So, how long does it take for intermittent fasting to work?
You started intermittent fasting a whole week ago. This morning, you stood on the scale, looked at that irritating number that somehow has the staying power of a red wine stain on white carpet, and thought, “How long does it take for this intermittent fasting thing to work, anyway?”
Now you’re hovering anxiously over your fasting tracker, wishing you could speed things up but feeling stumped on how to do so.
We’ve got you. Come with us for a spin through how — and when — results show up with intermittent fasting, plus the lowdown on what can get you stuck and how to fix it.
What is intermittent fasting?
Intermittent fasting is an approach to how you eat that involves putting time limits around when you eat. Outside of those designated eating times, you fast.
Say you follow the 16:8 intermittent fasting schedule. On 16:8, you’d consume all your meals, snacks, and any calorie-containing drinks within 8 hours. For the remaining 16 hours of the day, you’d drink only zero-calorie drinks, like water and black coffee. It’d look something like this:
- 9 AM to 5 PM: Eat all your meals, snacks, and calorie-containing drinks.
- 5 PM to 9 AM: Fast.
- Repeat.
How does it work?
So, how does intermittent fasting work? Well, there are two main ways intermittent fasting drives results.
First, it helps to create a calorie deficit (when you eat fewer calories than you burn) by restricting the time you eat. For instance, with 16:8, say you finish eating at 5 PM. Any food you’d normally eat after 5 PM gets naturally struck from your daily diet.
Of course, you can override this and eat just as much in your 8-hour eating window as you usually would during a full day, but the idea is that less time = less food.
Second, intermittent fasting works by stimulating ketosis. This means that after 8–12 hours of not eating (longer for some people), your body has no more sugar to burn for energy. It switches fuel and starts burning fat for energy instead. As there’s still no food coming in, it’s the fat stored in your body that gets used.
What are the benefits of intermittent fasting?
There are many benefits of intermittent fasting. A few well-studied benefits are:
- weight loss [1]
- improved insulin sensitivity [1]
- reduced inflammation [2]
- better blood pressure [3]
- lower cholesterol levels [1]
- improved heart health [4]
There are others, too, so:
- Does intermittent fasting cause a slower metabolism? No, it doesn’t seem to.
- Can it help preserve muscle mass while losing weight? Yes, it can (assuming adequate protein intake).[5]
- Does it improve sleep? It’s possible [6] — but more studies are needed to say for sure.
- How about improving brain health? Again, potentially [7], but we need more studies on this.
One exception we’ll note here is autophagy (the process by which the body clears out old, damaged cells). This is often claimed as a benefit of fasting, but given that most of the research on this was done on animals, we don’t think it can be reliably claimed just yet.
How long does intermittent fasting take before seeing results?
How long it takes to see results from intermittent fasting, whether that’s weight loss or some other health goal, will depend on factors like your age, gender, any medical conditions, what you eat, how active you are, your stress levels, and so on. The length of your fasts also plays a big role.
It also depends on what results you’re hoping to see. Different results show up at different times. Let’s look at this from a couple of angles.
How long does it take to see weight loss results from intermittent fasting?
Research shows it can take anywhere from 2 to 10 weeks to lose between 7 and 11 lbs on intermittent fasting.[8] That’s a loss of roughly 1 lb a week (give or take), which is an excellent pace to shoot for. It’s steady, safe, and sustainable.
Any dietary habit change will take a few weeks to show a result because that new thing you’re doing needs to settle in. By week 4, for instance, you’ve ironed out the glitches and hit your stride, which allows you to start working your habits with the consistency that generates progress. It’s frustrating but normal (and for some, it’ll take longer, so don’t be disheartened if the end of week 2 isn’t the magic moment for you!)
The fastest way to get where you want to go is to focus on consistency, not speed.
That said, results are a big piece of what keeps our motivation stoked. So it’s not enough just to say, “Hey, intermittent faster — be patient!!” Luckily there are some intermittent fasting results you will see in those first few weeks (and beyond) that’ll tell you it’s working. Focusing on these whenever the scale gets stubborn and won’t budge is a great way to:
- stay motivated to keep going
- prove to yourself you’re doing it right
What are some other common results to look out for?
When your weight is stuck, here’s the secret to staying in the game:
look for (and celebrate) the non-scale victories.
What is a non-scale victory, you ask? They come in as many forms as you can think of. Let’s get into it.
