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This article is part of a series:
→ Part 1 — Fat oxidation
→ Part 2 — Fat adapting
→ Part 3 — Low carb diets
→ Part 4 — Low carb & performance
→ Part 5 — Carbs are your friend
→ Part 6 — Carb periodisation
→ Part 1 — Fat oxidation
→ Part 2 — Fat adapting
→ Part 3 — Low carb diets
→ Part 4 — Low carb & performance
→ Part 5 — Carbs are your friend
→ Part 6 — Carb periodisation
Nutritional manipulations for training. Part 6 of 6:
Carb Wars: A New Hope. Carbohydrate periodisation.
Thomas Solomon PhD.
Updated: 22nd April 2024.
As Cassian Andor once said, “Rebellions are built on hope”. I have discussed many different routes to increasing fat oxidation rates during exercise and the training manipulations you can use to reduce your carbohydrate availability. But a persistent low carb diet will likely reduce your economy and endurance performance. If you are an athlete with a habitual low-carb munching habit looking to be the best you can be, you would be wise to join the carbohydrate periodisation rebellion. Hear all about it in this final part of my series on nutritional manipulations for training.
Reading time ~17-mins (3500-words).
Or listen to the Podcast version.
Or listen to the Podcast version.
I have previously discussed how you can use acute nutritional strategies for lowering carbohydrate availability in and around certain sessions — “train low” and “sleep low” — and how you can adopt a chronic low-carb/high-fat dietary strategy for the same purpose — “live low”. As you now know, lowering your carbohydrate availability decreases muscle glycogen levels, increasing fat oxidation rates during exercise and promoting exercise adaptations, particularly those that help you be more “aerobic” for longer — creating more energy-producing mitochondria in your muscles and more enzymes to catalyse those energy-producing reactions.
A chronic low-carb/high-fat dietary approach, ketogenic or not, may therefore seem like a great idea for giving your endurance performance a high-octane fuel injection. Yes, you may indeed very likely increase your run-time-to-exhaustion at a low exercise intensity due to your increased ability to “burn” fat for longer. But, the downside is that you will also become less economical — burning more oxygen at a given pace — and you will blunt your muscles’ capacity for burning glucose, the more economical and more rapidly burning fuel that is required to meet the demand of high-intensity exercise... The consequence of which is that you will most likely decrease your race performance when operating at high intensities.
That doesn’t sound like an admirable goal.
No matter how that sounds and despite what we have all learned from the 100-years of the Carb Wars, there are still many folks who continue promoting the low-carbohydrate diet approach for excelling as an endurance athlete. Well, since rebellions are built on hope, if you sit on that side of the fence, I have one suggestion for you… Why not rebel and use the best of both worlds?
By the late 2000s, it became clear that starting a workout with low muscle glycogen — “train low” — causes a bigger increase in expression of genes that trigger mitochondrial biogenesis and fuel substrate metabolism (here, here, here, and here). However, endurance performance was not improved by “training low” (here, and here), likely because low carbohydrate availability decreased the athletes’ ability to sustain high-intensity workloads during the sessions in these studies.
On the contrary, “sleep low” training allows for high carbohydrate availability to support an evening high-intensity session while using low carbohydrate availability to help boost the adaptations to low- to moderate-intensity session the following morning (here, here, here, here, and here).
Consequently, carbohydrate periodisation combines “train low”, “sleep low”, and “train high” approaches, aiming to manipulate exercise adaptations while maintaining fuel availability when you need it most. This method is simplified into a more-eloquent conceptualisation by James Morton’s group: That is, to provide carbohydrate relative to the demands of your upcoming session while aiming to deplete muscle glycogen to levels within the glycogen threshold that are necessary to elicit optimal adaptations. Therefore, during sessions intended to boost your endurance, it may help enhance your fat burning capacity and mitochondrial biogenesis to use low carbohydrate availability, but high-intensity “quality” sessions that are designed to increase your speed, power, and race-day prowess are best performed with high carbohydrate availability.
This sounds great, but maybe you are wondering...
In the modern era, several large-scale cohort studies (here, here, here, here, and here) show there is a mismatch between recommendations and practice — many athletes do not achieve energy availability and/or carbohydrate availability guidelines. But anecdotal evidence suggests that many successful endurance athletes use a carbohydrate periodisation approach, either knowingly — like Chris Froome — or unwittingly — any athlete who does sessions before breakfast. Case studies have reported that some elite marathoners use carbohydrate periodisation in their training, while observational cohort studies have also found that some road racers (but not track/middle-distance) self-report using carbohydrate periodisation methods, as do some elite road runners and race-walkers. Furthermore, anecdotal accounts from Sweat Elite and Adharanand Finn also document that Kenyan distance runners — arguable the best endurance runners on the planet — adopt carbohydrate periodisation principles as part of their habits of daily living. Observations that are supported by published studies documenting frequent use of “train low” approaches among world-class East African distance runners.
