Intermittent Fasting on the Ketogenic Diet: What You Need to Know

The LMNT community is full of keto dieters and intermittent fasters. If you’re one of them, this article will give you a few extra tips to optimize these dietary systems. And at the very least, it will refresh your memory on how to do them right.

After all, the keto diet and intermittent fasting are both extremely hot topics right now. And hot topics often come with a whole smorgasbord of misinformation. When they come up, you don’t want to be the person gazing at your hands, hoping someone changes the subject to Planet Earth. No—it’d be much better to contribute some clinical evidence, dispel a few myths, and help better folks’ health in the process.

Here’s one to chew on: Keto and intermittent fasting aren’t so different, from a metabolic perspective. Essentially, both programs help you transition toward burning fat for energy, rather than a store-full of glycogen. This is a good place to be in for weight loss, body recomposition, and several other health benefits.

Even if you aren’t keto, you might find something useful here. There’s a reason the keto diet and intermittent fasting are so popular: when done properly, they work.

I’ll cover each regimen separately, then discuss how to overcome challenges related to going keto, fasting, or both. And then our five minutes together will be up—but don’t worry, there’s always more where that came from.

Keto Diet Primer

Unless you’re marooned without WiFi and received a paper copy of this article via carrier pigeon, you’ve probably heard of the ketogenic diet. The keto diet—which entails restricting carbs to 30-50 g of effective carbs per day—has swept the Western world.

Keto is best known as a weight loss diet, but it didn’t start out that way. It was formulated back in 1921, (happy centennial to the ketogenic diet!) as a treatment for childhood epilepsy. At deeper levels of ketosis, children experienced fewer and less severe seizures.

Ketosis, by the way, is the fat-burning state provoked by carb restriction. In the absence of carbohydrates, your liver burns fat (body fat or dietary fat) and produces molecules called ketones. These ketones then fuel your brain and body with usable energy (ATP).

If you regularly eat carbs, ketosis isn’t your default state. On a carb-containing diet, you rely primarily on glucose for energy. But when you remove a significant portion of those carbs, this balance shifts towards ketones and fatty acids. In other words, you burn more fat and less glucose on keto.

This shift is largely mediated by the hormone insulin. When you eat carbs, insulin rises to mop up the resulting blood sugar. So when you restrict carbs (the main rule of keto), insulin stays low, allowing you to access body fat. This is a gross oversimplification, of course, but one that’s good enough for our purposes here.

There are a number of health benefits linked to ketosis. We’ll skim them here, but check this article for a deep dive on that evidence.

Ketosis Health Benefits

  • Weight loss
  • Appetite control
  • Stable energy
  • Mental acuity
  • Diabetes reversal
  • Potential adjunctive therapy for cancer and neurodegenerative disease

By now you’re probably wondering how to eat keto. The standard advice is to mainline fat, but we take a different approach based on the scientific literature and working with thousands of folks through the Healthy Rebellion and Ketogains community. Briefly, here’s what we recommend.

How To Eat Keto

  • Eat whole foods.
  • Consume under 30 grams of net carbs per day. (Net carbs = total carbs - fiber - sugar alcohols).
  • Eat about 1 gram of protein per pound lean body mass. (100 to 200 grams for most people).
  • Fill in the rest with fat, depending on your goals.

The key to ketosis is the carb limit. That’s what keeps insulin low and facilitates fat adaptation.

But protein is the goal. It’s essential for structuring muscle and connective tissue, and most people don’t get enough!

Lastly, think of fat as a lever. If you’re trying to lose weight, lever your fat intake down, even as low as 50 grams. If you’re trying to gain or maintain, ratchet it up.

So protein is a goal, carbs are a limit, and fat is a lever. That’s how we like to think about macronutrients on keto.

Intermittent Fasting Primer

Intermittent fasting is more about when you eat, not what you eat. When you practice intermittent fasting, you take periodic breaks from calories. That’s basically it.

These intermittent food breaks range from 12 to 36 hours on a daily or semi-daily basis. Anything over 36 hours is generally considered an extended fast.

The main “flavors” of intermittent fasting are:

  • 12/12. A 12 hour daily overnight fast.
  • 16/8. 16 hours of fasting, 8 hours of feeding.
  • OMAD. One meal a day.
  • 5:2. 2 non-consecutive days of modified fasting per week.
  • ADF. Alternate day fasting.

(I go into more detail on fasting protocols in this post. Check it out.)

Like I said earlier, intermittent fasting and the keto diet have similar metabolic effects. Blood sugar stays low, insulin stays low, and fat is burned for energy. Nothing keeps insulin low like eating nothing!

And so the benefits of intermittent fasting are largely congruent with the benefits of ketosis. Fasting, after all, is the other main portal to a ketogenic state.