Early non-scale victories
In the first week or so of intermittent fasting, your waist may feel and look slimmer, and you may feel less bloated. Keep going, and this reshaping of your midsection will likely continue. In one study, for instance, women who were overweight or living with obesity lost 4% to 7% of visceral fat (a kind of belly fat that sits around your abdominal organs) over 6 months.[9]
A 2019 study showed benefits in the cardiovascular health of those who tried intermittent fasting for four weeks.[10] In another study, intermittent fasting for seven to ten days reduced abdominal pain, bloating, diarrhea, nausea, and anxiety in those with irritable bowel syndrome (IBS).[11]
And there’s evidence that one to two fasts could improve your sugar and fat metabolism, hormone levels, and sleep.[12]
Now, these results won’t stick around unless you keep fasting, but as early wins, they’re pretty cool.
Longer-term non-scale victories
Over the longer term, your body will change in all sorts of ways through consistent, well-done intermittent fasting. Be alert for these changes — every single one is a win!
From years of working with clients, we know that those who pay attention to these wins — and afford them the same status as losing lbs— are far more likely to stay the course and achieve better results overall.
Look out for:
- looking slimmer in photos
- your clothing fitting better
- being able to wear a smaller size jeans or shirt
- moving more easily and/or with less pain in your joints
- walking for longer and/or without getting breathless
- improvements in health markers, like blood pressure or cholesterol levels
- better sleep
- feeling more mentally focused and clear
- having more energy
- feeling calmer, brighter, and more positive
- clearer skin, stronger nails, and glossier hair
- feeling more confident in your appearance
- feeling more at peace with your eating habits
These are all outcomes that stem from healthful nutrition, which is one part of doing intermittent fasting in a result-generating way (i.e., fasting alone isn’t enough. We’ll talk more about that later).
How can you measure your results?
The time-honored way of measuring results from dietary changes is the scale.
Yet the scale tells you only one thing about what’s happening — the weight lost. Yes, that one thing may be super important to you, and that’s valid. But it’s important to know the limitations of what the scale tells you — and how to properly use it and interpret the information it gives you.
1. Your weight will fluctuate during the day and week. Measure yourself at the same time of day, on the same day each week, to keep your readings as comparable as possible.
2. What you eat directly before weighing in can impact your results. If you have a heavy night of alcohol and/or salty food, for instance, you’ll see some water retention in your weight the next day. Let your salt and water levels normalize and weigh again the following day. (This is usually the only time we go against point #1 above.)
3. Slow weight loss means the process is working. Often, we hear, “I only lost 0.8 lbs, SIMPLE! Why is this not working???” To which we say (gently and with genuine compassion): if your weight is dropping, it is working. Weight loss is slow. Yes, it may feel like it goes on fast and easy and comes off slow and with intense effort, and that’s not fair. We agree it’s not fair. But that’s the process. Celebrate your small losses for the wins they are.
This is why it’s not always helpful to focus too much on how long you need to do intermittent fasting before seeing results. It can push you into an impatient frame of mind that makes slower progress harder to swallow. In the words of Elsa from Frozen, let it go. It’ll be easier to trust the process.
4. You can’t measure non-scale victories on the scale. We’re stating the obvious here but for good reason. Think about how you can measure the other progress you see and care about. We have a few ideas to get you started.
- To see changes in your body shape and size:
- Take pictures every couple of weeks.
- Once a month, try on an item of clothing you’d like to fit into.
- To notice improvements in how your body moves, feels, and performs:
- Map out a walk. Notice how your body feels while doing it and how long it takes you. Repeat that walk every 2–4 weeks.
- If you have joint pain, keep a diary and record how your joints feel each day. Look for changes over time.
- Get your health markers measured, and make an appointment to have them re-measured in 3–6 months.
- To observe how other things are changing:
- You can use an observation diary for anything qualitative you’d like to improve. Try recording how you slept, your energy levels, how confident you feel, and so on, and watch the trend over time.
You may have to think outside the box (especially the small metal one on the bathroom floor), but it’s possible to find a way to track and measure progress in any area that’s important for your health journey. If you’re feeling stumped, why not join the SIMPLE Facebook community for support and ideas? Take our SIMPLE quiz to get your intermittent fasting journey started, then jump into the FB group and make the most of the camaraderie and hive mind. We’re all here to help.
What are some possible reasons for not seeing changes?
If you’re not seeing results, you may (understandably) start feeling suspicious that intermittent fasting doesn’t work. Don’t kick it to the curb just yet — there are lots of levers you can pull to get things moving.
