The effects of low and high glycemic index foods on exercise performance and beta-endorphin responses

Abstract

Τhe aim of this study was to examine the effects of the consumption of foods of various glycemic index values on performance, β-endorphin levels and substrate (fat and carbohydrate) utilization during prolonged exercise. Eight untrained healthy males underwent, in a randomized counterbalanced design, three experimental conditions under which they received carbohydrates (1.5 gr. kg-1 of body weight) of low glycemic index (LGI), high glycemic index (HGI) or placebo. Food was administered 30 min prior to exercise. Subjects cycled for 60 min at an intensity corresponding to 65% of VO2max, which was increased to 90% of VO2max, then they cycled until exhaustion and the time to exhaustion was recorded. Blood was collected prior to food consumption, 15 min prior to exercise, 0, 20, 40, and 60 min into exercise as well as at exhaustion. Blood was analyzed for β-endorphin, glucose, insulin, and lactate. The mean time to exhaustion did not differ between the three conditions (LGI = 3.2 ± 0.9 min; HGI = 2.9 ± 0.9 min; placebo = 2.7 ± 0.7 min). There was a significant interaction in glucose and insulin response (P < 0.05) with HGI exhibiting higher values before exercise. β-endorphin increased significantly (P < 0.05) at the end of exercise without, however, a significant interaction between the three conditions. Rate of perceived exertion, heart rate, ventilation, lactate, respiratory quotient and substrate oxidation rate did not differ between the three conditions. The present study indicates that ingestion of foods of different glycemic index 30 min prior to one hour cycling exercise does not result in significant changes in exercise performance, β-endorphin levels as well as carbohydrate and fat oxidation during exercise.

Comparison between Preexercise Meals Intake Effect with Different Glycemic Load on Exercise Performance in Female Athletes

“…No significant difference observed in their work output performance among three meals but serum FFA were higher in LGI compare with HGI meal [17]. Despite, the controversial observations in individuals' exercise performance after low vs high GI meals, there was a relative shift in substrate utilization from carbohydrate to fat utilization, following low GI meals [16,21]. In our study RPE increased during the exercise period in both…”

“…They observed that runners who consumed low versus HGI foods (30 vs 72), at 45 minutes priorto the exercise reflected a significant improvement in their 40-km performance [15]. Some of studies show no improvement in exercise performance after receiving LGI meals comparing with HGI meals [16][17][18]. Febbario et al studied receiving low or HGI meals on trained men (52 or 85) or even placebo (diet jelly) at 30 minutes before a cycling period, at 70% VO2max.…”

“…They observed that participants' run time was higher after intaking LGI foods than the mentioned time after HGI foods; and the end of the exercise, serum FFA concentrations were higher after LGI than HGI meal [11]. There are some studies in support of these beneficial effects [14,15], however several studies found no different effect in TTE of athletes [16,17,18]. A study by Jamurtas and colleagues showed that ingestion of foods with LGI or HGI at 30 minutes prior to one-hour cycling did not show any significant changes in TTE values [16].…”

“…There are some studies in support of these beneficial effects [14,15], however several studies found no different effect in TTE of athletes [16,17,18]. A study by Jamurtas and colleagues showed that ingestion of foods with LGI or HGI at 30 minutes prior to one-hour cycling did not show any significant changes in TTE values [16]. The GI indicates only the type of carbohydrate, ignoring the total amount of CHO in a typical meal.…”

The effect of laserpuncture at the LI4 Hegu point on the plasma levels of β-endorphin in healthy subjects

“…This study was conducted on healthy subjects aged 18-44 years, because this age group is active and productive and has not yet undergone the changes in β-endorphin metabolism that occur in the elderly [9]. This study also limited the consumption of foods and medications that may affect β-endorphin levels [10,11]. Subjects with a BMI of 18.5-25 were part of the inclusion criteria to reduce the likelihood of metabolic differences that may affect β-endorphin levels [12,13].…”