Carbohydrate (CHO) foods
taken prior to, and while exercising, enhance long-lasting (> 1
hour) performance by sustaining blood glucose levels. However, it is unclear
which amount, type and form of CHO increases endurance.
The current study
investigated the effects of a natural
food product such as raisins in comparison with commercial sport chews. The CHO supplement
effects, on the metabolism, gastrointestinal (GI) tolerance and endurance
performance, were tested in 11 male runners.
Each runner went through 3
cycles of being randomly
assigned to either intake raisins (31g), chews (Clif bar, 3 pieces) or water
only. At the
end of each cycle, the runners participated in an 80min treadmill run and a
5-km time trial (TT). GI indicators were noted, perceived exertion (RPE)
recorded and a blood sample taken at 20min intervals.
Other parameters monitored every 20-min
included oxygen consumption (VO2), heart rate (HR), respiratory
exchange ratio (RER), blood lactic acid, serum free fatty acids (FFA),
glycerol, insulin, plasma glucose, electrolytes, creatine kinase and GI
The study results show no differences between the groups with
regards to VO2, HR, electrolytes, lactic acid, glycerol and RPE. The
mean plasma glucose and RER, during the 80min run, were considerably higher
with chews as compared with water alone. However, serum FFA was higher with water only as opposed to
raisins and chews. Serum insulin was highest in the chews
group than in the raisins and water groups. Plasma creatine kinase, for the
second half of the 80 min run, was highest with raisins. The TT was faster in both the carbohydrate
compared with water alone, while GI trouble was mild for all treatments.
Thus, raisins and chews equally increased running
ability with no noteworthy differences in GI condition.
Reference: Natural versus Commercial
Carbohydrate Supplementation and Endurance Running Performance; Brandon Too et
al; BMC Journal of the International Society of Sports Nutrition 2012