Intermittent fasting

History:

Fasting is one of the most ancient and widespread healing traditions in the world and is used in religious practices in many cultures (1-2). In the modern era, the idea of intermittent fasting (IF) was brought about through books such as The Warrior Diet, through celebrities' success on the diet, and media involvement. Intermittent fasting is a pattern of eating that does not change what you eat, it changes when you eat. It is believed that this meal pattern helps to burn stored fat during the fasting day and the meal following the fast allows the body to relax. While intermittent fasting continues to evolve there are three major types: alternate-day fasting, periodic fasting, and time-restricted feeding (1). The meal pattern differs slightly across subtypes, but all promote prolonged fasting with restricted calorie intake when eating. Media and publications have played a big role in the buzz of intermittent fasting (e.g. documentary Eat Fast, Live Longer by Micheal Mosley, The 5:2 Diet by journalist Kate Harrison, etc).

Purpose:

Intermittent fasting refers to periods of voluntary abstinence from food or drinks. While it is a key component in religious practice, it has gained increasing popularity and is being practiced for weight loss (3). Recent studies have been focusing on intermittent fasting’s possible effects on reducing diet-related diseases, such as metabolic syndrome and diabetes.

General dietary practices:

There are three main categories of IF: alternate-day fasting, periodic fasting, and time-restricted feeding (1).

  • Alternate-day fasting involves alternating between a 24-hour "fast day" followed by a 24-hour "feast day"

    • Complete alternate-day fasting: calories are not consumed on fast days

    • Modified alternate-day fasting: allows the consumption of some calories on fasting days typically, with a target of 20-25% of basal needs

  • Periodic fasting otherwise referred to as whole-day fasting involves any period of consecutive fasting of more than 24 hours. The 5:2 diet is commonly seen where you eat normally for five days and fast for two. During the fasting days, about 25% of regular daily caloric intake, may be allowed instead of complete fasting.

Time-restricted feeding consists of only eating during certain hours of the day. For example, a 16:8 refers to fasting 16 hours of the day followed by 8 hours of non-fasting. 20:4 is also a common ratio used.

Key concerns:

People with certain medical conditions should not fast without consulting with a doctor first. Individuals who take medications for blood pressure or heart disease are at an increased risk of electrolyte abnormalities from fasting (4). IF may lead to unhealthy eating behaviors on non-fasting days because of the biological push to overeat after fasting (4). There are concerns about hypoglycemia during fasting days and the risk of nutrient deficiencies. Disordered eating and eating disorders may develop, which can be dangerous and cause harm. While individuals may be practicing IF for weight loss, the effect may not differ from that of a traditional calorie-restricted diet. If IF is not practiced properly people are at risk for starvation, which subsequently may lead to malnutrition and infectious disease. Common side effects include headache, impaired thinking, irritability, fainting, dehydration, weakness, and hunger.

Further Resources:

Websites: 

Apps: Zero- Fasting Tracker, BodyFast Intermittent Fasting 

Books: The Complete Guide to Fasting by Dr. Jason Fung, MD and Jimmy Moore

**The information presented provides an overview of the diet along with credible resources to refer to in order to learn more. This is not intended to make any dietary recommendations, rather an education tool for our clients.**

Reference:

  1. Intermittent fasting. En.wikipedia.org. https://en.wikipedia.org/wiki/Intermittent_fasting. Published 2020. Accessed July 26, 2020.

  2. Kerndt PR, Naughton JL, Driscoll CE, et al: Fasting: The history, pathophysiology and complications (Medical Progress). West J Med 1982 Nov; 137:379-399

  3. Monique Tello. Intermittent fasting: Surprising update - Harvard Health Blog. Harvard Health Blog. https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156. Published 2018. Accessed July 26, 2020.

  4. Publishing H. Not so fast: Pros and cons of the newest diet trend - Harvard Health. Harvard Health. https://www.health.harvard.edu/heart-health/not-so-fast-pros-and-cons-of-the-newest-diet-trend. Published 2019. Accessed July 26, 2020.