Intermittent fasting and keto—a simple guide by SIMPLE
Intermittent fasting and keto seem to go hand in hand.
Many people do them together.
Why is that?
Well, it’s thought that as intermittent fasting (IF) causes ketosis, adding the keto diet to your IF efforts will maximize the fat-burning and wellness results you can get.
So … double whammy. If you do keto AND intermittent fasting, you can burn body fat like no tomorrow. Right?
Well, let’s see if that’s true.
Here’s everything you should know about intermittent fasting and the keto diet.
- The keto diet is a high-fat, low-carb diet.
- Both keto and intermittent fasting stimulate ketosis.
- Combining them may increase fat loss, but there’s limited research on this.
- Eating a varied, enjoyable diet and planning your meals will increase consistency and results.
- There are some risks to be aware of, like nutrient deficiencies, muscle loss, and “keto flu.”
What is intermittent fasting?
Intermittent fasting is a way of eating that includes periods of fasting—i.e., your calories are restricted for a while—alternated with you eating your regular diet.
There are several different intermittent fasting routines, such as:
- time-restricted eating (TRE), like 16/8 or 14/10
- the 5:2 diet
- the Warrior Diet
- alternate day fasting
Probably the most popular method of IF is 16/8 intermittent fasting. On this protocol, you have an 8-hour eating window and a 16-hour fasting window (much of which happens overnight).
Lots of people use IF to lose weight, but there are many other benefits of intermittent fasting, from reduced inflammation to better blood sugar control to decreased belly fat.
You can read more about the various IF plans and their effects here: intermittent fasting for beginners.
What is the keto diet?
The keto diet is one of THE most popular diets around right now. (Thanks, Mr. Atkins.)
On keto, your diet would be:
- high fat (about 80% of your daily food intake)
- low to moderate protein
- very low carb (around 20–50 g a day)
The idea is that, by eating such a low-carb diet, your body will have to use fat for energy instead of glucose, and over time, fat will become your primary fuel source.
This is what’s known as being in ketosis, and it causes weight loss because, by keeping insulin levels low, we are better able to break down excess fat.
Keto has been shown to be effective for weight loss. And it’s thought to have a few other things going for it too. For instance, it may:
On the face of it, keto seems easy. And tasty! One of fat’s most winning features is that it makes food taste great, so who wouldn’t want to believe that eating more high-fat foods would be a party all the way to the weight loss bank?
Yet it’s not quite as easy—or perhaps even as effective—as it seems.
In order to achieve that all-important super-low-carb state, a keto diet dumps foods like whole grains and fruits. So our intake of fiber and micronutrients, which we need for health, takes a big hit.
And, while the keto diet appears to work for weight loss, much of that may be water weight (which isn’t really the kind of weight loss we hanker after, is it?). Add to that the fact that any diet with a strict macronutrient split is pretty dang tough to stick to, and it’s far from clear that keto is the answer to your weight loss goals long-term.
The short-term effects of keto on weight loss are fairly well demonstrated. But beyond that, the evidence is thin on the ground.
Finally, more studies are needed before we can confidently say that keto has a positive impact on conditions like high blood pressure, polycystic ovary syndrome (PCOS), diabetes, or Alzheimer’s disease.
Overall, it’s this lack of research on how keto performs long term that makes us stroke our beards in a questioning manner.
Keto and intermittent fasting: how do they work together?
The thing that clearly links keto and intermittent fasting is ketosis.
The keto diet increases levels of ketones in the body. Fasting does the same. Because of that, it might seem smart to pair the two things.
So let’s say you start out on keto, and that gets you into a ketotic state. The theory goes that adding intermittent fasting can take that to the next level.
IF might help you cut a few calories by shrinking your eating window. Or ketosis may decrease your appetite so that you feel fuller on less food, so throwing an intermittent fasting protocol in with your keto diet seems like an easy win.
Either way, it’s this double hit of ketosis-producing approaches that’s thought to have the power to bust you through a weight loss plateau and keep on driving results.
Intermittent fasting and a keto diet meal plan
Say you decided to pair 16/8 intermittent fasting with a keto diet. What would you eat, and when?
Let’s look at some sample day’s eatin’.
