Carb Cycling and Cyclical Ketogenic Dieting

Posted on 24/01/2020 last updated 08/06/2020

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Weight loss is quite easy provided you are in a generally good state of health. All you need to do is ensure that your calorie balance is negative (i.e eat fewer calories than your body requires for maintenance) over a given period, typically 1-3 days. Maintaining muscle mass, optimal health, performance and sanity, however, is a little more difficult.

An athlete (that’s you – if you ‘train’, you are an athlete) needs to ensure enough protein is consumed to maintain as positive a nitrogen balance as possible. Nitrogen balance (the comparison between nitrogen consumed mostly via protein and nitrogen excreted via urine etc) is used as a proxy measurement of muscle gain or loss, and it’s pretty well established that a positive or neutral nitrogen balance indicates muscle gain or at least retention (1).

Essentially we consume nitrogen in the protein that we eat and a lot of that is stored in muscle tissue. We also constantly ‘turn over’ muscle tissue in our body, releasing nitrogen for excretion.

When excretion exceeds intake, we have a problem.

Eating a bunch of protein isn’t quite enough, though – it’s also important that an athlete maintains quality stimulus with resistance training in order to reduce the chances of muscle loss along with fat mass (2). This is a challenge in and of itself as low calorie dieting can make training intensity and volume difficult to maintain. You are eating fewer calories (and probably fewer carbs) meaning that there is less proverbial fuel in the proverbial tank. Over time this can lead to fatigue and excessive soreness, but in the short term it can make long(er) sessions really hard to manage at all.

A second issue that one may encounter when trying to lose fat is known as adaptive thermogenesis. This term describes one of the ways in which your body responds to low calorie dieting: During a dieting phase, in essence, your metabolic rate slows down. It does this for a number of reasons, and a lot of it is accounted for by the fact that you are now carrying a lot less weight around with you, but around 10% of it is not (3). This is caused by adaptations your body makes in order to try to halt your weight loss (annoying I know) as this is seen by your system as a thread to survival.

One commonly used method to overcome both of these phenomena is carbohydrate cycling, a process which involves reducing carb intake for a set period, and then increasing them again for another period. There are a number of different methods of applying carb cycling when trying to control both bodyweight and performance, each with their own strengths and limitations.

In this article I’m going to look at a two of the more common types of carb cycling and give you some background info that will help you decide on their usefulness in whatever situation you or your client will encounter.

The first I will discuss is known as cyclical ketogenic dieting (CKD), where the athlete will consume very little carbohydrate for days or weeks at a time, and then ‘carb up’ for a set duration (varying from one meal to 12 hours or longer).

Cyclic Ketogenic Diets

Ketosis involves consuming so few carbohydrates that you literally starve your brain of what it needs to function (Your brain runs on glucose). This causes an evolutionary ‘safety switch’ to activate, and your liver starts to make ketone bodies out of amino acids and fatty acids. These ketone bodies become your body’s new primary fuel source. Staying in ketosis (or indeed on very low calories) can be detrimental, however.

Training on a low carb diet is, as mentioned earlier, very difficult to do over the longer term. Muscle glycogen depletes and this carries some unique challenges – first of all resistance training is anaerobic in nature meaning that it requires carbohydrate based energy to be optimal. In short, you’re not able to train as hard or for as long. Secondary to this, glycogen is stored per gram in a muscle cell alongside 1-3 grams of water – this hydrates the muscle and creates an anabolic environment. Deplete glycogen, reduce anabolism.

Finally, as you diet in this manner, the hormones leptin, ghrelin and T3 are all adversely affected which, in essence, make you burn fewer calories and eat more. Not good.

To counteract the above, a periodic refeed is included in CKD plans which involves reducing protein and fat, then jacking carbohydrate intake up enormously (4,5,6). This is purported to refill glycogen and overcome the hormonal adaptations listed above. At the most basic level, this is an extremely low carb diet maintained for a very long time, with periodic ‘carb ups’.

This dieting method has both pros and cons which I will discuss here.


First thing I’ll say is that CKD dieting is hard. You are required to keep a constant eye on your carb intake and count your grams to ensure you stay under around 30g per day on low days (This is the generally accepted threshold for ketosis though intakes of less than 100g will typically result in a nutritional ketogenic state (7). Not all plans recommend 30g, with 50 being another common number) whilst keeping fat intake high and protein moderate.

