16/8 Intermittent Fasting: What You Need to Know

Intermittent fasting is an amazing tool that is rapidly gaining popularity these days — and for good reason!

For everything from weight loss and fat burning to decreasing disease risk and making meals simpler — intermittent fasting has become very popular if you’re looking to improve overall health and reach your nutrition and/or fitness goals.

But, the question many people ask is — will intermittent fasting help get my body into ketosis faster?

In this article we’ll cover:

By the end of this article, you’ll have all the tools to rock it!

Want even more help? Download our free Intermittent Fasting eBook here!

Let’s go.

What exactly is 16/8 intermittent fasting?

Intermittent fasting (IF) itself is simply eating within a certain daily window of time and fasting outside of that window.

There are several different types of intermittent fasting but the16/8 method is typically the most common.

Those who partake in IF often describe their routine by breaking up 24 hours into when they are consuming food versus when they are not. For example, the number of hours fasted followed by the eating window hours.

So, 16/8 fasting means eating within a window of eight hours each day — such as from 12pm to 8pm — and not eating during the remaining 16 hours.

The windows can vary based on the individual. Someone might only eat within a six-hour window (18/6) or four-hour window (20/4).

Intermittent Fasting and Ketosis

One of the best things about fasting is that it can help get us into that sweet metabolic state of fat burning faster — that sweet state of ketosis.

The two are related for three reasons:

  1. For our bodies to get into ketosis, we must be fasting in some sense — either by not eating any food at all or by keeping carbs extremely low. When we’re in ketosis, it means the body is breaking down fat for energy.
  2. Since IF obviously involves fasting, it can help our bodies deplete glucose stores at a faster rate and speed up the process of running on fat.
  3. Many people who start a ketogenic diet will begin by fasting to help them enter ketosis more quickly.

So, is 16/8 intermittent fasting guaranteed to get you into ketosis? Well, not exactly.

There are a few potential issues that can prevent you from getting into a fully fat burning, ketogenic state.

Concerns About the 16/8 Window

While intermittent fasting alone is still great, some issues can arise when it’s combined with a non-ketogenic diet. When following a higher carb-based diet, once the fasting window ends, the body switches back to glucose-burning mode and bumps you out of ketosis (if you were in ketosis at all).

If we go from eating a “normal” amount of carbs to shifting our carbs to very low, it can take around two days for the body to even enter ketosis.

That means if you’re eating whatever you want during the eight-hour window, you might not be giving your body enough time to get into ketosis at all.

(And remember, it’s always smart to test your ketone levels to be sure you’re in ketosis.)

However, there is a way to remedy this and increase your chances of entering and staying in ketosis — that is, simply following a ketogenic diet.

So, how can the ketogenic diet be used along with intermittent fasting to help you get into ketosis faster and keep you there longer?

Intermittent Fasting and the Ketogenic Diet

The ketogenic diet is centered around:

  • High fat intake
  • Moderate protein intake
  • Very low carbohydrate intake

It is designed to deplete your body of glucose (sugar) and trigger the breakdown of fat into ketones for energy. The ketogenic diet “starves” our bodies of glucose in the same way as fasting, while still being able to eat and provide essential nourishment.

So basically, the ketogenic diet and intermittent fasting are a match made in heaven.

How Intermittent Fasting and The Keto Diet Complement Each Other

There are three compelling reasons to combine IF with a keto diet:

#1: Intermittent Fasting Might Not Be Enough

The 16/8 fasting window may not be enough to get you into ketosis. Even if you do end up in ketosis but then 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 we start fasting again.

#2: The Ketogenic Diet Makes Fasting Easier

Eating a ketogenic diet allows our bodies to become keto-adapted (running on fat and not depending on glucose).

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

Therefore, your intermittent fasting window won’t be a struggle because you won’t feel as hungry as you wait until the next feeding period.

#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, the high level of fat in the keto diet makes it much easier to stay satisfied and eliminates those intense feelings of hunger and cravings throughout the day.

This is perfect for someone doing intermittent fasting.

Perfect Keto founder @dranthonygustin does intermittent fasting on the regular without feeling hungry because he eats nutrient-dense, high-quality keto meals in between his fasting window, like this one:

How to Get Into Ketosis using the 16/8 Method

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

To get yourself into ketosis, consider doing a more intense modified fast in the days leading up to starting your ketogenic diet. This is can be more effective for spurring a faster transition into a ketogenic state.

Taking exogenous ketones can also help with the transition period, especially for reducing any side effects.

If you’re set on the 16/8 method, try using a macro calculator and following the ketogenic diet macro ratio below to give you the best shot of getting (and staying) in ketosis.

Keto Macros

This reduces hunger, increases satiety and prevents glucose spikes that affect ketosis during feeding periods.

Don’t Just Bank on 16/8 Intermittent Fasting for Ketosis

Whether or not 16/8 intermittent fasting will get you into ketosis depends on what you’re eating during the eight-hour feeding window.

For best results, combine a ketogenic diet with your intermittent fasting routine (and perhaps consider a longer-modified fast at first) to speed up your transition into ketosis.

Don’t forget to download your free Intermittent Fasting eBook, and get ready to rock IF!

Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.

Over the last few years, he has treated thousands of patients with movement rehab, internal diagnostics, and natural interventions, including NFL, MLB and NBA champions. After growing his sports rehab and functional medicine clinics to six locations in San Francisco, he shifted his mission to help as many people as possible achieve optimal health and well-being.

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Responses (44)

  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.

  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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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!

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. ”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.

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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?

  20. 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

  21. 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?

  22. 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. 🙂

  23. 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!!!

  24. 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.

  25. 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?

  26. 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.

  27. I was told as long as you don’t consume more than 50 calories, you are not breaking your fast.

  28. 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.

  29. 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?

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

  31. 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.

  32. 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.

  33. 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.

  34. 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.

  35. 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!

  36. 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.

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