Testing natural foods and endurance sports performance.
Carbohydrates are very valuable for supporting endurance sport performance. 100 years of research has clearly demonstrated that ingesting carbohydrates before and during a race can improve performance. This research has led to guidelines for the amount and types of carbohydrates that are most effective (1). For example, someone going on an intensive 2 hour bike ride will typically be advised to eat and drink around 60g per hour. What is the best type of carbohydrate to choose? There is an enormous choice of supplements designed for athletes, from gels and bars to drinks and sweets. Alongside these supplements there are good real food choices such as dried fruit or bananas that are also popular among athletes. Which is the best choice? Is there a difference between commercial supplements and natural foods?
This question has been tested in some experiments including two studies looking at raisins in comparison to commercial supplements. Raisins have higher fibre and a lower glycemic index (62) than commercial supplements such as gels (typically 88 or higher) or energy bars. This lower glycemic index means that the sugars from raisins enter the bloodstream more slowly. This may be advantageous for consumption before a ride but during the ride athletes generally look for sugars that can be used rapidly. Furthermore the extra fibre in raisins could slow digestion and potentially lead to stomach complaints. These facts suggest that raisins might lead to worse performance outcomes during sports than commercial supplements. So what happened when they were tested?
The first study compared raisins to sport gels for cyclists (2). Eight trained road cyclists took part in a crossover study design. After eating raisins or gel in a controlled dose (1g carbohydrate per kg bodyweight) the riders completed a performance test. This meant rifing 45 minutes at 70% VO2max followed by 15 minutes at maximal output. The researchers found no significant difference in performance between the two foods. Blood glucose were similar but the raisins led to higher levels of free fatty acids in the bloodstream suggesting high fat oxidation.
The second study compared raisins to ‘sports chews’ in runners (3). 11 runners completed three different performance tests to compare raisins, the supplement and plain water. The test was 80 minutes of running on a treadmill at 75% VO2max followed by a 5km race. The supplement and raisins were dosed at 35g prior to the test and 14g per 20 minutes during the test. The results showed no significant difference between the two carbohydrates but both led to better performance than the plain water, around a minute quicker time for the 5km test. The sports chews led to a greater insulin response than the raisins.There was no difference between the reported stomach complaints for either source of carbohydrate.
These experiments show that natural, carbohydrate rich foods can match the performance outcomes of commercial supplements. Recreational athletes can therefore enjoy natural, tasty foods without sacrificing performance. Further research is needed to show how natural foods perform in longer events and at higher levels of competition.
- Jeukendrup A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports medicine, 44 (Suppl 1), S25–S33. https://doi.org/10.1007/s40279-014-0148-z
- Kern, M., Heslin, C. J., & Rezende, R. S. (2007). Metabolic and performance effects of raisins versus sports gel as pre-exercise feedings in cyclists. Journal of strength and conditioning research, 21(4), 1204–1207. https://doi.org/10.1519/R-21226.1
- Too, B.W., Cicai, S., Hockett, K.R. et al. (2014). Natural versus commercial carbohydrate supplementation and endurance running performance. J Int Soc Sports Nutr 9, 27. https://doi.org/10.1186/1550-2783-9-27