An American who has eaten nothing but potatoes for the last two months ended his challenge yesterday (1 December) – after losing a stone and a half in weight.

Chris Voigt, head of the Washington State Potato Commission, started the extraordinary diet on 1 October to counter claims that potatoes were unhealthy.

Since then he has only eaten potato products, ranging from jackets to gnocchis and McDonald’s chips, but he did slip up once when he accidentally licked his finger while making his sons a peanut butter sandwich.

Mr Voigt claimed he lost 21lbs, lowered his cholesterol level by 60 points and reduced his blood-sugar level – a cause of diabetes – too. The family food budget was also lowered as he fed himself for just £9.40 a week.

“Physically I feel great,” said Mr Voigt, who weighed 14 stone at the start of his diet.

“I sleep well at night and have lots of energy and there have been no side effects. I am not encouraging anyone to go on my crazy diet and neither would my doctor.

“But many people regard potatoes as unhealthy and I was determined to prove that there is a lot of nutrition in potatoes.”

Food and health experts raised concerns about a potato-only diet because it did not include important vitamins like C, A and K, calcium and omega three.

Mr Voigt was planning his first decent meal in months – a belated Thanksgiving turkey supper – complete with roast potatoes.