Intermittent Ketosis: Can You Be Part-Time Keto?

Written by Tim Skwiat, MEd, CSCS, Pn2

Intermittent Ketosis

There are more people than ever on the keto bandwagon, and it’s hard to blame them. The ketogenic diet is surrounded by tremendous acclaim. The growing body of scientific research shows that keto supports a long list of health benefits. But let’s face it, for most people, sticking to a ketogenic diet can be impractical and downright hard.

What if you didn’t have to be on a full-fledged ketogenic diet yet still bear the fruit of the keto tree? What if you could be part-time keto and reap even greater rewards? It’s not only possible, intermittent ketosis may be an even better approach.

Find out more about intermittent ketosis and how to put it into practice today!

Benefits of a Ketogenic Diet

When it comes to the ketogenic diet, there’s little denying it can result in profound benefits. And while some claims are anecdotal, some have been scientifically demonstrated only in animals, and some are downright outrageous, a well-formulated ketogenic diet can support a long list of health benefits including: 1

  • Weight management
  • Appetite management
  • Metabolic health and glycemic control
  • Cognitive function and brain health
  • Heart health
  • Healthy aging
  • Improved markers of inflammation and oxidative stress

More and more, the therapeutic potential of the ketogenic diet, which was initially designed to treat drug-resistant epilepsy, is being recognized for conditions like:

  • Cancer
  • Autism
  • ALS
  • Parkinson’s
  • Alzheimer’s
  • Traumatic brain injury
  • Type 2 diabetes
  • Metabolic syndrome
  • Polycystic ovary syndrome (PCOS)
  • Acne
  • And more.

That being said, we’ll be talking about non-medical purposes.

Now, if you ask me, the effectiveness of the ketogenic diet can be traced back to its #1 RULE: Limit carbs to 30 grams or less per day. Simple as that. Of course, keto is more complex and nuanced than that, but honestly, this is THE rule. It sets the stage for two mission critical things, which are largely responsible for the lion’s share of benefits associated with keto:

  1. Nutritional ketosis
  2. Dietary displacement

In the case of the latter, by following the rule, your menu of food options gets limited tremendously. You take a ton of ultra-processed, calorie-dense, highly-palatable “foods” off the table. And when you do that consistently over time…Voilà! Improvements in virtually all aspects of life and health ensue.

In other words, it’s not just about what you are eating. It’s arguably more about what you are not eating (read: processed junk food and abundant amounts of added sugar and poor-quality fats/oils).

In the case of nutritional ketosis (defined as ketone levels ≥ 0.5mM)—a powerful metabolic state during which the body is burning primarily fat (ketones are derived from fats)—it’s becoming increasingly apparent that elevated ketones have an array of important signaling functions (e.g., regulating inflammation and gene expression). And the metabolic shift to increased ketone use may be the secret behind a majority of the benefits of the ketogenic diet. 2,3

(For a deeper dive into nutritional ketosis, including the important differences between it and ketoacidosis, check out this article.)

Want to know some good news? You don’t necessarily have to follow “the rule” to reap the same benefits. In other words, you can tap into nutritional ketosis without being full-time keto. And let’s face it, anyone can limit their consumption of ultra-processed junk foods—at least intermittently.

Benefits of Intermittent Ketosis

Should we be living in a constant state of ketosis (which is the goal of a standard ketogenic diet)?

I don’t think so, and science journalist, author of New York Times best-selling book Genius Foods, and host of one of my favorite podcasts The Genius Life, Max Lugavere agrees, “If you are doing it for medical reasons, follow the advice of your doctor. For most people, intermittent ketosis makes more sense, allowing you to achieve some of the benefits of nutritional ketosis while also allowing for liberal consumption of veggies and low-sugar fruits.4

Now, if you’re familiar with Max’s work or any of my ramblings, you know we don’t typically pull things out of thin air, especially bold statements like these, which are rooted in science and human physiology. Naturally, that leads to some questions. For starters, what are the advantages of intermittent ketosis?

  • Metabolic flexibility. The human body is designed to efficiently and effectively switch between using carbs and fats for fuel. Swinging the pendulum too far in one direction or the other (which keto does) for extended periods of time may lead to health complications. Intermittent ketosis promotes metabolic flexibility.
  • Dietary flexibility. A standard ketogenic diet severely limits the menu and volume of plant-based, carbohydrate-containing foods, including many healthy options like vegetables, fruits, legumes, nuts, and seeds. Intermittent ketosis promotes dietary flexibility by affording you a greater menu of options and being less restrictive on quantities.
  • Athletic performance. While a ketogenic diet naturally increases the body’s use of fat for fuel, the research is, at best, conflicting when it comes to keto and exercise and athletic performance. 5, 6, 7 While high-intensity, short-duration sports and activities seem to suffer the most, even endurance performance can be adversely affected. On the other hand, intermittent ketosis may promote exercise and athletic performance through improved metabolic flexibility.
  • No “keto flu?” There’s likely to be an adaptation period when making any significant dietary and lifestyle adjustments. However, few dietary changes elicit quite the profoundly palpable constellation of maladies as a strict ketogenic diet. One of the advantages of my preferred approach to intermittent ketosis, however, is likely to be a figurative express lane past those symptoms.

