Cyclic Ketogenic (CK) eating alternates periods of ketogenic eating with periods of low- to moderate-carb eating
Why do it? In short, for optimizing health and longevity, there is no one perfect way to eat all the time. Rather, ‘optimal’ is likely achieved by oscillating between a ketogenic diet and a low-carb diet
There are significant benefits to CK over strict keto: improvement in a number of metabolic markers, easier adherence, better metabolic flexibility, healthier gut flora/digestion and supporting stores of energy in the muscles and liver
This is the version of Cyclic Keto we’ve found to produce the best results:
Ketogenic periods are 2-3 weeks in duration and follow macronutrient ratios of 65-80% fat | <7% digestible carb | 5-10% fiber | 10-20% protein
- Low-carb periods are 8-14 days in duration and follow macronutrient ratios of 50-70% fat | <20% digestible carb | 5-10% fiber | 10-25% protein
At Synchro, we practice Graceful Keto - an approach to the ketogenic diet that aspires to be smarter, more beneficial and generally ‘higher-vibe’ than the standard grease-, meat-, and cheese-saturated (not to mention dogma-saturated!) version of Keto you see most places.
One of the 5 core principles of Graceful Keto is Cyclic Ketogenic (CK) eating. There are a lot of different ways to do CK, but the basic idea is that with CK you systematically alternate periods of full-on ketogenic eating with periods of non-ketogenic eating.
We’ll dive into the details of the approach to CK we’ve found to produce the best results, but first let’s look at why CK is a good idea in the first place.
Why Cyclic Keto?: The Benefits
1. We Like Things That Are Easier
As much as we’d love to pretend that being on a strict keto diet is a breeze at every turn, this wouldn’t be super honest. We live in a carb-saturated world and eating keto often means having to pass up delicious foods, particularly when eating out with your non-keto friends.
If you’re anything like us, cycling on and off of keto will be a world easier mentally and emotionally.
If your goal is to lose weight with a ketogenic diet, I think this works in your favor. Having 2-3 week keto periods where you eat hypocalorically (that is, eating fewer calories than your body uses) alternating with 10-day low-carb periods where you eat isocalorically (eating about the same amount of calories as your body uses) will not be the fastest way to lose weight, but it will be more enjoyable and thus, sustainable - meaning you’re more likely to keep the weight off once you lose it.
2. Build Metabolic Flexibility
By alternating between periods of full ketosis and low-carb eating, you’ll be building what we call “metabolic flexibility”, meaning that your body has the capacity to efficiently make use of whatever fuel source you give it.
Similar to how non-ketogenic eaters struggle to efficiently use fats for energy, when people are in ketosis for an extended period, they can sometimes struggle to efficiently process carbohydrates when they do eat them. Their blood sugar and insulin levels spike dramatically and their energy levels crash shortly thereafter.
We believe flexibility is desirable in most areas in life, and your metabolism is no exception.
3. Show Your Microbiome Some Love
The bacteria in our gut (aka our ‘microbiome’) have been neglected, misunderstood and occasionally assaulted (by antibiotics) to our great detriment. In the past 10 years or so, we’ve learned that these bacteria not only contribute to digestion and nutrient absorption, but are also essential for immune function and even hormone signaling in the body. Screw up these bacteria and things go downhill quickly for the body as a whole. (oh btw - there’s 3x as many bacteria in your gut as there are “human” cells in your body)
Maintaining a thriving microbiome gets a little complicated on a ketogenic diet, as these bacteria eat indigestible fibers and starches (aka ‘prebiotics’) that are typically found in starchy, carby foods. You can and should do a lot to support these bacteria by taking a well-formulated prebiotic supplement (...like Pre•Bios), even when you’re not eating strict keto. In addition, cycling off the ketogenic diet and giving your microbiome some starchy foods every once in a while will do a lot to keep them happy.
4. Refill Glycogen Stores
When your body wants to store fuel for quick access at some point in the future, it does it in the form of glycogen, in your muscles and liver.
Glycogen is essentially a bunch of sugar molecules stuck together, and your body generally only produces it when you’re eating carbohydrates.
If you do strenuous workouts, even if you’re in ketosis, your body will usually want to pull on glycogen stores for quick energy at some point in your workout. Having some glycogen available in the muscles allows you to train harder and for longer.
Cycling out of ketosis onto a low-carb diet lets your body refill these glycogen stores, which will stick around even when you switch back into ketosis. If you’re a serious endurance athlete, you might benefit from cycling out of ketosis more frequently, but for most of us the 2-3 weeks ketosis, 10 days low-carb rhythm is enough to keep adequate stores of glycogen around.
5. Eat Like Your (Distant) Ancestors For Ideal Metabolic + Hormonal Balance
Bear with me here...This section gets a little technical, but really it’s really the core of why the Cyclic Ketogenic diet is so beneficial.
In general, metabolic and hormonal markers tend to move in a resoundingly positive direction on the ketogenic diet. Inflammation is reduced, mitochondrial function (i.e. your cells’ energy production) is improved, insulin and blood sugar levels stabilize...all of these are resoundingly positive. 
The flip side of this is that prolonged periods in ketosis can also slightly lower thyroid function and reduce beneficial anabolic/growth metabolism in some people. Even the benefits listed in the paragraph above tend to drop off after prolonged periods in ketosis.
