The Complete Guide to Intermittent Fasting 16/8 - Perfect Keto

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The Complete Guide to Intermittent Fasting 16/8


Intermittent fasting is an effective fasting method with research-backed health benefits, including healthy weight loss, better cognitive function, and lower inflammation. It has become a popular tool for improving overall health and reaching nutrition and fitness goals. The most well-known, approachable, and sustainable method is intermittent fasting 16/8.


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What Is Intermittent Fasting 16/8?

intermittent fasting 16/8

Intermittent fasting (IF), also known as time-restricted feeding, means eating within a specific daily window of time (feeding period) and fasting outside of that window (fasting period).

There are several different types of intermittent fasting, but the 16/8 method is the most popular because it’s the easiest.

Doing an 16/8 intermittent fast means that you fast for 16 hours and eat only within an eight-hour window throughout the day, such as from noon to 8 p.m.

The easiest approach is to skip breakfast and have your first meal later in the day. For example, if you finish dinner by 8 p.m., you wouldn’t eat again until midday the next day.

Keep in mind 16/8 intermittent fasting is only one approach. The windows can vary based on what works for you. While some people might only eat within the same eight hours a day, others might only eat within a six-hour window (18/6) or four-hour window (20/4).

How the 16/8 Intermittent Fasting Diet Works

Like exercise, restricting calories is a helpful metabolic stressor. Eating within a certain time frame pushes your body in a different metabolic direction than if you were eating all the time.

Intermittent fasting can cause autophagy, which is a crucial defense mechanism against malignancy, infection, and neurodegenerative diseases. It’s basically your body’s way of cleaning out cells that aren’t performing at their best.

Research finds short-term fasting is an effective way of starting neuronal autophagy (cleaning up brain cells that aren’t doing well), therefore protecting your brain against neurodegenerative diseases[*].

Intermittent fasting also triggers a beneficial metabolic reaction that includes[*]:

  • A decrease in inflammatory markers
  • Reduced blood glucose levels and insulin
  • An increase in the neurotrophin BDNF

These are powerful changes that can lead to several health improvements.

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Health Benefits of 16/8 Intermittent Fasting

Adopting this eating style may seem difficult if you’ve never tried it before, but once you get used to it, it’s easy to follow. Plus, the research-backed benefits make it an excellent tool to improve your health.

Intermittent fasting 16/8 has been researched for its ability to improve multiple aspects of your health.


#1: Fat Loss

Intermittent fasting can help both healthy and overweight adults lose weight and body fat effectively. Human intervention trials have consistently found IF significantly reduces weight[*] as your body is in a fat-burning mode more often.

In almost any type of fasting, losing weight is a natural byproduct because you’re consuming fewer calories.

#2: Improved Cognitive Function

Another perk of intermittent fasting is that it can improve brain function, boost focus, and get rid of brain fog.

Studies find that restricting calories moderately can[*][*]:

  • Protect the brain by reducing oxidative damage to cellular proteins, lipids, and nucleic acids
  • Elevate levels of BDNF, an important neurotrophin that is needed for synaptic plasticity

#3: Lower Inflammation

IF is also great for your brain and might help you think clearer. Intermittent fasting, or restricting calories, also lowers markers of inflammation, which in turn aids cognitive function and protects your brain health[*].

#4: Lower Blood Pressure

Research finds intermittent fasting can help reduce blood pressure. According to a recent study, people that restricted eating habits to a smaller period of time lost weight from a lower calorie intake, which then helped them lower their blood pressure[*].

#5: Blood Sugar Control

Intermittent fasting is also an excellent tool for blood sugar regulation. Research has found that IF reduces blood sugar, insulin, and improves insulin sensitivity[*].

#6: Better Metabolic Health

Due to the different beneficial effects of intermittent fasting on health markers, it supports overall metabolic health.

Research finds intermittent fasting can improve metabolic profiles and reduce the risk of obesity and obesity-related conditions such as non-alcoholic fatty liver disease, and chronic diseases such as diabetes and cancer[*].


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#7: Longevity

The positive effects IF can have on your metabolic health, inflammatory markers, and blood sugar levels may contribute to a longer lifespan and healthy aging.

Even though human trials are still needed to measure IF’s impact on longevity, multiple animal studies show calorie restriction results in an increased lifespan[*].

Another way intermittent fasting can improve your health is by facilitating ketosis.

