What is Intermittent Fasting: An Introduction for Beginners


Written by Colette Heimowitz, M.Sc. on March 25, 2020.

Intermittent fasting (IF) is the method of cycling between periods of fasting and eating.* IF has taken off in popularity recently for its potential to help manage weight, stabilize blood sugar, and improve metabolism, among other benefits. 1 While IF has become increasingly popular, it is still somewhat of a controversial approach, and it is not recommended for those with eating disorders, or who are pregnant or nursing.

Intermittent Fasting for Weight Loss

Fasting is nothing new—even the term breakfast is in reference to “breaking the fast” between dinner and your morning meal. For most people who are fasting for weight loss, the main goal of IF is to encourage the body to burn up excess stored energy, which will hopefully lead to losing excess body fat.

The idea behind intermittent fasting is that increasing the time between meals helps blood sugar and insulin levels naturally go down, 2 which, similar to a low carb diet, will help your body get into fat burning mode. 3 Furthermore, if you have insulin resistance, the time spent with low levels of circulating insulin may help resolve your insulin resistance. 4

Intermittent Fasting Plans and Hours

There are many approaches to IF—which we will discuss in greater detail.

Time Restricted Eating

This is a term used to describe the variety of fasting approaches breaking up the day into a set amount of time for fasting, and a set amount of time for eating. This can be as short as a 12-hour fast, followed by 12 hours of eating (12:12) to as long as 23:1. There are many approaches to intermittent fasting. Each method has its benefits, but finding the most effective approach depends on finding what works best for you and your goals.

16-Hour Fast

Our preferred intermittent fasting plan to pair with keto diets, many people find this 16:8 pattern quite approachable. It can be achieved by fasting for 16 hours a day, while consuming your meals within an 8-hour window. For example, if you were to finish eating dinner at 7 p.m. on Monday, you would not consume your next meal until 11 a.m. on Tuesday.

The 16:8 option may be the best intermittent fasting plan for weight loss because it’s more sustainable, can be combined with a low carb diet, and allows you to take in vital macronutrients.

Alternate-Day Fasting

Among the many types of fasting, alternate-day fasting probably has the most science-based evidence behind it. Typically, this approach consists of eating normally one day, followed by restricting calories quite significantly the next day—usually in the realm of 500 calories per day. This pattern repeats every other day: one day of normal eating, one day of restricted calories.

Another approach to alternate-day fasting is to eat normally five days a week, restricting calories to 500 per day on the remaining two days of the week. There are usually no requirements when those 500 calories are consumed. 

One Meal a Day (OMAD)

Other names for this type of approach are 20:4 or the “Warrior Diet.” OMAD intermittent fasting is based on the concept of fasting for 20 hours a day and consuming all calories during a 4-hour window. It draws its inspiration from historical texts suggesting that the ancient Spartans and Romans only ate one meal per day. 

Longer Fasts

As people become more acquainted with IF, they may start to read about 24+ hour fasts. We don’t typically encourage people to follow this protocol. We believe that eating a low carb diet provides a complete nutritional profile that doesn’t require you to deprive yourself of food for days on end. We encourage anyone who is planning on doing a longer fast to consult with a healthcare professional who specializes in this approach.

Atkins and Intermittent Fasting

For many people, low carb diets and intermittent fasting go hand-in-hand. IF is not necessary on a low carb diet, however, because your body will already be trained to burn fat for fuel and your diet will already help control your blood sugar levels. But as long as you are meeting your caloric requirements during your eating window, fasting after dinner for 12 to 16 hours each night could give your digestive system a needed break. This is also beneficial as nighttime eating is often when mindless snacking on hidden carbs occurs.

If you’d like to try IF while living low carb, try making your calorie cutoff around 6 p.m. – 7 p.m. Squeezing in a morning workout in a fasted state can also help put you in the fat-burning zone—as long as you feel up to it.** Just remember that chronically consuming too few calories has the potential to slow down your metabolism, which will hinder your weight- and fat-loss goals.

While IF has become increasingly popular, it is still a somewhat controversial approach and is not recommended for those with eating disorders or those who are pregnant or nursing. As with starting any new diet or exercise routine, consult with your doctor or healthcare provider for guidance on whether intermittent fasting is right for you.

Learn more healthy tips, find inspiration and motivation, and connect with our online community when you start your Atkins journey today. And for more information on intermittent fasting, check out our IF FAQ or IF meal plans.

* Before starting IF, consult with your doctor or healthcare provider for guidance on whether IF is right for you. 

** Before adding in exercise to your IF program, consult with your doctor or healthcare provider for guidance on what’s right for you. 

Further Reading
PubMed Central, National Library of Medicine, 2022, A scoping review of intermittent fasting, chronobiology, and metabolism

Chronobiology plays a crucial role in modulating many physiologic systems in which there is nutritional synergism with meal timing. Given that intermittent fasting (IF) has grown as a flexible dietary method consisting of delayed or early eating windows, this scoping review addresses the effects of IF protocols on metabolism as they relate to clinical nutrition and the circadian system.

Further Reading
PubMed Central, National Library of Medicine, 2021, Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians

Type 2 Diabetes is a metabolic disorder characterized by hyperglycemia that causes numerous complications with significant long-term morbidity and mortality.

Further Reading
PubMed Central, National Library of Medicine, 2021, Effect of Dietary Strategies on Respiratory Quotient and Its Association with Clinical Parameters and Organ Fat Loss: A Randomized Controlled Trial

The relation between changes in respiratory quotient (RQ) following dietary interventions and clinical parameters and body fat pools remains unknown. In this randomized controlled trial, participants with moderate abdominal obesity or/and dyslipidemia (n = 159) were randomly assigned to a Mediterranean/low carbohydrate (MED/LC, n = 80) or a low fat (LF, n = 79) isocaloric weight loss diet and completed a metabolic assessment.

Further Reading
PubMed Central, National Library of Medicine, 2019, Dietary support in insulin resistance: An overview of current scientific reports

Over the past 30 years, a significant increase in the prevalence of insulin resistance (IR) has been observed. It is associated with more frequent occurrence of impaired glucose tolerance, diabetes, excessive weight, cardiovascular diseases, and endocrine disorders.

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