Does intermittent fasting work?
In a world where “miracle” remedies and “magic” solutions are showcased everywhere, from billboards to nightly news to your social media feed, it can be tricky to sort through all the hyperbole, exceptions, and twisted truths to distinguish fact from fiction.
This filtering process can be incredibly convoluted when it comes to health and nutrition, especially because everyone’s body is different, and everyone has different needs and goals.
As one of the most popular eating routines of the last decade, intermittent fasting (an approach that involves switching between periods of fasting and periods of eating on a regular schedule) has certainly been the inspo for many amateur detective efforts and internet deep dives. That’s not an exaggeration: second only to keto, and more recently veganism, intermittent fasting has been one of Google’s most-searched food routines for the last several years. In 2020 alone, the term was googled close to 12 million times.
So, does intermittent fasting work? And, most importantly, if it does, how do you know if it will work for you?
Our experts have separated science from scams and broken down everything you need to know about intermittent fasting and how it works in a super simple way. After reading our guide, you’ll know whether this eating routine might be a good one to try — without invading your browser with hundreds of tabs and manic-googling late into the night.
Key takeaways
- Intermittent fasting involves a repeated pattern of eating and fasting that focuses on when you eat rather than what you eat.
- It works by creating a calorie deficit and priming your body to burn fat to use as fuel.
- Extensive research has linked intermittent fasting to loads of potential health benefits, like lower inflammation, a healthier heart, and improved brain power.
- It may also be an effective way to lose weight.
- While intermittent fasting is generally safe, it’s not appropriate for everyone, so consult your primary care provider before trying it.
So, does intermittent fasting really work?
Much like our frenemy Google, we also get asked one question above all else: intermittent fasting — does it work?
The short answer is yes. And it’s not magic.
It’s science.
Intermittent fasting works by creating a calorie deficit. That means you will be primed to burn fat instead of sugar to use as fuel, which, in the most basic terms, can be a health-promoting process for lots of different internal systems and body stuff.
Now, whether intermittent fasting works for you — and what specifically it does “work” for — is a longer answer.
Extensive research has linked intermittent fasting to a wide range of health benefits, like weight loss [1], reduced body fat [2], lower systolic blood pressure [3], and reduced inflammation [4]. However, things like physical activity, preexisting health conditions, what you eat and drink, and other lifestyle factors can impact its effectiveness. Plus, how you define “effective” will depend on your goals, needs, and approach.
Everybody is unique: intermittent fasting may have different impacts on different people, and it may not be right for everyone. To see if intermittent fasting might help you achieve your health goals or reach / maintain your ideal weight, take our SIMPLE quiz. We also always recommend consulting your primary care provider or dietitian before making any significant changes to your eating routine.
What is intermittent fasting exactly?
As far as eating habits go, intermittent fasting is a piece of cake: it’s eating, then fasting, on repeat.
You can even still eat that piece of cake, too, because intermittent fasting doesn’t restrict what you eat — it’s all about when you eat.
Yep, that’s right: with this food routine, no foods are completely off-limits. (Though just to be clear, we don’t recommend daily servings of cake or living that Willy Wonka lifestyle!)
There are several different types of intermittent fasting plans, and your specific eat-fast-repeat routine can vary. Some plans are daily, while others are based on alternate days or weekly schedules. Some also involve different fasting and eating windows.
Whatever type of intermittent fasting you do, the fundamental component of each plan is the same: for a defined period, you take a complete break from eating.
So, why does intermittent fasting work?
After each meal, your body gets to work on turning the food you just ate into helpful body stuff, like energy, fat, muscle, and brain power. Once it spends a few hours digesting and distributing everything, it’s happy to chill in what’s called a post-absorptive state for the next 8–12 hours. After that internal R&R, your body then enters a fasted state.
That’s where the using-fat-as-fuel magic happens — well, “magic” in the scientifically-explained biological sense.
