Is intermittent fasting good for you?
That’s what we’re here to find out.
Of course, what we suspect you really want to know is whether fasting will help you achieve your goals. Improve your health. Lose weight. Transform your body. Feel better about yourself. Feel better within yourself.
Making progress on these priorities matters. And people say intermittent fasting (IF) can make a difference.
We’ll cut through the hype and look at what the science says about exactly why intermittent fasting is thought to be so good for you.
Let’s see what stands up to our SIMPLE scrutiny.
- Intermittent fasting is an approach to nutrition that alternates fasting and eating.
- It has many health benefits, like improved blood sugar control, lower blood pressure, and reduced inflammation levels.
- It can help you lose weight and fat and decrease your risk of some common chronic diseases.
- IF could improve your gut microbiome.
- IF does have some risks, like nutrient deficiencies and dehydration, and it’s not safe for everybody.
What is intermittent fasting?
Intermittent fasting is a dietary approach that alternates periods of eating and not eating.
Those periods of not eating are called fasts.
You could fast every day using a time-restricted eating protocol (TRE). TRE fasts are between 12–20 hours and typically include zero calories.
Or, you could fast a few times a week, using a method like 5:2 or alternate day fasting (ADF). Fasts with these methods are usually 24 hours and include 500/600 calories.
At its heart, intermittent fasting is SIMPLE. There aren’t any complex rules about what you should and shouldn’t eat—nothing is off-limits during your eating window. (That said, you’ll get the best results from eating a healthy, balanced diet; check out what to eat while intermittent fasting to learn more.)
During your fasting window, you’d stick to drinks with zero calories or whatever foods you like to make up your 500/600 calories.
Why not try it for yourself? It’s the best way to really understand it. Check out our SIMPLE quiz, and we’ll help you get started!
What happens to your body when you are fasting?
So, why bother fasting? What does it actually do for / to your body?
Well, when you eat in a regular way throughout the day, the food you eat provides energy for whatever you’re doing.
When you fast, your body doesn’t get that ready energy supply coming in. So it has to draw on the energy it has stored.
First, it’ll turn to glucose and burn through your glycogen stores. Then, it’ll switch to using your fat stores. This happens anywhere upwards of eight hours into your fast and is called ketosis.
This is the metabolic switch that draws many people to try intermittent fasting. Through a SIMPLE, regular back-and-forth between eating and fasting, we can prompt this fat-burning state to occur, which can have several benefits for our health.
Is fasting an effective way to lose weight?
One of those benefits is weight loss.
Plenty of studies have shown intermittent fasting is just as good as regular calorie-counting diets for weight loss — including the 2022 study, where both IF and calorie-counting dieters lost weight (17 lbs and 14 lbs, respectively).
Where IF has the edge, you might find, is in the lack of calorie counting you have to do!
Another study with 101 participants looked at the effects of two specific intermittent fasting methods: 16/8 intermittent fasting and alternate day fasting (ADF).
At a three-month follow-up, those doing 16/8 had lost an average of 9.7 lbs, and the ADF-ers lost 32.6 lbs on average.
Clearly, the effect of any dietary change is an individual thing. What works for one person may not work for another. With intermittent fasting, the science suggests that it supports you by helping to control your appetite, improve your hormonal profile in weight-loss-supportive ways, and naturally reduce your calorie intake by reducing the amount of time you have available for eating.
But what matters most of all is this:
Can you stick to it?
If you can, the evidence suggests it could definitely be an effective way to lose weight.
Benefits of intermittent fasting
But why else is fasting good for you? What other neat things can it do for your body, mind, and life?
Let’s check out IF’s Top Five Headline Benefits.
- Your risk of diabetes drops
Intermittent fasting has been shown to help improve our body’s ability to manage blood sugar , which means a lower risk of pre-diabetes and type 2 diabetes.
Alternate day fasting also has a positive impact on improving insulin sensitivity and blood sugar control.
If you’re concerned about your HbA1c, IF could help get it into a good range.
- Your body fat goes down; your muscle sticks around
IF can also help reduce body fat.
For maximum muscle-preserving benefits, pairing IF with strength exercises and a balanced, protein-rich diet is a strong move.
- IF can make you brainier
It’s not just your body: Intermittent fasting is good for your mind too.
Studies suggest that cognition (a fancy word for thinking) can be enhanced.
