Intermittent Fasting for Beginners
Page Medically Reviewed and Edited by Cyrus Khambatta, PhD
The Ultimate Beginner's Guide to Intermittent Fasting
Intermittent fasting is a dietary strategy that focuses on manipulating the timing of your food intake, rather than changing the balance of macronutrients in your food (like a high-fat keto diet or a low-fat, plant-based, whole-food diet).
Though focusing on schedule rather than food consistency is unconventional, the evidence supporting the practice of intermittent fasting is powerful. As it turns out, humans are not only able to survive and function during long periods of calorie restriction, but actually derive a number of health benefits from the fasted state.
In this article, we’ll explore intermittent fasting and the science behind it. We’ll also touch on a few examples of intermittent fasting schedules, explore some challenges newcomers might face, and discuss how to determine if intermittent fasting is right for you.
Table of Contents
What Is Intermittent Fasting?
Intermittent fasting is, at its most basic level, breaking up your daily or weekly eating schedule into two periods of time: fasting windows and eating windows.
During your fasting periods, you restrict the number of calories you consume to as close to zero as possible. However, you can also drink water and other zero calorie drinks like black coffee, green juices, and teas.
Then, during your eating periods, you consume meals as normal to hit your daily calorie goals, either to maintain or lose weight.
Ultimately, that’s it. Intermittent fasting is truly that simple.
Below, we’ll go into some popular schedules, as well as how this process works.
Popular Fasting Schedules
There are many different ways to execute this intermittent fasting diet strategy, usually centered around the amount of time spent during the day or during the week fasting.
To date, there has been little clinical research done to prove which, if any, of these strategies are most effective, other than the likelihood that more time fasting may produce more benefits.
We recommend picking the time frame and schedule that work best for you.
Alternate-Day Fasting (ADF)
On one day, you’ll eat as normal to hit your target calorie requirement (which may be adjusted or increased based on a two-week average). Then, on the next day, you won’t eat at all.
Think of alternate day fasting as a light switch that’s either “on” or “off.” “On” days signal that you’re free to eat without restriction, and “off” days signal that it’s time to perform a 24-hour fast.
This strategy is very powerful and can help you lose weight quickly, but it tends to be relatively difficult for beginners to adopt.
Difficulty: Medium to hard for beginners, challenging to sustain over time.
16:8 Intermittent Fasting
The 16:8 intermittent fasting plan is one of the most common forms of intermittent fasting. In this strategy, you have an 8-hour window during the day that is considered your feeding window (for example, from 12:00pm to 8:00pm).
Then, you fast for the remaining 16 hours, from 8:00pm to 12:00pm the next day. Many people consider this one of the easier and less intrusive forms of intermittent fasting because it tends to require skipping only one meal (usually breakfast), and most of your fasting window occurs when you’re asleep.
Difficulty: Easy for beginners and easy to sustain over time.
Similar to the 16:8 strategy, the 20 hour fast strategy simply divides up the day into 4 designated eating hours and a 20 hour fasting window.
The key trade-off between this diet and the 16:8 strategy is in the extra four hours added to fasting, which often results in a compressed eating schedule (with one larger meal at either end of the 4 hour period).
Difficulty: Medium for beginners and can be challenging to sustain over time.
A 24-hour fast usually takes place as a part of a weekly schedule of intermittent fasting rather than a daily one. In this strategy, you simply choose one day of the week to stop eating, and keep your diet unrestricted for the rest of the week.
Some people find this strategy to be easier than 16:8 or 20 hour fasting because they choose a day for their fast, rather than specific hours of eating and not eating.
Difficulty: Easy for beginners and easy to sustain over time.
5:2 Intermittent Fasting
Just like the 24 hour fast strategy, 5:2 intermittent fasting manages your food intake over the course of 7 days.
The only difference is that in the 5:2 plan you choose two days to fast, rather than one day, while the rest of the week you eat as normal.
Typically the two days you choose to fast should separate days and not be consecutive. Every fasting day should be followed by one or two non-fasting days to avoid the need to have to fast for 48 hours in total.
Difficulty: Easy for beginners and easy to sustain over time.
OMAD (One Meal a Day)
Perhaps the most concentrated form of day-to-day intermittent fasting, OMAD (one meal a day) is… well, exactly as the name would suggest. In this strategy, you condense your calories for the day into one meal, and stick to water, tea, or black coffee to stay hydrated and energized.
OMAD is a divisive strategy. For some, OMAD is restrictive and limiting, while for others, it’s almost a relief to only focus on one meal a day. Some people also report that it can be hard to eat an entire day’s worth of calories in one meal without resorting to junk food or filler.
Difficulty: Medium for beginners and can be challenging to sustain over time.