On your average day, you likely won’t go that long without eating, so intermittent fasting is a straightforward way to intentionally trigger this natural body phase. Plus, having less time to eat means we generally eat less (which creates that calorie deficit).
Does intermittent fasting work for weight loss?
We know reaching or maintaining your happy weight can feel like quite the ride sometimes — and it’s usually more of a tilt-o-whirl than a steady path to progress.
And it doesn’t exactly put the “fun” in “fun fair.”
That’s why a lot of our users ask about intermittent fasting and weight loss: with no calorie trackers, no restrictive meal plans, and no extra-demanding workout requirements, it definitely carries appeal as a more consistent, manageable approach to weight goals. But does fasting work for weight loss?
The good news: it can!
Quite a bit of research connects intermittent fasting to various physiological benefits that may individually or collectively lead to weight loss, at least in the short term (up to 12 months).[5] Some research also suggests intermittent fasting could likewise be used to help maintain your ideal weight.[6]
There is some fine print, though: while the existing research is extensive, a lot of studies are focused on specific populations (like people living with obesity or other preexisting health conditions) or cis-gendered men and women. We need more inclusive research before we can confidently say that intermittent fasting is the key to weight loss for everyone.
Likewise, some research suggests intermittent fasting may not necessarily be better for weight loss than calorie-restriction diets [7], and it may not lead to weight loss benefits without other lifestyle changes.[8]
Whether intermittent fasting is your one true pairing for safe, effective weight loss also depends in part on your beautiful, unique self — it’s not a good match for everybody. But if you’re tired of counting macros, micromanaging meal plans, or riding the same rollercoaster loop, it might still be worth a try.
Is intermittent fasting healthy?
You know how swimming superstar Michael Phelps ate 8,000–10,000 calories during his peak training years? Or how NBA legend LeBron James went over two months without any sugar, carbs, or dairy?
Nutrition strategies when it comes to what, when, and how you eat can vary significantly from person to person.
So, while generally speaking, intermittent fasting is safe and can benefit both your body and mind (we’ll get into the “how” shortly), everybody responds to fasting differently, and fasting may not be a good fit for you. There are also some circumstances where fasting isn’t recommended as a health-promoting eating routine (we’ll outline those categories later, too).
To find out if intermittent fasting might be a healthy choice for you and your body, you should check in with your primary care provider. If fasting is on your metaphorical table, our SIMPLE quiz can also help you figure out which approaches might suit you best.
Can intermittent fasting actually improve your health?
Does intermittent fasting actually work in terms of improving your health?
Again, everybody is different. That means the effects of intermittent fasting will be different, too.
There are lots of different benefits of intermittent fasting that can boost your health, but there are also some potential downsides and fasting side effects.
Think of it like a game of Mario Kart: sometimes it’s a path toward exciting power-ups, and sometimes it’s like hitting a slippery banana peel.
If we didn’t just lose you with that millennial analogy, here’s the bottom line: there are so many different variables involved in a person’s health, so some of those fasting benefits may not always translate to improved health for everyone.
But in the next section, we’ve rounded up the science so you can understand what to expect, even if you may not experience these improvements and setbacks yourself.
Health benefits and risks of intermittent fasting
What might intermittent fasting do for you? Let’s take a look at the evidence and see.
Lower inflammation
Inflammation contributes to many chronic and acute illnesses, like high blood pressure and heart disease. Some studies have linked intermittent fasting to reducing inflammation and inflammatory diseases.[4] These findings may be more likely for those living with overweight and obesity.
Lower risk of type 2 diabetes
Intermittent fasting can reduce insulin resistance [9], and decrease both cholesterol and blood glucose levels for individuals living with overweight and obesity [10] — all of which are factors that can lower your risk of developing type 2 diabetes and generally improve your metabolic health.
