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Does Intermittent Fasting Work? How It Works & What to Know


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Medically reviewed by Dr G. Michael DiLeo, MD

does intermittent fasting work

Intermittent fasting is also sometimes called time-restricted eating or time-restricted feeding. Unlike the traditional diets that focus on the number of calories that you consume daily,  it prioritizes, instead, intermittent fasting schedules each day. Thus, it partners two weight-loss strategies that combine for more effect, together, than the mere addition of each alone, i.e., reduced calories (because you’re not eating at night and/or have fasting days) + consumption during that part of the day when metabolism for burning calories is most robust.

Can the right eating pattern help your body burn fat more effectively? How does intermittent fasting work, anyhow? 

The health benefits may go beyond the elimination of stubborn fat stores. Here’s how you can achieve and maintain a healthy weight through different types of intermittent fasting.

What Is Intermittent Fasting?

Intermittent fasting[1] begins at hour zero[2], the second that you’ve officially finished your last meal of the day. 

In this fed state, you’re asked to avoid eating for anywhere from twelve to eighteen hours, allowing your body to work its magic uninterrupted. This period of abstinence is called a “fasting window,” the most important responsibility you have when trying out this lifestyle.

Outside of your fasting window, you’re pretty much free to eat what and when you want. Of course, good sense should prevail, or you’ll miss out on one aspect of combining the two weight-loss strategies cited above. There is an art to eating on this diet, however—it’s different for everybody, and your genetics, fitness levels, line of work, and available free time will all play a role in how your diet evolves.

The idea may be considered akin to the so-called “caveman” diet, also known as the Paleo diet. Long ago, before human beings had consistent and reliable access to food at all times, our bodies developed the ability to survive between windfalls of meat or gathered food. It’s a back-to-basics mentality, and the research backing the most promising claims related to intermittent fasting is relatively strong.

An Old Trick Remembered

In the prehistoric diet upon which humans survived, there was no strategy. It was just “eat whenever you could.” As it turned out, eating and metabolism generally were based on a circadian rhythm; after all, we have evolved on a planet with night and day. We have also used this light-dark cycle to hunt and gather and then eat by daylight, and rest and allow repair of the injuries of the day at night, when we could devote the most energy to renewal for the next day to follow.

Intermittent fasting is a revisiting of this method–necessary for early humans but still effective for modern people. It still makes sense: eat during the window you’re most active, which burns more energy. It’s how we evolved; it’s how we are at our best.

While our ancestors didn’t have the luxury of choosing when they ate, science has substantiated that fasting windows, even when manipulated in creative ways, still work for weight loss. Consider the tweaks to this prehistoric concept in the next section. 

Different Types of Intermittent Fasting

Continuous calorie restriction comes in several forms. The main vein within the community, simple time-restricted eating, asks that the faster abstain from eating for at least twelve hours a day. Some go much longer, up to around seventeen hours.

You have a couple of other options in this realm, of course, aside from just varying the eating window that you prefer. Some of the most popular intermittent diets:

  • The 5:2 Diet[3]: For five days a week, you’re free to eat what you want, when you want. On the other two days, your fasting days, you’ll be asked to eat fewer calories than you would normally—generally, 500 calories a day for women, and 600 for men[4]. Of the IF diets available, the 5:2 Diet seems to have minimal metabolic disturbances/side effects[5] and is considered a safe acceptable weight-loss diet[6] strategy.
  • Eat-Stop-Eat: This diet[7] calls for at least one 24-hour fast per week, periods in which nothing is eaten at all.
  • Alternate-Day Fasting: Alternate-day fasting[8] kicks things up a notch; you’ll be expected to fast completely every other day. Certainly not for the faint of heart.
  • The Warrior Diet[9]: This type of diet is much looser and more freewheeling than some of these other options. The main idea: you’ve got one big meal a day. You don’t necessarily need to maintain a strict fast between each daily blowout, as the diet allows you to nibble on fruits, vegetables, juices, and other light fares throughout the day.

For many beginners, the idea of going a full 24 hours without food is enough to raise a couple of eyebrows. Take it from us, though—it truly does get easier with practice, and the other health benefits of fasting, aside from decreased fat mass, really are incredible. You’ll look great, but, more importantly, you’ll feel incredible.

How Does Intermittent Fasting Work?

The impact that a fasting diet can have on your overall health might just astonish you. As only one example, there’s the effect that a fast has on your gastrointestinal microbiota[10]–a commonly-cited example—every person on this planet can benefit from improved gut health. What is it about fasting that gets things moving?

Improved gastric emptying, a keener metabolic response to the new fuel, and an enhanced ability to process the insulin and glucose already in our systems help eliminate dangerous biomarkers throughout the body. A fast is cleansing and detoxifying, clearing the way for the good bacteria in your intestines to flourish. An improved gut microbiome can also use the right bacteria to optimize nutrition and sugar absorption.

