A Seattle woman is aiming to go 100 days without eating to prove that humans can "live on light".
Naveena Shine says she believes it is possible for humans to survive without food and is conducting what she describes as an experiment to prove it.
The 65-year-old, originally from Britain, has been consuming just water and "one, maybe two cups of tea a day" since May 3. Other people have previously claimed to be able to survive without food and water, although no one has ever proven it to be possible and some have died attempting it.
Dr Ronald Hoffman, medical director of the Hoffman Centre and host of a weekly health talk podcast, said it was "delusional to think that you can escape the laws of biology".
"Plants have what are called choroplasts that contain chlorophyll and they have the ability to capture energy from sunlight," Hoffman said. "Humans don't have cholorphyll or chloroplasts. No humans do. It is impossible for a human to have that."
Hoffman said if Shine continued to not eat food her organs would eventually fail and she would die.
Shine contends that "a doctor can't see living on light because he looks through different lenses" and has said she is not undergoing medical tests during the experiment.
She said she had experienced a "calling" that inspired her to stop eating. "It came as an idea that became so powerful, I knew I had to do it," Shine said. She had heard of others who claimed to be able to forgo conventional nutrition, including a friend who claimed to have survived without food for three years.
Shine is not doing any special exercises or performing other procedures in order to "live on light" - a process she describes as "not necessarily literal".
In 2003, American illusionist David Blaine survived 44 days in a glass box without food, while last year a Swedish man claimed to have survived two months in his car eating just handfuls of snow. While experts believe it is possible to survive for up to two months without food, should Shine survive for 100 days her feat would be unprecedented.
While Shine says her inspiration to eschew food does not come from a particular set of beliefs, her website praises Jasmuheen, an Australian woman who describes herself as an "ambassador of peace" and "international lecturer", and whose teachings that it is possible to subsist on light alone have been linked to the deaths of four people.
Jasmuheen claims to have lived for years on light alone, but tried and failed to go without food and water for 10 days in an experiment for Australian television programme 60 Minutes in 1999. A network doctor noted that after 48 hours Jasmuheen displayed symptoms of dehydration, stress and high blood pressure.
So far Shine has lost 14kg, although in a post on Facebook she said her weight has been holding at 58kg.
In video updates posted to Facebook and her website, Shine has reported feeling light-headed when bending down and when getting up from a seated position. She said she had a couple of days where she threw up bile, but otherwise was in good condition.
She said she had started adding "a package of EmergenC" into her water, which she said had no nutritional value, although the website of the supplement shows that a typical package does contain 25 calories and a number of vitamins and minerals.
The tone of her Facebook updates has changed as time has elapsed, with it appearing last week that Shine would not put herself at risk if she continued to deteriorate. On Monday she wrote that she would not drop down below 54kg; suggesting an end to her attempt might be in sight.