Carb cycling on a low-carb or keto diet: What you need to know

If you are doing a low-carb or keto diet, you may have heard of carb cycling, also called carbing up or cyclical keto. But the name can mean different things to different people.

What exactly is carb cycling? How do you do it? Who should, or should not, consider carb cycling? Read on to learn what the science and key experts in the field have to say, and make sure you read to the end to learn practical tips about how it might work for you.

It’s important to note that not much evidence exists about the effects of carb cycling while following a baseline low-carb diet. This guide attempts to combine information from existing data with expert clinical experience to provide the best, most evidence-informed resource on the topic.


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What is carb cycling?

Carb cycling is any planned temporary or cyclical increase or decrease in carbohydrate intake. While carb cycling can apply to any type of diet, even high-carb diets, this guide focuses on carb cycling for people following low-carb or keto diets.

For example, someone eating a very low-carb, ketogenic diet may decide to increase their carb intake to come out of ketosis, with a plan to return to ketosis after a specified time period. This is carb cycling.

At first, it may seem counterintuitive. If the point of low-carb diets is to reduce carbs, why would someone want to increase them purposefully?

Perhaps not everyone should. Some individuals may find carb cycling causes more harm than benefit.

However, others may see potential benefits from carb cycling, such as improved athletic performance by increasing carbs before a competition.

Others may achieve better long-term low-carb compliance by cycling carbs one or two days per week or a couple of weeks every few months. And still, others may want to cycle carb intake seasonally to mimic presumed ancestral evolutionary patterns.


Who can benefit from carb cycling?

Athletes are the individuals most likely to benefit from carb cycling. But even here, the science is tricky.

Some studies show that in the short term, low-carb diets can hurt athletic performance.1 After proper long-term adaptation, however, low-carb diets may improve endurance exercise for some. Still, others feel best when spending most of the time eating low-carb, and increasing carb intake right before or right after their athletic activities.2

Another potential benefit is if someone sees a lifetime of limiting fruit, bread, pizza, and other favorite high-carb foods as depressing and a significant barrier to committing to a low-carb diet. Knowing they can temporarily return to their higher-carb favorites for a week every couple of months might increase their chance of success.

Yet, some find the opposite to be true, so it is essential to know how you will respond. Will carbs trigger unchecked cravings or binges? We address this further in our section about who should not try carb cycling.

Lastly, some may want to mimic our ancestors’ dietary pattern as closely as possible. As Seattle physician, Dr. Ted Naiman says: “I think that with the exception of the past few hundred human generations, our species has always been on a cyclical ketogenic diet and I think it makes a lot of sense to cycle carbs if looking at diet through an evolutionary lens.”3

Although data on what our ancestors ate is imperfect, it makes sense that many would eat a very low-carb diet consisting mostly of game and meat during the winter months when vegetation was less plentiful. During the spring and summer, they would eat a higher-carb diet with the seasonal availability of berries, tubers, and other plant species.4

Today’s society has erased any need to eat seasonally. You can get berries shipped to Alaska from South America in the dead of winter, and hydroponic gardens can even redefine the definition of “eating locally.”

Some believe that eating very low carb or being in ketosis year-round may not be healthy or appropriate if it does not mimic our ancestral patterns. While there is no data to prove if this is the case or not, if you believe we should resort to evolutionarily consistent eating patterns, you may want to consider increasing carb intake during the late spring, summer, and early fall.


Who should not try carb cycling?

If you are just getting started on a low-carb diet, you probably shouldn’t experiment with carb cycling just yet.

As San Diego-based physician Dr. Brain Lenzkes said, “I do not recommend carb cycling for those starting out on a low-carb journey. Many have true carb addiction and cycling can lead them down the wrong path.”5

If there are any signs of carbohydrate addiction, or difficulty controlling cravings, then introducing carbs can be a slippery slope from which it is difficult to recover.

Some may have trouble maintaining the quality of carbs they eat, immediately being drawn to high-sugar, highly processed carbs. And others may have a hard time weaning off the carbs after the specified period, regardless of the carbs’ quality.