As we mentioned earlier, fasting alone isn’t enough to generate the kind of results you may be hoping for. To really make it work, it’s gotta be paired with other aspects of healthy living, like nutrition, exercise, quality sleep, and so on.
With that in mind, here are some reasons why it might feel like it’s taking several light years for intermittent fasting to show a result. Maybe you’re
- eating too many calories
- not eating enough high-quality nutrition
- not fasting for long enough
- on the wrong intermittent fasting schedule
- not sleeping enough
- skipping meals
- not drinking enough water
- exercising too much
- experiencing chronic stress
- not eating enough protein
- eating too many processed foods
- not being consistent
You can read more about these in our guide to why intermittent fasting may not be working. Don’t be downhearted if you’re getting tripped up. We all make plenty of intermittent fasting mistakes on the way to nailing it!
It’s also worth noting that you may benefit from first speaking with your doctor if you have or are currently experiencing eating disorders or disordered eating behaviors.
How much weight can you lose?
As we saw earlier, some research shows that in 10 weeks, you can lose between 7 and 11 pounds. Other research has shown a weight loss of 0.8% to 13% body weight between 2 and 26 weeks in people who are overweight and living with obesity.[13]
However, your body is unique, and your results will be too. How much weight you can lose will be based on factors like your age, gender, medical history, activity levels, food choices, etc.
So forget about comparing yourself to anyone else. Instead, bring curiosity to this question. How much weight can you lose if you stick to your intermittent fasting practice for, say, three months? Give it your best shot and find out!
5 tips on how to get better results with intermittent fasting
Before we get into the 5 tips, check out our intermittent fasting for beginners guide. It’ll help you choose the right fasting schedule for you and give you the basics. To really hit the ground running, take our SIMPLE quiz and use the fasting and food trackers on our app to help you stay focused and on track.
Now that you’ve done that, let’s look at how to ace your results!
1. Eat mindfully
Intermittent fasting can help you bring more conscious awareness to your eating patterns and choices.
It’s super easy to roll outta the day and into an all-evening graze-fest. By putting an after-dinner cut-off in place and fasting during the evening, you’re more able to notice what pulls you to eat (aside from hunger) and what triggers your cravings.
This simple act of paying attention will give you data that’ll help you improve your eating overall, which in turn will increase your results. (Spoiler alert: this awareness trick really helps if emotional eating is a thing for you.)
2. Take a crash course in fasting-friendly, healthful nutrition
As we’ve talked about, how long before intermittent fasting works will be very influenced by what you eat and drink. So, to get you well-versed in the kind of nutrition that leads to awesome results, here are our top three Must Reads:
Take your time to digest (see what we did there!) this info — your nutrition choices are a lynchpin of your success.
3. Have patience
It may sound like an odd tip for getting better results, but impatience is a surefire way to hamstring your results.
A lack of patience often leads to a lack of consistency and/or early quitting. It comes with thoughts like, “Screw this; it’s not working. What’s the point?!” and “I can’t be bothered to try this hard if this is all I have to show for it.”
We feel you on the frustration, but hang in there. While it’s easy to get snagged on the question, “How fast does intermittent fasting work? And can it work faster, please!”, results come to those who wait … and who practice healthful eating, structured fasting, and regular movement (plus other complimentary lifestyle habits) while they do so.
4. Get active
If you want to boost your intermittent fasting results, move ya body.
It doesn’t have to be fancy or hard. It doesn’t even need to be “exercise.” Moving more in any way will increase your calorie burn. Things like:
- Can you make your meetings into walking meetings? (You can also do this with phone calls.)
- Could you wash up manually instead of using the dishwasher?
- Could you cycle to work? (Stay safe out there; helmets on!)
- Could you do a yoga flow while watching TV?
Some of these are “exercise,” while others are just getting more movement into your day. Both will help quicken the pace of your results.
5. Track your consistency
Once you’re in the groove with intermittent fasting, using a habit tracker to monitor your consistency and keep you focused is a solid next step.
Choose around three daily habits that are a top priority for you to master, like:
- complete a 14-hour fast
- eat X grams of protein
- drink 2 L of water
and record your progress with these every day for a few weeks. Once you have these three habits on lock, switch them out for another three, and focus on locking those down next. And so on.
When do you see results from intermittent fasting? When you:
- get focused, and
- track your consistency to get a true picture of how you’re doing.
SIMPLE’s expert opinion and final thoughts
You know as well as we do — when you’re trying to lose weight, sometimes the scale isn’t your friend and stays stuck despite your best efforts.
