Intermittent Fasting and How to Modify It for Keto

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Imagine sitting down to a full meal and eating as much as you want. Imagine feeling excited to eat a pile of lightly sautéed broccoli, a piece of poached white fish and a beet-arugula salad with a sprinkling of feta cheese. Imagine finishing your dinner and not wanting anything else … until noon the next day.

Seem like a total fantasy? It isn’t, though you can’t be blamed for thinking it might be. Our society is obsessed with crunchy chips, fluffy breads, sky-high cakes and creamy ice creams. If you’re one of the people to whom that list still calls, though you desperately wish it wouldn’t, that’s okay. But it might make you feel better to imagine one last thing:

Imagine that list didn’t fill you with longing. Imagine you could finally stop eating unhealthy foods and overeating, ditch those extra pounds and inches, and use food as its meant to be used: a tool for energy, so you can get back to living the life of your dreams.

Well, good news. Both intermittent fasting and the ketogenic do does just that, changing not only the foods you eat but the way your body processes them. Many people have already felt the benefits of keto, and are now wondering how to take it to the next level.

Today, we’re here to discuss one of the simplest ways to do that: by introducing intermittent fasting to your keto eating plan. While plenty of research exists about both ways of eating individually, not much has been written on how to combine them safely, effectively and for maximum satiety (fullness). Let’s remedy that with a quick look at what both of these diets are and how to use them in tandem. Whether you currently follow keto and are interested in adding fasting to your toolkit, or haven’t tried either and are wondering how they intersect, we’ve got you covered.

What Is the Ketogenic Diet?

The ketogenic diet is one on which the body transitions from using glucose as its primary energy molecule and begins to use ketones instead. Both can be used to power the body in daily tasks such as thinking and movement, but for the most part, the Western Diet relies on glucose.

Glucose is readily available in the form of carbs, from grains to fruit to processed sugar. When we eat any of these foods, the body quickly transforms them into glucose and dumps them into the bloodstream, which are then transported around the body by insulin for use in various tasks. Excess glucose is taken up and stored as fat. The fat we already have stored does not get used, because glucose is always being added to the system.

The ketogenic diet removes carbohydrates, and therefore glucose, from the system. Your body still needs energy, of course, so it will instead look to fat – stored energy. Your liver will begin processing that fat, producing ketones that can be used in the place of glucose.

The result? Fat stores decrease, and by avoiding glucose, you avoid adding to them. Thus far, keto has proven very beneficial in reducing obesity, lowering cholesterol and helping people maintain a much higher level of overall health, as, for example, discussed in a study helmed by Hussein M Dashti, et al.

Ketogenic Diet Food Pyramid

What Is Intermittent Fasting?

Naturally, we cannot understand how the two modes of eating intersect until we understand the second one.

Also known as time-restricted feeding or TRF, intermittent fasting is a pretty simple concept: You reduce the window of time in which you eat. If you’re used to eating from 8 a.m. to 8 p.m., for instance, you restrict eating from 10 a.m. to 8 p.m., or perhaps noon to 8 p.m. The window depends on what works for each individual, and some take it so far as to eat one day on, one day off.

Intermittent fasting too has promising benefits, according to The Harvard Gazette, including potentially lengthening lifespan. According to RM Anson, et al, “Dietary restriction has been shown to have several health benefits including increased insulin sensitivity, stress resistance, reduced morbidity, and increased life span.” In other words, it’s a pretty good idea.

How Can You Modify Intermittent Fasting to Fit the Keto Diet?

Okay, so how do the two intersect? Again, it’s pretty simple. You eat the foods allowed on the ketogenic diet, but eat them within the window you’ve set for yourself. This may take some practice, and the longer you’re on both diets, the more you’ll be able to restrict your feeding – both timewise and food-wise – without feeling hungry.