The observations that some successful elite athletes use carbohydrate periodisation in their toolbox combined with the knowledge that “train low” and/or “sleep low” practices enhance post-session molecular signalling in muscle, leads to an obvious question...
Supernova 1 showed that athletes who adapted to a low-carbohydrate ketogenic diet increased their oxygen cost of exercise — reduced economy — and did not improve their 10 km race performance, while athletes eating a high-carb diet or a periodised carbohydrate diet improved their economy and their 10 km race performance. In simple terms, Supernova 1 showed us that world-class endurance athletes need carbohydrate to optimally adapt to intense training and perform at their best.
Figure from Burke et al. (2016) J Physiol.
Race times for IAAF sanctioned 10 km race walk events in elite race walkers undertaken pre‐ (Race 1) and post‐ (Race 2) 3 weeks of intensified training and high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 8), or ketogenic low carbohydrate, high fat (LCHF, n = 9) diets. * = Significantly different from pre‐treatment (P < 0.01).
But when we are looking to understand the wicked and nuanced problem of training for endurance performance, average changes are not so useful — you are an n of 1 after all. Fortunately, Burke’s team kindly published their raw data on Fig Share. So, I calculated the odds ratios and relative risks of the athletes’ performance improvements…
An athlete’s expected chance of having an increase in 10 km race performance is 75 out of 100 people on a high-carb diet, 71 out of 100 on a periodised carb diet, and just 10 out of 100 on a low-carb diet, while the chance of a decrease in race performance is 25 out of 100 on high-carb, 29 out of 100 on periodised carb, and a massive 90 out of 100 on a low-carb diet. This means that an athlete’s relative risk of worsening their performance following a 3-wk intensive training block when following a low-carb ketogenic diet is 4 vs. a high-carb or 3 vs. a periodised carb diet, i.e. they are 3 to 4-times more likely to get worse. Meanwhile, an athlete’s relative risk for improving their performance during an intense training block is 8 when following a high-carb diet and 7 when on a periodised carb diet (vs. a low-carb ketogenic diet)... In non-gobbledegook, in comparison to low-carb keto diet folks, following an intense training block, high-carb diet munchers are 8-times more likely to improve their race performance and athletes gobbling a periodised carbohydrate diet are 7-times more likely to improve.
In the same year, Laurie-Anne Marquet published a similar study where 21 triathletes were randomized to two groups completing a 3-week intervention. This time they compared 6 g/kg/day of carbs distributed over each day to a periodised carbohydrate approach that combined “train-high” (interval sessions with high-CHO availability), “sleep-low”, and “train-low” (fasted easy sessions). Athletes who followed the carbohydrate periodisation strategy improved their cycling economy, anaerobic cycling capacity, and 10 km running time trial performance.
In 2017, Niels Ørtenblad’s lab in Denmark followed with a 4-week study of 26 elite endurance athletes (triathletes and cyclists) who were randomised to a periodised carbohydrate group or an evenly-distributed carbohydrate group. On 3 days per week, athletes completed a morning high-intensity interval session followed by a moderate-intensity ride 7-hours later. In between sessions, the carbohydrate periodisation group consumed a low-carb diet (1 g/kg; “train low”) while the other group received a high-carb diet (6 g/kg). After 4-weeks, markers of mitochondrial adaptations, VO2max, and 30-minute TT performance increased, but there were no differences between groups, indicating that carbohydrate periodisation solely using a “train low” approach does not enhance training adaptations.
And, in 2024, Prieto-Bellver and colleagues randomised 17 highly-trained cyclists (VO2max = 71) to either a periodised carbohydrate group or a high-carbohydrate group for 5 weeks. They found no between-group differences in the changes in carbohydrate or lipid oxidation, heart rate, lactate, carbohydrate oxidation, lipid oxidation, time-to-exhaustion, or maximal lactate steady state (MLSS), a performance test designed to identify the higher power output where blood lactate is steady. This suggests that, in highly trained endurance athletes, carbohydrate periodisation during a training block is not superior to a high carbohydrate diet.
So, the burning question is...
The work of the Carlsberg-funded 1920 Nobel Laureate, August Krogh showed that recent diet “probably” influences metabolic fuel choice during low-to-moderate intensity exercise as well as people’s ability to perform exercise. A century later, we are armed with the knowledge that chronic low-carb ketogenic diets indeed increase “fat burning” during exercise but also increase the oxygen cost of exercise and blunt training-induced performance gains when trying to race at a high-intensity. Therefore, just like August Krogh’s funding source would say, “It is probably best not to put all your eggs in the fat burning basket”. Successful training is multi-faceted and should not be reduced to a single input like being fat-adapted or maximising your fat oxidation rates.