The Health Benefits of Intermittent Fasting
There are two main keys to intermittent fasting. The first is that a regimented schedule can make it easier to stick to your target calorie balance. When you’re only making one or two meals, and not eating throughout the day, keeping track is just a simpler process.
The second key is a biological process called autophagy. When your body has finished digesting and processing the energy from your meal, you enter a fasted state. Your cells still need energy, but the readily-available energy from your meal has been used or stored.
To ensure that your cells continue to function, autophagy begins, in which your body breaks down stored fats, excess proteins, and damaged cells, and “recycles” them into energy that your cells can use.
This has a number of benefits for your overall health, which we’ll touch on below.
In many ways, this makes sense. When your body requires energy, but can’t get it from food, it resorts to fat-burning as a part of autophagy which leads to fat loss and improved body composition.
Intermittent fasting can be even more effective as a method to lose weight and burn fat when combined with other forms of dieting especially if you monitor your calorie intake during your eating window.
Though the direct mechanism of this process is still being studied, one theory is that the body is able to focus more specifically during separated eating and fasting windows.
In fasting windows, your body is able to ‘focus’ on burning fat thanks to autophagy, while during feeding windows your body has readily available nutrients to build muscle.
Do Amino Acids Break a Fast?
The key to intermittent fasting is keeping calories as close to zero as possible to make sure your body does not leave its fasted state and end autophagy.
Very small amounts of protein (amino acids) may not break a fast, but estimates are that you should keep consumption under 100 calories for the duration of your fast.
Improve Insulin Sensitivity
The next two benefits from intermittent fasting both pertain to your diabetes health. After researchers discovered that Ramadan fasting affected individuals’ insulin resistance, scientists have continued to explore the relationship between fasting and insulin sensitivity.
And the results have been very positive. During autophagy, your cells are more likely to burn through stored fats, reducing the insulin levels required for them to accept blood glucose. The result: improved blood glucose control and sensitivity to insulin.
Support Healthy Blood Glucose (Blood Sugar) Levels
The secondary effect from autophagy and intermittent fasting improving your insulin sensitivity is that it also becomes easier to manage your blood glucose and keep them within healthy levels.
For people with prediabetes, type 2 diabetes, and even type 1 diabetes, this can be incredibly significant, and represents a powerful tool in controlling (in the case of type 1 diabetes) or even reversing (in the case of type 2 diabetes and prediabetes).
Prevent Heart Disease
Studies have also shown that intermittent fasting has a broad cardioprotective effect that helps promote better cholesterol, lower blood pressure, and reduce your risk for heart disease.
Part of this is certainly due to weight loss and better insulin sensitivity, which are proven to increase cardiovascular health, but some research has found cardiovascular benefits even with no calorie restriction.
Lengthen Your Lifespan
Another area where autophagy has benefits is in the reduction of oxidative stress and premature aging. Oxidative stress is caused by free radicals, high-energy molecules in your body that can damage cells and increase your risk for degenerative diseases like cancer.
During autophagy, as your body recycles unneeded cellular material, some of what gets recycled are damaged cells and dysfunctional protein, which both reduce the cause and the effects of oxidative stress.
Overall, this is why there’s been a clear link between intermittent fasting and longevity.
Support Brain Health
There is a strong and increasingly-studied link between cardiovascular health and your brain health, which shows that keeping your blood pressure, blood glucose, and cholesterol in their ideal ranges helps promote all-round cognitive function.
This is especially true in terms of degenerative diseases like Alzheimer’s, which is now being referred to as type 3 diabetes.
One of the many ways that intermittent fasting and its benefits can have a powerful effect on not just your physical fitness, but your overall health as well.
Safety and Side Effects of Intermittent Fasting
In most cases, intermittent fasting has been shown to be safe and effective, with limited-to-no side effects. However, there are certain aspects of this dietary strategy to be aware of, and certain conditions that may make intermittent fasting difficult.
Especially for beginners in intermittent fasting, the adjustment period away from other dietary strategies can be an obstacle.
In the early stages of adjusting to intermittent fasting, it’s easy to get cranky or lightheaded, especially if you’re used to eating frequently. However, in most cases your body (and brain) adjust over time, and many people have found that if you drink water and other liquids, this hunger can subside.
Another concern for beginners in intermittent fasting is overeating their target amount of calories either on their first meal after a fasting period or on their last meal before a fasting period. It’s easy to get caught up in hunger pangs or overeat, which can cause weight gain.
Both of these obstacles are usually possible to overcome, but can definitely present a bump in the road.
Another case to be aware of intermittent fasting is if you have a history of eating disorders. Though many people report that the regimented style of eating can actually help provide order to their diet, some people often report that intermittent fasting worsened their disorders.