The hormone IGF-1 is probably the most instructive here . The ketogenic diet has been shown to lower serum IGF-1 levels, which is generally looked at as a positive thing (in adults) as it slows markers of aging and disease. That seems pretty straightforward on the surface, but it gets a bit more complicated as IGF-1 is also necessary for growth and regeneration in the body, specifically in the brain. The ideal is definitely not perpetually high IGF-1 or low IGF-1, but somewhere in the middle...or, more likely, an oscillation between the two.
So what to make of these seeming contradictions?
Well, if you think about it terms of evolution and genetics, it starts to make a bit more sense. Humans have only been farming for about ten thousand years. The vast majority of human and primate history is hunter-gatherers, who would go long periods with little to no food at all (and thus, in fasting ketosis). At some point they would find food and eat abundantly. It makes sense that our genetics would be optimized for feast-to-famine cycles.
Research supports this idea that the ideal metabolic and hormonal state is likely not achieved by eating any one way indefinitely, but rather by alternating periods of ketogenic eating, non-ketogenic eating and fasting (we’ll get to this later).
Graceful Cyclic Keto: A Step-By-Step Guide
There are a lot of different variations of Cyclic Keto, this is our version designed to optimize for the benefits listed in the section above.
Prerequisite: Build The Metabolic Machinery For Ketosis
Before you can start with a cyclic ketogenic diet, you’ll first have to follow a ketogenic diet strictly for a minimum of four weeks.
For the cyclic ketogenic diet to work, your body has to first build up levels of the enzymes (i.e. “metabolic machinery”) in your gut, liver, muscles and brain that are responsible for digesting fats and converting them to energy. This takes a bit of time, and the only way the body will do this is if you spend an extended period on a ketogenic diet.
If you try to go straight from a non-ketogenic diet onto a cyclic keto diet, it’s likely your energy levels will drag and you’ll never get into a rhythm that feels good. Four weeks of full-ketogenic is generally enough time to let the body adapt.
I strongly recommend doing the transition to a ketogenic diet methodically and gradually, as I’ve laid out in great detail in this guide to entering ketosis.
1. Ketogenic Periods (2-3 Weeks)
In your ketogenic periods, aim for the following macronutrient ratios:
65-80% fat | <7% digestible carb | 5-10% fiber | 10-20% protein
At 2000 calories/day, this means:
>144-178g fat | <35g digestible carbs | 40-80g fiber | 50-100g protein
- High levels of protein suppress ketogenic metabolism, so if you push the upper end of that range for protein (or exceed it), you’ll want to balance this by consuming a lot of highly-ketogenic fats (like C8 MCTs from Ketobasis) to make sure your ketone levels stay high enough and you don’t kick yourself out of ketosis.
- Generally speaking, the more you exercise, the more you’ll be able to push the upper end of those protein and carbohydrate ranges without bumping yourself out of ketosis.
- Some cyclic ketogenic diets will allow for shorter ketogenic periods than this. While many people will feel fine transitioning in and out of ketosis on shorter cycles, they’re likely missing out on the bulk of the metabolic and hormonal benefits of ketosis.
2. Low-Carb Periods (8-14 Days)
In your low-carb periods, aim for the following macronutrient ratios:
50-70% fat | <20% digestible carb | 5-10% fiber | 10-25% protein
At 2000 calories/day, this means:
111-155g fat | <100g digestible carbs | 40-80g fiber | 50-125g protein
- The cyclic ketogenic diet works because, even when you’re not in a strict ketogenic period, your “metabolic machinery” for ketosis will hang around for a while. If you’re newer to ketosis, this period will be shorter and you’ll want to keep your low-carb periods closer to 8 days than 14 to ensure you don’t have to deal with a rough transition back to ketogenic eating.
- Even if you’ve been fully keto-adapted for years, it’s best to keep low-carb periods under 14 days. That hard-earned metabolic machinery will go away!
- You’ll notice that fats still make up the bulk of your calories here. This is also a critical part of what makes the cyclic ketogenic diet work. Your body will continue to use fats for energy, which will encourage it to maintain the ketogenic metabolic machinery for longer than it would if you were eating a higher-carb diet in these non-keto periods.
3. (Optional, but highly recommended) 18-24 Hour Modified Fast
When switching from a low-carb period to a ketogenic period, it can take some people 2-3 days to build up enough ketones to be fully back in ketosis, and their energy levels will drag as a result.
You can almost completely eliminate this by doing a short, 18-24 hour fast on your first day of switching back to ketogenic eating.
We’ve found the easiest way to do this is to eat an early dinner on your last day of low-carb eating (finishing at 5pm, for example) and then not eating another meal until (at least) mid-day the next day. If you eat a full meal at 11am the next day, this would have already been 18 hours. This is way easier than you’re probably thinking.
This will send a strong signal to your body to switch back into full ketogenic mode. If you get a bit of light-to-moderate exercise in these 18-24 hours (a 1hr walk, for example), you’re almost guaranteed to be back in ketosis when your break your fast.
To help speed the transition back into ketosis, you can modify the fasting period by consuming 15-30g of highly-ketogenic fats (like C8 MCTs from Ketobasis). This will raise your ketone levels, making the fast a bit easier, while also sending a signal to your body that it’s time to get back to full ketogenic metabolism.