Through these metabolic pathways, fasting intermittently may be able to help you avoid a myriad[11] of chronic health conditions like diabetes, cancer, obesity, hypertension, autoimmune disorders, cardiovascular disease, and neurodegenerative issues later on down the line.

An intermittent eating plan reinforces the natural circadian rhythm[12] of our metabolism. This is a sensible return to the way we have evolved to survive. It also can be used to overcome disordered eating and even emotional eating by establishing a new eating pattern. Many reports that the adjustment has helped them build a new, positive relationship with their food. 

Psychologically, when people don’t have rules, they don’t do well. This is a truism on every level of living. Rules and limitations are comforting, for they let you seek the comfort of knowing what is allowable or not. Called discipline, it is the hallmark of raising children; but this discipline never really ends, does it? We continue to do well when we follow “the rules,” no matter what they are or where they apply. People are just better self-managed with “knowns.” 

As such, intermittent fasting and fasting windows are just rules. If you have no rules when it comes to eating, well, then, here you are reading this article for help. IF is just another discipline in life and it’s amazing how comfortable you can be with it once you’ve gotten used to it. 

Some attribute its good effects to changes in hormonal patterns and quality of sleep. Again, you’re resuming how we were meant to be. Essentially, you’re reprogramming your entire body, improving and standardizing circadian oscillations at the cellular level, and within many different systems. 

The hunter-gatherer, at the mercy of what game or crops were available, walked a fine line between feast and famine or, better stated, using sugar for metabolism and converting to ketosis (“gluconeogenesis”), that escape mechanism against starvation. The intermittent fasting diets recreate that vacillation to good effect. (When one of these predominates, it’s unhealthy, as in diabetes or ketoacidosis, respectively–both disease states.) This is why alternating between eating and fasting is proposed in these intermittent fasting strategies.

With proper balance, insulin is secreted at exactly the right time; your liver knows exactly when it needs to be producing more bile or metabolizing fat for energy. Suddenly, your entire body is operating in perfect harmony. It’s a profound experience.

What Are The Benefits Of Fasting?

The fasting solution is, indeed, a compelling one. Some of the other benefits of a daily or weekly intermittent fast might also include the following:

  • Intermittent fasting can help you achieve a normal blood sugar and increase your sensitivity to insulin, giving you a finer degree of control over your resting blood glucose levels
  • Fasting regularly has been shown to lead to better health outcomes in terms of your cardiovascular health—lower blood pressure, the reduction of visceral fat stores and low-density cholesterol and triglycerides, and other key indicators of heart health
  • Fasting also promotes longevity and offers neuroprotective benefits by reducing oxidative stress[13]
  • And, of course, the big one: intermittent fasting in any capacity can help you burn more body fat—intermittent fasting is especially helpful[14] when it comes to your body composition. When done right, you’ll be less likely to lose muscle mass[15] and more likely to lose weight in fatty deposits throughout the body.

One of the most influential factors when trying this diet for many will inevitably be the practice of restricting food at night[16] when many of us are less than interested in healthier food options. Too many people enjoy the bulk of their daily calorie intake during this time, along with the expected amount of eating throughout their daytime waking hours.

Calorie restriction during this vulnerable time in the evening won’t guarantee that you will burn calories and lose weight, but it can help you achieve preferential fat loss and lower blood sugar by having you wait until the morning when many of us are more easily agreeable to healthy food choices like lean protein, complex carbs, and good fats.

Final Thoughts: Intermittent Fasting and Alternate-Day Fasting Are So Worth It

Intermittent fasting really does work, but so far the literature cites only the short-term, pending further study, which may just confirm its success for long-term practice. The important thing to remember is that it’s not a temporary fix, but a jumping-off point for a change in your lifestyle to one of sensible moderation. 

However, a great diet doesn’t necessarily need to be low-calorie. Instead of suffering from hunger, you can orchestrate a less painful diet by incorporating the strategy that cooperates with your metabolism–intermittent fasting and other fasting window concepts. Giving your body time to process everything that you put into it is one of the most effective ways to combat chronic conditions like diabetes, heart disease, and others. This applies equally to any type of fasting ritual—alternate-day fasting, the 5:2 diet, or anything else you come across.

Is it difficult to get used to? Your first few days might be a drag, but it doesn’t take long to get the hang of it. Rules get easier to follow as times go on. Keep yourself busy and focus on how you feel – you might not be able to fight off a saber-tooth tiger like your ancestors, but you might be inspired to pick up a meditation practice with all of your newfound energy.