Your brain’s neuroplasticity and stress resilience get a boost, and your risk of neurodegenerative and psychiatric disorders is reduced.
That’s kinda cool, right? You might be able to improve the condition of the pink blob of matter in your head simply by how you approach your eating.
- Your heart gets healthier
Intermittent fasting is a heart helper for sure.
Many studies provide evidence that IF improves the body in all sorts of heart-healthy ways, some of which we’ve already talked about, like improved insulin sensitivity and lower body fat.
But we also get reduced blood pressure, lower levels of inflammation, and better cholesterol levels in the mix with IF.[19,20,21]
Every one of these nudges your risk of heart disease down.
Not bad, IF, not bad at all!
- A happier gut
The gut and the role it plays in your health is currently a Hot Topic, and there’s growing evidence to suggest that intermittent fasting could be a friend to your gut microbiome by:
What does all that mean in real-life terms?
When gut health benefits and IF benefits combine—talk about a win-win!
(We’ve laid out six more intermittent fasting benefits here, if you’re keen to keep learning.)
Risks of intermittent fasting
We’ve covered some of the reasons why it’s good to fast. Now let’s look at the dark side—intermittent fasting does have some risks.
Hunger and friends
Understandably, when you first start a fasting protocol, one of the things you’ll experience is hunger.
You’ll also be on a first-name basis with tiredness and grouchiness. Maybe a headache or two will drop by. You might not sleep as soundly for a little while. Your energy might tank.
Nobody panic. All of this is temporary. It. Will. Pass.
You could become dehydrated
When you’re fasting, you gotta get organized with your water intake.
Without the water that comes from the food you eat (about 20%–30% of your overall fluid intake), and as your body burns through its glycogen stores (which causes the loss of stored water, too), you run the risk of not getting enough.
So, drink lots of water (sadly, gin doesn’t count).
Your food choices might get a little … iffy
Sometimes fasting will kick off your hunger and cravings hard, you’ll hit toddler mode, and when that happens … yeesh. It gets a lot tougher to make good food choices.
To get the most from IF, you need to make good food choices more often than not, and fierce hunger and cravings can get in the way. You can beat it, though! It just takes practice.
That said, some extra insights into how to fast well and build great habits around food could really help. Give our SIMPLE quiz a go and hook yourself up with our app. We have lots of great, practical ideas on how to navigate challenges like this.
Nutrient deficiencies (and constipation) can occur
When you restrict your eating to specific time windows or calorie counts, it can be easy to undereat.
Not enough food equals not enough nutrients, which means you won’t feel or perform at your best.
A specific side note here: not enough fiber equals not enough … umm, how to say this politely … Number Two time.
There are lots of reasons to make sure you eat enough!
Some unwanted habits might pop up
Intermittent fasting has got an inevitable element of restriction.
For some, food restrictions can provoke some challenging feelings, thoughts, and behaviors.
Look after yourself as you fast and pay attention to these signals. If IF doesn’t feel like a supportive approach for you, stop.
Who should avoid intermittent fasting?
There are some people who need to avoid intermittent fasting.
If you see yourself on the list below, don’t try IF without your doctor’s permission and support:
- are pregnant, breastfeeding, or trying to conceive
- take any medicines (especially those which affect blood glucose or blood pressure levels)
- have nutritional deficiencies
- are very active and/or have high daily energy demands
- are under 18 or over 75 years old
- have (or are at risk of having) an eating disorder or have a history of one
- have a health condition, like diabetes or anemia
- have a Body Mass Index (BMI) in the “underweight” category
Is intermittent fasting right for you?
We’ve addressed the question of whether intermittent fasting is good for you.
Here’s the next big one: Is intermittent fasting right for you?
It doesn’t matter how many benefits IF has if it’s not something you can practically and sustainably do because none of the benefits persist if you don’t persist—meaning that once you stop IF-ing, your body fat, blood pressure, cholesterol, etc., will likely return to how they were before.
Whichever IF protocol you choose has to be something you can do long term. So, how will you know if IF is right for you?
First, ask yourself: Am I safe to try it?
If yes, then how does it feel as you think about it? Does fasting every day / week feel doable? Could it fit into your lifestyle?
If yes—even if you’re not quite sure—try it out. Pick a protocol and get started. Our intermittent fasting for beginners guide will have you up and running in no time.
