So let’s start with what it is…
There are loads of versions of IF all over the internet, but according to the journal of the Academy of Nutrition and Dietetics association (1), they can be grouped into 3 main methods:
Alternate day fasting – As the name suggests, this involves consuming no food or drink every other day, and eating a regular diet on the alternate days.
Modified fasting – This method is the basis of the 5:2 diet and allows you to consume around 20-25% of your calorie requirements on the planned fasting days, which occur 2 days per week. On the other 5 days you eat a normal balanced diet.
Time restricted fasting – This allows you to consume a regular diet but within a specific time period, usually of 8 hours. For example, if you consume your first meal at 10am you wouldn’t eat any more meals after 6pm. So would have a fasting period of around 16 hours. This appears to be the most popular method of IF and many people choose to skip breakfast in order to eat their meals later in the day.
The big question…does it work?
In a review of 13 studies (1) of healthy, overweight and obese participants it was found that most methods of intermittent fasting resulted in weight loss for the individuals. The main source of energy for the body is carbohydrate, but after a few hours of fasting, the body’s carbohydrate stores have been depleted and it will start to burn fat instead. It has been suggested that a period of fasting encourages the body to use fat as its main energy source, which can ultimately lead to weight loss.
BUT it was noted that these IF studies were all conducted over a short period of time and more research is required to determine the long term effects of following an IF diet. I wouldn’t recommend trying to follow an alternate day fasting diet for a long period of time, as there is no research to show the impact that intense hunger on fasting days has on the body.
It is a well-known fact that a good night’s sleep leads to a healthier diet and lower calorie consumption, when compared with a poor night’s sleep. Therefore it is suggested that time restricted fasting can have a positive impact on your sleeping pattern and quality of sleep. Although research is limited, some studies have suggested that restricting yourself to a period of 16-20 hours without food allows the body’s natural hormonal cycles and physiological processes to operate undisturbed, resulting in a better biological rhythm (2) .
Reduced Disease Risk
In studies conducted on rats, intermittent fasting has consistently promoted a reduced risk of developing cardiovascular disease, diabetes and Alzheimer’s (3). It has been suggested that these periods of IF encourage certain molecular processes which help to improve health.
BUT more research needs to be done to determine if the same positive effects can be reproduced in humans.
There is research to suggest that intermittent fasting can counteract certain disease processes, but more research is needed in order to ensure the positive effects in rats can be mimicked in humans. IF could also be a useful tool to improve sleep and aid weight loss when used alongside regular exercise and smart food choices.
However, if you have ever suffered from an eating disorder, are pregnant, have diabetes or a metabolic disorder I would highly recommend that you do not try this diet. For anyone else thinking of giving it a go, take it steady and introduce fasting periods gradually to allow your body time to adjust. As always, if you are thinking of making big changes to your diet, always have a chat with your GP first.
Intermittent Fasting and Human Metabolic Heath
- Ruth E. Patterson PhD,1,2
- Gail A. Laughlin, PhD,1,2
- Dorothy D. Sears, PhD,1,3
- Andrea Z. LaCroix, PhD,1,2
- Catherine Marinac, BA,1,4
- Linda C. Gallo, PhD,5
- Sheri J. Hartman, PhD,1,2
- Loki Natarajan, PhD,1,2
- Carolyn M. Senger, MD,1,2
- María Elena Martínez, PhD,1,2
- Adriana Villaseñor, PhD1,2
- J Acad Nutr Diet. 2015 Aug; 115(8): 1203–1212.
Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet.
- Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JA, Ellisman MH, Panda S
- Cell Metab. 2012 Jun 6; 15(6):848-60
Impact of intermittent fasting on health and disease processes
Ageing Research Reviews
Volume 39, October 2017, Pages 46-58