Research shows fasting can change our biochemistry, reduce inflammation, protect metabolic, cardiovascular and neurological health, assist in managing autoimmune diseases, mental health, neurodegenerative diseases and digestive health, while significantly enhancing longevity.
But which type of fasting is the best?
READ: Could fasting work for you?
Types of fasting
The 5:2 Diet: Perhaps the most well known type of fasting is the 5:2 diet, which became popular after a BBC documentary featuring science reporter Michael Mosley detailed the benefits of intermittent fasting in 2012. This diet encourages people to fast for two days a week and eat normally for five days. During the fasting days, men are allowed to eat 600 calories (2,500 kJ) and women 500 calories (2,100 kJ). This model of fasting can lead to significant weight loss, decrease intra-peritoneal fat, and improve cardiovascular and metabolic biomarkers. While it gets fantastic results for some people, in others it can lead to overeating on non-fasting days, which seems to negate some of the benefits. It may also have an impact on socialising during the fasting days, so perhaps best suits people who have a predictable schedule.
Extended overnight fasting: This my favourite model of fasting and the one I use most in clinic for people who need to lose weight, lower inflammation, and rest their digestive system. It is ideal for people with insulin resistance and achieves great results within three months. This is a flexible model of fasting and works on a sliding time scale. In any one 24-hour period, people fast for 16 hours and can eat two nourishing, well balanced meals in the remaining eight hours. Usually people start their fast at 8pm and end it at noon the following day. This is ideal for busy people who usually eat on the run in the mornings anyway. Sadly the average Australian breakfast is high in carbohydrates and sugar and low in nutrients, so often missing out on this no great loss. Extended overnight fasting also promotes a mindful approach to food, as people are more likely to plan their two main meals in advance. It gets great results for weight loss without cutting out any of the main food groups. It is a user-friendly way of accessing the benefits of fasting.
Alternate day fasting: This more extreme version of intermittent fasting has been the subject of a number of studies. As the name suggests, people fast on alternate days, consuming only one small meal (around 25 percent of normal daily calories) on fast days. It gets great results for weight loss, and improves insulin sensitivity and a range of cardiovascular markers. It can be difficult to manage socially however, and you should consult you health practitioner for support while fasting.
Calorie restriction: While not strictly a fasting regime, this is worth mentioning here as it achieves similar benefits. Calorie restriction achieves good results in weight loss, while lowering cardiovascular disease and diabetes risk. This dietary intervention involves cutting back the total amount of calories consumed by between 20-50 percent each day. While this achieves good results in weight loss, it is very difficult to adhere to long-term and can lead to binge eating and rebound weight gain.
READ: Could fasting work for you?
Which type of fasting is best?
A recent review of the literature compared the efficacy of calorie restriction against intermittent fasting and alternate day fasting, and found that while calorie restriction achieved slightly better results in weight loss, losses in visceral fat, improvements in insulin sensitivity and decreases in total fasting insulin levels were comparable across the three groups.
While intermittent fasting is generally considered a safe therapeutic form of caloric restriction, prolonged fasting falls into a different category and should never be attempted without professional supervision. I never recommend prolonged fasting in practice, but I am mentioning it here so people understand the potential health risks. It has profound effects on the body’s physiology and is more likely to cause health complications.
The first couple of days of fasting triggers the rapid mobilisation of glycogen stores from our muscles and liver. Between days two and seven of a prolonged fast we start to burn fat stores as a fuel; however, after that the body will start to catabolise protein from our muscle as fuel, which can lead to significant problems.
Prolonged fasting may also affect hormonal balance in some women and can cause disruption to the menstrual cycle and negatively impact fertility. Pregnant and breastfeeding women and children should never fast.