A popular new diet in which enthusiasts eat normally for five days and fast for two days needs to researched more before it can be declared safe, according to one of Ireland's leading nutritionists.
The 5:2 Diet recommends you eat just 500 or 600 calories on "fasting days", and eat normally for the rest of the week, or "feeding days" as they are known.
This regime began to draw public attention in August 2012 through the documentary 'Horizon' presented by British physician and journalist Dr Michael Mosley, but the diet lacks substantial medical evidence to establish it as a safe, healthy weight-loss method.
"It's the next big thing," said Dr Muireann Cullen, manager of the Nutrition and Health Foundation. "We've had Atkins Diet, the Maple Syrup Diet and the Cabbage Soup Diet. While it does look promising, more research needs to be done."
Claimed benefits include a longer life expectancy, weight loss, lower cholesterol and glucose levels, and protection against Alzheimer's disease.
However, Dr Cullen cautions: "Much of the research for the diet has been based on animal trials rather than clinical studies on humans. The effect of the diet on degenerative diseases has not been proven at this moment in time. But it will be interesting to see future research in the area."
The popularity of the diet has resulted in a number of best-selling books in Ireland but it poses many concerns for nutritionists.
Reducing the intake of micronutrients such as iron or calcium could present problems for those already low on these vital nutrients.
"Most Irish adults have an insufficient calcium intake with 1 in 2 women and 1 in 5 men expected to develop osteoporosis in their lifetime. Furthermore, reducing iron intake could present a problem for women as iron levels already decrease during menstruation," said Dr Cullen.
"Some people following the 5:2 diet report feeling irritable, losing concentration and lacking energy.
"Even though you are on a diet, it is still necessary to exercise. If you don't have the energy to exercise then that's a problem."
She finds many dieters following the 5:2 pattern tend not only to overeat on the days they are not fasting, but also find sustaining the diet extremely difficult.
Dr Cullen advised that if a person wishes to lose weight to focus on "tried and tested methods" rather than fad diets. She recommends the use of the food pyramid as a guide and a simple four-point plan:
- Get adequate exercise.
- Pay attention to portion sizes.
- Watch the frequency of your meals.
- Look at how you cook your foods.