Updated: Oct 19, 2020
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There is increasing interest on Intermittent Fasting (IF) which can be defined as an eating pattern that alternates periods of eating and extended fasting.
It can get confusing as there are several categories of IF and their popularity vary according to the region. The most important are:
Alternate day fasting – you eat normally one day and fast or have a very low-calorie diet (25% of your usual calories) the day after.
Energy restriction –The most popular is the 5:2 approach where you pick two days a week for a very low-calorie diet.
Time restricted feeding – you do daily IF by eating in a shorter period of time during the day. A popular approach is the 16:8 where you eat for 8 hours and fast for 16.
All the studies done in mice and rats consistently showed that when subjected to intermittent fasting they get cardio-metabolic benefits and their lifespan is significantly increased. The mechanism is complicated: reduced oxidative stress, inflammation, improved glucose regulation, etc. There is some metabolism switching from the use of carb for fuel to the use of fat. The effects seem to go beyond just caloric restriction. I know I lost you already!
What does it mean for humans?
The animal data is promising but it does not translate into consistent benefits in humans.
Some studies suggest that IF is about as effective as a typical low-calorie diet for weight loss. It makes sense as by making you eat fewer meals, intermittent fasting can lead to an automatic reduction in calorie intake.
In addition, some scientific reports suggest that IF can improve blood lipids and glycemic control (less insulin is produced during fasting), decrease blood pressure and inflammatory markers. Unfortunately, other studies show no weight loss or cardiometabolic benefits. A potential benefit of IF is that it makes healthy eating simpler: fewer meals to prepare, cook and clean up after.
Probably the easiest way to get into IF is to gradually reduce the time window in which you consume food to allow for a fasting period of around 16 hours. Many people who want to try IF choose the 16:8 method because it allows you to eat whatever you want for an 8-hour window and then fast for 16 hours until 8 am the next day. During the fasting period, you can drink water, tea, coffee, and even diet soda. It appears that the benefits are proportional to the length of the fasting period and that they are greater when eating early -between 8 am and 4 pm- compared to eating late -after 5pm- skipping breakfast and lunch.
IF regimens have increased in popularity during the past decade. While there is some solid science behind IF, the jury is still out until new studies become available. Irrespective of the results, it might not be a long-term solution for maintaining weight loss as it can be challenging to have a social life and enjoy dining out and gatherings, which aren't conducive to a time-restricted way of eating.
Share your experiences if you’ve tried intermittent fasting.