If you’re not quite ready to jump in just yet, that’s OK. Let’s address the next juncture …
Which IF method should you choose?! Let’s take a look at the options.
Types of intermittent fasting
There are a number of possibilities, but once you whittle them down to what’s effective and safe, it’s not so overwhelming.
We’ll guide you through it so you can see which fasting schedule might suit your lifestyle best.
Time-restricted eating (TRE)
First up, we have …
This gives you a daily eating window of eight hours.
The fasting period is 16 hours, and a lot of this happens overnight while you’re asleep. (That really helps with the hunger and irritability, honestly.)
If 16 hours sounds like a lot, you can get your intermittent fasting feet wet by starting with a shorter fast like 14/10 or even 12/12.
The Warrior Diet
On the Warrior Diet, the fasting window is longer: 20 hours.
This means your eating window is just 4 hours long!
That could be a toughie for making sure you nourish your body properly (remember the nutrient deficiency risk from earlier?), so we suggest you don’t choose this protocol as your first foray into fasting.
The 5:2 diet
The 5:2 diet is the one you might have heard of at the gym or around the office. It’s quite a popular way to practice IF.
With 5:2, you fast two days a week. On your fast days, you’ve got 500/600 calories to play with, so it’s not a strict, 0-kcal, 24-hour fast.
The rest of the week, you eat as you wish.
Alternate day fasting (ADF)
Alternate day fasting (ADF) also has fast days that include 500/600 calories.
Though with ADF, these fast days happen every other day. So Monday, you eat as you like; Tuesday, you fast. Wednesday, you eat; Thursday, you fast. And so on, like a relay race.
These four IF approaches we’ve just talked about are our top picks.
The next two we’ll cover, we don’t recommend.
Eat Stop Eat
Eat Stop Eat lets you eat one full meal on your fast day, then that’s it. You’re done on the food front till the same time the next day. There are two days like this each week.
On the other five days, how much you eat and when is entirely your choice.
We don’t like this approach because the fasting period is 24 hours and zero calories. The risks of dehydration, nutrient deficiencies, hormonal disruption, and so on are far higher with a fast like this.
Water fasting makes our “please don’t try this at home” list because it involves going 24–72 hours with no food and drinking only water.
If you’re doing it with medical supervision, fine. Otherwise, it’s not a smart path to your goals. Any weight loss or health benefits you get from water fasting will be short-lived, and, again, the risks are pretty high.
SIMPLE’s expert opinion and final thoughts
If the question is:
“Is intermittent fasting good for you?”
Then the answer is:
So long as it’s safe for you medically, physically, and emotionally, there are a ton of positive health benefits that can come from taking an IF approach to how you eat.
For the right person, IF is health promoting. It adds value.
Are you that right person? If so, try our SIMPLE quiz and get started on your IF journey today.
Frequently asked questions about whether fasting is good for you or not
How long is it safe to fast?
If we’re talking about a zero-calorie fast, it’s likely safer to fast for less than 24 hours.
If you’re doing something like ADF or 5:2, where there’s a small amount of calories involved, a 24-hour fast is safe.
We wouldn’t recommend anything longer.
Is fasting for three days healthy?
Fasting for three days is not healthy. Your body needs nutrients, and it gets them from regular food. Unless you’re doing it under medical supervision, we wouldn’t recommend a three-day fast.
Is fasting good for the liver?
There’s no evidence to say that fasting is not good for the liver, but, equally, there is no evidence we know of that says it specifically benefits the liver either.
Can fasting affect blood pressure?
Fasting can affect blood pressure! Research suggests it has a positive impact.
What are the benefits of fasting?
The main benefits of fasting are improved insulin sensitivity, better cholesterol levels, reduced blood pressure, improved heart health, lower body weight, reduced body fat, and potentially better gut health.
Is it good to fast?
Is it good to fast in general? It seems so. Overall, the benefits look pretty sound.
Is it good for you to fast? Try it and see for yourself.
- Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG 3rd, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity . 2018 Feb;26(2):254–68.
- Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA, Hills AP, et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418 Pt 2:153–72.
- Liu D, Huang Y, Huang C, Yang S, Wei X, Zhang P, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med. 2022 Apr 21;386(16):1495–504.