If your interest is to train to see maximal gains in endurance performance, the experimental evidence convincingly shows us that the periodised carbohydrate approach out-performs a low-carb ketogenic diet, which reduces running economy and impairs endurance race performance. But, the experimental evidence also demonstrates that carbohydrate periodisation offers no further advantage to endurance performance than the traditional “train high” approach. For this reason, carbohydrate periodisation has been widely discussed by eminent scholars in sports nutrition (here, here, here, and here) but it is not an inherent part of sports nutrition position statement guidelines from either the American College of Sports Medicine (ACSM) or the International Society for Sports Nutrition (ISSN). This may change as more studies are published, but recent systematic reviews and meta-analyses of the current evidence show that carbohydrate periodisation offers no advantage to endurance performance over normal (high) carbohydrate availability (see Gejl and Nybo, 2021). So, for now, carbohydrate periodisation is a suggestion, not a rule.
You might, therefore, ask yourself, “why don’t I just train with a high carb availability all the time?”. Good question. And, indeed you can — daily consistency is far easier to adopt in real life, especially for regular athletes who are not supported by Supernova’s fine team of chefs and dieticians to fine-tune your periodised carb behaviour. Furthermore, field observations made in the training camps of Kenyan and Ethiopian distance legends (see here, here, and here), find that the daily food intake of these East African endurance masters is a carbohydrate hullabaloo — they eat approximately 9-10 g/kg carbohydrate per day contributing ~65-75% of daily calories! Mimicking the best might not be such a bad idea.
But, there are practical advantages of training with carbohydrate periodisation. By occasionally “training low” and/or “sleeping low” you take the stress out of always having to consider your nutrition. Such practices can also help with time management. For example, getting up to train in the morning doesn’t have to mean arising at 5 am to eat, wait 2-hours, then train before work — you can simply wake up, implement your gingerbreadman-prevention protocol (poop), get dressed, and rock and roll… Plus, if we once again observe and learn from the best, Sweat Elite and Adharanand Finn have documented that the best endurance runners on the planet adhere to carbohydrate periodisation principles as part of their habits of daily living. Such observations are also supported by experimental evidence showing frequent use of “train low” approaches among world-class East African distance runners. I’ll say it again: mimicking the best might not be such a bad idea. But also remember that this is just one small factor that contributes to their success — we do not know if East Africans would be just as good if they did not periodised their carb intake
So, yes, you could use a carbohydrate periodisation strategy and it is superior to a persistent “train low” strategy but it does not appear to be an essential replacement for a persistent “train high” strategy.
That is my empirical evidence. But implementing carbohydrate periodisation with precision is tricky.
When I discuss carbohydrate periodisation with my athletes, it is common to hear that they would plan to reduce carb intake by skipping meals. This is not ideal because it is a fast route to a state of low energy availability — meaning that total energy intake and protein intake needs will not be met and their desired adaptations will not arise. Consequently, I typically need to carefully discuss these nuances and provide some education.
Taking a “fuel for the work required” approach by providing carbohydrate relative to the demands of your upcoming session while also aiming to finish your sessions within the glycogen threshold necessary to elicit optimal adaptations, requires expert knowledge of nutrition and energy metabolism. And, even if you had the knowledge, you cannot take muscle biopsies to measure glycogen in between every session. But life is full of surprises and, thanks to José Areta’s and Will Hopkins’ 2018 meta-analysis of all known glycogen depletion studies, you can make a well-informed estimate. I used their data to create a simple fuel for the work required tool, which you can use to estimate your basal glycogen levels, the amount of glycogen you use in your sessions, and how many carbohydrates you need to eat after a session to replenish glycogen.
To further extend your knowledge and learn how a “train low” and “sleep low” carbohydrate periodisation training programme might look, I suggest consulting the examples provided by Louise Burke and her colleagues (Burke et al. 2020, Stellingwerf et al. 2018, and Marquet et al. 2016) or you can use my simple framework as a guide at veohtu.com/fuelfortheworkrequired (see image at the end of this article).
When operating at high intensities, when oxygen delivery to muscles becomes a limiting factor because you are approaching your VO2max, it is entirely intuitive that your body will try to use the most economical fuel to use less oxygen while continuing to produce ATP at the rate it needs to keep moving forward with speedy grace (or, at the very least, a speedy war face). Therefore, I would encourage you to, “consider your race goals and then consider your power output and metabolic needs to achieve those goals”. Are you logging all your training miles to try to run slow? Are you trying to impress your competitors with how far you can go without food? Are you trying to impress your competitors (or the Gods of grammatical riddles) with how fast you can run slowly? No, of course not. You probably want to break your PBs and win races.
The evidence that a persistent low-carb ketogenic diet is good for athletic performance is weak. At best, a low-carb high-fat diet approach yields comparable performance outcomes when compared to a high carbohydrate diet but the bulk of evidence shows that low-carb high-fat diets impair endurance performance. No experimental or epidemiological evidence has ever shown that a high-carbohydrate diet impairs endurance performance. And, the best endurance runners on the planet — East Africans — habitually eat a high carbohydrate diet to support their high training load.