10 AM: Scrambled eggs with avocado
1 PM: Salmon with bok choy and olive oil
3 PM: Brazil nuts
5:30 PM: Steak with spinach and bell peppers
10 AM: Keto cinnamon smoothie
1 PM: Garlic and herb crusted salmon with broccoli
3 PM: Olives
5:30 PM: Spinach and swiss cheese omelet
10 AM: LCHF green protein smoothie
1 PM: Scrambled egg with cheese, peppers, and onion
3 PM: Celery sticks with unsweetened nut butter
5:30 PM: Dark chicken meat with kale and cauliflower
That should give you an idea of how keto plus intermittent fasting might look day to day.
In essence, it’s lower-carb veggies plus fats and proteins, all timed to fit within your eating window. Check out this infographic for a visual of some key healthy fats.
Should you combine keto and intermittent fasting?
Now that we’ve covered the basics, let’s get to the real questions. Should you combine a keto diet with intermittent fasting? What might you need to consider in order to decide whether that’s the right approach for you?
Some things to think about:
How does eating a high-fat diet feel to you?
Do you like steak, salmon, eggs, seafood, and poultry? How about avocado, olives, nuts, cheese, Greek yogurt, and cream? Are these high-fat, keto-friendly foods you can build your daily menu around?
What would it be like to go so low carb for you?
20–50 g of carbs a day is quickly going to be swallowed up by the veggies you need to pack in.
These veggies are important (and not just for good bowel function, though do bear that in mind). They bring nutrients and will help control your hunger and cravings. By contrast, a bagel, which is roughly 50 g of carbs, will provide limited nutrition and appetite management.
So, how do you like collard greens, spinach, Swiss chard, bell peppers, zucchini, kale, and cabbage? (This isn’t an exhaustive list; other vegetables are available.) Can you work with those day to day?
Are you cool with the lack of research?
There is a lack of quality research on what happens when intermittent fasting and keto are combined. Bottom line: it might work, it might not. You’d be your own experiment here.
Is it safe for you to try?
There are people who should avoid mixing fasting with keto. We’ll cover that shortly.
Five tips for combining intermittent fasting with the keto diet
Choose the right IF plan for you
The intermittent fasting plan that’ll work best with your keto diet is whichever one works best for you, full stop. Which fits your lifestyle best? Which makes it easiest to manage your hunger?
If you don’t know, try out a couple and see. We can help you get started. Take our SIMPLE quiz, and we’ll recommend an IF protocol that will suit you well.
Listen to your body
When you’re intermittent fasting on keto, your body will tell you how things are going. Pay attention to those signals.
Do you feel energized, alert, and comfortable (despite feeling hungry at times)? Cool. Keep going.
Do you feel cranky, exhausted, and foggy-headed? Then it might not be the best fit for you.
Eat foods you like
The success of any diet plan stands or falls on how much you enjoy eating that way.
If you love liver, make it a regular feature.
If you hate kale, you hereby have our permission to never touch it again.
Find the foods that work for you.
Learn to meal plan
Keto and intermittent fasting will only give you results if you are consistent in applying them in your life.
A habit that helps a TON with that is meal planning. The more you can plan your meals ahead of time, the more likely you are to eat those meals.
We give you all you need to get started here: how to meal plan.
Keep your diet varied
One of the potential pitfalls of adding intermittent fasting and keto together is not getting enough nutrition.
Don’t get stuck only eating steak and eggs. Make the most of the full range of foods keto can offer, and be sure to eat enough during your eating window.
(Side note: If intermittent fasting is not working for you, eating too little can be one of the main reasons why.)
Who should try an intermittent fasting keto diet?
If you have been following a keto diet for a couple of weeks and …
you feel good and …
you don’t have any health conditions that make it a bad idea …
then combining intermittent fasting and your keto diet is likely an OK move. For full belts and suspenders here, get the official OK from your doctor.
Who should avoid trying an intermittent fasting keto diet?
- have a history of eating disorders
- are pregnant or breastfeeding
then we’d suggest you don’t do either keto or intermittent fasting to protect your health and well-being.
And if you:
- have a health condition like diabetes or chronic kidney disease
- are on prescription medication
- are under 18 or over 65 years old
then we’d also suggest steering clear unless you have your doctor’s blessing.
Health benefits of combining a keto diet with intermittent fasting
So, what are the benefits of doing this one-two punch of the keto diet with intermittent fasting? Here are some of the results you could potentially expect.
Keto plus intermittent fasting could get your body into ketosis faster—or more reliably—than doing either one alone.
Some people may not reach ketosis just with intermittent fasting because, for some, it takes a longer fast than they are comfortable or able to do. Adding keto to the mix provides another stimulus for your body to achieve that state.