How to Do Intermittent Fasting 16/8

intermittent fasting 16/8

To do intermittent fasting correctly and reap all the health benefits, here’s what to do:

  • Pick your fasting window: Choose what the hours of fasting will be. The easiest approach is to have an early dinner and skip your morning breakfast. For example, eating only from 1 p.m. to 9 p.m.
  • Have healthy meals during your eating window: A bad diet during your eating window can offset the metabolic benefits of intermittent fasting, so stick to nutritious whole foods. Here’s a list of the best keto-friendly foods to eat.
  • Eat fatty, satisfying meals: While you don’t need to be keto to try intermittent fasting, eating fatty foods will make it a lot easier and sustainable. Keto foods are healthy and satisfying, so you won’t be hungry during your fasting window. Practice smart snacking and you’ll do great.

Intermittent Fasting and Ketosis

One of the best things about fasting is that it can help you get into ketosis faster.

The two are related for a few reasons:

  1. For your body to get into ketosis, you must be fasting in some sense — either by not eating any food at all or by keeping carbs extremely low. When you’re in ketosis, it means your body is breaking down fat for energy.
  2. Intermittent fasting helps deplete your glucose stores at a faster rate, which speeds up the process of running on fat.
  3. Many people who start a ketogenic diet begin by fasting to enter ketosis more quickly.

So, is intermittent fasting 16/8 guaranteed to get you into ketosis? No, but it can help get you there if you do it along with a keto diet.

Intermittent Fasting 16/8 and the Keto Diet

intermittent fasting 16/8

There are three compelling reasons to combine intermittent fasting with a keto diet.

#1: Intermittent Fasting Is Not Enough to Keep You in Ketosis

The 16/8 fasting window may not be enough to get you into or keep you in ketosis. Even if you do end up in ketosis, if you continue to eat a diet with even a moderate amount of carbs it’ll probably kick you out of ketosis each time.

This can result in unpleasant side effects such as the keto flu and being overly hungry each time you start fasting again.

#2: The Keto Diet Makes Fasting Easier

Eating a ketogenic diet allows your body to become keto adapted (running on fat and not depending mainly on glucose).

This makes intermittent fasting much more comfortable because there’s no switching between glucose and ketones, thus eliminating the feeling of needing to eat every few hours.

#3: The Ketogenic Diet Keeps You Satisfied

Another great perk of the keto diet is its high level of satiety.

Not only does ketosis itself tend to stifle hunger, but the high level of healthy fat in the keto diet also makes it much easier to stay satisfied in a fasted state and eliminates those intense feelings of hunger and cravings throughout the day.

This is perfect for someone doing intermittent fasting.

How to Get Into Ketosis Using the 16/8 Method

While 16/8 intermittent fasting itself is not the only way to get into ketosis, it’s a good start.

To get into ketosis, the best way is to combine a healthy ketogenic diet with intermittent fasting. Taking exogenous ketones can also help with the transition period and reduce side effects.

Concerns About 16/8 Fasting

Intermittent fasting, especially the 16/8 approach, is completely safe and beneficial. Contrary to common belief, moderate calorie restriction is a healthy practice that improves your metabolic health.

However, if you’re using it to get into ketosis, it might not be enough to get you there. If your fasting goal is to enter ketosis, you also need to follow a keto diet.

The Bottom Line on Intermittent Fasting 16/8

intermittent fasting 16/8

Intermittent fasting is a safe and powerful tool for improving your health. To recap:


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  • The 16/8 intermittent fasting approach means you fast for 16 hours and eat only in an eight-hour window.
  • Fasting triggers autophagy, which is needed for healthy metabolism.
  • IF has plenty of research-backed health benefits including better brain function, lower blood sugar levels, and lower inflammation.
  • Fasting can be a great way to get into ketosis, but it’s not the only way.
  • If you want to use fasting for ketosis, it’s ideal if you do it while following a keto diet.


63 thoughts on “The Complete Guide to Intermittent Fasting 16/8

  1. I still don’t understand how many days in a row you have to do a fast. I guess if you are on a keto diet is is as many as you can do right. Iam new and have done 3 already. I have had some uncomfortalble side effects. but I found out it was due to lost of electrolights and I used chicken broth and more salt to make that go away. How many green veggies should I be eating in the 8 hour window? It all seems very confusing. I know lots of fat and no low fat cause of sugar.

    1. It’s 16/8 HOURS (out of 24 per day).

      EX: You don’t eat in the evening and in the morning, but from noon the next day, until 8 o’ clock in the evening you do eat.

      You eat every single day.

    2. I was on a keto diet for about a year and quite easily lost 70 lbs. At 150 lbs, I was exactly where I wanted to be. The problem is that the rest of the world does not eat that way and you are always out of step in restaurants, parties, and even at family meals.
      Intermittent fasting and regular exercise was my answer for weight maintenance. You can eat pretty much whatever you want without craving or self-denial. It easily became my normal.
      I must admit that I am uncertain if intermittent fasting will cause you to lose the weight, but it is much superior regarding real world weight maintenance.
      I am an IF devotee for the rest of my life! Good luck.