Periodising your carbohydrate availability can help augment some of the intended training adaptations of a low-carb diet while ensuring you have high carbohydrate availability to maintain high power output during key sessions and races — fuel for the work required. But, although this approach is inherent for East African distance maestros, the carbohydrate periodisation strategy has not been shown to offer additional performance benefits over the traditional high-carbohydrate diet approach. As an athlete, maintaining a healthy eating pattern is key and consistency is the best way to maintain a good habit. Periodising carbohydrate availability is an inconsistent nutritional pattern and, if you get it wrong by inadvertently reducing total energy intake or compromising micronutrient intake, all your hard work will be undone.
Without the support of expert knowledge, juggling “train low / sleep low” and “train high / sleep high” strategies may not be appropriate for you. Without such support, you might ponder, “Why introduce a risky inconsistent nutritional pattern over a consistent nutritional pattern that has never been shown to impair performance?”. Because running before breakfast — “train low” — or not eating after a night time run — “sleep low” — might offer practical or logistical advantages. So, if you are curious, to help implement such strategies while maintaining optimal habits of daily eating to meet your specific carbohydrate (and protein) intake needs, thoroughly educate yourself in nutrition and energy metabolism or seek dietary counselling from a nutritionist or dietician.
Or… you could do as the Kenyans do:
Thanks for joining me on this “Nutritional manipulations for training” series. The high vs. low carb debate has been rampant my whole life and it re-emerges from time to time. It will “probably” never stop becauseCarlsberg needs to keep selling beer the world needs an answer and many of the folks debating it forget one important detail: the purpose of their diet. No doubt, we have yet to hear the end of this “never-ending story”. Who knows, perhaps Wolfgang Petersen will direct the Hollywood version? Until that time, keep training smart.
Image Copyright © Thomas Solomon. All rights reserved.
A chronic low-carb/high-fat dietary approach, ketogenic or not, may therefore seem like a great idea for giving your endurance performance a high-octane fuel injection. Yes, you may indeed very likely increase your run-time-to-exhaustion at a low exercise intensity due to your increased ability to “burn” fat for longer. But, the downside is that you will also become less economical — burning more oxygen at a given pace — and you will blunt your muscles’ capacity for burning glucose, the more economical and more rapidly burning fuel that is required to meet the demand of high-intensity exercise... The consequence of which is that you will most likely decrease your race performance when operating at high intensities.
That doesn’t sound like an admirable goal.
No matter how that sounds and despite what we have all learned from the 100-years of the Carb Wars, there are still many folks who continue promoting the low-carbohydrate diet approach for excelling as an endurance athlete. Well, since rebellions are built on hope, if you sit on that side of the fence, I have one suggestion for you… Why not rebel and use the best of both worlds?
A new hope. Welcome to carbohydrate periodisation.
By using context and perspective, I previously helped you reformulate the boring and uninspired low-carb vs. high-carb debate by considering the question, is carbohydrate a friend you train with regularly or a friend you see from time to time? If you habitually adhere to a low-carbohydrate ketogenic diet and are looking to maximise your endurance performance — that is run as fast as you can for a long time — instead of persistently “living low”, I would encourage you to consider purposefully mixing “train low”, “sleep low”, and “train high” approaches. Consider using carbohydrate periodisation; a method where you occasionally instil low carbohydrate availability in and around some training sessions — “train low” and “sleep low” — while ensuring high carbohydrate availability during key sessions — “train (and race) high”.By the late 2000s, it became clear that starting a workout with low muscle glycogen — “train low” — causes a bigger increase in expression of genes that trigger mitochondrial biogenesis and fuel substrate metabolism (here, here, here, and here). However, endurance performance was not improved by “training low” (here, and here), likely because low carbohydrate availability decreased the athletes’ ability to sustain high-intensity workloads during the sessions in these studies.
On the contrary, “sleep low” training allows for high carbohydrate availability to support an evening high-intensity session while using low carbohydrate availability to help boost the adaptations to low- to moderate-intensity session the following morning (here, here, here, here, and here).
Consequently, carbohydrate periodisation combines “train low”, “sleep low”, and “train high” approaches, aiming to manipulate exercise adaptations while maintaining fuel availability when you need it most. This method is simplified into a more-eloquent conceptualisation by James Morton’s group: That is, to provide carbohydrate relative to the demands of your upcoming session while aiming to deplete muscle glycogen to levels within the glycogen threshold that are necessary to elicit optimal adaptations. Therefore, during sessions intended to boost your endurance, it may help enhance your fat burning capacity and mitochondrial biogenesis to use low carbohydrate availability, but high-intensity “quality” sessions that are designed to increase your speed, power, and race-day prowess are best performed with high carbohydrate availability.