Diet Doctor Medical Review Board member Dr. Michael Mindrum agrees. He states, “Often when patients want to take a break from a low-carb diet, they aren’t wanting to indulge in lentils and beans but are missing potato chips, ice cream, and other triggering foods. If these foods are made part of one’s routine under the cloak of ‘carb cycling,’ it can lead to further challenges in adherence.”

Addressing your risk of cravings and potential carb addiction takes top priority before considering carb cycling.

Also, some people feel much worse when adding carbs back into their diet. It is not uncommon for people to feel an immediate return of many of the symptoms that low carb helped them eliminate.6

Feelings of hunger, mental fog, low energy, bloating, and more may occur in some people after they reintroduce carbs. For these individuals, any theoretical benefits from carbs are unlikely to outweigh the physical side effects.7

Lastly, it is always helpful to assess the reasons for going low carb. Was it to lose weight? To treat or reverse type 2 diabetes, PCOS, metabolic syndrome, or other health conditions? If so, monitoring markers for your underlying health condition is an essential aspect of whether you should do carb cycling.

For instance, if you got your blood sugar readings under good control with a low-carb diet, make sure they stay under reasonable control when experimenting with carb cycling. You won’t be doing yourself any favors if you find your blood sugar readings are back in the diabetes range, undoing all the gains you achieved by following a more stringent low-carb diet.


Can carb cycling impact my health?

Some research suggests that suddenly increasing carbs may be dangerous for those following a low-carb diet. One study found an increase in markers of blood vessel damage when low-carb eaters drank a 75-gram glucose solution.8

As we detailed in a prior post, this study has serious weaknesses, and we need to interpret the results with caution. However, one of the take-home messages is that low-carb eaters may need to slowly increase their carb intake rather than ingesting a lot of rapidly digested carbs all at once.

Along those same lines, clinical experience with low-carb patients going for an oral glucose tolerance test suggests that those who increase their carb intake gradually over three days perform better than those who do not.9

Some have concerns that chronic carbohydrate reduction can adversely affect thyroid or adrenal function, especially for women. One study found diets low in calories and carbohydrates caused a more rapid reduction in T3 hormone production than higher-carb diets.10 And another found significant thyroid hormone changes in kids being treated with ketogenic diets for epilepsy.11

However, these studies did not document clinically symptomatic thyroid dysfunction and did not explore carb cycling as an intervention. Even fewer studies exist investigating carb cycling and adrenal function.

Therefore, the use of carb cycling for thyroid or adrenal health, or specifically for women, remains speculative.

Can carb cycling have positive health benefits? Perhaps. However, adequate scientific studies have not been conducted on those eating low carb.

Some experts, such as Robb Wolf and Dr. Ted Naiman, feel that carb cycling will have no adverse effects and may help with long-term compliance for the right person. That said, whether or not carb cycling will have benefits for weight loss and metabolic health has not been investigated in clinical trials.


Carb cycling for athletic performance

Carb cycling for athletic performance may look different depending on whether an athlete’s goals are competing on an elite level, competing with friends on the weekend, or just competing with themself.

Carb cycling may also be different if you are most concerned about body composition, endurance sports (e.g., long-distance running or cycling), or sports with short bursts of activities (e.g., tennis or martial arts).

Is eating more carbs necessary for athletes? Not necessarily. Some evidence shows that keto-adapted athletes efficiently burn fat for fuel and can improve both their body composition and exercise performance without carbs.12

Not all studies agree that low-carb diets benefit athletic performance. Two studies from Dr. Burke and colleagues showed reduced 30-kilometer race walking performance after 12 weeks on a keto diet.13

These studies did not test carb cycling. However, other studies suggest that adding both carbs and fat to an already fat-adapted individual can improve glycogen utilization, and muscles may be able to continue burning fat for fuel even after the introduction of carbohydrates.14

These mechanistic findings and anecdotal experiences have led some to promote the “train low, compete high” model. Simply put, that means training while eating minimal carbohydrates and increasing carb intake prior to competition.15 However, this has not been studied in controlled trials.

