Having just completed the Caledonian Challenge (a 54 mile hike which takes place every year in Scotland for charity), I’ll admit to having energy sources on the brain and that got me to thinking about the concept of carb loading. Carb loading is a very popular phenomenon in marathon training, elite athletics and other exercise events. However, does this concept hold up?
Generally it is suggested that in order to carb load, you need to increase your carbohydrate intake to 8-10 grams per kilogram of body weight1. The theory behind this is that by eating more carbohydrate than normal for a few days before an event, the storage form of glucose, glycogen, will build up in the muscle tissue. This will then be available for the enzyme glucagon to convert back to glucose for energy as needed.
A number of studies have investigated this over the years and the consensus is that carb loading increases the time until exhaustion sets in, thus improving overall success in exercise2. However glycogen conversion typically takes longer to provide the energy required than plasma glucose as the latter only requires respiration to release energy. As such carb loading alone is not enough to provide the immediate energy requirements, although ultimately it does enable a more prolonged exercise period. Give it a try and see for yourself!
Edited by Sarah Spence
- Two interesting articles on this are found on BBC Good Food at http://www.bbcgoodfood.com/howto/guide/carb-loading-explained and Runner’s World at http://www.runnersworld.co.uk/nutrition/60-second-guide-carb-loading/3961.html
- Hawley J.A., Schabort E.J., Noakes T.D. and Dennis S.C., 1997, Carbohydrate-Loading and Exercise Performance: An Update, Sports Med., 24(2):73-81; Bosch A.N., Dennis S.C. and Noakes T.D., 1993, Influence of carbohydrate loading on fuel substrate turnover and oxidation during prolonged exercise, Journal of Applied Physiology, 74(4):1921-1927