This sounds great, but maybe you are wondering...
Do elite athletes use carbohydrate periodisation?
Sometimes science is waaay behind practice. Carbohydrate periodisation is a sexy-sounding phrase but the principle is not new. Ernst van Aaken aka The Running Doctor, German coach to many-an-elite marathoner and perhaps inventor of the “long slow distance” thing, had his athletes do fasted long runs and twice-a-day sessions without food — “train low” — among fed sessions... in the 1950s!In the modern era, several large-scale cohort studies (here, here, here, here, and here) show there is a mismatch between recommendations and practice — many athletes do not achieve energy availability and/or carbohydrate availability guidelines. But anecdotal evidence suggests that many successful endurance athletes use a carbohydrate periodisation approach, either knowingly — like Chris Froome — or unwittingly — any athlete who does sessions before breakfast. Case studies have reported that some elite marathoners use carbohydrate periodisation in their training, while observational cohort studies have also found that some road racers (but not track/middle-distance) self-report using carbohydrate periodisation methods, as do some elite road runners and race-walkers. Furthermore, anecdotal accounts from Sweat Elite and Adharanand Finn also document that Kenyan distance runners — arguable the best endurance runners on the planet — adopt carbohydrate periodisation principles as part of their habits of daily living. Observations that are supported by published studies documenting frequent use of “train low” approaches among world-class East African distance runners.
The observations that some successful elite athletes use carbohydrate periodisation in their toolbox combined with the knowledge that “train low” and/or “sleep low” practices enhance post-session molecular signalling in muscle, leads to an obvious question...
Does carbohydrate periodisation enhance performance?
I previously delved deep into Louise Burke’s Supernova studies, in which her team examined the effects of 3-weeks of a low carb ketogenic diet on race performance in world-class endurance athletes. But, I did not reveal all. While Burke and her colleagues compared a low-carb ketogenic diet to a high-carb diet, there was also a third group — a carbohydrate periodisation intervention that combined “train low” and “sleep low” approaches.Supernova 1 showed that athletes who adapted to a low-carbohydrate ketogenic diet increased their oxygen cost of exercise — reduced economy — and did not improve their 10 km race performance, while athletes eating a high-carb diet or a periodised carbohydrate diet improved their economy and their 10 km race performance. In simple terms, Supernova 1 showed us that world-class endurance athletes need carbohydrate to optimally adapt to intense training and perform at their best.
Race times for IAAF sanctioned 10 km race walk events in elite race walkers undertaken pre‐ (Race 1) and post‐ (Race 2) 3 weeks of intensified training and high carbohydrate availability (HCHO, n = 9), periodised carbohydrate availability (PCHO, n = 8), or ketogenic low carbohydrate, high fat (LCHF, n = 9) diets. * = Significantly different from pre‐treatment (P < 0.01).
×
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The replication study, Supernova 2, reproduced those findings to a T. Following the 3-week intensive training camp, on average, high-carb athletes got 2.2 minutes quicker in a 10 km race while periodised carbohydrate athletes got 1 minute quicker. However, the low-carb keto folks got 1.4 minutes slower, even despite switching to a 2-week high-carb diet and tapering their training after the intervention.
But when we are looking to understand the wicked and nuanced problem of training for endurance performance, average changes are not so useful — you are an n of 1 after all. Fortunately, Burke’s team kindly published their raw data on Fig Share. So, I calculated the odds ratios and relative risks of the athletes’ performance improvements…
An athlete’s expected chance of having an increase in 10 km race performance is 75 out of 100 people on a high-carb diet, 71 out of 100 on a periodised carb diet, and just 10 out of 100 on a low-carb diet, while the chance of a decrease in race performance is 25 out of 100 on high-carb, 29 out of 100 on periodised carb, and a massive 90 out of 100 on a low-carb diet. This means that an athlete’s relative risk of worsening their performance following a 3-wk intensive training block when following a low-carb ketogenic diet is 4 vs. a high-carb or 3 vs. a periodised carb diet, i.e. they are 3 to 4-times more likely to get worse. Meanwhile, an athlete’s relative risk for improving their performance during an intense training block is 8 when following a high-carb diet and 7 when on a periodised carb diet (vs. a low-carb ketogenic diet)... In non-gobbledegook, in comparison to low-carb keto diet folks, following an intense training block, high-carb diet munchers are 8-times more likely to improve their race performance and athletes gobbling a periodised carbohydrate diet are 7-times more likely to improve.
×
![]()
Besides the Supernova studies, as of 2021, just a couple of other studies have experimentally tested the carbohydrate periodisation approach. In 2016, Laurie-Anne Marquet and colleagues in France and Australia randomised 11 trained cyclists into two groups, each completing a 1-week intervention of 6 training sessions plus either periodised carbohydrate intake — “sleep-low” — or the same 6 g/kg/day of carbs distributed over each day. The outcome: the carbohydrate periodisation group improved their 20 km time trial performance, due to a change in pacing strategy with higher power output during the second part of the test.
