Diet fads come and go. The latest diet promising weight loss is the 5:2 diet, also called the 'Fast diet'. In 2012, British GP-turned television journalist Michael Mosley was the human guinea pig in the BBC science series Horizon, on the subject of intermittent fasting. Intermittent fasting is an eating pattern in which a person eats minimally for a nominated period of time – eg, 16 to 48 hours – in between periods of normal food intake.
In the case of the 5:2 diet, a person has a regular balanced diet, without restricting calories, for five days of the week. For two other non-consecutive days, they must restrict their eating to one quarter of the usual intake. For a woman, this equates to about 500 calories, or about 2100 kilojoules a day. On the 5:2 diet, Mosley lost nine kilos and reversed the type 2 diabetes he had developed.
Jean Hailes for Women's Health has never been an advocate of dieting, instead good health," says Jean Hailes naturopath Sandra Villella. As research into nutrition continues, it's important that new information is taken into consideration. This means only taking it from reliable sources, deciding whether the advice suits your needs and if you can follow it long term.
Fasting is not new. Over the centuries, people have fasted – or abstained completely from eating and drinking – at certain times of the year due to religious or cultural practices. There is also a theory that our bodies are designed to fast. Throughout human history, our diets have varied across climates, seasons and geographical regions; we have grown used to feast and famine. Our bodies are also naturally made to fast at night, which is important to our circadian rhythms, which occur across a 24-hour light-dark cycle. This ensures our bodies work properly, giving us optimal sleep, gut health and weight control.
Whichever eating path you choose, your intake needs to be varied and include the core food groups of a balanced nutritous diet.
A recent review of scientific literature shows that intermittent fasting diets such as the 5:2 diet can result in weight loss. A review of scientific studies showed that 11 of the 13 trials reported weight loss ranging from 1% to 8% for individuals. However, only two studies found significant weight loss in those following some type of fasting plan. One study of adults who were normal weight, overweight and obese indicated that intermittent fasting is not physically or mentally (mood) harmful. Another study also suggested that intermittent fasting does not cause disordered eating, limit the ability to exercise or upset the menstrual cycle of women who are overweight or obese.
However, long-term safety from such issues among people of a normal weight isn't known. On a practical level, the 5:2 diet is believed to work well in terms of the 'psychological comfort' it provides people. This is because while the fasting day may be hard, knowing that the next day is a normal eating day can be reassuring, as opposed to a diet with ongoing calorie restriction. Also, the delayed gratification can make food more enjoyable and satisfying
Jean Hailes dietitian Stephanie Pirotta believes it is the "simplicity" of the 5:2 diet that makes it appealing for many people. "We are receptive to healthy-eating approaches that are easy to follow, help people to maintain a healthy body weight, and make people feel good," she says. "This regimen of intermittent fasting has become popular as a possible strategy for weight loss, metabolic health, disease management and prevention. If you're generally healthy and have a positive relationship with food, then it might be worth considering." Ms Pirotta stresses, however, that what is eaten should be varied and part of the core food groups of a balanced nutritious diet, keeping junk food and sugary drinks to a minimum.
One issue with the science behind the benefits of intermittent fasting is that the evidence is often drawn from animal studies. There is also little evidence to show that intermittent fasting is any more beneficial than a daily calorie restriction plan. Human trials investigating the 5:2 diet have only been small and for short periods of time. More valid and reliable studies with more people over longer periods of time are needed to conclusively show its efficacy.
Also, the 5:2 diet does not give any guidance on what types of food to eat (ie, vegetables, fruit, meat, etc), so there is a risk that the person's diet may not be balanced. It may also produce side effects such as fatigue, headaches, constipation and lowered mood. Ms Pirotta says although research to date at times may "point in the right direction", she would "always urge women to see professional advice" until there was more evidence to support the 5:2 diet. "Before embarking on an intermittent fasting diet, make sure you see an accredited practising dietitian or GP," she says. "Discuss your health needs and your lifestyle, and devise a plan that suits you. It may well be the 5:2 diet that is recommended, but make sure you check first."
One part of their health that women often do not consider when embarking on a fasting diet is their hormones. Jean Hailes endocrinologist Dr Sonia Davison says it is vital for women to understand their daily hormonal patterns and how diets affect the body. She says our circadian rhythms are also important in governing our hormones. "We really are designed to feed and be active during the day and then rest at night," Dr Davison says. "For example, not eating too much in the evening helps the body to function and undergo the necessary biological processes designed to keep us healthy. Eating plans such as the 5:2 diet can help us to avoid overeating in the evening and put more thought in to when we eat." Dr Davison says some of her patients had reported success with the 5:2 diet. Reported benefits included weight loss, improvements across patients' metabolic markers (eg, lowering cholesterol and insulin in the blood), improved sleep and energy levels
"Eating plans such as the 5:2 diet can help us to avoid overeating in the evening and put more thought in to when we eat." – Dr Sonia Davison, Jean Hailes endocrinologist
However, Dr Davison says the 5:2 diet will not suit everyone; she would not recommend it to pregnant women, or elderly or frail people prone to falls. She says some people with diabetes might also risk having low blood sugars with the fasting required, so would need "careful advice" from their health professionals. "People should work within a framework and ensure they have their 'safety barriers' in place," says Dr Davison. "If, for example, a woman undertakes a strict interpretation of the 5:2 diet and notices her periods have turned off, then this is a warning sign to review the eating plan. "It's about working out the best approach with your health professional. If the 5:2 enables you to lose weight, improve your health, and live your life to the fullest, then what's not to lose?"
Three things to know:
- Fasting is the practice of restricted eating.
- The 5:2 diet is one type of intermittent fasting diet, in which normal eating is interspersed with fasting.
- Studies show fasting might result in weight loss, but more long-term research is needed.