Carbohydrate Periodisation
In this final of three articles (Carbs or fats? Ketogenic diet), Coach Kevin looks at reintroducing carbohydrates after becoming ‘fat'-adapted’ through a low-carb, high-fat diet. This is pertinent to those who are working in a low-carb environment but want to perform. Carbohydrate periodisation is all about timing your intake to facilitate bouts of higher intensity training or racing. Read on to find out more.
My last article in this series had assumed that you’d decided that it made sense for you to try a ketogenic diet, described some of the potential benefits, and suggested how to get started from an athlete’s viewpoint. This article is for those who have been on keto for a little while and have adjusted enough so that they have resumed all, or nearly all, aspects of their ‘normal’ training.
Hopefully, you have noticed that you are less reliant on regular carbohydrate intake during exercise - while not always necessary. You should feel, or have proven to yourself, that you can go much longer during the steady sessions without the need to take any additional energy on board. This will be due to having up-regulated your fat metabolism to supply more energy at relatively higher intensities.
Some people won’t need to look any further than this. As long as their fat metabolism can supply enough energy to produce a speed or pace that is good enough for their training and racing, then there is no need to do anything more than consider hydration and electrolyte levels. They can forget about carb intake during races. There are many examples in blogs and forums where the authors describe this, and they are happy with their level of performance. If you scan these articles, I expect you’ll find more people who are ‘completers’, than ‘competers’. This highlights that just because you can do something doesn’t mean it’s the optimal solution. Of course, there is absolutely nothing wrong with taking this approach, but if you have started down the keto journey and are looking for your best possible performance, then there are other things to consider.
The first thing to think about is that while you are in a low carbohydrate state, you are forcing your body to burn fat – over a period of time, and this is how you transition into what a lot of people refer to as ‘fat adaptation’. This can take a varying amount of time, probably around 3 – 6 months. Just as you could well have been nearly exclusively relying on carbohydrates to provide for your energy needs at race pace, if you’ve now done a 180-degree flip and are just as reliant on fat, you might not need to eat anything during a race but has this actually made you faster? If you are an ultra or long-duration athlete, the answer to this question could actually be yes – especially if there are no ‘racing’ demands, i.e. you can choose your own pace and stick to it all day long. Suppose you are performing at the competitive end of any distance of event. In that case, you may need to respond to other athletes with changes in pace, and in these situations, the psychological boost you may receive by being able to hold on to a surge in pace should not be underestimated.
So the ideal situation is to be good at burning fat (the longer your race, the more emphasis you should place on this), but nearly all of us could still benefit to a greater or lesser degree from the boost in energy availability that carbohydrates can provide when pushing the higher intensities. So how do we manage to optimise the use of both of these systems?
You can think of this along the same lines as the same approach to training intensity, i.e. time spent in endurance/base training vs higher intensity work. I don’t have any magic proportions for you (like 80%/20%, however, that might be a good starting point), but the theory is the same and is based on the same physiological systems.
So taking the training example, the first stage is to ensure that you have a strong aerobic base – this is gained via long steady efforts, and once this is achieved, layering on top of the high-intensity work, which can bring further improvements. From a nutritional point of view, the equivalent is to maximise your fat oxidation rates through a keto or low carb diet for 3 – 6 months. As mentioned earlier, this is the stage where I am presuming you are at.
So how do you now move to the second stage and be able to swing the focus back round to effective higher intensity training without losing the fat burning side of things? The answer is to bring back in some carbohydrates, but how you do this needs to be carefully considered to not just push you back towards the body’s favourite situation, a reliance on carbs.
The key is in timing – give your body what it needs for the job you are asking it to do. This is generally referred to as ‘carbohydrate periodisation’. So, for example, the evening before a long steady ride, stick to low carb or keto, and perhaps even skip breakfast (but take some food with you on your ride just in case, or maybe to have something a couple of hours into the ride if it will last longer than this). In this instance, even in a low glycogen stores situation, fat will provide for most, or all of your energy needs, assuming that you have already up-regulated that system. As an additional bonus, the low glycogen levels during endurance intensity exercise will maximise the adaptation signal your body receives from aerobic exercise.
Conversely, perhaps you have a high-intensity interval workout planned for early next morning – so ensure that you eat some carbs the night before to top up muscle glycogen and have a small, easily digestible carbohydrate breakfast before your session to maximise blood glucose levels. These two examples take duration and intensity as the variables to guide carbohydrate requirement – rising as one or both of these factors increase; this study goes into the subject in detail and offers suggestions on amounts of carbohydrate (and protein) for the four possible options.