In the same year, Laurie-Anne Marquet published a similar study where 21 triathletes were randomized to two groups completing a 3-week intervention. This time they compared 6 g/kg/day of carbs distributed over each day to a periodised carbohydrate approach that combined “train-high” (interval sessions with high-CHO availability), “sleep-low”, and “train-low” (fasted easy sessions). Athletes who followed the carbohydrate periodisation strategy improved their cycling economy, anaerobic cycling capacity, and 10 km running time trial performance.
In 2017, Niels Ørtenblad’s lab in Denmark followed with a 4-week study of 26 elite endurance athletes (triathletes and cyclists) who were randomised to a periodised carbohydrate group or an evenly-distributed carbohydrate group. On 3 days per week, athletes completed a morning high-intensity interval session followed by a moderate-intensity ride 7-hours later. In between sessions, the carbohydrate periodisation group consumed a low-carb diet (1 g/kg; “train low”) while the other group received a high-carb diet (6 g/kg). After 4-weeks, markers of mitochondrial adaptations, VO2max, and 30-minute TT performance increased, but there were no differences between groups, indicating that carbohydrate periodisation solely using a “train low” approach does not enhance training adaptations.
And, in 2024, Prieto-Bellver and colleagues randomised 17 highly-trained cyclists (VO2max = 71) to either a periodised carbohydrate group or a high-carbohydrate group for 5 weeks. They found no between-group differences in the changes in carbohydrate or lipid oxidation, heart rate, lactate, carbohydrate oxidation, lipid oxidation, time-to-exhaustion, or maximal lactate steady state (MLSS), a performance test designed to identify the higher power output where blood lactate is steady. This suggests that, in highly trained endurance athletes, carbohydrate periodisation during a training block is not superior to a high carbohydrate diet.
So, the burning question is...
Should you use a carbohydrate periodisation strategy?
Endurance races are not competitions of who has the highest fat oxidation rate, endurance races are won by athletes who are economical AND fast — for example, Jim Walmsley, the world mountain running champ, Western States 100 mile record holder, 1:04 half-marathoner and 2:15 marathoner. Famous “keto” athletes who are smart and world-class — Zach Bitter comes to mind — don’t win big races while “keto”. They are in a state of nutritional ketosis during a lot of their training but for key sessions and on race day, they line up in a state of high carbohydrate availability. In the face of that, many “keto” folks maintain that a persistent ketogenic diet and being in a continual state of ketosis are the way forward for maximising endurance performance. But, as I have said before, “celebrity endorsement is not a green-light for scientific merit”. And, no Olympic champion in distance races has ever won gold with a low carbohydrate availability.The work of the Carlsberg-funded 1920 Nobel Laureate, August Krogh showed that recent diet “probably” influences metabolic fuel choice during low-to-moderate intensity exercise as well as people’s ability to perform exercise. A century later, we are armed with the knowledge that chronic low-carb ketogenic diets indeed increase “fat burning” during exercise but also increase the oxygen cost of exercise and blunt training-induced performance gains when trying to race at a high-intensity. Therefore, just like August Krogh’s funding source would say, “It is probably best not to put all your eggs in the fat burning basket”. Successful training is multi-faceted and should not be reduced to a single input like being fat-adapted or maximising your fat oxidation rates.
If your interest is to train to see maximal gains in endurance performance, the experimental evidence convincingly shows us that the periodised carbohydrate approach out-performs a low-carb ketogenic diet, which reduces running economy and impairs endurance race performance. But, the experimental evidence also demonstrates that carbohydrate periodisation offers no further advantage to endurance performance than the traditional “train high” approach. For this reason, carbohydrate periodisation has been widely discussed by eminent scholars in sports nutrition (here, here, here, and here) but it is not an inherent part of sports nutrition position statement guidelines from either the American College of Sports Medicine (ACSM) or the International Society for Sports Nutrition (ISSN). This may change as more studies are published, but recent systematic reviews and meta-analyses of the current evidence show that carbohydrate periodisation offers no advantage to endurance performance over normal (high) carbohydrate availability (see Gejl and Nybo, 2021). So, for now, carbohydrate periodisation is a suggestion, not a rule.
You might, therefore, ask yourself, “why don’t I just train with a high carb availability all the time?”. Good question. And, indeed you can — daily consistency is far easier to adopt in real life, especially for regular athletes who are not supported by Supernova’s fine team of chefs and dieticians to fine-tune your periodised carb behaviour. Furthermore, field observations made in the training camps of Kenyan and Ethiopian distance legends (see here, here, and here), find that the daily food intake of these East African endurance masters is a carbohydrate hullabaloo — they eat approximately 9-10 g/kg carbohydrate per day contributing ~65-75% of daily calories! Mimicking the best might not be such a bad idea.