Not every strategy is for everyone, so if you’re concerned about intermittent fasting, consider discussing with your nutritionist, therapist, or doctor and finding the strategy that works for you.
Type 2 Diabetes
If you struggle to control your blood glucose (blood sugar) due to type 2 diabetes (or any other form of diabetes), you should be careful when you first begin intermittent fasting, and experts recommend working with a doctor or nutritionist.
Even though intermittent fasting is incredibly beneficial for diabetes health in the long term, introducing sudden changes to your eating habits can cause fluctuations in your blood glucose and insulin levels.
Managed properly with the support of a doctor (and exogenous insulin as needed), these problems can be mitigated safely, but it’s always better to be cautious.
Intermittent Fasting for Women
In general, there are no more severe risks for women intermittent fasting than there are with men, other than the usual fluctuations in mood, energy, and hormonal balance due to weight loss.
However, there is one case in which intermittent fasting is likely not a good idea, which is if you are pregnant or trying to conceive.
Providing your body with a steady stream of nutrients as needed can be crucial, especially to your baby’s health, so we recommend talking with your doctor if you’re thinking about following this strategy during conception or pregnancy.
In all likelihood, you may simply pause your intermittent fasting for the short-term, and then resume after childbirth.
Does Intermittent Fasting Work?
If done correctly, intermittent fasting can be a powerful tool to lose weight, adjust your body composition, and drastically improve your cardiovascular health, insulin sensitivity, and overall health (including risk for chronic disease).
And, intermittent fasting can be combined with other lifestyle changes like a plant-based diet and daily movement to see major improvements fast.
However, there is a definite adjustment to this technique, one that can present challenges to beginners. It may take a little while to discover a fasting plan that works with you, especially if you’re currently struggling with type 2 diabetes.
That’s why we recommend working with your dietitian or healthcare professional when making this change. With their help, you can find a plan that works for you, monitor the changes in your body, and notice the marked improvement to your body and overall health.
Amla Green has strict guidelines for scientific references in our articles, and we rely on peer-reviewed studies, academic research institutions, governmental organizations, and reputable medical organizations. We do our best to avoid using non evidence-based references in all articles. The references in this article are listed below.
“Azevedo, Fernanda Reis de, Dimas Ikeoka, and Bruno Caramelli. “Effects of Intermittent Fasting on Metabolism in Men.” Revista Da Associação Médica Brasileira 59, no. 2 (March 1, 2013): 167–73.” ”https://doi.org/10.1016/j.ramb.2012.09.003"
“Cabo, Rafael de, and Mark P. Mattson. “Effects of Intermittent Fasting on Health, Aging, and Disease.” Edited by Dan L. Longo. New England Journal of Medicine 381, no. 26 (December 26, 2019): 2541–51.” ”https://doi.org/10.1056/NEJMra1905136"
“Cardiovascular Risk Factors and Brain Health: Impact on Long‐Range Cortical Connections and Cognitive Performance.” ”https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6405561/"
“Carlson, Olga, Bronwen Martin, Kim S. Stote, Erin Golden, Stuart Maudsley, Samer S. Najjar, Luigi Ferrucci, et al. “Impact of Reduced Meal Frequency Without Caloric Restriction on Glucose Regulation in Healthy, Normal Weight Middle-Aged Men and Women.” Metabolism: Clinical and Experimental 56, no. 12 (December 2007): 1729–34.” ”https://doi.org/10.1016/j.metabol.2007.07.018"
“Catenacci, Victoria A., Zhaoxing Pan, Danielle Ostendorf, Sarah Brannon, Wendolyn S. Gozansky, Mark P. Mattson, Bronwen Martin, Paul S. MacLean, Edward L. Melanson, and William Troy Donahoo. “A Randomized Pilot Study Comparing Zero-Calorie Alternate-Day Fasting to Daily Caloric Restriction in Adults with Obesity.” Obesity (Silver Spring, Md.) 24, no. 9 (September 2016): 1874–83.” ”https://doi.org/10.1002/oby.21581"
“Cho, Yongin, Namki Hong, Kyung-won Kim, Sung joon Cho, Minyoung Lee, Yeon-hee Lee, Yong-ho Lee, Eun Seok Kang, Bong-Soo Cha, and Byung-Wan Lee. “The Effectiveness of Intermittent Fasting to Reduce Body Mass Index and Glucose Metabolism: A Systematic Review and Meta-Analysis.” Journal of Clinical Medicine 8, no. 10 (October 9, 2019).” ”https://doi.org/10.3390/jcm8101645"
“Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss.” ”https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836017/"
“Grajower, Martin M., and Benjamin D. Horne. “Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus.” Nutrients 11, no. 4 (April 18, 2019).” ”https://doi.org/10.3390/nu11040873"
“Intermittent Fasting: Women vs. Men | ISSA.” ”https://www.issaonline.com/blog/index.cfm/2018/this-hot-diet-trend-is-not-recommended-for-women"
“Johnstone, A. “Fasting for Weight Loss: An Effective Strategy or Latest Dieting Trend?” International Journal of Obesity (2005) 39, no. 5 (May 2015): 727–33.” ”https://doi.org/10.1038/ijo.2014.214"
“Malinowski, Bartosz, Klaudia Zalewska, Anna Węsierska, Maya M. Sokołowska, Maciej Socha, Grzegorz Liczner, Katarzyna Pawlak-Osińska, and Michał Wiciński. “Intermittent Fasting in Cardiovascular Disorders—An Overview.” Nutrients 11, no. 3 (March 20, 2019).” ”https://doi.org/10.3390/nu11030673"
“Moro, Tatiana, Grant Tinsley, Antonino Bianco, Giuseppe Marcolin, Quirico Francesco Pacelli, Giuseppe Battaglia, Antonio Palma, Paulo Gentil, Marco Neri, and Antonio Paoli. “Effects of Eight Weeks of Time-Restricted Feeding (16/8) on Basal Metabolism, Maximal Strength, Body Composition, Inflammation, and Cardiovascular Risk Factors in Resistance-Trained Males.” Journal of Translational Medicine 14 (October 13, 2016).” ”https://doi.org/10.1186/s12967-016-1044-0"
“Shariatpanahi, Z. Vahdat, M. Vahdat Shariatpanahi, S. Shahbazi, A. Hossaini, and A. Abadi. “Effect of Ramadan Fasting on Some Indices of Insulin Resistance and Components of the Metabolic Syndrome in Healthy Male Adults.” The British Journal of Nutrition 100, no. 1 (July 2008): 147–51.” ”https://doi.org/10.1017/S000711450787231X"
“Tinsley, Grant M, Natalie K Butler, Jeffrey S Forsse, Annie A Bane, Grant B Morgan, Paul S Hwang, Peter W Grandjean, and Paul M La Bounty. “Intermittent Fasting Combined with Resistance Training: Effects on Body Composition, Muscular Performance, and Dietary Intake.” Journal of the International Society of Sports Nutrition 12, no. Suppl 1 (September 21, 2015): P38.” ”https://doi.org/10.1186/1550-2783-12-S1-P38"
“Varady, K. A. “Intermittent versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss?” Obesity Reviews: An Official Journal of the International Association for the Study of Obesity 12, no. 7 (July 2011): e593-601.” ”https://doi.org/10.1111/j.1467-789X.2011.00873.x"
“Varady, Krista A., Surabhi Bhutani, Emily C. Church, and Monica C. Klempel. “Short-Term Modified Alternate-Day Fasting: A Novel Dietary Strategy for Weight Loss and Cardioprotection in Obese Adults.” The American Journal of Clinical Nutrition 90, no. 5 (November 2009): 1138–43.” ”https://doi.org/10.3945/ajcn.2009.28380"
“Wegman, Martin P., Michael H. Guo, Douglas M. Bennion, Meena N. Shankar, Stephen M. Chrzanowski, Leslie A. Goldberg, Jinze Xu, et al. “Practicality of Intermittent Fasting in Humans and Its Effect on Oxidative Stress and Genes Related to Aging and Metabolism.” Rejuvenation Research 18, no. 2 (April 1, 2015): 162–72.” ”https://doi.org/10.1089/rej.2014.1624"
“Welton, Stephanie, Robert Minty, Teresa O’Driscoll, Hannah Willms, Denise Poirier, Sharen Madden, and Len Kelly. “Intermittent Fasting and Weight Loss.” Canadian Family Physician 66, no. 2 (February 2020): 117–25.”
Page Medically Reviewed and Edited by
Cyrus Khambatta, PhD
Cyrus Khambatta, PhD, is a cofounder of Mastering Diabetes and Amla Green is an internationally recognized nutrition and fitness coach who has been living with type 1 diabetes since 2002. Using an evidence-based approach to nutrition and fitness, he first reduced his own insulin usage by more than 40%, and has educated thousands of people with all forms of diabetes how to reverse insulin resistance using food as medicine. Cyrus earned a Bachelor of Science in Mechanical Engineering from Stanford University in 2003, then earned a PhD in Nutritional Biochemistry from the University of California at Berkeley in 2012. He is the co-host of the annual Mastering Diabetes Online Summit, a featured speaker at the Plant-Based Nutrition and Healthcare Conference (PBNHC), the American College of Lifestyle Medicine (ACLM) Conference, Plant Stock, and has been featured on Forks Over Knives, NPR, PBS, KQED, Fast Company, and is the author of the upcoming book Mastering Diabetes.
- Cyrus Khambatta