Carb Cycling and Cyclical Ketogenic Dieting

Posted on 24/01/2020 last updated 08/07/2020

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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. 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.

One commonly used method to overcome this issue 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 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 carbohydrates for fuel; you literally cannot utilise fatty acids for energy through anaerobic metabolism. 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.

To counteract the above, a periodic refeed is included in CKD plans which involves reducing protein and fat, then jacking carbohydrate intake up enormously (3,4,5). 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’ – typically a week of consuming a higher fat, very low carb and moderate protein diet followed by a weekend of a very high carb, very low-fat approach.

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

CONS

The 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 (6). Not all plans recommend 30g, with 50 being another common number) whilst keeping fat intake high and protein moderate.

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: just don’t eat many carbohydrate containing foods.

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 training performance dips - 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 (7). The idea of a CKD is to counteract this but depending on your training volume it may not be able to.

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 (8). 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 (8). 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! And this is before we talk about the potential for bingeing during your refeed weekends...

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!

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.

PROS

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, you 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. This is somewhat reminiscent of the FINAL form of carb cycling that I’ll discuss, though, so don’t dismiss it entirely just yet.

Generally when doing a weekly cycling aproach, 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?

CONS

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 you’re highly active on one day you can eat more, but if you were 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 you were 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 (10). 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 sure -fire 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.

PROS

There are many 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 good way to manage a low overall carb intake for those who have a relatively low total need 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.

The big secret

All of the above seems relatively complicated, right? It requires a bunch of tracking and planning and checking your calendar to see if you can eat bread today; some people are cool with this but a lot are not and so it might be useful to remember that you can get MOST of the benefits of the above approach without any of the cons by simply doing this:

Track your calories and protein, let the rest fall where it may.

As I’ve already said the evidence suggests that fluctuations in body composition, especially while dieting, are not affected by your relative carbohydrate or fat intake with both low carb and low fat diets leading to the same outcomes. The most obvious way to apply this, therefore, is to simply not worry about how much of each you eat.

This makes controlling your food intake FAR easier because it literally halves the numbers you pay attention to (going from 4 to 2), but moreover it enables as much variation as you could want. Want a big fatty steak today? Go for it. Is tomorrow a big bowl of pasta day? Awesome. There really is no downside!

As hinted at above, those with a more athletic mentality may be better off skewing their intake more towards carbohydrates than fats, but unless you’re an extremely high performing competitive athlete the difference in your quality of life that will result from a moderate carb intake vs a high carb intake if the former lets you enjoy your food more isn’t a simple case of ‘performance comes first’.

In out experience this is the most effective way to track your numbers if you’re going to do that, and it lets carbohydrate cycling happen far more organically. As we’ve discussed the primary benefits of carb cycling are to do with preference and food enjoyment though this comes at a cost of increased rigidity, so this truly is the best of both worlds!

Final thoughts

When it comes to carb-cycling I tend to think about it as a tool which can be implemented if needed. If an athlete is looking to lose fat or maintain weight whilst improving performance carb cycling according to preference with a slightly higher skew towards carbs on a daily basis tends to be the best approach going, without any intentional cycling of anything.

If, however, someone prefers a ketogenic or low carbohydrate approach and so intentionally reduces carbohydrates most of the time, some kind of cycling to place carbohydrates before workouts in some way is generally a far better option and it is in THIS light that we suggest you view the whole thing.

If a person likes to eat more carbs: don’t cycle. Just let them eat to preference, varying things as they go

If a person typically reduces their carb intake when left to preference: a few intentional high carb days aren’t such a bad idea!

References

  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. Friedl KE, et al. Endocrine markers of semistarvation in healthy lean men in a multistressor environment. J Appl Physiol 2000;88:1820-1830.
  4. de Rosa G, et al. Thyroid function in altered nutritional state. Exp Clin Endocrinol 1983;82:173-177.
  5. 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
  6. Effects of Carbohydrate Restriction on Strength Performance. Leveritt, Michael; Abernethy, Peter J
  7. 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
  8. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. Sachs et al.
  9. 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
  10. 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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