Intermittent Fasting
Intermittent Fasting (IF)
Brief description
Involves an eating pattern where no food is consumed within dedicated periods of time. It has been found to more closely mimic human eating patterns.
How to perform
Example of approaches to intermittent fasting:
Alternate day – every 24 hours no food is consumed. Water can be taken on fasted days.
5:2 – 2 days per week involve a very low-calorie diet.
Time restricted feed – e.g 16/8 (16 hr fast, 8 hr eating window)
B2 Regimen – 2 large meals/day (usually 14 hour fast)
Weekly 1 day fasting – water-only diet 1 day per week, then regular eating on the other days.
Evidence base
In 27 trials (944 participants), IF resulted in weight loss (ranging from 0.8% - 13%).
The practical length of a fast to effect changes in body weight appeared to be 16 hours. Exercise doubled weight loss in some trials.
IF appeared to improve levels of blood glucose and Hba1c in diabetic participants(1).
Why does it work?
IF plays on the concept of ‘metabolic switching’ where the body switches from using glucose as an energy source (in the feeding state) to fatty acids from triglycerides in adipose/fat tissue (in the fasted state).
Insulin is the main driving hormone in the feeding state, delivering glucose into the cells for energy use. In the fasted state, glucagon is released causing the breakdown of liver stored glycogen for energy.
The ‘metabolic switch’ is initiated when the liver has depleted its stores of glycogen and has to then rely on ketone formation.
This usually occurs after 12 hours.
Production of fatty acids (via triglyceride oxidation) and subsequent ketones, stops the process of cholesterol production and fat storage (as this energy is required for the body). This process also preserves muscle mass and function(2).
References
Welton S, Minty R, O'Driscoll T, Willms H, Poirier D, Madden S, et al. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020;66(2):117-25.
Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, 3rd, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-68.
