Every so often, a new diet comes along that captures the public's attention. And 2013 looks set to be the year of the 5:2 diet. Rather than restricting food on a daily basis, which is the traditional approach to dieting, 5:2 means you cut your kilojoule intake for just two, non-consecutive days a week - then eat normally the rest of the time.
On fasting days, men can eat around 2500 kilojoules and women 2100 kilojoules, around a quarter of the recommended daily kilojoule intake. There are no rules on what you can and can't eat - you just need to stick within the kilojoule limit.
For women, a sample fast-day menu is a breakfast of two eggs with 50 grams of smoked salmon and black coffee or tea (1000 kilojoules) and another meal of 120 grams of grilled chicken with steamed vegetables (1100 kilojoules). You're encouraged to drink plenty of water and green tea throughout the day, and men can add a slice of multi-grain bread and a handful of strawberries.
So does it work? A three-month trial led by research dietician Dr Michelle Harvie at the Genesis Breast Cancer Prevention Centre in Manchester, UK, found that women who ate 2720 kilojoules a day twice a week lost nearly twice the amount of weight of those on a daily low-kilojoule diet.
But the 5:2 diet is not just about weight loss. The same study showed the 5:2 women also reduced their risk of breast cancer by up to 40 per cent. Other studies have suggested intermittent bouts of fasting could lower your risk of heart disease, stroke, cancer and diabetes.
Research scientist Dr Mark Mattson at the US National Institute on Ageing in Baltimore believes it could also protect against degenerative diseases such as Parkinson's and Alzheimer's. In mice trials, Mattson found that fasting every other day increased the production of neurotrophic factors, including brain-derived neurotrophic factor (BDNF), thought to help protect human brains from Alzheimer's disease. Mattson is now planning a study looking at the effects of the 5:2 diet on 20 women who are at risk of developing dementia. "This pilot study would be the first to examine brain effects during 5:2 calorie restriction," Mattson says.
Meanwhile, Dr Leonie Heilbronn at the University of Adelaide's Discipline of Medicine is trying to find out if fasting for three non-consecutive days per week can help reduce the risk of diabetes and cardiovascular disease in humans. "The studies to date haven't really looked at the length of fast that's required or how often you need to do it," says Heilbronn. "But we're hoping to get to the point where, if we can prove it works for three days a week, can we show improvement at two days or even one day a week?"
Louise Jennings, 47, a nurse, has been on the 5:2 diet since September 2012. "I've lost three kilograms and dropped a dress size, but I'm mainly doing it for the health benefits," she says. "I had Hodgkin's lymphoma when I was 21, so I have an increased risk of developing breast cancer because of the radiotherapy treatment. Anything that puts my body into repair mode and could help prevent further cancers is worth trying. Drastically cutting kilojoules is hard. But I know the next day I can eat whatever I like and that makes it easy."
The intermittent fasting regime is hugely popular in Britain, thanks to a BBC documentary, 'Eat, Fast and Live Longer'. Medical journalist Dr Michael Mosley, who presented the BBC documentary, lost more than six kilograms after following the 5:2 regime for five weeks. His levels of insulin-like growth factor 1 (IGF-1), a risk factor for colorectal, prostate and breast cancer, also dropped by 50 per cent.
"People are probably most interested in weight loss, but I'm personally most interested in the other health benefits, particularly to do with the brain," Mosley says.
"The two real threats for health in the future are going to be diabetes and dementia, and both of those are significantly impacted by intermittent fasting."
Kellie Bilinski, spokesperson for the Dieticians Association of Australia and an accredited practising dietician, urges caution. "Some people say fasting can be a good thing, but I think most of the evidence is pointing to kilojoule restriction as opposed to fasting," she says. "In humans, the stronger evidence is if we restrict our kilojoules slightly [on a daily basis], that's what can be helpful with ageing, and obviously preventing weight gain."
Mosley acknowledges that it's early days for intermittent fasting and the 5:2 diet. "We're at the stage where there are quite a lot of questions and relatively few definite answers," Mosley says. "I feel like I'm right at the beginning of something that could be big or could not be. That's the great thing about science; you never quite know, as it takes a period of time to establish whether it's significant or not."
- Daily Life