Overnight fasting has an additional upside: It tunes up your circadian rhythm. By not snacking overnight, you align your 24 hour wake / sleep cycle, a cycle that regulates about one third of your genome. It’s a simple habit with a huge payoff.

Our ancestors experienced this payoff. Back in Paleo times, intermittent fasting was part of life—albeit unintentionally. When food was scarce, you ran off body fat. When food was plentiful, you feasted—refilling your fat stores. This oscillation of fasting and feeding helped our hairy cousins stay metabolically flexible.

Given that food is available 24/7 in our cushy, Westernized lives, intermittent fasting doesn’t occur naturally the way that it used to. Fourth meals are a thing. This hasn’t been good for human health. It’s a big reason why we have an obesity and diabetes epidemic.

Keto Intermittent Fasting Challenges and Solutions

Keto and fasting come with overlapping sets of obstacles. Here are some of the biggest areas that trip people up.

Challenge #1: Hunger

When you fast—even intermittently—hunger is inevitable. Some worry, however, that the cravings will become so unbearable that you’ll end up snacking on your arm.

The first thing to realize is that hunger is natural. Dizziness or lightheadedness is not, but hunger is.

Second, hunger ebbs and flows. It doesn’t spiral upwards to infinity, but rather stabilizes over time.

What You Can Do: Go Keto First. This hunger-control benefit is another reason why these regimens work so nicely together. Going keto first helps you better access body fat for energy. This won’t eliminate hunger during a fast, but it will help stabilize hunger hormones like ghrelin and neuropeptide Y.

Challenge #2: Keto Flu

Most people don’t consume enough electrolytes. Period. But on a keto diet or intermittent fasting regimen, the potential for deficiency is magnified.

That’s because a low insulin state (due to carb restriction) makes you excrete more sodium and fluids through urine. If these aren’t replaced, you’ll end up dehydrated and electrolyte deficient.

The resulting cluster of symptoms—headaches, fatigue, weakness, cramps, etc.—are often called keto flu. Luckily, it’s an easy fix.

What You Can Do: Drink Electrolyte Water. We recommend taking 5000 mg sodium, 1000 mg potassium, and 200 mg magnesium on top of food sources. Consume these electrolytes with fluids to keep your energy up and prevent keto flu symptoms—also, spread them out! I wouldn’t down all that at once unless you enjoy disaster pants.

LMNT was formulated for exactly this purpose—and is ideal for those on low-carb or fasting regimens—but feel free to whip up electrolyte homebrews if you have spare time and are fairly taste-agnostic.

Challenge #3: Sleep Issues

Many folks have trouble going to bed hungry, and it’s not just a psychological quirk. In fact, fasting increases alertness chemicals like adrenaline and orexin-A that can make relaxation difficult.

What You Can Do: Back Off The Fasting. If you can’t sleep, consider backing off to an easier fasting regimen. For example, step down to 16/8 from ADF. The benefits of fasting probably don’t outweigh the harms of sleep deprivation. When in doubt, listen to your body!

Challenge #4: Digestion

When you shift to a keto diet, your gut bacteria shift too. This can cause changes in digestion, often resulting in constipation and diarrhea.

What You Can Do: Play With Fiber. Try increasing your intake of non-starchy vegetables. This extra fiber should keep your gut bugs happy and move things along down there. Keep in mind, however, that increasing fiber isn’t always the solution for gut issues. In fact, low fiber diets have been shown to be effective in reducing IBS symptoms. You’ll have to experiment to see what works best.

Challenge #5: Muscle Maintenance

To build muscle requires resistance training, a caloric surplus, and adequate protein. On keto and fasting regimens, people often fall short on the final two criteria.

Let’s zoom in on the protein goal. Along with insufficient electrolytes, insufficient protein is one of the main mistakes folks make on keto. Why? Because people take “high-fat” to mean a plate full of fat, with some protein on the side. But since fat contains 9 calories a gram, and protein only 4, your plate should actually be centered around protein.

What You Can Do: Bump Up Protein. To gain or maintain muscle, shoot for about 1 gram protein per pound of lean mass.

What You Can Do: Shorter Fasts. Lean towards shorter fasts (12 to 16 hours) to ensure adequate calories. These calories provide the raw materials required to build muscle.

Succeeding on Keto Intermittent Fasting

I’ve seen the keto diet, intermittent fasting, or some combo work for a lot of people.

But these approaches aren’t for everyone -- there’s no one size fits all solution. Some folks just do better with some carbs. Some do better with frequent feedings. It’s hard to add muscle if you’re aggressively compressing your feeding window.

I’m not suggesting you should pound muscle milk every 45 minutes (unless you really want a digestive challenge!), but maybe 13 or 14 hours of fasting is where you top out. And that’s okay.

Anyway, I believe keto and intermittent fasting are worth experimenting with. Use the tips from this article to get started, and let me know how it goes in the comments!