Fasting diet popular but is it really safe

A new "fast diet" is gaining popularity in the Bay with Tauranga dieters praising its effectiveness in shedding kilos.

But Bay medical experts warn that intermittent fasting fosters unhealthy eating patterns and, for some, could lead to eating disorders.

The Fast Diet Recipe Book will be launched in the Bay on Monday, with the original book The Fast Diet, in the top 10 books of all sold in New Zealand last week.

The 5:2 diet or "Fast Diet" is spreading via word of mouth, said one fan, local teacher Rawia Cotterill.

The diet's premise was to eat normally for five days a week and then on two non-consecutive days limit calorie intake to as low as 500 calories.

The co-author of The Fast Diet, Michael Mosley said this would not only lead to weight loss but health benefits, including improvements in cholesterol, blood pressure and insulin sensitivity.

Since starting the diet five weeks ago, Cotterill has lost almost 2.5kg.

Angela Frieswyk, a Tauranga clinical nutritionist, was sceptical.

"As there is no long-term research ... the jury is out ... I have to reserve judgment about the proposed metabolic benefits."

Frieswyk noted the reported side effects.

"... headaches, dizziness, lethargy, bowel changes, moodiness and hunger. No surprises there."

Ohauiti psychotherapist and eating specialist Jane Cook said the diet's appeal, with its feast-famine cycle could lead to eating disorders.

Cook's standpoint was not just professional. She had a 15-20 year experience of anorexia.

"The fasting diet then raises the possibility of the social-medical focus on treating one eating disorder (obesity) increasing the possibility of occurrence of other eating disorders ... This was my adolescent experience."

Ms Frieswyk acknowledged the diet can achieve results - but questions the longevity.

"This diet may work in the short term, just as any other calorie restriction diet would work. The question is, will people keep the diet up?"