Protein cannot be too high as overeating protein will prevent ketosis owing to the fact that excess amino acids undergo glucogenesis and become glucose, and without fat you can’t enter a ketogenic state at all, as ketone bodies require fat to be created. Once these things are in place you then hit a different set of specific numbers on ‘refeed’ days. This means that dietary accuracy and number crunching is important, whereas traditional low carb dieting or traditional calorie reduction can be much simpler to keep an eye on.

The second issue with a CKD is that you will typically feel lethargic during the lower carbohydrate periods until you become ‘fat adapted’. The primary fuel for brain activity under normal circumstances is glucose, but it CAN resort to using ketone bodies if it needs to. This adaptation takes some time, however, and how long it takes for YOU is difficult to predict.

As already explained, you’ll probably feel your performance dips during training - and this is NOT something you can adapt to. Anaerobic activity requires glucose, and without it you’ll struggle to sprint, lift, jump or, really, anything lasting less than 20-30 seconds (and sometimes more). Lipids (Fat) CAN provide a good source of fuel for aerobic energy, but nevertheless the last 100m of an endurance race, the heavy deadlift you need for your total or the sprint for the try area, the part that really matters, is fuelled by carbs. Carbohydrate restriction, therefore, will over time cause training intensity and quality to dip (8).

A third thing which must be mentioned is that low carbohydrate diets (generally classed as under 150g of carbohydrates per day, but there’s no real ‘official’ threshold for what we call ‘’low’’) actually perform just as well as full ketogenic diets (under 30g) when tested for differences in body composition (9). This means that the very strict carbohydrate reduction won’t actually give you any metabolic advantage when compared to a regular lower carbohydrate intake, but will more than likely make you feel worse and cause your training to suffer more.

Another thing that one must bear in mind here is that according to long term data, low carbohydrate diets don’t actually give better results than calorie-matched low fat diets (10). This means that working hard to keep your body in ketosis, as well as dealing with the bad breath, nausea and possible difficulties eating socially, probably won’t actually give you any benefits anyway!

Additionally, very low carbohydrates, by design, restrict the consumption of whole grains, legumes, fruit and a lot of vegetables. You are largely restricted to a small amount of cruciferous vegetables, fungi or sea flora. This poses a huge risk of nutrient deficiency and a very low intake of dietary fibre meaning it must be dealt with carefully. Many ketogenic dieters must supplement a lot of vitamins and minerals to maintain optimal health, including calcium, vitamin D, thiamine and even vitamin C! (11).

Next consider that protein is kept moderate. As we know, increased protein is needed in order to maintain muscle mass whilst in a calorie deficit. Reducing this in order to stay in ketosis risks losing more than you typically would on a higher protein intake.

A final point here is that a periodic refeed, so included not only to improve glycogen stores but to ensure that hormonal balance is maintained, doesn’t work as well as you might hope. Leptin and Grehlin may fall back into line during the reefed, but just like any diet (I’m stressing this point, this is not only the case for CKD’s), as soon as calories go back down, the hormonal adaptations do, too.

That said, refeeds are a necessary part of dieting which has a host of benefits, but they need to be kept under strict control (something which may prove difficult if the dieter is feeling deprived or is craving the carbohydrates that they are accustomed to eating regularly) because the metabolic improvements generally don’t counteract the caloric intake that can occur, and this veritable binge can actually eliminate any fat loss progress made during the week (12).

In sum, training is harder, the diet is hard to stick to, you don’t really get any benefits from being in ketosis that wouldn’t happen on any other diet with the same calorie value, and a reefed can potentially turn into overconsumption which ‘cancels out’ a week of dieting.


There are few positives to a Cyclical Ketogenic Diet, however.

Firstly, once you become accustomed to the degree to which you must watch your intake, it becomes a lot easier to maintain a state of ketosis. Unlike a low fat diet which generally restricts dietary choices to a great degree, ketogenic dieters can enjoy a great deal of foods which are often considered ‘bad for you’ in the eye of the general public and this affords one a lot of enjoyable meal options which is a fantastic way to increase dietary adherence. Pork belly, hard cheese and streaky bacon are typically celebrated by CKD dieters. Couple this with the fabled carb-fests which make up ‘refeeds’, and you have a diet which, despite being restrictive, can be enjoyable to some folks.