In addition, a well-designed approach to intermittent ketosis is likely to bear much of the same fruit you’d expect from a ketogenic diet, including:

  • Weight management
  • Appetite management
  • Cognitive function (energy, focus, mental clarity, alertness)
  • Metabolic health and glycemic balance
  • Heart health
  • Longevity (mitochondrial biogenesis, SIRT1 activation, preservation of muscle mass)
  • Stress resistance

And there’s more. Because a well-designed intermittent ketosis approach (see Option B below) involves intermittent metabolic switching between time periods of negative calorie balance and positive energy balance, researchers believe it can optimize brain health and general health, including enhanced insulin sensitivity, reduced abdominal fat, maintenance of muscle mass, reduced resting heart rate, and reduced blood pressure. 8

Admittedly, there’s a fair amount of speculation behind the purported benefits of intermittent ketosis. However, I assure you I’m not a magician pulling these out of a hat like a bunny. Researchers consider “metabolic switching” (what I’m calling intermittent ketosis), which refers to repeating cycles of metabolic challenge (i.e., ketosis) followed by a recovery period (i.e., eating, resting, and sleeping), to be a powerful tool to “optimize brain function and increase resistance to injury and disease.” 8

So, how might you go about achieving a state of intermittent ketosis?

Option A: Modified Ketogenic Diet

While the standard ketogenic diet (where you limit carbs to 30 grams or less per day) is the most common, there are two modified versions worth mentioning:

  • A cyclical ketogenic diet (CKD). A CKD basically combines the standard ketogenic diet (5 – 6 days per week) with 1 – 2 days of carb loading. This approach has traditionally been popular with bodybuilders and other athletes who need to be able to perform at higher intensities. While the rationale behind the CKD seems solid, in practice, it tends to be quite difficult, both physically and psychologically. I don’t typically recommend this approach.
  • A targeted ketogenic diet (TKD). A TKD consists of eating (i.e., targeting) carbs around workout times. Generally speaking, a TKD involves consuming some high-glycemic carbs pre- and/or post-workout. The most common practice among keto dieters is to take in as little as 15 grams of carbs 20 – 30 minutes pre-workout with the goal of improving performance. If you prefer, you can choose to consume carbs post-workout.

Overall, I think a TKD has application and may be a more practical, flexible, and long-term approach compared to the standard ketogenic diet. However, I don’t think either of these options is the best approach to intermittent ketosis.

Option B: Intermittent Fasting + Exercise

Surely you’ve heard the phrase, “There’s more than one way to skin a cat.” Well, this rings true for nutritional ketosis. Actually, there are two dietary modifications that can induce nutritional ketosis: 1. Severe carbohydrate restriction (i.e., ketogenic diet); and 2. Fasting.

As a matter of fact, when scientists first grasped the therapeutic potential of fasting (i.e., heightened levels of ketones), they formulated the ketogenic diet, which was specifically designed to mimic a fasting state. After all, you can fast only so long before negative consequences take hold. In other words, there’s a point at which fasting is no longer therapeutic, and the ketogenic diet has the potential to overcome that barrier (as a medical tool for epilepsy, for example).

All that being said, the point is that fasting is the most powerful tool to “flip the metabolic switch,” which is what researchers define as “the body’s preferential shift from use of glucose to fatty acids and fatty-acid derived ketones.” 3 Put differently, fasting switches the metabolism from fat-storing mode into full-fledged fat-burning mode, which also ramps up the body’s production of fat-derived ketones (i.e., ketogenesis).

Another important point is that researchers use the word “preferential” when talking about the flip of this metabolic switch because “there is now a growing body of research to indicate ketones are the preferred fuel for both the brain and body during periods of fasting and extended exercise.” Speaking of which…

I like to think of exercise as a fasting accelerant. That is, exercise accelerates the depletion of the body’s stores of liver glycogen, the term used to refer to carbohydrate stored in the liver. Depletion of liver glycogen is one of the key signals to the body to ramp up ketogenesis. In other words, exercise hastens the rate the body flips the metabolic switch (from glucose to fat and ketones). 8

Simply put, fasting PLUS exercise is a formidable combination to induce nutritional ketosis.

Now, when I say fasting, I’m specifically referring to the various forms of intermittent fasting, such as alternate-day fasting, periodic fasting, time-restricted feeding, and a fasting-mimicking diet. Of these, while alternate-day fasting is backed by the most research, time-restricted feeding is the most popularly practiced.