One thing that makes testing low-carb athletic performance difficult is the need for fat adaptation. Studies on fuel-burning adaptation suggest you need around four weeks to adapt properly.16 However, this is for everyday living situations. The same is not known for exercise performance, and some anecdotal evidence suggests it may take six months or more to properly adapt for performance.17

Studies on those not eating a low-carb diet suggest that post-exercise carbs may help build muscle, while others suggest that as long as someone eats adequate protein after exercise, carbs don’t add to muscle synthesis.18

How do we remedy all the conflicting information? Here’s a summary:

  1. Ketosis likely benefits endurance sports more than shorter, more intense sports.
  2. Full performance adaptation to fat-burning may take more than six months.
  3. Carb cycling may help some perform better, especially when they train with few carbs and then increase carb consumption for competitions.
  4. Carbs may help athletes who require shorter, more intense bursts of energy.

If your livelihood depends on a few seconds of improvement, you should probably stick with what works for you. But suppose your livelihood doesn’t depend on your athletic performance. In that case, the health and wellness improvements from eating low carb may outweigh any small change in physical performance from cycling carbs.

Keeping a proper perspective of what matters most is essential. If cravings and food binging is not a problem for you, don’t be afraid to experiment with adding or subtracting carbs to see how you physically perform and how your blood sugar responds.


How to test carb tolerance

Since there is no clear definition of what it means to be “carb tolerant,” there is no best way to test for it. However, we can define some parameters that may suggest someone can tolerate carbs, and we can then describe ways to measure that response.

For instance, blood sugar and insulin response to eating carbs may be the two most important metrics. An oral glucose tolerance test (OGTT) is traditionally used to measure one’s response to glucose.19

Even better is the Kraft test, which is an OGTT measuring both glucose and insulin levels. As Dr. Kraft showed, abnormally high insulin responses likely precede abnormally high glucose responses, thereby allowing us to identify those at risk much sooner than waiting for blood sugar to climb too high.20

A standardized test like an OGTT allows you to compare your response to others who have taken the same test. Is your response more similar to those with insulin resistance or type 2 diabetes? Or is it closer to those who are “metabolically healthy?”

For many, a better measurement may be a “real-world” tolerance test. You likely aren’t going to be drinking an overly concentrated, synthetic glucose drink in your daily life, so why should you test your response to it?

Instead, you can test your tolerance to sushi, sweet potato, or even margaritas and cookies (as mentioned by Dr. Peter Attia in the Diet Doctor Podcast). While you can’t measure at home insulin levels, you can measure your glucose response to real-world foods.

The best way to do this is first to measure your blood sugar before you eat. This is time zero. Then eat the carbs you want to test. Check your blood sugar at one and then two hours after eating. If, after two hours, your blood sugar hasn’t returned to your pre-meal baseline, continue checking at hourly intervals until it does.

Of course, the more frequently you test, the more information you will get. You can measure your blood sugar every 15 minutes if you would like, but that is a lot of finger sticks.

This is where a continuous glucose meter, or CGM, can provide value. With a CGM, every food and every meal is its own tolerance test. All you have to do is pay attention to the readings before and after the meal.

Here are general guidelines to shoot for when deciding how to interpret your glucose responses:

  1. The lower the total rise and the shorter duration of the rise are both signs of a healthier response.
  2. A “normal” blood sugar response to food is defined as being below 140 mg/dL (7.8 mmol/L); prediabetes is between 140 and 200 mg/dL (7.8 to 11 mmol/L), and type 2 diabetes is a blood glucose above 200mg/dL (11.1 mmol/L).21
  3. Shooting for lower blood glucose is always reasonable. Just because 140 mg/dL (7.8mmol/L) is defined as normal doesn’t mean you should be happy with it. As Dr. Casey Means discussed in the Diet Doctor Podcast, it is likely best to aim for even lower values, closer to 120mg/dL (6.6mmol/L)
  4. Research suggests that in the absence of diabetes, the highest post-meal glucose peak should be within one hour, but in those with type 2 diabetes, it usually peaks at two hours.22

Remember the important tip we mentioned earlier: If you have been eating a low-carb diet, consider testing after gradually increasing carbs over three days.23


Different protocols for carb cycling and best carbs to use when cycling

Cycling carbs does not mean eating any kind of carbs you want. The quality of the carbs still matters, and we highly recommend focusing on less processed, more complex carbs.