If you have spent a while following a strict ketogenic diet, you may have to bring the carbs back slowly, in stages, as you may have blunted your ability to process carbohydrates. In this case, keep the levels of carbs lower than suggested in the study above and be guided by what feels comfortable (what you have lost are the enzymes and bacteria required to digest carbohydrates, which could well leave you feeling bloated and uncomfortable). The amount needed could be quite different to someone else, depending on your energy requirements, amount of fat oxidation, and ability to digest, so experiment and try to slowly ramp up and find a balance that works for you.
Also, consider that as someone who uses fat for a decent proportion of their energy requirements, that taking on a fast-acting form of fat can also help energy levels. While, in theory, the fat ‘fuel tank’ is vast, there are several different places where the body looks for fat to use, just like glycogen. Providing an exogenous (external) source of the fastest acting fat known, 6 – 8g of medium-chain triglycerides (MCTs), along with some carbohydrates (usually 15 - 30g) in your water bottle, seems to work for a lot of fat-adapted athletes. Sfuels is certainly the leader in this field and offers many different products that provide both fat and carbs in energy drinks and bars.
You also need to think about re-fuelling afterwards and providing the appropriate fuel beforehand and during. Perhaps that long steady ride ended up going way longer and harder than you expected. In that case, if you have significantly depleted your glycogen stores, the best thing you can do is to replace them post-exercise. (For those keto followers who worry at this point that you will be kicked out of ketosis, you’ll probably find you have a lot more scope than you think, assuming that you really did work hard – of course, trial and error will guide you on how much to take back in). Don’t forget that even on a ketogenic diet, when pushing yourself hard, you can still deplete your glycogen reserves – this will take much longer and have significantly less impact than someone who relies on carbs, but it is possible all the same.
Also, do not forget that you still need to take on an appropriate amount of calories globally. Just because you can swim, ride or run without constantly having to take on fuel at the time, your body will still need it at some point to maintain a healthy balance and provide a good base for recovery. Yes, the urgency is perhaps not there compared to other athletes who eat more carbs, but don’t let yourself slide into an unplanned calorie deficit just because you don’t feel that hungry a lot of the time after you train. As blood ketones increase, appetite is naturally suppressed, so you could well finish that long easy workout and not feel the need to eat for quite a while.
A carbohydrate periodisation approach is not at all limited to those who are already on a keto or low carb diet; however – in fact, most of the research is based on a ‘normal’ carbohydrate diet. In these instances, much more care needs to be taken when carrying out the ‘low glycogen’ workouts, from both a fuelling safety net and intensity point of view. For keto athletes, low glycogen levels are entirely normal, and the body is used to this. For those who are less able to ramp up the fat-burning to compensate, there is the danger that these sessions can be both unpleasant (high RPE compared to usual) and difficult to manage without dropping into hypoglycaemia or bonking, as its also commonly known. The additional stress that these sessions can create on the body (on top of exercise stress) should not be ignored. However, you can also expect this to decline over time and with practice. With the introduction of Continuous Glucose Monitors (CGMs), there is a way to measure this directly and not have to rely so much on feel - watch this space for TTH’s view on how to use these devices and what they can add as a training tool.
In summary, once fat-adapted, consider adding carbohydrates back into your diet at strategic times (carbohydrate periodisation). The longer and more intense the workouts the, greater the need for carbs if performance is the primary goal. Keep carb levels low for steady endurance efforts, and bring them back in for more strenuous workouts based on how much you expect to be testing your limits. Also, keep in mind that we are all individual and experiment with the carbohydrate levels that seem to work for you to increase performance. The end result could give you a much wider ‘race day tolerance’ from a nutrition point of view and hopefully make you faster to boot!
Kevin opened a B&B for cyclists in France in 2014, & then a year later decided to start a cycle coaching (level 3) qualification. This was mainly in order to be able to better support his guests (but also to make his own training more effective too). At the B&B he runs the odd training camp for cyclists but mainly offers coaching advice while guiding guests. An engineer by background, he happy diving into all sorts of training data, but also understanding that coaching is about much more than just the numbers!
After being introduced to triathlon by a good friend & then taking part in races for a couple of years he decided that a level 2 coaching course with British Triathlon was the way forward, completing this in 2019.
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