Do note that both the ketogenic diet and intermittent fasting require restricting the body. If not done carefully, this can result in a state of hunger beyond what your body can handle – i.e. hunger not based on cravings, but instead on true lack of nutrients or calories. Not good. The best advice, therefore, is to start with one or the other, then slowly incorporate the second.

For instance, a solid approach would be to start the ketogenic diet, first cutting out sugars and processed carbs. Then you can cut out the “healthier” but still not keto-approved carbs such as grains and fruits. These are less likely to stimulate cravings, so are a good way to ease into keto. They still produce glucose, however, so eventually they have to go.

Once you’ve gotten comfortable with the keto diet, it’s time to introduce intermittent fasting. Start by cutting off your eating at night, not allowing yourself to snack past a certain pre-decided time, even if you feel hungry. Once that’s comfortable, start pushing breakfast back by half an hour every few days or so.

You’ll know when you’ve reached the limit of safely pushing it back because your hunger will become real (a difference you’ll soon be able to feel). You have your window. Again, people report widely differing schedules, but women usually leave a 10-hour feeding window, while men eat within an 8-hour span. It’s probably not a good idea to do 24 hours on and off, since the body is already restricted to burning its own fat and you don’t want to enter a starvation state.

What Foods Should You Eat… and When?

It is beyond the scope of this article to go through every food you can and can’t eat on keto, so head here for a comprehensive guide. Instead, let’s talk a few rules to follow when combining keto and intermittent fasting:

  • Make sure to eat a very protein-heavy meal at night to get you through to the next feeding time
  • Eat protein first thing when your feeding window opens up to ensure you get the energy you need
  • Have protein and green veggies with every meal
  • Wait half an hour after feeling hunger pangs to assure yourself they’re real
  • Try drinking a glass of water before eating; sometimes when we feel hungry, we’re just thirsty
  • Eat high-fat foods for snacks
  • When you crave carbohydrates, eat fats and protein
  • Distribute your meals however you want to within your fasting window, whether that means grazing, three squares or two larger meals

How Should You Deal with Hunger Cravings?

Our obsession to carbohydrates is real. For instance, according to researchers Nicole M. Avena, et al, sugar has been found to cause true addictive behavior in humans. Our brains are wired to want it, so we seek it, eat it, get a burst of energy, crash, and seek more. Over time, we get habituated to it, so that if we dont eat it, something seems “wrong.” That’s because it releases dopamine and true, honest-to-goodness opioids in our brains – and when our drugs disappear, we get unhappy.

So especially when you first axe carbs and reduce the hours in which you can eat, cravings and feelings of hunger will be a reality. It’s important to understand that a feeling of hunger is not the same as true hunger. Even more importantly, you have to assess cravings realistically. If you really, really want chocolate, are you truly hungry? Maybe. Or maybe, for instance, your body just needs magnesium. According to NaturaLife, this often manifests as a desire for chocolate, which is rich in magnesium.

This gives you a few choices. You can take a supplement and see if that helps with your cravings. You can also eat some chocolate – preferably 85% dark or completely unsweetened to respect the low-carb rules. Or you can just wait out the craving, which in any case you will need to do if you’re inside your fasting window.

Chocolate, obviously, is not the only example of this effect, so when you’re craving a food, the answer may be as simple as some quick Googling to find out what that food contains much of, and getting that nutrient some other way.

Because intermittent fasting and the ketogenic both naturally encourage your body to eat fewer calories, you will likely see a drop in your hunger levels over time as you habituate. Once you cut out sweets, carbohydrates, fried foods and others that spark the crash-and-crave cycle, your body is less likely to want food when it isn’t hungry. However, if you restrict your calories too far, you may experience true hunger. At that point, it’s important to look at how many calories you’re eating and reassess what your body needs.

Should You Count Calories?

Intermittent fasting and the ketogenic diet both operate on the assumption that once you restrict your body to the food it actually needs, rather than the food it would just enjoy, you will have far fewer cravings. Thus, you’ll be less likely to eat food you don’t need. This leads to the widespread assumption that if you use these eating plans, you don’t need to count calories.