Secondly, ketogenic dieters generally report a dramatic reduction in hunger pangs and a much more stable energy level throughout the day due to the regulation of blood sugar which occurs on a lower carbohydrate intake and the satiating nature of a high fat diet. This makes concentrating at work easier and can stop cravings for that bit of chocolate that you said you weren’t going to eat but it’s 3pm and you feel a bit tired and you’ve been really good this week and you squatted earlier and…

A final and somewhat obvious advantage is that, due to the glycogen depletion and subsequent scale weight drop which dieters will experience, initial progress is rapid which can be motivating to people who have a history of failed diets, meaning they are more likely to stay on course.

All in all I don’t recommend CKD’s for most. They can be incredibly effective, but they aren’t without their limitations – and they aren’t necessarily ‘better’ than ‘easier’ methods.

So if ketogenic diets aren’t the best way to go, what else is there? The other form of carbohydrate management I’m going to talk about today is the idea that one has High, low and (sometimes) medium days throughout the week, depending on how your training is set up.

Weekly carbohydrate cycling

This method of dieting is probably the more common method of carb cycling. Typically one will have a set number of protein and fat grams every day, and your carbohydrate intake (and therefore calorie intake) will vary throughout the week as dictated by your training/preferences.

As a note, there is another form of this diet whereby calories stay the same every day but carbs and fats undulate throughout the week. High carb on training days and higher fat on rest days. I won’t be talking about this method because there is no reason to do this. Some dieters may prefer this approach simply due to food preferences and that’s absolutely fine – anything that makes a diet easier to adhere to is a good idea – but this approach is borne from the idea that carbs cause weight (fat) gain if you don’t train, or that you need to train to ‘earn’ carbs. Both of the above are false.

Generally a dieter will have predominantly medium days then a high day on the day of, or sometimes the day before, a heavy or high volume session and low days on light training or off days. This setup makes logical sense, you fuel training and don’t fuel rest, but does it hold up?


Advocates of carbohydrate cycling which is set up based around training often (but not always – a lot of coaches use carb cycling for very different reasons listed below, so be aware of this mistake but don’t tar all with the same brush and assume that everyone is misguided) misunderstand one fundamental aspect of human metabolism, and that is the idea that the body works in 24 hour cycles. The assumption is that if one is highly active on one day you can eat more, but if one was to eat the same high calorie number on a less active day you would store fat, or halt fat loss.

What actually happens is that calorie and therefore fat balance works over a far longer period.

You are constantly storing and using up fat at varying ratios. After a meal you store more than you burn, you store more after a large meal than a small one, more after a meal containing a lot of fat than a ‘leaner’ one, and during exercise or periods between meals you burn more than you store. Over the course of a week or so, it is the overall balance which dictates fluctuations in body composition.

Due to this longer term balance, fat loss would be equal if one was to simply average the same intake over the course of a week rather than undulating intake with training.

Secondly, if you undergo a high volume workout, or one which is relatively difficult and deplete stored glycogen, it can take 46 hours to replenish fully (13). This means that if you reduce carbohydrates drastically the day after a depleting workout because you aren’t training on that specific day, you may not fully recover even after two days which will affect performance and, by proxy, body composition improvements over the long term.

A third issue is that weekly carbohydrate cycling can be problematic from a mental health standpoint for those who are already prone to disordered eating tendencies – the kind of people who are drawn to the fitness industry, physique competitions, and therefore this kind of dieting practice (AGAIN – I’m not saying everyone, by a HUGE longshot. It’s a generalisation, and an accurate one, but nothing more – before I get all kinds of trolling). It is very easy to get into the habit of ‘earning’ carbohydrates and then being hesitant to eat them on days where activity is low; a surefire symptom of a poor relationship with food. If a dieter succeeds on a diet such as this, they can easily adopt the mindset that they aren’t ‘’allowed’’ carbs unless they have trained, in extreme cases possibly causing a risk of over-exercising and a binge/purge cycle.


There are a lot more positive things which can be said about this form of dietary setup, despite the fact that, just like the CKD, it doesn’t give any actual metabolic advantages over a constant dietary intake. Remember – diets don’t need to ‘work’ better from a physiological standpoint for them to ‘work’ better for other reasons.

