A new fad weight-loss diet might actually encourage the onset of type 2 diabetes, new research has found.
The 5:2 Diet, also known as the 'Fast Diet', encourages people to almost starve themselves two days a week, whilst eating normally the other five. Its celebrity fans reportedly include Benedict Cumberbatch, Miranda Kerr and Jimmy Kimmel.
On fasting days, you're meant to limit yourself to 500 to 600 calories (2000-2500kj).
But while trimming down would normally reduce body fat and the risk of type 2 diabetes, researchers at the University of Sao Paulo in Brazil are saying not so fast to the Fast Diet.
"Recently, intermittent fasting diets have gained general popularity for weight loss, however evidence on their success has been contradictory and there is a lack of knowledge and some debate on their potentially harmful long-term health effects," said lead researcher Ana Bonassa.
"Previous research has also shown that short-term fasting can produce molecules called free radicals, which are highly reactive chemicals that can cause damage to the body at a cellular and may be associated with impaired organ function, cancer risk and accelerated aging."
And that's exactly what they found when they put mice on the rodent equivalent of a 5:2 Diet for three months.
Although their body weight decreased as expected, they grew more belly fat, their pancreas showed insulin damage and there were increased levels of free radicals.
"This is the first study to show that, despite weight loss, intermittent fasting diets may actually damage the pancreas and affect insulin function in normal healthy individuals, which could lead to diabetes and serious health issues," said lead researcher Ana Bonassa.
So while overweight people might experience a rapid and desirable weight loss, they might ironically actually be increasing their chances of type 2 diabetes.
Michael Mosley, the British broadcaster widely credited with popularising the diet, slammed the research in an opinion piece for the Mail on Sunday. He said the diet the rats were on was "extreme" and the results contradicted "so many other animal and human studies of intermittent fasting".
"It flies in the face of everything research into fasting diet has proven over the years."
The research is yet to be published, but was presented over the weekend at the European Congress of Endocrinology.