Another guest blog for GGB from Marc Lathwaite, The Endurance Coach, www.theendurancecoach.com
Official guidelines in the 1990’s were unanimous in their recommendation of high carbohydrate intakes for athletes. This recommendation was to ensure adequate glycogen recovery on a daily basis (glycogen is the term given to carbohydrate stored in the liver and muscles).
Recommendations for endurance athletes have been as high as 60-75% of total dietary energy intake supplied in the form of carbohydrate (American Dietetic Association 1993). High carbohydrate intake has been shown to prevent ‘over-reaching’ (the step prior to over-training) during periods of intense training and it is this evidence which has promoted the use of high carbohydrate diets for endurance athletes.
Take a step back…
The majority of endurance athletes do not train at high intensities for 52 weeks of the year. It is likely that training will vary from month to month depending upon the phase of the training plan. Autumn months may be reserved for lighter training or ‘active recovery’, leading into a phase of base training. During spring the athlete will progressively build towards the summer season and higher intensity sessions will be introduced. This change in training volume and intensity is termed ‘periodisation’.
Despite these changes in volume and intensity throughout the year, athletes tend to stick to the same high carbohydrate diet. Amongst nutritionists however, there is a growing trend towards ‘dietary periodisation’ which in simple terms is the adjustment of your dietary intake to match and support your phase of training.
If your training and racing requires you to complete a high number of miles at low to moderate intensities, fat oxidation (the use of fat to produce energy) is very important. Using a higher amount of fat will allow you to save glycogen (stored carbohydrate) and maintain your training and racing intensity for longer periods of time. Increased fat oxidation is generally one of the key objectives during the ‘base training phase’.
Reducing glycogen stores have been shown to increase fat oxidation during low and moderate exercise sessions and for this reason, a high carbohydrate intake may conflict with the objectives of this training phase. Changing your daily eating habits and your intake during training sessions can significantly impact upon the outcomes of this training phase.
Many amateur athletes vary their training within a regular week. Monday might consist of a long, easy session and Tuesday might well be a high intensity interval workout. The objectives of each session are very different and potentially your day to day diet could vary to reflect these objectives. Simply altering the timings of your food intake and the percentages of carbohydrate, fat and protein has a significant impact upon each individual session within the week.
Eat low and train high…
Training at low to moderate intensities, for long periods of time, in a low carbohydrate state to encourage fat usage, is a relatively well practiced technique amongst experienced endurance athletes (although should be approached with caution by less experienced athletes). More recently the research has been directed towards the potential benefits of completing high intensity training in the same low carbohydrate state.
The majority of studies have been designed to include 2 groups of athletes.
1. Group 1 alternated on a daily basis between a steady exercise session of 60-90 minutes and then on the following day a high intensity interval session.
2. Group 2 completed a 60-90 minute steady exercise session in the morning, then a few hours later on the same day, did a high intensity interval session. The following day was a rest day.
Group 1 had plenty of time to refill their glycogen stores between training sessions (24 hours) whilst group 2 were not able to do so. Due to the fact that they had trained in the morning, they started the afternoon interval session in a low carbohydrate state.
What were the outcomes?
In the majority of studies the activity of key enzymes involved in energy creation from fat and carbohydrate were increased significantly more when training in a low carbohydrate state. During sub-maximal exercise there were significantly higher levels of fat oxidation within muscle mitochondria (structure within cells where energy is created).
The studies also showed a significant increase in key signalling proteins (AMP & MAPK) within muscle cells. These signalling proteins are related to ‘gene expression’ and in simple terms they encourage specific genes to generate the specific proteins required for mitochondria growth and other training adaptations.
Remember, when we train, the whole purpose is that training will lead to changes such as mitochondrial growth (plus many others), that’s how we get faster and that’s the response we are looking for.
Interesting points to discuss
During the interval training sessions the athletes who were in a low carbohydrate state performed below their normal levels (understandably). Their power output or speed was lower than those who had higher carbohydrate levels and this has a ‘psychological impact’ i.e. the athletes were concerned that they were losing fitness.
When the groups were tested at the end of the training phase, they both improved by the same amount. The ‘end of trial test’ to measure improvement was generally no more than an hour of high intensity exercise. Performance in longer events is not as widely researched and guidance is limited.
Exercising in a low carbohydrate state places a great deal of strain on your immune system and nervous system. Guidance is limited and inconclusive but in simple terms treat as you would any other training session. Training places stress on your body and all its systems, if you don’t allow adequate recovery you will start to ‘over reach’. Training in a glycogen depleted state adds greater stress and may require a slightly longer recovery period. In simple terms, if you are training every day and struggle to recover on a daily basis, the sudden addition of low carbohydrate training will probably tip you over the edge!
There is a huge amount of research needed and physiologists are scratching the surface. There are gains to be made from training at low to moderate intensities in a low carb state (base training) and also by periodising your diet on a yearly, monthly and weekly basis. Greater fat oxidation during longer exercise sessions or races will result in greater carbohydrate sparing which will have potential benefits.
For harder training sessions your performance will suffer if you are carbohydrate depleted, recovery may take longer and the benefits are still unclear.
Next month we will further examine how to periodise your diet on a yearly, monthly, weekly and daily basis. We will provide practical advice with regards to how this can be implemented to enhance your training and competition performance.
For now, stay healthy and go steady out there…
Image courtesy of Bicycle Images; photographer Farid