+ 18 sources

Health Canal avoids using tertiary references. We have strict sourcing guidelines and rely on peer-reviewed studies, academic researches from medical associations and institutions. To ensure the accuracy of articles in Health Canal, you can read more about the editorial process here

  1. Ganesan, K., Habboush, Y. and Sultan, S. (2018). Intermittent Fasting: The Choice for a Healthier Lifestyle. Cureus. [online] Available at: https://www.cureus.com/articles/12903-intermittent-fasting-the-choice-for-a-healthier-lifestyle ‌
  2. Stockman, M.-C., Thomas, D., Burke, J. and Apovian, C.M. (2018). Intermittent Fasting: Is the Wait Worth the Weight? Current Obesity Reports, [online] 7(2), pp.172–185. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5959807/
  3. ‌Lishan Li (2021). Effect of 5:2 Intermittent Fasting Diet for Weight Loss among Overweight and obese College Students. Frontiers in Medical Science Research, [online] 3(4), p.-. Available at: https://francis-press.com/papers/4378 ‌
  4. Hajek, P., Przulj, D., Pesola, F., McRobbie, H., Peerbux, S., Phillips-Waller, A., Bisal, N. and Myers Smith, K. (2021). A randomised controlled trial of the 5:2 diet. PLOS ONE, [online] 16(11), p.e0258853. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8598045/ ‌
  5. Hajek, P., Przulj, D., Pesola, F., McRobbie, H., Peerbux, S., Phillips-Waller, A., Bisal, N. and Myers Smith, K. (2021). A randomised controlled trial of the 5:2 diet. PLOS ONE, [online] 16(11), p.e0258853. Available at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0258853 ‌
  6. Scholtens, E.L., Krebs, J.D., Corley, B.T. and Hall, R.M. (2020). Intermittent fasting 5:2 diet: What is the macronutrient and micronutrient intake and composition? Clinical Nutrition, [online] 39(11), pp.3354–3360. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0261561420300856 ‌
  7. Collier, R. (2013). Intermittent fasting: the next big weight loss fad. Canadian Medical Association Journal, [online] 185(8), pp.E321–E322. Available at: https://www.cmaj.ca/content/185/8/E321.short ‌
  8. Varady, K.A., Bhutani, S., Klempel, M.C., Kroeger, C.M., Trepanowski, J.F., Haus, J.M., Hoddy, K.K. and Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition Journal, [online] 12(1). Available at: https://pubmed.ncbi.nlm.nih.gov/24215592/ ‌
  9. Shetty, A.K., Kodali, M., Upadhya, R. and Madhu, L.N. (2018). Emerging Anti-Aging Strategies – Scientific Basis and Efficacy. Aging and disease, [online] 9(6), p.1165. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6284760/ ‌
  10. Patterson, R.E., Laughlin, G.A., LaCroix, A.Z., Hartman, S.J., Natarajan, L., Senger, C.M., Martínez, M.E., Villaseñor, A., Sears, D.D., Marinac, C.R. and Gallo, L.C. (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics, [online] 115(8), pp.1203–1212. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/ ‌
  11. Longo, Valter D. and Mattson, Mark P. (2014). Fasting: Molecular Mechanisms and Clinical Applications. Cell Metabolism, [online] 19(2), pp.181–192. Available at: https://pubmed.ncbi.nlm.nih.gov/24440038/ ‌
  12. Panda, S. (2016). Circadian physiology of metabolism. Science, [online] 354(6315), pp.1008–1015. Available at: https://pubmed.ncbi.nlm.nih.gov/27885007/
  13. ‌Collier, R. (2013). Intermittent fasting: the science of going without. Canadian Medical Association Journal, [online] 185(9), pp.E363–E364. Available at: https://www.cmaj.ca/content/185/9/E363.short
  14. ‌Stockman, M.-C., Thomas, D., Burke, J. and Apovian, C.M. (2018). Intermittent Fasting: Is the Wait Worth the Weight? Current Obesity Reports, [online] 7(2), pp.172–185. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5959807/ ‌
  15. International Journal of Food Sciences and Nutrition. (2021). Effectiveness of intermittent fasting to potentiate weight loss or muscle gains in humans younger than 60 years old: a systematic review. [online] Available at: https://www.tandfonline.com/doi/abs/10.1080/09637486.2020.1868412 ‌
  16. LeCheminant, J.D., Christenson, E., Bailey, B.W. and Tucker, L.A. (2013). Restricting night-time eating reduces daily energy intake in healthy young men: a short-term cross-over study. British Journal of Nutrition, [online] 110(11), pp.2108–2113. Available at: https://pubmed.ncbi.nlm.nih.gov/23702187/ ‌

Medically reviewed by:

Michael DiLeo

Emma Garofalo is a writer based in Pittsburgh, PA. A lover of science, art, and all things culinary, few things excite her more than the opportunity to learn about something new." It is now in the sheet in the onboarding paperwork, apologies!!

Medically reviewed by:

Michael DiLeo

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