A healthier heart
By lowering inflammation, cholesterol, blood sugar, and insulin resistance, intermittent fasting may also support our cardiovascular health and increase our heart’s resistance to possible pathogens.[11,12]
A healthier brain
Some studies suggest that intermittent fasting can promote healthy brain aging and enhance circulating BDNF (a protein that plays an important role in the growth and survival of nerve cells), which may lead to an increase in BDNF in the brain, too.[13,14]
Metabolic changes
When we cut calories, our metabolism can slow down (annoying, yes, but it’s a self-preservation mechanism to make sure our body can continue existing on more limited amounts of fuel). So we’re often asked: does intermittent fasting slow your metabolism, too? Some research suggests fasting may introduce beneficial metabolic changes, like increasing your metabolic rate and your ability to oxidize fat.[15,16,17]
However, there is not enough strong evidence to suggest that intermittent fasting definitely increases metabolic rate (and some studies do show it may decrease [18]), but pairing fasting with strength training and lean protein can promote lean muscles and lower body fat percentages.[19]
Hormonal changes
Some research suggests that assigned-at-birth men and women may respond differently to intermittent fasting because it may decrease certain reproductive hormones while not affecting others.[20] A reduction in androgens (such as testosterone) could be beneficial for women with polycystic ovarian syndrome but detrimental to men. However, existing research is very limited and fails to explore the effects of fasting specifically on trans men and women and individuals currently on hormone replacement therapy.
Mood changes
While some studies suggest intermittent fasting may reduce symptoms of anxiety and depression [21], others also suggest it could increase negative emotions and decrease positive emotions.[22] At present, it’s not clear who may or may not benefit from fasting when it comes to mood. What we do know is that it is common when you initially start fasting to feel hungrier, crankier, or grouchier. But don’t worry! You won’t be hangry forever. After a week or two, these feelings will pass, and you’ll be enjoying all those intermittent fasting health benefits.
Decreased concentration
Your brain needs certain nutrients from food to function and perform cognitive processes.[23] Following a fasting-based food routine can lead to depriving your brain of these nutrients if you aren’t careful in planning your meals, and these deficits can lead to things like brain fog, headaches, and fatigue.
Higher risk of disordered eating
Intermittent fasting helps bring more conscious awareness to your eating habits and what you eat. While this mindful focus can be a helpful motivator for people looking to introduce more nutrient-dense foods into their routines, it can also lead to disordered relationships with food or exacerbate disordered eating tendencies.[24,25] This is why we always emphasize that fasting is not suitable for anyone with an eating disorder history.
Pros and cons of intermittent fasting
| Pros | Cons |
| No fully-off-limits foods | Requires careful meal planning |
| No calorie-counting | Difficult to manage around life events if poorly planned |
| Offers an easy-to-follow structure | Difficult to manage around life |
| Offers an easy-to-follow structure | More intense exercise can be challenging |
| Doesn’t require specialty ingredients | Not appropriate for everyone |
| Inexpensive |
Pros
Intermittent fasting is all about when you eat, not what you eat — depending on which approach you take, you can choose to skip breakfast, lunch, or dinner — so it can be a more flexible, approachable eating routine for people tired of calorie-counting or food restrictions. Since it doesn’t require any specialty foods or kitchen gadgets — you just eat as you normally would during your eating windows — your shopping bills won’t increase either. It’s also fairly easy to follow (in theory) since you just need to keep an eye on the clock and stick to whatever fasting / eating schedule you’ve set.
Cons
While you can, to some extent, eat what you want during your eating window, you still need to plan your meals carefully to ensure you’re getting all the nutrients you need for the day. Depending on your commitments and which intermittent fasting approach you choose, it can also be difficult to manage your fasting windows around social commitments, school or work schedules, and other life events.
Physical activity can also be tricky since too much exertion without the proper fuel in your body can lead to injury, breaking down muscle tissue, and/or feeling unwell. The most significant con, though, is that this eating routine isn’t appropriate or health-promoting for everyone, so you need to be sure it’s safe for you before trying it.
Is intermittent fasting right for you?