Each of these methods can effectively “flip” the metabolic switch. The metabolic switch typically occurs about 12 – 36 hours into fasting (after you stop eating). Of course, this can vary considerably depending on diet composition, energy expenditure, and exercise during the fast. sup>3

The cool thing is when you add intense and/or prolonged exercise to the intermittent fasting mix, the metabolic switch gets flipped on sooner and/or more deeply. For example, if you exercise 8 – 10 hours into a fast, you’re likely to flip the switch earlier than expected. Or, if you exercise 12 – 14 hours into a fast, you’re likely to flip the switch to a greater degree (i.e., higher levels of ketones).

My IF + Exercise Plan

Having said all that, more research is needed to give us more insight into the proper combinations, types, and timing of exercise and intermittent fasting. Generally speaking, I prefer daily time-restricted feeding. And I like to recommend some fairly low-intensity activity early in the day (such as taking a walk or doing some light yoga) along with plenty of physical activity throughout the day (assuming one is fasting during this time).

Then, I like to schedule more intense activity (for example, strength training and/or interval training) toward the tail end of the fasting window, and I like to follow that by opening the feeding window (within 2 – 3 hours of completing the workout). Overall, when it comes to time-restricted feeding, I find a 6-hour feeding window (with an 18-hour fasting period) offers a nice balance of benefits. I do, however, think it’s open to experimentation and personal preference.

One of the biggest benefits of this intermittent ketosis approach is that you only restrict when you eat. You do not necessarily have to restrict what or how much you eat. In other words, you don’t have to observe strict ketogenic diet rules (no carb counting per se). And in the case of the latter, condensing the amount of time you eat typically takes care of how much you eat.

Interestingly, to reap the greatest rewards and fully reverse the metabolic switch (to turn on the other key metabolic pathways), it appears to be critical to consume a non-restrictive, varied diet (i.e., eat some carbs). But keep in mind the second root that we can trace back the benefits of the ketogenic diet to: dietary displacement. In other words, eat real food and ditch the junk to reap the greatest benefits.

Bonus Intermittent Ketosis Tip: MCT Oil

Ever heard of medium-chain triglycerides (MCTs)? They’re a unique type of fat in that they are shorter in length (i.e., carbon atoms) compared to the majority of dietary fats. As a result, they are metabolized and transported differently in the body. Because of this, MCTs are associated with a laundry list of benefits.

For instance, they are directly transported to the liver where they are quickly and efficiently burned for energy. Along these lines, they bypass fat tissue, which makes them less likely to be stored as fat.

One of the most noteworthy benefits of MCTs is they are known to be highly ketogenic, which means once they get to the liver, they are readily converted into ketones. In particular, the MCT C8 (caprylic acid) increases ketones three times greater than the MCT C10 (capric acid) and four times greater than coconut oil. In other words, C8 is the most ketogenic MCT.

This has application because it means adding MCTs—more specifically, C8—when fasting can ramp up ketone levels and perhaps accelerate the body’s metabolic shift to burning fat and ketones.

Intermittent Fasting Awaits

While the ketogenic diet has grown by leaps and bounds in popularity and it has shown promise for a variety of health benefits, I’m not convinced we’re designed to live in a constant state of ketosis. In other words, I don’t think full-time keto is an appropriate long-term approach for an otherwise healthy individual.

Having said that, there appears to be tremendous upside to time periods where ketones are elevated, and that may be best interspersed with periods of normal eating (i.e., non-restrictive, non-ketogenic diet). From an evolutionary perspective, alternating periods of fasting (little or no food) with periods of recovery (eating and resting) seems to make quite a bit of sense.

If you give this approach a try, I’d love to hear your feedback. And if you have questions, I’d love to hear those too!

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References

  • 1. Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013 Aug;67(8):789–96.
  • 2. Newman JC, Covarrubias AJ, Zhao M, Yu X, Gut P, Ng C-P, et al. Ketogenic Diet Reduces Midlife Mortality and Improves Memory in Aging Mice. Cell Metab. 2017 Sep 5;26(3):547-557.e8.
  • 3. Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, et al. Flipping the metabolic switch: understanding and applying the health benefits of fasting: flipping the metabolic switch. Obesity. 2018 Feb;26(2):254–68.
  • 4. Negrin S. This is what science journalist Max Lugavere wants you to know about the ketogenic diet [Internet]. LIVESTRONG.COM. 2018 [cited 2019 Jan 15].
  • 5. Chang C-K, Borer K, Lin P-J. Low-carbohydrate-high-fat diet: can it help exercise performance? J Hum Kinet. 2017 Mar 12;56:81–92.
  • 6. Zinn C, Wood M, Williden M, Chatterton S, Maunder E. Ketogenic diet benefits body composition and well-being but not performance in a pilot case study of New Zealand endurance athletes. J Int Soc Sports Nutr. 2017 Jul 12;14(1):22.
  • 7. Wroble KA, Trott MN, Schweitzer GG, Rahman RS, Kelly PV, Weiss EP. Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. J Sports Med Phys Fitness. 2018 Apr 4;
  • 8. Mattson MP, Moehl K, Ghena N, Schmaedick M, Cheng A. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018 Feb;19(2):63–80.