- Chair SY, Cai H, Cao X, Qin Y, Cheng HY, Ng MT. Intermittent Fasting in Weight Loss and Cardiometabolic Risk Reduction: A Randomized Controlled Trial. J Nurs Res. 2022 Feb 1;30(1):e185.
- Ravussin E, Beyl RA, Poggiogalle E, Hsia DS, Peterson CM. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. Obesity . 2019 Aug;27(8):1244–54.
- Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018 Jun 5;27(6):1212–21.e3.
- Patterson RE, Laughlin GA, LaCroix AZ, Hartman SJ, Natarajan L, Senger CM, et al. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015 Aug;115(8):1203–12.
- Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Netw Open. 2018 Jul 6;1(3):e180756.
- Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661–74.
- Wilkinson MJ, Manoogian ENC, Zadourian A, Lo H, Fakhouri S, Shoghi A, et al. Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome. Cell Metab. 2020 Jan 7;31(1):92–104.e5.
- Moro T, Tinsley G, Bianco A, Marcolin G, Pacelli QF, Battaglia G, et al. 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. J Transl Med. 2016 Oct 13;14(1):290.
- Barnosky A, Kroeger CM, Trepanowski JF, Klempel MC, Bhutani S, Hoddy KK, et al. Effect of alternate day fasting on markers of bone metabolism: An exploratory analysis of a 6-month randomized controlled trial. Nutr Healthy Aging. 2017 Dec 7;4(3):255–63.
- Kim G, Kim JH. Impact of Skeletal Muscle Mass on Metabolic Health. Endocrinol Metab (Seoul). 2020 Mar;35(1):1–6.
- Laurens C, Grundler F, Damiot A, Chery I, Le Maho AL, Zahariev A, et al. Is muscle and protein loss relevant in long-term fasting in healthy men? A prospective trial on physiological adaptations. J Cachexia Sarcopenia Muscle. 2021 Dec;12(6):1690–703.
- Templeman I, Smith HA, Chowdhury E, Chen YC, Carroll H, Johnson-Bonson D, et al. A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults. Sci Transl Med [Internet]. 2021 Jun 16;13(598).
- Kim C, Pinto AM, Bordoli C, Buckner LP, Kaplan PC, Del Arenal IM, et al. Energy Restriction Enhances Adult Hippocampal Neurogenesis-Associated Memory after Four Weeks in an Adult Human Population with Central Obesity; a Randomized Controlled Trial. Nutrients [Internet]. 2020 Feb 28;12(3).
- Mattson MP, Moehl K, Ghena N, Schmaedick M, Cheng A. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018 Feb;19(2):63–80.
- Malinowski B, Zalewska K, Węsierska A, Sokołowska MM, Socha M, Liczner G, et al. Intermittent Fasting in Cardiovascular Disorders-An Overview. Nutrients [Internet]. 2019 Mar 20;11(3).
- Harvie MN, Pegington M, Mattson MP, Frystyk J, Dillon B, Evans G, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes . 2011 May;35(5):714–27.
- Ahmed A, Saeed F, Arshad MU, Afzaal M, Imran A, Ali SW, et al. Impact of intermittent fasting on human health: an extended review of metabolic cascades. Int J Food Prop. 2018 Jan 1;21(1):2700–13.
- Ahmed N, Farooq J, Siddiqi HS, Meo SA, Kulsoom B, Laghari AH, et al. Impact of Intermittent Fasting on Lipid Profile-A Quasi-Randomized Clinical Trial. Front Nutr. 2020;7:596787.
- Su J, Wang Y, Zhang X, Ma M, Xie Z, Pan Q, et al. Remodeling of the gut microbiome during Ramadan-associated intermittent fasting. Am J Clin Nutr. 2021 May 8;113(5):1332–42.
- Zeb F, Wu X, Chen L, Fatima S, Haq IU, Chen A, et al. Effect of time-restricted feeding on metabolic risk and circadian rhythm associated with gut microbiome in healthy males. Br J Nutr. 2020 Jun 14;123(11):1216–26.
- Patterson RE, Sears DD. Metabolic Effects of Intermittent Fasting. Annu Rev Nutr. 2017 Aug 21;37:371–93.
- Cuccolo K, Kramer R, Petros T, Thoennes M. Intermittent fasting implementation and association with eating disorder symptomatology. Eat Disord. 2022 Sep-Oct;30(5):471–91.