Diary of a CEO host Steven Bartlett has been criticised by health experts for amplifying harmful health misinformation on his No 1-ranked podcast, potentially putting cancer patients at risk.

The Dragons’ Den star is facing questions after guests on the podcast put forward unfounded healths claims, for example that cancer can be treated by following a keto diet.

Health experts warned that the assertions could have serious consequences for people who were severely ill and discouraged listeners from following some of the advice.

On Friday, an investigation by the BBC World Service found that guests were faced with little or no challenge. Experts told the BBC that failing to question these disproven claims was dangerous because it created a distrust of conventional medicine.

In an analysis of 15 health-related podcast episodes, the broadcaster found each contained an average of 14 harmful health claims that went against extensive scientific evidence.

However, Flight Studio, the podcast production company owned by Bartlett, said guests were offered “freedom of expression” and were “thoroughly researched”.

The podcast, launched in 2017, has 7 million subscribers. Last year, its monthly views increased from 9 million to 15 million.

In the eight-month window analysed by the BBC, some guests billed as health experts shared misleading claims including anti-vaccine conspiracies, stating that Covid was an engineered weapon, that poly-cystic ovarian syndrome, autism and other disorders could be “reversed” with diet and that evidence-based medication is “toxic” for patients, downplaying the success of proven treatments.

Heidi Larson, an expert in public confidence in healthcare, told the BBC: “They [the guests] are way overstretching. It sends people away from evidence-based medicine. They stop doing things that might have some side effects, even though it could save their life.”

In an episode in October, Dr Thomas Seyfried told Bartlett that the treatment of cancer could be helped by following a keto diet, the BBC said. He compared modern cancer treatments to “medieval cures”.

In another podcast episode in July, doctor Aseem Malhotra said the “Covid vaccine was a net negative for society.”

A spokesperson for Flight Studio maintained that each guest episode was thoroughly researched prior to commission.

“DOAC offers guests freedom of expression and believes that progress, growth and learning comes from hearing a range of voices, not just those Steven and the DOAC team necessarily agree with,” they added.

They said the BBC had looked at only 15 episodes of nearly 400 published to date.

“For any reporting to focus on less than 4% of episodes with an extremely limited proportion of guests – some of whom have featured on the BBC – to create a broader, and in our opinion, partial narrative is disappointing, misleading and frankly, disingenuous,” they added.

In August, two nutrition adverts on Facebook for diet app Zoe and food replacement supplement Huel that featured endorsements by Bartlett were banned by the advertising watchdog for being “misleading”.

Bartlett praised the products in three sponsored posts shared on Facebook in February and March. However, the Advertising Standards Authority (ASA) claimed that the adverts were misleading as they did not make it clear that Bartlett was an investor in Zoe and a director of Huel.