Examples include vegetables (both above-ground and root veggies), nuts and seeds, lower glycemic fruit, beans, lentils and other legumes. If you want to add grains, we recommend whole grains and so-called “ancient grains,” such a millet, amaranth, or barley, as these are less likely to be highly processed and refined.

There is no best protocol for cycling carbs, as the schedule depends on your goals.

Seasonal cycling is likely the most straightforward protocol to understand. It can be as simple as this:24

October to March: 20 grams of carbs per day
April to September: 100 grams of carbs per day

This pattern may more closely match the seasonal availability of game, berries, and vegetation that our ancestors may have encountered.

Another popular protocol is adjusting carb intake according to your athletic or training schedule. An example could be like the following:

  Exercise type Amount of carbs
Monday: High volume, high-intensity training 150 grams
Tuesday: Moderate intensity training 100 grams
Wednesday: Rest day 20 grams
Thursday: Moderate intensity training 100 grams
Friday: Rest day 20 grams
Saturday: High volume, high-intensity training 150 grams
Sunday: Rest day 20 grams

 

Or, for those who are physically active but not training or competing, it could look like the following:

  Exercise type Amount of carbs
Monday: Long walk in the morning 50 grams, consumed mostly in the morning25
Tuesday: Moderate walk day 20 grams
Wednesday: Resistance training in the afternoon 50 grams, consumed mostly in the afternoon
Thursday: Rest day 20 grams
Friday: Long walk in the morning 50 grams, consumed mostly in the morning
Saturday: Fun day with family and friends 20 grams
Sunday: Resistance training in morning 50 grams, consumed mostly in the morning

 
 

Lastly, if you plan to test your ability to carb cycle, remember to increase your carbs first gradually. Here is an example.

Amount of carbs
Monday: 10 grams
Tuesday: 20 grams
Wednesday: 50 grams
Thursday: 75 grams
Friday: Test carb tolerance using a blood glucose meter as we described in the previous section

 

To help guide you even further, here is an example of a 100-gram carb day exercising in the morning:

Breakfast: Fried eggs and yogurt 31 grams carbs
Snack: 1 cup mixed almonds/pistachios/cashews 16 grams of carbs
Lunch: Ground turkey Chili 18 grams of carbs
Dinner: Oven-baked salmon with root veggies 21 grams of carbs
Dessert: 1 cup mixed blue/rasp/strawberries 16 grams of carbs

 
 

Or if you prefer to not snack or have dessert, you can add any of the following to your meals:

1 cup Edamame: 15 grams of carbs
1 cup sweet potato: 27 grams of carbs
1 cup parsnip: 24 grams of carbs
1 cup lentils: 40 grams of carbs

 
 

And an example of a 50-gram carb day.

Breakfast: Low carb banana blueberry pancakes 18 grams of carbs
Lunch: Butternut pasta with tomato sauce and garlic mushrooms 19 grams of carbs
Dinner: Low carb shepherds pie 15 grams of carbs

Feel free to explore our more than 1,000 recipes to mix and match and find the meals that work for you!


Summary

Is carb cycling right for you? That depends on your goals.

It may help some with endurance athletic performance, and it may help others with long-term compliance with a healthier diet.

Others who do better with consistency or who are more concerned with controlling their blood sugar may not benefit as much.

The most important place to start is defining your goals — and consider experimenting to see what works best for you.

Just remember, the quality of the carbs you eat still matters, so continue to focus on minimally processed whole food carb sources.

The science of carb cycling while following a baseline low-carb diet is still in its infancy. The key is to understand your goals and monitor your progress.