But, there are practical advantages of training with carbohydrate periodisation. By occasionally “training low” and/or “sleeping low” you take the stress out of always having to consider your nutrition. Such practices can also help with time management. For example, getting up to train in the morning doesn’t have to mean arising at 5 am to eat, wait 2-hours, then train before work — you can simply wake up, implement your gingerbreadman-prevention protocol (poop), get dressed, and rock and roll… Plus, if we once again observe and learn from the best, Sweat Elite and Adharanand Finn have documented that the best endurance runners on the planet adhere to carbohydrate periodisation principles as part of their habits of daily living. Such observations are also supported by experimental evidence showing frequent use of “train low” approaches among world-class East African distance runners. I’ll say it again: mimicking the best might not be such a bad idea. But also remember that this is just one small factor that contributes to their success — we do not know if East Africans would be just as good if they did not periodised their carb intake
So, yes, you could use a carbohydrate periodisation strategy and it is superior to a persistent “train low” strategy but it does not appear to be an essential replacement for a persistent “train high” strategy.
Putting “fuel for the work required” into practice.
As a coach, I have experienced a trend where increasing numbers of athletes want to adopt a low-carb diet. I have also noticed that increasing numbers of athletes who reach out to me for help are already low-carb munchers. In every case so far, I have discovered that such athletes continue their low-carb practice up to and on race day. In every case, I have remedied that with high-carb availability for key sessions and leading into race days and during races, with success every time.That is my empirical evidence. But implementing carbohydrate periodisation with precision is tricky.
When I discuss carbohydrate periodisation with my athletes, it is common to hear that they would plan to reduce carb intake by skipping meals. This is not ideal because it is a fast route to a state of low energy availability — meaning that total energy intake and protein intake needs will not be met and their desired adaptations will not arise. Consequently, I typically need to carefully discuss these nuances and provide some education.
Taking a “fuel for the work required” approach by providing carbohydrate relative to the demands of your upcoming session while also aiming to finish your sessions within the glycogen threshold necessary to elicit optimal adaptations, requires expert knowledge of nutrition and energy metabolism. And, even if you had the knowledge, you cannot take muscle biopsies to measure glycogen in between every session. But life is full of surprises and, thanks to José Areta’s and Will Hopkins’ 2018 meta-analysis of all known glycogen depletion studies, you can make a well-informed estimate. I used their data to create a simple fuel for the work required tool, which you can use to estimate your basal glycogen levels, the amount of glycogen you use in your sessions, and how many carbohydrates you need to eat after a session to replenish glycogen.
To further extend your knowledge and learn how a “train low” and “sleep low” carbohydrate periodisation training programme might look, I suggest consulting the examples provided by Louise Burke and her colleagues (Burke et al. 2020, Stellingwerf et al. 2018, and Marquet et al. 2016) or you can use my simple framework as a guide at veohtu.com/fuelfortheworkrequired (see image at the end of this article).
What can you add to your nutritional toolbox?
The “train low”, “sleep low”, or “live low” approaches are many routes to the same goal — reduced muscle glycogen and increased fat oxidation. But high fat oxidation does not equal high speed nor does it equal a high ability to resist fatigue when travelling at high speed — don’t forget about performance.When operating at high intensities, when oxygen delivery to muscles becomes a limiting factor because you are approaching your VO2max, it is entirely intuitive that your body will try to use the most economical fuel to use less oxygen while continuing to produce ATP at the rate it needs to keep moving forward with speedy grace (or, at the very least, a speedy war face). Therefore, I would encourage you to, “consider your race goals and then consider your power output and metabolic needs to achieve those goals”. Are you logging all your training miles to try to run slow? Are you trying to impress your competitors with how far you can go without food? Are you trying to impress your competitors (or the Gods of grammatical riddles) with how fast you can run slowly? No, of course not. You probably want to break your PBs and win races.
The evidence that a persistent low-carb ketogenic diet is good for athletic performance is weak. At best, a low-carb high-fat diet approach yields comparable performance outcomes when compared to a high carbohydrate diet but the bulk of evidence shows that low-carb high-fat diets impair endurance performance. No experimental or epidemiological evidence has ever shown that a high-carbohydrate diet impairs endurance performance. And, the best endurance runners on the planet — East Africans — habitually eat a high carbohydrate diet to support their high training load.
Periodising your carbohydrate availability can help augment some of the intended training adaptations of a low-carb diet while ensuring you have high carbohydrate availability to maintain high power output during key sessions and races — fuel for the work required. But, although this approach is inherent for East African distance maestros, the carbohydrate periodisation strategy has not been shown to offer additional performance benefits over the traditional high-carbohydrate diet approach. As an athlete, maintaining a healthy eating pattern is key and consistency is the best way to maintain a good habit. Periodising carbohydrate availability is an inconsistent nutritional pattern and, if you get it wrong by inadvertently reducing total energy intake or compromising micronutrient intake, all your hard work will be undone.
