A German scientist is being studied by colleagues after claiming to have eaten nothing for four years.
Cancer researcher Dr Michael Werner claims to get all his energy from sunlight.
He says he drinks only water mixed with a small amount of fruit juice.
Dr Werner has written a book about his experiences, saying that when he started the experiment he even managed to put on weight.
In his book, Living through the Energy of Light, he says: "I can't really explain what is happening on a scientific level in my case, but perhaps just a little bit of faith is all that is needed."
German colleagues who are investigating the source of Dr Werner's energy say only plants can synthesise energy from the sun, but so far they are at a loss to explain how he is managing to stay healthy.
Dr Helmut Oberritter, head of the German society for nutrition, said: "It is not possible to live on what one gets from fruit juice alone.
"There are lots of vital proteins and fats that are missing. Obviously this case needs a lot more investigating if we are to explain it."
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