Deciding whether or not intermittent fasting is right for you — or if fasting is good for you — is like shopping for the perfect outfit.
You never want the fit to be aspirational or too tight. Like every clichéd Hollywood makeover montage, you’re looking for something that is just right for you and only you. That means factoring in your body, style, needs, preferences, and budget.
If you’re wondering, “Does intermittent fasting work for everyone?” though, there are some people who should avoid fasting entirely.
Who should avoid intermittent fasting?
We recommend speaking with your primary care provider before making any decisions that may impact your health. You should be particularly cautious about intermittent fasting if you:
- Are pregnant, breastfeeding, or trying to conceive;
- Have a history of or are currently diagnosed with disordered eating;
- Have a medical condition (like diabetes);
- Are under the age of 18, or 80 years old or more; or
- Are prescribed medication (for example, anti-hypertensives, diabetes medications, or any that need to be taken with food).
5 pro tips for the best intermittent fasting results
If your doctor has given you the green light for intermittent fasting and you’re ready to give it a go, here are some tips from our experts on how to stay in the race, maximize performance, and get to the finish line.
1. Start slowly
Like most good things in life, intermittent fasting isn’t a quick fix or a sprint; it’s a marathon. Slamming on the gas from the get-go can just lead to burning out, so channel your inner tortoise and aim for slow and steady. Ease into the process and pick an approach that can work around your schedule, daily routines, and other commitments. While intermittent fasting for specific purposes (like weight loss) may require some slight rerouting of habits, you never want it to be a roadblock to getting on with your life.
2. Stay hydrated
Water is the most important fuel you can give yourself to keep you going for the long haul. It helps your body remove waste, burn fat, regulate blood pressure, and do a whole lot of other valuable tricks of the trade. If you’re not a fan of the plain stuff, you can superpower it with fruits, herbs, or spices. Some other low-calorie drinks like black coffee, diet soda, and plain, unsweetened green tea also contain a decent amount of water, but you’ll want to be conscious of caffeine and the potential side effects of artificial sweeteners.
3. Plan your eating and fasting windows carefully
Like any long drive, you’ll want to plan for pit stops along the way. To save yourself from meandering side roads or panicked last-minute stops, figure out what you need to get through your fasting windows safely and effectively and navigate your eating windows with nutrient-dense, health-promoting foods — while also factoring in occasional detours because life is too short to miss out on that weird roadside attraction (or, in the case of this metaphor, your favorite comfort foods).
Having an intermittent fasting meal plan can help you anticipate twists and turns and drift through any curves life throws into your path, so check out our guides on what to eat during intermittent fasting and what you can drink while fasting, as well as what breaks a fast to help you map out what works for you. In general, a good rule of thumb is to aim for whole grains, lean protein, leafy vegetables, fruits, legumes, calcium-rich foods, and healthy fats like nuts and seeds.
4. Adjust your exercise routine according to your eating schedule
Intermittent fasting and physical activity can go together, but it’s not just about “eat less, move more” — if you push your body too hard without enough fuel, it’s eventually going to spin out. Instead, you want to manage the type, level, and length of physical activity according to your goals, needs, and well-being. We’ve gathered everything you need to know about intermittent fasting and working out so you can figure out a smart and sustainable plan that suits both your body and the track you’re trying to stick to.
5. Practice self-compassion, not self-judgment
Particularly when you’re just starting out, intermittent fasting can be a bumpy, pothole-ridden ride. Respecting your limits and praising your milestones rather than dwelling on missed turns and stewing in guilt will take you far in reaching whatever destination you’ve set as your end goal.
Simple’s expert opinion and final thoughts
The team here at Simple all agree: the best eating routine is the one that is right for your unique body — and one that you can stick to. When thinking through potential intermittent fasting plans, you want to make sure your needs, goals, preferences, and lifestyle are top of mind.
While all intermittent fasting approaches can benefit your body and mind, everyone responds to fasting differently, and fasting may not be a good fit — or work — for you.