But that’s only partially true, because in the absence of carbs, some people do turn to other foods. Meat, for instance, can be addictive due to the dopamine it releases upon consumptions and the opiates it contains. Some over-rely on nuts for their fat content. These foods are perfectly acceptable and healthy, but not if you just turn to them automatically.

Calorie counting is a tool, therefore, to see whether or not you’re eating roughly the amount a person your age, weight and exercise level should be eating. If you are, you don’t need to track every day.

What Role Do Traditional Appetite Suppressants Play?

Appetite suppressants are great, because they tell your body to put off those hunger pangs just a bit longer. That enables your body to wait until your feeding window opens up, as well as to Just Say No to the non-keto-approved foods we often crave when we’re hungry.

Both coffee and black tea are approved for both the keto diet and for consuming while still in the fasting window. These are good choices in the morning, before your feeding window opens up – especially at first, when your body will complain about having to wait to eat. As time goes on, you may find you have no trouble waiting to eat, even without hot beverages, but you can freely use this tool for the rest of your life. For obvious caffeine-related reasons, this is not a great tactic before bed.

Homemade chicken stock is also a good way to tide yourself over when you’re hungry, because it offers a jolt of protein and fills your tummy without you consuming too many calories. However, while it’s a great keto move at any time, note that chicken stock is food – as opposed to coffee or tea – and so technically shouldn’t be consumed outside the feeding window. Within the window, though, it’s a great tactic for the stretch between meals.

Putting a little coconut milk, almond milk or cream in your coffee and tea is also fine, but again, all are food and so must be consumed inside the feeding window.

Keto and Intermittent: A Match Made in Heaven?

At the end of the day, the ketogenic diet and intermittent fasting play very nicely together. The biggest danger when combining the two is that you might fall prey to the desire to restrict food even further, and thereby unintentionally enter a starvation state. Or alternatively, that in restricting carbs and feeding times, you will over-rely on the foods and times that are allowed.

That isn’t likely, however, if you’re eating what your body tells you to eat. Especially after a few months of using both methods simultaneously, you will learn to eat when hungry and not eat when not hungry. It may seem like a miracle right now, but trust in the fact that eventually, it will just be your reality.

About the Author Nate Arnold

I started this website because it was hard to find trustworthy, evidence-based information about the ketogenic diet. Information that was published and peer reviewed by respected scientific journals. After years of research, I'm sure you'll achieve great results in a healthy way following my advice. I do my best to translate scientific research jargon into plain English. Remember, it's always a good idea to consult a doctor before starting a new diet!

5 thoughts on “Intermittent Fasting and How to Modify It for Keto”

  1. i was wondering would having a protein shake with just one scoop of protein powder mixed with water count as eating food in the non eating window? even if the protein powder was zero carbs and keto friendly?

    • Yes, Protein powder contains fats and protein. Both have calories and would count as food. Would be fine within your eating window.

  2. I read that you shouldn’t have protein shakes when fasting.,….maybe because of high carb content and artificial sweeteners added,….I thought the same as you and have used the Whey protein powder in the past but it’s not recommended,…I ditched my “expensive” whey powder and am losing 4/5 pounds a week on my 16/8 fasting program.

  3. In your window of time of non eating can you drink powerade Zero? It has 150 mg sodium, 35 mg potassium less than 1g carbs

    • Its all based on your personal goals. If your following the IF plan then all you are supposed to have is water, coffee, or tea. If you want to loosely follow the IF plan then you can add whatever you want. I look at it this way. If its zero calories then its probably ok and not giving your body anything it can convert to energy. I drink diet soda durring my window, powerade zero, gatorade zero. Whatever I feel like drinking as long as it is zero calories. It is whatever you decide to follow and how strict you decide to be. Its your diet journey and your life do what feels right to you. If your loosing weight and happy then I don’t see a problem with it.


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