/ Dr. Bret Scher

 

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Learn how to do a keto diet

 

  1. Journal of Physiology 2017: Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walker [randomized trial; moderate evidence]

    PLOS One 2020: Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible [randomized trial; moderate evidence]

  2. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  3. [Individual clinical experience; very weak evidence]

  4. As mentioned earlier, the science on evolutionary nutritional patterns is flawed. Here is a talk by Amber O’Hearn addressing some of these studies and concepts: Learning about ketosis through evolutionary studies

  5. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  6. This is based on consistent clinical experience of practitioners who use low-carb diets. [weak evidence]

  7. This is based on the consistent clinical experience of low-carb practitioners. [weak evidence]

  8. Nutrients 2019: Short-term low-carbohydrate high-fat diet in healthy young males renders the endothelium susceptible to hyperglycemia-induced damage, an exploratory analysis
    [nonrandomized study, weak evidence]

  9. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  10. Metabolism 1986: The effect of varying carbohydrate content of a very-low-caloric diet on resting metabolic rate and thyroid hormones [nonrandomized study, weak evidence]

  11. Journal of Pediatric Endocrinology and Metabolism 2017: Changes of thyroid hormonal status in patients receiving ketogenic diet due to intractable epilepsy [nonrandomized study, weak evidence]

  12. Metabolism 2016: Keto-adapted athletes increase fat oxidation and preserve muscle glycogen. Metabolic characteristics of keto-adapted ultra-endurance runners [nonrandomized study, weak evidence]

    Sports Medicine 2013: Strategies of dietary carbohydrate manipulation and their effects on performance in cycling time trials [overview article; ungraded]

    The following study showed that 12 weeks of keto-adaptation helped exercise performance and body composition.

    Metabolism 2018: Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes [nonrandomized study, weak evidence]

    And the following three-month pilot study of CrossFit athletes found a keto diet benefited performance.

    Sports 2018: The three-month effects of a ketogenic diet on body composition, blood parameters, and performance metrics in CrossFit trainees: A pilot study [randomized trial; moderate evidence]

  13. Journal of Physiology 2017: Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walker [randomized trial; moderate evidence]

    PLOS One 2020:Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible [randomized trial; moderate evidence]

  14. The following paper reviews how MCT oil plus carbs slow depletion of glycogen in fat-adapted individuals, or those whose bodies have learned to burn fat for fuel instead of carbs

    Journal of Sports Science 1997: Nutritional strategies for promoting fat utilization and delaying the onset of fatigue during prolonged exercise [overview article; ungraded]

    And the following mechanistic study shows that fat burning muscles can maintain that physiology for a few days even after eating more carbs.

    Nutrients 2020: Intramuscular Mechanisms Mediating Adaptation to Low-Carbohydrate, High-Fat Diets during Exercise Training [mechanistic study article; ungraded]

  15. Scandanavian Journal of Medicine and Science in Sports 2010 Fueling strategies to optimize performance: training high or training low? [overview article; ungraded]

  16. Here is an article written by Harvard physician Dr. David Ludwig explaining the science behind fat adaptation with a low-carb diet

  17. This is based on the consistent clinical experience of low-carb practitioners. [weak evidence]

  18. The following study showed that consuming carbs post-exercise may help build muscle, but this was not studied in low-carb diets.

    Journal of Applied Physiology 1985: Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise [randomized trial; moderate evidence]

    But the following suggests that if someone eats adequate protein after exercise, then carbs don’t add to muscle synthesis.

    American Journal of Physiology, Endocrinology and Metabolism 2007: Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis [randomized trial; moderate evidence]

  19. An oral glucose tolerance test, or OGTT, involves a fasting blood sugar test. You then drink a 75-gram carbohydrate drink and repeat glucose testing at one and two hours to see how high your blood sugar climbs.

  20. Laboratory Medicine 1975: Detection of Diabetes Mellitus In Situ [nonrandomized study, weak evidence]

    Diabetes Research and Clinical Practice 2016: Identifying hyperinsulinaemia in the absence of impaired glucose tolerance: An examination of the Kraft database [nonrandomized study, weak evidence]

  21. Diabetes Care 2001: Postprandial blood glucose [overview article; ungraded]

  22. Journal of Diabetes Science and Technology 2007: Continuous glucose profiles in healthy subjects under everyday life conditions and after different meals [non-controlled study; weak evidence]Diabetes Care 2001: Postprandial blood glucose [overview article; ungraded]

  23. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  24. This is one example, and many variations exist.

    The idea is to focus on seasonally available foods and spend six months in ketosis and six months out of ketosis. You can see our visual guide showing what 20 grams and 50 grams of carbs look like on your plate.

  25. It may be better to eat your carbs shortly before or after your physical exertion