First, this is a very simple method to control your overall intake without paying much attention to specific tracking of macronutrients. Simply consume carbohydrates before and after training, possibly also during the session and at other times during ‘high activity days’, and reduce or eliminate them elsewhere. Eliminating a macronutrient almost always causes a decrease in overall calorie intake, and this can therefore be a viable fat loss tool for people not wanting to count numbers.

Secondly, this is a good way to manage a low overall carb intake for those who’s total needs are quite low but who are counting. For someone approaching the end of a hard diet who has a very restricted intake, placing the bulk of that intake around the heaviest sessions of the week might be enough to be sure they can perform at their best, maintaining the most lean tissue possible. This, in my opinion, is the main reason for anyone to carb cycle and something I implement myself with a lot of clients.

Simply use the same calculations as you usually would to set intake, but ‘skew’ it like so:

  • Calorie need for fat loss: 2200
  • Protein need: 200g – 800kcal
  • Fat need: 75g – 675kcal
  • Remainder from carbs: 180g – 725kcal

You could then say that this means per week they have 1260g carbs to play with. If I’m working with someone I may therefore say that on 3 resting days, the client will have 100g carbs, meaning that on training days they are able to have 240g to fuel performance.

Another positive here is that it can make a diet more interesting and therefore easier to stick to. An athlete may find on some days they can eat a lot of breads, rice, cereal, pasta and other delicious carb based foods while on other days sausages, cheese and nut butters are on the menu – if a typical high carb or fat approach is taken with no variation, these things can become cravings and on a typical moderate approach the portion sizes of both need to be carefully considered, but a carb cycle allows the best of both worlds.

Finally, unlike CKD’s mentioned above, the carb intake on ‘low’ days is almost always still allows for a lot of vegetables, meaning that this method doesn’t cause any of the nutritional deficiencies that can be experienced with harsher regimes.

Final Thoughts

When it comes to carb cycling I tend to view it as a tool which can be implemented if needed. If an athlete is looking to lose fat or maintain weight whilst improving performance I like to carb cycling in a weekly fashion but only when a need arises – generally most people can diet without any change day to day. If a client is very overweight it may even resemble a CKD as calories can be very low on some days affording rapid weight loss, safely, with a client who is clinically obese (14) (though rarely do I ever drop carbs to 50g or less).

I do this because a higher carb intake prior to training days (or on training days for clients who train in the evening, meaning they can ‘fuel up’ during the day) might increase performance a little – but I think it’s important that this is communicated to my clients so they aren’t under the impression that carbs are ‘bad’ or ‘fattening’, or that they will inhibit fat loss in some way.

As always, I recommend that you don’t do this by yourself for the first time, though. If you think you need to implement carb cycling at any point, get yourself a coach. It’s never a bad investment!


  1. Antonio and Lowery (2012). Dietary Protein and Resistance Exercise. CRC Press
  2. Research Gate : Influence of exercise training on physiological and performance changes with weight loss in men (External Link)
  3. Douyon L, Schteingart DE. Effect of obesity and starvation on thyroid hormone, growth hormone, and cortisol secretion. Endocrinol Metab Clin North Am 2002;31:173-189.
  4. Friedl KE, et al. Endocrine markers of semistarvation in healthy lean men in a multistressor environment. J Appl Physiol 2000;88:1820-1830.
  5. de Rosa G, et al. Thyroid function in altered nutritional state. Exp Clin Endocrinol 1983;82:173-177.
  6. Krieger et al (2006). Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: a meta-regression. Am J Clin Nutr 2006;83:260 –74
  7. Effects of Carbohydrate Restriction on Strength Performance. Leveritt, Michael; Abernethy, Peter J
  8. Johnston CS et. al. Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets. American Journal of Clinical Nutrition. (2006) 83: 1055-1061
  9. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. Sachs et al.
  10. Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores1,2 Abdul G Dulloo and Jean Jacquet
  11. Piehl, K. (1974), Time Course for Refilling of Glycogen Stores in Human Muscle Fibres Following Exercise-Induced Glycogen Depletion. Acta Physiologica Scandinavica, 90: 297–302.
Ben Coomber and Tom Bainbridge
Ben Coomber & Tom Bainbridge

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