For some, fasting has delivered unexpected benefits - including being more focussed. Photo: Getty
For three weeks this year scientist Dr Amanda Salis went from sunrise to sundown each day without eating a thing. After a 5am breakfast - fruit salad, nuts and wholegrain bread - she went to work knowing that for the next 12 hours nothing would pass her lips.
She was doing what millions of Muslims around the globe do each year – fasting during Ramadan. But for her it wasn't about religious observance. Instead, Salis, from the University of Sydney's Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders, wanted to learn more about how partial fasting affected metabolism and weight.
"I think the fasting approach has potential and we should find out more."
Fasting, as if you hadn't noticed, is the hottest thing in weight loss since the Dukan Diet got the credit for Kate Middleton's waistline. This current trend is for intermittent fasting – an on- again- off-again approach with periods of normal eating punctuated by periods of food restriction. With Michael Mosely's The Fast Diet, for instance, you eat normally for five days of the week and on the other two days you eat much less: just 2000 to 2400 kilojoules - roughly two California rolls, a large cappuccino and a banana. Some studies suggest weight loss is only one advantage of intermittent fasting and that it may improve blood sugar control and help prevent heart disease too.
Salis, author of The Don't Go Hungry Diet, is one of the last people you'd expect to give fasting a go. As someone who once struggled with obesity, she knows that food restriction can trigger overeating. Yet along with a two kilo weight loss, her fasting experience delivered unexpected benefits - including being more focussed.
"I had headaches, I felt lightheaded and found it hard to concentrate but after a few days I got used to it," she says. "I knew I was working with limited reserves so I changed the way I worked – instead of doing three things at once like I usually do, I focussed on one thing at a time and I was no less productive. If anything I was more productive and I didn't allow myself to get wound up about things that sap my energy."
She also realised how often she used lattes and snacks through the day – not necessarily as fuel but as a 'crutch' to get through difficult tasks.
"It was liberating to know I could get through the hurdles of work without them. But what I really loved was how much I appreciated the taste of simple food at the end of the day," she says. "I didn't eat any more at dinner than I usually would either although sometimes I'd have a slice of toast and peanut butter later."
Another concern about food restriction is that it can hinder weight loss by slowing down the metabolic rate causing the body to burn kilojoules more slowly. Salis's fast was part of a small study with 13 other fasters and although the results aren't finalised, early findings suggest that partial fasting through the day doesn't slow the metabolic rate.
"I think the fasting approach has potential and we should find out more," she says.
But although Salis believes intermittent fasting may be a sustainable weight management approach for some people, it's not for everyone.
"For someone with an eating disorder like anorexia, bulimia or compulsive eating, it's probably best to avoid it. I'd also suggest people see their doctor before fasting – if you don't have good liver and kidney function it can leave you open to problems."
She also recommends trying to maintain a daily protein intake of at least 0.8 gram of protein per kilo of body weight – this prevents muscle loss which can slow metabolism down – and to fast with other people.
"This motivates you to stick with it. I fasted with my husband – I think if I'd tried to do it alone, I would have spent my mornings fasting and my afternoons eating to make up for it. "
What do you think of intermittent fasting?