To learn more about which intermittent fasting protocol might work best for you and get tips on when and how to get started, stay motivated, and achieve your goals, head to our SIMPLE quiz today. We’re here to set you up for success, whatever that looks like for you.
Frequently asked questions about if intermittent fasting actually works
How long does it take for intermittent fasting to work?
Since everybody is different, how long it takes for intermittent fasting to work — if it works at all — is different, too. Some people may notice results in a week, while for others, it may take several. Plus, whether it “works” also depends on what goals you have for fasting. We know it’s tough not having clear benchmarks to track, so we always recommend starting small and testing out different methods to see what feels best. And if you’re still feeling stuck, we have our “intermittent fasting not working” troubleshooting guide.
Does intermittent fasting work for belly fat?
Although some studies suggest that intermittent fasting can reduce belly fat and associated metabolic risk factors in certain conditions [26,27], existing research is limited to small populations meaning that it might not work for everybody.
How much weight can you lose in a month with intermittent fasting?
How much weight you lose in a month with intermittent fasting depends on your starting weight and medical conditions, the food you eat during your eating windows, and other factors like your lifestyle, age, and activity level. While some people experience more rapid weight loss, the healthiest — and most enduring — weight loss is gradual. Losing one or two pounds a week is safe and effective.
Does the 16:8 intermittent fasting work?
As with any eating routine, whether the 16:8 intermittent fasting approach works depends on a lot of individual factors. The majority of studies around the benefits of time-restricted eating have focused on this approach (as opposed to other time-restricted eating routines like 12:12, 14:10, or 20:4), and we recommend it as a good place to start if you’re skeptical or concerned about fasting since it simply extends the natural daily fast that happens when you’re sleeping.
What is the most effective intermittent fasting method?
The most effective intermittent fasting method — and the one that is safe, effective, and provides more lasting results — is the one that is right for your unique body. It should also be an eating routine that you can stick to.
There’s no one-size-fits-all way to intermittent fast, so before beginning any method, ask yourself what feels the best and most sustainable for you and know exactly what you’re hoping to achieve with intermittent fasting so your needs and goals guide every step of your approach.
- Abeyasekera KN. Benefits of Intermittent Fasting: A Systematic Review of Randomized Clinical Trials. Physician Assistant Studies. (2020).
- Patikorn C, Roubal K, Veettil SK, Chandran V, Pham T, Lee YY, Giovannucci EL, Varady KA, Chaiyakunapruk N. Intermittent fasting and obesity-related health outcomes: an umbrella review of meta-analyses of randomized clinical trials. JAMA network open. 2021 Dec 1;4(12):e2139558-.
- Wang W, Wei R, Pan Q, Guo L. Beneficial effect of time-restricted eating on blood pressure: a systematic meta-analysis and meta-regression analysis. Nutrition & Metabolism. 2022 Nov 8;19(1):77.
- Wang X, Yang Q, Liao Q, Li M, Zhang P, Santos HO, Kord-Varkaneh H, Abshirini M. Effects of intermittent fasting diets on plasma concentrations of inflammatory biomarkers: a systematic review and meta-analysis of randomized controlled trials. Nutrition. 2020 Nov 1;79:110974.
- Seimon RV, Roekenes JA, Zibellini J, et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015;418 Pt 2:153-172. doi:10.1016/j.mce.2015.09.014
- Johnstone A. Fasting for weight loss: an effective strategy or latest dieting trend?. International Journal of Obesity. 2015 May;39(5):727-33.
- Freire R. Scientific evidence of diets for weight loss: Different macronutrient composition, intermittent fasting, and popular diets. Nutrition. 2020 Jan 1;69:110549.
- Lowe DA, Wu N, Rohdin-Bibby L, Moore AH, Kelly N, Liu YE, Philip E, Vittinghoff E, Heymsfield SB, Olgin JE, Shepherd JA. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA internal medicine. 2020 Nov 1;180(11):1491-9.