  2. I am type 2 diabetic. Been on diet since
    Aug 2017 and lost 23 pounds. I it daft for me to do the 16/8? Usually jut have coffee until around noon. Would no be hard for me to do the 16/8. Really need to get rid of another 20 pounds.

    1. Hi Jackie, 16/8 intermittent fasting is definitely a good option for anybody. Just make sure you consult with your doctor and make sure you’re tracking your sugar levels diligently

  3. I’m new here, i use the 16/8 pattern and i start my feeding window frm 6:30 breakfast to 2:30 wc is exactly an 8hr feeding pattern. . is that ok?

  4. For those looking into getting into these fad diets. They all work, to an extent. The “best” diet is most certainly the one that you can most adhere to. That being said, so long as you are in a caloric deficit, you will lose weight! Face it, what is the point when you diet down and can not keep the weight off? You will most certainly rebound and end up right where you started. Consult with your doctor first and foremost for health and welfare issues and follow-up with a professional. Your health is of utmost importance. Take care everyone.

    1. That’s what happened to me. I was in ketosis for a year, lost 125lbs, but then I started eating again and poof, back came 90 of the 125 pounds 🙁 I’m finding it more difficult to get back into the swing of eating under 20 carbs a day. I find myself starving, or carb starved as it’s called, and it’s proving to be difficult, even with the meal replacement drinks. I’m going to try this fasting and see if that will help me get back to skinny, but be able to keep it off.

      1. Sounds like your problem was going back to the way you use to eat. Maintaining weight lose is simple. Eat clean and portion your food and exercise a few times a week. Stay away from all fast food, high carb foods, lower alcohol intake and sugar. If anyone thinks that they can just go back to their old ways after losing weight, they are just plain crazy. People get fat for a reason so why would anyone think it wont come back without a permanent lifestyle change.

  5. I am very new to this. Looking to eat healthy and lose weight. Nothing has worked for me. I am doing 16/8 fasting. I have not figured out what foods I need. Wondered what foods I should start my 8 hours with. I am excited about this way of eating.

  6. I’m 65 and I retired recently. I tried this for one week, and I must admit I particularly watched the clock all day long. I was very intergetic, and my depression subsided most of the time. At one week I weight myself, and thought why am I doing this if I’m not losing weight? So I went off and now I feel like I drag most of the day. I’m getting back on…enough said.

    1. I’m also 65 years old. I started 16/8 fasting with a Keto diet two weeks ago and lost 5 lbs. I felt icky on days 3&4, but I had read about the Keto flu, so I wasn’t worried. It’s not just the scale that shows a difference. My clothes are fitting me much more comfortably. Good luck, Edwina!

      1. I’m 69 and doing IF and cycling in and out of ketosis for 5 months. I feel very, very good and I’m down 2 sizes. I’ve steadily been losing weight for 2.5 years. I love it. It’s freedom. I do 18/6

  7. Just began this 16:8 IF with Keto. I track macros and split them into two meals for my eating window. It works out to 40grams of protein each meal.. Isn’t this a lot of protein in one meal? Should I do less than my macros say because it’s two meals instead of three? Just checking because I thought I read somewhere about not consuming too much protein in a meal. Thank you.

  8. ”Maintaining weight lose is simple. Eat clean and portion your food and exercise a few times a week. Stay away from all fast food, high carb foods, lower alcohol intake and sugar. If anyone thinks that they can just go back to their old ways after losing weight, they are just plain crazy.”

    So wrong and inaccurate in so many levels I really don’t know where to start in trying to correct such an ignorant statement. I don’t know if you are being sarcastic in this post… 1st of all it is not ‘simple’ in any way to avoid bad foods-our primitive brain cries out for them and when we diet it cries out louder. That is the big reason dieting is soo hard to stick to, it’s putting the body and mind under very unnatural conditions.

  9. 3 days in a 16:8 ration – my body loves it. I don’t feel famished and look forward to my 8 hrs of eating window. I keep calories in check with a healthy balanced diet. My exercise begins after my last hour of fasting, I eat a few fruits (mango and raspberries) and an avocado (topped with a homemade crushed walnut dressing) and I’m good to lift weights and run. My body feels light and healthy. Amazing solution to any fitness junky.