This doesn’t necessarily mean you’re doing anything wrong or that it’ll never move. It often means that other things are happening — things that need to happen before the scale can move. At times like this, look for those non-scale victories.
If the non-scale victories aren’t showing up either … that’s the time to start looking at your process. Where might you be losing ground?
Focus your energy more on looking for signs of progress — and changing your actions if they’re nowhere to be seen — than wondering, “When does intermittent fasting start working?!” There’s no definitive answer to that. There’s only what is happening and what you can do to optimize or kickstart the results you want.
Take our SIMPLE quiz and tell us all about you. We’ll help you get up and running, show you the fasting ropes, and give you everything you need to crush this lifestyle — and your goals!
Final note: Be aware that intermittent fasting may not be for you, especially if you are pregnant, underweight, have a history of or an active eating disorder, take any medications, or have anemia. We recommend that you first speak with your doctor before making any changes to your lifestyle.
Frequently Asked Questions about how long it takes for intermittent fasting to work
How do you know if intermittent fasting is working?
You know intermittent fasting is working by tracking your results!
First, know what you want to get from fasting — is it weight loss? Improved blood pressure? A flatter belly? Once you know, figure out how to track that thing regularly, so you can see progress.
If you’re wondering how long before you see these results from intermittent fasting, we’ve got you covered.
How much weight can you lose in a month with intermittent fasting?
How much weight you can lose in a month with intermittent fasting will vary from person to person. According to research, it’s possible to lose between 7 and 11 lbs between 2 and 10 weeks on intermittent fasting.[8] That’s a loss of roughly 4 lbs a month, which is in line with the recommended 1–2 lbs a week.
Why is 16 hours the magic number for fasting?
16 hours isn’t really the magic number for fasting as such. The 16:8 intermittent fasting protocol is just one that’s been well studied and has shown positive results. The “magic” number of fasting hours for you will be the one you can do most consistently and successfully over the long term.
What foods won’t break a fast?
Pretty much all foods will break a fast. You can read more about that in our article about what breaks a fast!
Does sleep count as fasting?
Unless you eat in your sleep, yes — sleep counts as fasting!
Does intermittent fasting have any side effects?
There are a few intermittent fasting side effects. These tend to occur in the first couple of weeks of fasting, and they generally pass when you hit your stride.
- Gu L, Fu R, Hong J, Ni H, Yu K, Lou H. Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials. Front Nutr. 2022 May 2;9:871682.
- Wang X, Yang Q, Liao Q, Li M, Zhang P, Santos HO, et al. Effects of intermittent fasting diets on plasma concentrations of inflammatory biomarkers: A systematic review and meta-analysis of randomized controlled trials. Nutrition. 2020 Aug 12;79-80:110974.
- Yang F, Liu C, Liu X, Pan X, Li X, Tian L, et al. Effect of Epidemic Intermittent Fasting on Cardiometabolic Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Front Nutr. 2021 Oct 18;8:669325.
- Stockman MC, Thomas D, Burke J, Apovian CM. Intermittent Fasting: Is the Wait Worth the Weight? Curr Obes Rep. 2018 Jun;7(2):172–85.
- 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 [Internet]. 2020 Aug 6;12(8).
- 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 [Internet]. 2019 May 30;11(6).
- Ooi TC, Meramat A, Rajab NF, Shahar S, Ismail IS, Azam AA, et al. Intermittent Fasting Enhanced the Cognitive Function in Older Adults with Mild Cognitive Impairment by Inducing Biochemical and Metabolic changes: A 3-Year Progressive Study. Nutrients [Internet]. 2020 Aug 30;12(9).
- 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.
- Klempel MC, Kroeger CM, Bhutani S, Trepanowski JF, Varady KA. Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women. Nutr J. 2012 Nov 21;11:98.
- Stekovic S, Hofer SJ, Tripolt N, Aon MA, Royer P, Pein L, et al. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metab. 2019 Sep 3;30(3):462–76.e6.
- Kanazawa M, Fukudo S. Effects of fasting therapy on irritable bowel syndrome. Int J Behav Med. 2006;13(3):214–20.
- Stratton MT, Albracht-Schulte K, Harty PS, Siedler MR, Rodriguez C, Tinsley GM. Physiological responses to acute fasting: implications for intermittent fasting programs. Nutr Rev. 2022 Feb 10;80(3):439–52.
- Welton S, Minty R, O’Driscoll T, Willms H, Poirier D, Madden S, et al. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020 Feb;66(2):117–25.
