There is much debate in sports nutrition forums around carbohydrates and the necessity of intake for fueling, including the restoration of muscle and liver glycogen as an essential goal of recovery between training sessions. This is where the concept of periodized nutrition, or rather, manipulating nutrient availability around training, comes into play. The idea behind using nutritional strategies to optimize training adaptations is not new, and today most of the research has been around the skeletal muscle. When we focus specifically on carbohydrate availability, the most typical used protocol is train high and train low.
Training high refers to training with high carbohydrate availability (muscle and liver glycogen levels are high at the start of exercise, and/or carbohydrates are consumed during exercise). There are two main reasons for training high. First, it allows for training at high intensities and/or for a long period of time (both are cornerstone principles of preparation for triathlon success) and the second is to train the gut to reduce gastrointestinal (GI) issues which plague many athletes.
Training low is the general term to described training sessions done in a low carbohydrate-availability state, e.g. low muscle and liver glycogen, low carbohydrate intake during or after exercise, the LCHF (low carb high fat or keto diets), or a combination of these. The basic premise is that glycogen availability is tightly linked to the expression of specific proteins which regulate gene transcription involved in training adaptations. Therefore, if you introduce training stress in a low glycogen state, a greater enhancement of metabolic pathways to improve fuel capacity will occur. Note, however, the big sticking point here is that although these adaptations do occur, there is no evidence to show that they convey a performance benefit and there is some evidence to show there may be a negative effect on performance due to changes in the body’s ability to use exogenous carbohydrate (eating carbs) during exercise.
The beauty of periodization of nutrition is just like the periodization of training: you can implement strategies to figure out if they work for you, in the off-season, and/or away from racing. It may be that you want to try training low in a significant aerobic building phase to enhance mitochondrial protein expression (so your muscles rely more on fatty acids at lower intensities). Or you may want to try super-compensating carbohydrate as you get closer to racing to improve your gut to reduce incidences of GI distress.
Below is an outline to help you decide how to implement periodizing carbs and why. Remember, even if you are reducing your carbohydrate intake, or manipulating when you eat it, do not sacrifice total calorie intake as you do not want to fall into a low energy state or experience Relative Energy Deficiency in Sport (RED-S).
Train low (glycogen) session
In a non-fasted state, go out for your usual morning session to end up with reduced muscle and liver glycogen. Reduce your normal post-exercise carbohydrate consumption so that sub-optimal intake occurs across the day/before your evening session. The afternoon or early evening session will be done with reduced pre-exercise carbohydrate availability. Depending on the timing of both sessions, the total time considered in a state of low carbohydrate availability could range from three to eight hours.
Recovery low/sleep low strategy
Both muscle and liver glycogen are reduced during an evening training session. Carbohydrate intake is then withheld in recovery or sub-optimal intakes occur so your next morning session is completed with low pre-exercise carbohydrate availability. Depending on the timing of both sessions, the total time considered in a state of low carbohydrate availability could range from eight to 14 hours.
Train high (glycogen + exogenous carbohydrate) session
Training sessions deliberately commenced with high muscle and liver glycogen following optimal pre-training and in-training fueling. In this approach, promotion of high training intensity, duration, training of the gut, and practicing in-competition fueling are the goals.
Combination of targeted carbohydrate availability training and recovery approaches
The above approaches are deliberately implemented over a 24- to 48-hour period. In this model, an initial train high session should be done for hitting the training intensity and duration needed, then the next session would be done in a low availability state due to combination of sleep low, recover low, and a low daily absolute carbohydrate intake.
Using this model, carbohydrate availability can be adjusted, before, during, and/or after each training session in an attempt to take advantage of the cellular signaling responses that may occur with carbohydrate restriction at each of these time periods.