  10. Hi, I posted yesterday and my results are in after 4 days. I started the week at 140lbs and I’m now at 134lbs – 135lbs. I eat between 1500 – 1800 and walk every day 45 minutes. I weight trained on Tuesday and Wednesday, cardio Thursday, weight train again today with cardio(Friday). Only for 45 minutes per session – I can’t afford much time on my lunch hours. More details for you women out there who are mothers and who work full time: start with walking 30 minutes a day, fast pace.

    I’ll adjust my fasting times if there’s a party on the weekend, and I also drank coffee with milk in it in my mornings. So, I yeah I’m not a professional or serious faster here… I’m having fun and have been always active so, it’s a joy to train every day. Keep positive and know your body and its limits 🙂 If anyone is reading, I’ll report back at the end of July. I don’t have a goal for weight.. I focus on inches..I don’t even think this is relating to the article at this point…. best to you all!! xo

  11. fast 16 h minimum . try to go as high possible. some days will be easier
    than others. i set a very minimum goal of 16 h and then sometimes i end up being at 20-22. i lost a lot of weight so far in 6 month.
    I eat one big meal a day and one or two small meals
    i eat everything but try to stick to protein such as cheese, yogourt, meat.
    don’t neglect fruit because you need vitamins. try to eat them every other day maybe or so (or try everyday with moderation because of the sugar content). If you go to 22 then you could eat more carbs and sugary stuff but still try moderation. I found myself enjoying more the good stuff anyway such as fruits (a lot more than before)
    for weight loss add some work out (twice a week is enough) if you stick to your IF.
    also IF is not only about calories. It is about chemical reaction involving insulin and ketose. with discipline you can reset your metabolism so that it wont store as much fat and it will help with sugar regulation in the body.

  12. I have been doing the 16/8 intermittent fasting for a year now. I have lost 140 lbs to date and completely off insulin and metformin for my type II diabetes!!! It works

  13. 65 years old have MS so can’t move as much as most people but have been doing 16:8 for almost 2 months and I love It haven’t lost a lot of weight ( 5 lbs ) but am losing fat. I count calories and carbs ( prediabetic ) . Question is does this sound normal and will drinking coffee with Stevia break my fast?

  14. You can still get great benefits while sneaking in a cup of coffee however if you want optimal results nothing should enter your stomach other than water while fasting. Not even meds. One of the reasons that the intermittent fasting is so effective is that the enzymes in your gut are allowed to rest. Your 8 hour window should start as soon as anything other than water is ingested which includes coffee. Again, that is the strict answer but you can certainly still get good benefits even if you have your coffee during your fast

  15. I am keen to start this diet having heard about it on television.
    I like others don’t think I can do it without a cup of coffee in the morning. Would black coffee with equal be better than a white coffee with equal.
    Realising won’t get optimum results but how successful is it likely to be?

  16. Hi,
    Instead of water can I drink green tea? I’m very interested in starting the 16/8. I’ve just got back from China and brought back amazingly fresh just picked green tea.
    Please advise. 🙂

  17. I am on my 5th week on 16/8.i have lost significantly amount of weight.i just love it,feel lighter.usually eat proteins ,vegetables ,fruits sometimes a little carbs..i break my fast and eat through out till 8pm.between 8pm and 12pm ,i constantly drink water and green tea which makes me feel good when i am on ketosis.i think 16/8 and keto is almost one thing.they just work the same,but what i have noticed is that 16/8 combined with keto diet works perfectly well.good like guys,this is the way to go especially for us ladies!!!

  18. Ketosis is not a desirable state for the body. It means the body is in distress. You lose weight, but you are not in a peak state physically or mentally. You brain requires carbs. More so after any fasting period even if that is only for 7-9 hours while you sleep.

  19. Hi, you mentioned that during fasting you should only have water, not meds. I need to take my epilepsy and ms (gabapentin & Keppra) meds 12 hourly. 6am and 6pm. Is this why the 16:8 isn’t working for me?

  20. Annie, I have to take my anticonvulsants at 12 hour intervals as well. I’ll be taking them with water in the am. I won’t be eating till 10 am and I will restart my fast after 6 pm. Just starting today. Hoping to to kick my ketosis into high gear. Very optimistic. We all have things we have to work around and deal with, this is one of mine. Keto is for me and I think IF is too. Keep you posted.

  21. Just curious, how many calories does the average woman consume during the day while on 16/8. I’m very eager to do this but I’m wondering how the heck I’m going to get enough calories in with only 2 meas.

  22. Hi everyone, I need to make a change. If I can achieve some weight loss through IF and Ketosis, I’m willing to give this a try but I do believe it’s important to be well informed. How can I get more information please?