Without the support of expert knowledge, juggling “train low / sleep low” and “train high / sleep high” strategies may not be appropriate for you. Without such support, you might ponder, “Why introduce a risky inconsistent nutritional pattern over a consistent nutritional pattern that has never been shown to impair performance?”. Because running before breakfast — “train low” — or not eating after a night time run — “sleep low” — might offer practical or logistical advantages. So, if you are curious, to help implement such strategies while maintaining optimal habits of daily eating to meet your specific carbohydrate (and protein) intake needs, thoroughly educate yourself in nutrition and energy metabolism or seek dietary counselling from a nutritionist or dietician.
Or… you could do as the Kenyans do:
Keep it simple.
Train fasted sometimes.
Train fed other times.
Always support key sessions with a high carbohydrate availability, and
Always race with a high carbohydrate availability.
Train fasted sometimes.
Train fed other times.
Always support key sessions with a high carbohydrate availability, and
Always race with a high carbohydrate availability.
Thanks for joining me on this “Nutritional manipulations for training” series. The high vs. low carb debate has been rampant my whole life and it re-emerges from time to time. It will “probably” never stop because
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Disclaimer: I occasionally mention brands and products but it is important to know that I am not affiliated with, sponsored by, an ambassador for, or receiving advertisement royalties from any brands. I have conducted biomedical research for which I have received research money from publicly-funded national research councils and medical charities, and also from private companies, including Novo Nordisk Foundation, AstraZeneca, Amylin, A.P. Møller Foundation, and Augustinus Foundation. I’ve also consulted for Boost Treadmills and Gu Energy on their research and innovation grant applications and I’ve provided research and science writing services for Examine — some of my articles contain links to information provided by Examine but I do not receive any royalties or bonuses from those links. These companies had no control over the research design, data analysis, or publication outcomes of my work. Any recommendations I make are, and always will be, based on my own views and opinions shaped by the evidence available. My recommendations have never and will never be influenced by affiliations, sponsorships, advertisement royalties, etc. The information I provide is not medical advice. Before making any changes to your habits of daily living based on any information I provide, always ensure it is safe for you to do so and consult your doctor if you are unsure.
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About the author:
I am Thomas Solomon and I'm passionate about relaying accurate and clear scientific information to the masses to help folks meet their fitness and performance goals. I hold a BSc in Biochemistry and a PhD in Exercise Science and am an ACSM-certified Exercise Physiologist and Personal Trainer, a VDOT-certified Distance running coach, and a Registered Nutritionist. Since 2002, I have conducted biomedical research in exercise and nutrition and have taught and led university courses in exercise physiology, nutrition, biochemistry, and molecular medicine. My work is published in over 80 peer-reviewed medical journal publications and I have delivered more than 50 conference presentations & invited talks at universities and medical societies. I have coached and provided training plans for truck-loads of athletes, have competed at a high level in running, cycling, and obstacle course racing, and continue to run, ride, ski, hike, lift, and climb as much as my ageing body will allow. To stay on top of scientific developments, I consult for scientists, participate in journal clubs, peer-review papers for medical journals, and I invest every Friday in reading what new delights have spawned onto PubMed. In my spare time, I hunt for phenomenal mountain views to capture through the lens, boulder problems to solve, and new craft beers that send my gustatory system into a hullabaloo.
Copyright © Thomas Solomon. All rights reserved.
I am Thomas Solomon and I'm passionate about relaying accurate and clear scientific information to the masses to help folks meet their fitness and performance goals. I hold a BSc in Biochemistry and a PhD in Exercise Science and am an ACSM-certified Exercise Physiologist and Personal Trainer, a VDOT-certified Distance running coach, and a Registered Nutritionist. Since 2002, I have conducted biomedical research in exercise and nutrition and have taught and led university courses in exercise physiology, nutrition, biochemistry, and molecular medicine. My work is published in over 80 peer-reviewed medical journal publications and I have delivered more than 50 conference presentations & invited talks at universities and medical societies. I have coached and provided training plans for truck-loads of athletes, have competed at a high level in running, cycling, and obstacle course racing, and continue to run, ride, ski, hike, lift, and climb as much as my ageing body will allow. To stay on top of scientific developments, I consult for scientists, participate in journal clubs, peer-review papers for medical journals, and I invest every Friday in reading what new delights have spawned onto PubMed. In my spare time, I hunt for phenomenal mountain views to capture through the lens, boulder problems to solve, and new craft beers that send my gustatory system into a hullabaloo.
Copyright © Thomas Solomon. All rights reserved.