What is Intermittent Fasting?

Intermittent fasting refers to fasting for certain periods of time during the day or week. This could be true fasting (consuming nothing but water) or consuming significantly less energy (calories) than usual during the fasting periods.

There are three main types of fasting:

Types of fasting

Periodic fasting: fasting or eating a very low energy intake for up to 24 hours once or twice a week and eating according to your appetite on the other days. An example of this is the ‘5:2 diet’ where you fast for two days and eat your normal diet for the other five days each week.

Alternate day fasting: alternates fasting days (where you either completely fast or consume a very low energy diet) and feasting days, where you eat according to your appetite.

Time-restricted feeding: limits eating to a certain time period of the day. An example of this is the 16:8 diet where you restrict eating to 8 hours of the day and fast for the remaining 16 hours.

Many claims are made about the benefits of intermittent fasting but is it really the answer to good health and weight management?

What does the research say?

While intermittent fasting has been shown to result in weight loss and improvements in certain health markers, research to date doesn’t show that it is any more effective than continuous energy restriction (reducing your energy intake by a smaller amount on a daily basis).

In fact, several papers have been published, combining the findings of well-designed studies of intermittent fasting and all have concluded that intermittent fasting provides similar benefits for weight and metabolic risk factors (such as glucose and insulin levels, blood fats and blood pressure) to continuous energy restriction.

There are also very few longer-term studies looking at whether the benefits of intermittent fasting are sustained, and most studies have been in people without a chronic health problem so it’s not clear whether the same benefits would be seen in those with an existing health condition.

While you will be likely to see some weight loss and improvements in health markers with intermittent fasting, current research suggests you could achieve similar results by just eating a bit less each day.

However, if you decide you want to give intermittent fasting a go, it’s a good idea to speak with your doctor first, particularly if you have any existing health problems or take prescription medications. Fasting can affect the absorption of medications or increase their side effects. It’s also important to keep hydrated and not to fast when you are feeling unwell. And there are some people for whom fasting isn’t recommended, including pregnant and breastfeeding women, children under the age of 18 years, people with an eating disorder and those who are underweight.


Stockman MC1, Thomas D2, Burke J3, Apovian CM2. Intermittent Fasting: Is the Wait Worth the Weight? Curr Obes Rep. 2018 Jun;7(2):172-185.

Cioffi I1, Evangelista A2, Ponzo V3, Ciccone G2, Soldati L4, Santarpia L1, Contaldo F1, Pasanisi F1, Ghigo E3, Bo S5 Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med. 2018 Dec 24;16(1):371..

Harris L1, McGarty A1, Hutchison L2, Ells L3, Hankey C2. Short-term intermittent energy restriction interventions for weight management: a systematic review and meta-analysis. Obes Rev. 2018 Jan;19(1):1-13.

Headland M1, Clifton PM2, Carter S3, Keogh JB4.Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients. 2016 Jun 8;8(6).

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