  23. When doing the 16/8 fasting schedule. Do you have to eat all your macros in the 8 hour feasting window?

  24. Hi I work really crazy hours, mostly over night. How am I able to do this correctly when it’s hard for me to keep a regular eat and fast regimen when I sleep a lot during the day. And my schedule at work can be all over the place not just one set time frame. I would really like to try this but I need some help trying to figure out time frames that can fit my schedule.

  25. I’m on 12pm to 8pm and find it very easy to stick to, however I have been used to having a small glass of skimmed milk at bedtime which helps me to sleep. Am I breaking my 16 hour fast ? Perhaps I should just try water instead.

  26. Tony try unsweetened almond milk, it is basically fiber and water and we can’t use the calories from fiber. They have to list it though.

  27. End of the Month results:
    Dropped a total of 9-10 lbs within just two weeks.
    The last week of July I gave myself a break from the fast. Nothing changed, just water weight changed the number on the scale. I’m leaner now, it’s lovely. Now I’m back on my fasting of 18:6
    I’m going for the whole month of August – Love it, it works.

  28. I have switched out the sweets in my morning coffee and switched to double espresso with butter in the morning, and I can tell you, it’s working wonders – my belt size is dropping week by week and my body is more looking like someone in their 20’s than in my actual late 40’s.

    Keep up the great work, Dr Gustin!

  29. I started 16.8 a month ago and I have not lost any weight. I think I may have lost some cm’s but nothing noticeable. I don’t do the Keto with IF but I also eat good foods. What am I doing wrong.

    1. Hi Amy, yes, you can drink water or even take exogenous ketones on during a fast, it may help suppress your appetite.

    1. Hi Nicole, yes, you can drink water or even take exogenous ketones that can help suppress your appetite during a fast.

  30. I cant eat meat because I have a stomach problem and when I eat it it makes me sick. Is there anyway to do the keto diet without meat?

  31. I’m 51, a VERY picky eater (mostly vegetarian, no snack type foods), I spent most of my life only eating one meal a day. I was never hungry. About 10 years ago, I was at a job where everyone told me I wasn’t eating enough, or taking in “enough protein”. Mind you, I was older than most of them, LOOKED younger than they did and was super active (biking 25 miles every weekend, hiking, exercising 3-4 times a week) but I listened to them and added breakfast to my diet plus more protein drinks. I gained 30 lbs in one year despite all my activity. I decided to go back to intermittent fasting (I usually do 20/4 with the 4 hour window of eating five days a week, except on weekends when I eat breakfast), I lost all the extra weight, feel amazing, my doctors tell me I am super healthy, no medications… I personally think we are hyped up to believe we need to eat 5 small meals a day and exercise like a mad man and by the way, I know people doing this and they are overweight still. I think society pushes people to work out, to eat more protein and certain types of foods deemed “healthy” when intermittent fasting is more doable. You can still eat what you want to eat and that is key for me so yes, it is VERY sustainable long term.

  32. I’ve done the fasting but been doing 18/6, Each morning after doing it I’ve lost 1lb. Very happy with the results plus also saves money on food shopping.

    Still very new to it but have been relaxing it during the weekends to maybe 16/8.

  33. I have been doing 16/8 for about a month. I also do zero carb. I feel great and my arthritis pain is almost gone! I’m so glad because I was taking 6 Aleve a day. Now I’m taking none!

  34. I have read somewhere that you are supposed to do the 16/8 for 5 days a week and have 2 days off! Is this correct, or do you do it 7 days a week??

    1. You can do both and see which will fit you, Dani. It will mostly depend on your dietary needs and goal. If you’re new to IF, it’s recommended to do the 5 days a week and 2 days off.

  35. There is just to much to read and to figure out what to do. What do I eat in the 8 hours of eating time. Do you eat carbs/ you don’t eat carbs. ????????

  36. I’ve been doing 16/8 no w for six weeks and have lost 17 pounds ,,just steadily going on and it is a way of eating I can do for ever with the odd blip ,maybe because of social commitment ,,I drink mint tea or lemon balm out of my own garden just steeped in boiling water ,also some fruit teas ,,,but when I said ,on another site I was doing this ,,I was told in no uncertain terms I was encouraging others to break their fast ,,I would like views on this ? I eat normally in 8 hours but in my head probably not going over 2.000 calories ,,I’m a walking calorie book anyway ,

  37. I’m an 86 year old guy. I used to have a six-pack but now I have a gut. My weight is OK but I believe that my gut is unhealthy and especially unattractive to the ladies. I can handle the 16/8. Does it work on belly fat first?
    I also raise a 14 year old girl who wants to try the 16/8 just two days per week. Does that ever work?

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