growing up he "ate sugar cereal, drank sugary soda and gobbled down fast food", before becoming "a father of three and began building a business".

"Juggling the stress and grind, I let my health slip and gained 40 lbs (18kg) ... I'd fallen into a deep chronic depression," he wrote.

"Somewhere in that timeline, my body began developing an autoimmune process affecting my thyroid and then my stomach lining. It's called AIG."

According to the Global Autoimmune Institute, autoimmune gastritis is a chronic autoimmune disease in which the body's immune system attacks the stomach lining. The condition can lead to deficiencies in nutrients such as iron and Vitamin B12, and is associated with an increased risk of gastric cancer if left untreated.

The institute estimates that autoimmune gastritis affects between 0.5 and 4.5 per cent of adults worldwide, though Johnson said it affects 2 to 5 per cent. The Global Autoimmune Institute also notes that early symptoms are often non-specific, including abdominal pain, bloating and heartburn, and the condition may be overlooked.