Increased fat loss
When intermittent fasting and keto are done together, ketone levels in the body increase. Add to that the positives of intermittent fasting in regulating blood sugar and preserving muscle mass.
Then layer in the potential impact of keto on curbing appetite and boosting energy levels. All of that combined could be a recipe for enhanced fat loss results.
Health risks of combining a keto diet with intermittent fasting
As far as risks go, there are a few to be aware of.
A keto diet restricts the kinds of food you eat. And if you choose bacon, burgers, and butter too often over avocados, broccoli, and salmon, that restriction is intensified.
Intermittent fasting can restrict the amount of food you eat. And if you cut calories too much or choose an IF protocol with overlong fasts or too short an eating window, again, that restriction is increased.
All this can lead to you not getting sufficient nutrients to meet your body’s needs.
Combining intermittent fasting with keto can leave you short on protein.
Too little protein—especially if combined with too few calories overall—will push your body to break down your muscle mass for energy.
The less muscle mass you have, the slower your metabolism and the fewer calories you burn for every activity you do.
This means losing and/or managing your weight gets harder to do.
(*Not an actual flu.)
“Keto flu” is the name given to the side effects of the first couple of weeks of a keto diet, like:
- brain fog
- difficulty sleeping
These side effects are also those you may experience when getting started with intermittent fasting.
(Plus hunger, though there are ways to hack hunger while fasting.)
Women can experience intermittent fasting differently than men.
Hormones can get disrupted due to caloric restriction, for instance, which can interfere with fertility and the menstrual cycle.
To learn more, click to read the interplay between intermittent fasting and hormones and how to do intermittent fasting safely as a woman.
How to get started with an intermittent fasting keto diet
If you’ve decided to get started with intermittent fasting and a keto diet, here are a couple of tips.
Start with one, not both
We’d suggest getting up and running with just keto first or just intermittent fasting first.
Get comfy with one before adding the extra complexity of the other.
Taking things one step at a time is a fundamental principle of behavior change. The fewer things you try to change all at once, the higher your chance of success.
This slower start will also help your body get used to the changes.
Going from using glucose to primarily using ketones for energy is a pretty significant shift! As is going for 12–20 hours without food. Take it slow and give your body time to adjust to what’s happening internally.
Find the easiest first step
Another fundamental principle of change: make it easy on yourself.
What’s the easiest way you can start fasting?
- Add an extra hour to your existing overnight fast?
- Start with a 12/12 protocol?
What’s the easiest way you can start keto?
- Changing your dinner to be keto-friendly?
- Having salmon and eggs for breakfast?
Choose a low-hanging fruit action and build some momentum and confidence. You don’t have to go full steam ahead into a 100% keto diet plan with intermittent fasting attached.
Take your time.
SIMPLE’s expert opinion and final thoughts
There could be some positives from combining the keto diet and intermittent fasting.
But the research is pretty sparse, so we can’t say for sure.
Whether it will work for you, then, is a question only you can answer.
If intermittent fasting plus keto sounds like something you want to run with, you’re clear on the risks, and it’s safe for you to try it, go ahead and experiment a little.
We’d always suggest getting the all clear from your healthcare team first.
If you want to get going with intermittent fasting, we’re here for you. Try our SIMPLE quiz, and we’ll suggest a suitable IF plan. There are also a bunch of valuable articles, trackers, recipes, and more in our app, just waiting to help you hit your health goals!
Frequently asked questions about keto intermittent fasting
How many hours should you intermittent fast on keto?
How many hours you should do intermittent fasting on keto will be determined by the IF plan you follow. If you’re on 16/8, you’ll fast for 16 hours. If you’re on 5:2, the fasts are 24 hours (but with 500/600 calories).
We don’t recommend zero fasts of 24 hours or longer.
How much weight can you lose on keto and intermittent fasting?
You can initially lose weight pretty quick on keto and intermittent fasting, but that early weight loss is usually water weight. Check this out for more on intermittent fasting and the results you might see.
1–2 lbs. a week is a safe bet and a sustainable rate to lose weight.
Can intermittent fasting put you in ketosis?
Yes, intermittent fasting can put you in ketosis. That’s one of its main benefits!
Why am I not losing weight on keto intermittent fasting?
There are several potential reasons why you are not losing weight on keto intermittent fasting. Are you making any of these classic intermittent fasting mistakes?
How long does it take to see results from keto and intermittent fasting?
How long it takes to see results from keto and intermittent fasting will depend on how consistent you can be with them both. If you’re knocking it out of the park, results can start in the first few weeks.