Bryan Johnson promises his followers eternal life – or as close as you can get to it for a few hundred dollars a month.

The former SIlicon Valley mogul has declared himself “at war with death” and drawn international fascination for his spartan lifestyle, which his medical team claims has reversed his age by five years.

After reinventing himself as a wellness guru he founded the health company Blueprint, through which he sells supplements for fans to recreate his diet.

But now the multimillionaire is under pressure for reportedly making staff sign sprawling non-disclosure agreements (NDAs) and other legal documents, including one where employees had to agree that he would wear “little and sometimes no clothing”.

The controversy, first reported in The New York Times, is embarrassing for a man who has maintained an iron grip on his public image in the same way that he holds tight to his ascetic lifestyle despite being worth an estimated $200million (£155million).