- Albosta M, Bakke J. Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians. Clinical diabetes and endocrinology. 2021 Dec;7(1):1-2.
- Yuan X, Wang J, Yang S, Gao M, Cao L, Li X, Hong D, Tian S, Sun C. Effect of intermittent fasting diet on glucose and lipid metabolism and insulin resistance in patients with impaired glucose and lipid metabolism: A Systematic Review and Meta-Analysis. International journal of endocrinology. 2022 Mar 24;2022.
- Yang F, Liu C, Liu X, Pan X, Li X, Tian L, Sun J, Yang S, Zhao R, An N, Yang X. Effect of epidemic intermittent fasting on cardiometabolic risk factors: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition. 2021:803.
- Mattson MP, Wan R. Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. The Journal of nutritional biochemistry. 2005 Mar 1;16(3):129-37.
- Francis N. Intermittent fasting and brain health: Efficacy and potential mechanisms of action. OBM geriatrics. 2020 May; 4(2).
- Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early time-restricted feeding improves 24-hour glucose levels and affects markers of the circadian clock, aging, and autophagy in humans. Nutrients. 2019 May 30;11(6):1234.
- Patterson RE, Sears DD. Metabolic effects of intermittent fasting. Annual review of nutrition. 2017 Aug 21;37.
- Zauner C, Schneeweiss B, Kranz A, Madl C, Ratheiser K, Kramer L, Roth E, Schneider B, Lenz K. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. The American journal of clinical nutrition. 2000 Jun 1;71(6):1511-5.
- Heilbronn LK, Smith SR, Martin CK, Anton SD, Ravussin E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American journal of clinical nutrition. 2005 Jan 1;81(1):69-73.
- Al-Jafar R, Wahyuni NS, Belhaj K, Ersi MH, Boroghani Z, Alreshidi A, Alkhalaf Z, Elliott P, Tsilidis KK, Dehghan A. The impact of Ramadan intermittent fasting on anthropometric measurements and body composition: Evidence from LORANS study and a meta-analysis. Frontiers in Nutrition. 2023 Jan 17;10:10.
- Keenan S, Cooke MB, Belski R. The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. Nutrients. 2020;12(8):2349.
- Cienfuegos S, Corapi S, Gabel K, et al. Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. Nutrients. 2022;14(11):2343.
- Berthelot E, Etchecopar-Etchart D, Thellier D, Lancon C, Boyer L, Fond G. Fasting interventions for stress, anxiety and depressive symptoms: A systematic review and meta-analysis. Nutrients. 2021 Nov;13(11):3947.
- Wang Y, Wu R. The Effect of Fasting on Human Metabolism and Psychological Health. Dis Markers. 2022;2022:5653739.
- Gómez-Pinilla F. Brain foods: the effects of nutrients on brain function. Nature reviews neuroscience. 2008 Jul;9(7):568-78.
- Schueler J, Philip SR, Vitus D, Engler S, Fields SA. Group differences in binge eating, impulsivity, and intuitive and mindful eating among intermittent fasters and non-fasters. Appetite. 2023 Mar 1;182:106416.
- Ganson KT, Cuccolo K, Hallward L, Nagata JM. Intermittent fasting: Describing engagement and associations with eating disorder behaviors and psychopathology among Canadian adolescents and young adults. Eating Behaviors. 2022 Dec 1;47:101681.
- Arciero PJ, Poe M, Mohr AE, Ives SJ, Arciero A, Sweazea KL, Gumpricht E, Arciero KM. Intermittent fasting and protein pacing are superior to caloric restriction for weight and visceral fat loss. Obesity. 2023 Feb;31:139-49.
- Wilkinson MJ, Manoogian EN, Zadourian A, Lo H, Fakhouri S, Shoghi A, Wang X, Fleischer JG, Navlakha S, Panda S, Taub PR. Ten-hour time-restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome. Cell metabolism. 2020 Jan 7;31(1):92-104.