What is Intermittent Fasting (IF)?

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What is Intermittent Fasting (IF)?

Intermittent fasting is a popular diet that has garnered more than 210,000 searches in just October 2016 with numerous researches and studies. So, what exactly is it?

Different Types of Energy Restrictions

There are two different energy restrictions: Intermittent Energy Restriction (IER) and Continuous Energy Restriction (CER). Intermittent Energy Restriction (IER) involve restricting energy intake during a pre-determined amount of time and eating ad libitum (to satisfy appetite) vs. Continuous Energy Restriction (CER) which restricts energy intake for an extended time with no breaks at every meal. Intermittent fasting is considered as IER, whereas CER is cutting down calories per meal and having smaller portions or ditching certain unhealthy food groups.

Different Intermittent Methods

A quick breakdown of different intermittent (IF) methods:

- The 16/8 method: Also known as Leangains protocol. Restricts daily eating period to 8 hours, such as noon to 8pm followed by 16 hours fast.

- Alternate Day fast (ADF): Fasting for full 24 hours for once or twice a week. An example could be eating a dinner on Saturday night and fast until Sunday’s dinner.

- The 5:2 diet: Consuming only 500-600 calories on two days of the week but eat normally on the other days.

Benefits of Intermittent Fasting

So what are the benefits of IF? We will examine them in the following: Effects on physical activities/hormonal concentrations, glucose homeostasis/glycemic control, and impact of exercise.

Impact of exercise: In conjunction with exercising, subjects lost around 6kg and 2 units of BMI after an 12 weeks trial (Bhutani et al., 2013).

Glucose homeostasis/glycemic control: A high level of glucose in the blood is a primary symptom of diabetes, which is one of the most abundant degenerative disease in the current world. A lower point of glucose homeostasis will equal a lower glucose level in blood. After an 8 weeks trial, subjects shown a decrease in total cholesterol, LDL-C, triglyceride concentrations and total free fatty acid (FFA) concentrations (Varady et al. 2015, Bhutani et al. 2013).

Weight Loss: With the subjects on only IF without any exercise, the results were still positive. Subjects lost on average 4.6 kg, and 1.5% body fat after an 12 weeks trial (Ash et al. 2003).

Is intermittent fasting the best diet? Well no. Compared to CER, the results were mainly similar with no significant variations (Seimon et al. 2015). However, any type of caloric deficit will lead you one step closer to your goal. There is not such thing as the best diet for everyone but there is the best diet just for you.


Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., ... & Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and cellular endocrinology, 418, 153-172.

Ash, S., Reeves, M. M., Yeo, S., Morrison, G., Carey, D., & Capra, S. (2003). Effect of intensive dietetic interventions on weight and glycaemic control in overweight men with Type II diabetes: a randomised trial. International journal of obesity, 27(7), 797-802.

Varady, K. A., Dam, V. T., Klempel, M. C., Horne, M., Cruz, R., Kroeger, C. M., & Santosa, S. (2015). Effects of weight loss via high fat vs. low fat alternate day fasting diets on free fatty acid profiles. Scientific reports, 5, 7561.

Bhutani, S., Klempel, M. C., Kroeger, C. M., Trepanowski, J. F., & Varady, K. A. (2013). Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity, 21(7), 1370-1379.

Patterson, R. E., & Sears, D. D. (2017). Metabolic effects of intermittent fasting. Annual review of nutrition, 37.