Health, Exercise, and Sports Sciences ETDs

Jason Beam

Publication Date

9-5-2013

Abstract

Caffeine and chlorogenic acid are two compounds in green coffee beans that alter blood glucose disposal and insulin sensitivity. Caffeine has been shown to decrease glucose disposal and insulin sensitivity when taken 60 minutes prior to an oral glucose tolerance test in humans, whereas chlorogenic acid has been shown to increase glucose disposal and insulin sensitivity in humans. The purpose of this study was to investigate the effect of ingesting caffeine with dextrose or chlorogenic acid with dextrose immediately after an exhaustive bout of cycling on blood glucose and insulin disposal when compared to ingesting dextrose alone. Ten men (age: 26 ± 5 years; height: 179.9 ± 5.4 cm; weight: 77.6 ± 13.3 kg; BMI: 24.0 ± 4.3; VO2 peak: 55.9 ± 8.4 ml•kg-1•min-1) who were moderately to highly trained cyclists participated in this study. Each participant completed three experimental trials in random order the morning after abstaining from food, caffeine, and chlorogenic acid supplements for 12 hours. Each trial consisted of a 30-minute high intensity bout of cycling at 60% of peak power output (~90% HR max). Immediately after the exercise, each participant consumed 5 mg/kg body weight of caffeine plus 75 g of dextrose (CAF), 5 mg/kg body weight of chlorogenic acid plus 75 g of dextrose (CGA), or 5 mg/kg body weight of dextrose plus 75 g dextrose (PLA). Blood was drawn to measure glucose and insulin immediately before exercise, immediately after exercise, every 15 minutes during the first hour of recovery, and every 30 minutes during the second hour of recovery. The blood glucose and insulin area under the curve (AUC) and Matsuda insulin sensitivity index (ISI) were calculated for each trial. There were no significant time-by-treatment effects for blood glucose and insulin. The two-hour glucose and insulin AUCs, respectively, for the CAF (658 ± 74 mmol/L and 30,005 ± 13,304 pmol/L), CGA (637 ± 100 mmol/L and 31,965 ± 23,586 pmol/L), and PLA (661 ± 77 mmol/L and 27,020 ± 12,339 pmol/L) trials were not significantly different (p > .05). The ISI for the CAF (9.7 ± 5.2), CGA (12.1 ±7.9), and PLA (10.0 ± 7.3) trials were also not significantly different (p > .05). There was substantial inter-subject variability in glucose and insulin responses during the three trials that likely contributed to the non-significant findings. Pearson correlation analyses were conducted to investigate variables that contributed to this variability. Body mass index was highly related to insulin AUC for the CAF (r = .71), CGA (r = .80), and PLA (r = .73) trials. Relative VO2 peak was moderately-to-highly related to insulin AUC for the CAF (r = -.82), CGA (r = -.63), and PLA (r = -.63) trials. In conclusion, caffeine and chlorogenic acid may affect the bodys ability to regulate post-exercise insulin-mediated glucose transport into the exercised skeletal muscle through different mechanisms; however more research is warranted to verify this hypothesis. Additionally, body composition and training status should be similar to lessen the variability between subjects for investigations of glucose tolerance and insulin sensitivity.'

Keywords

oral glucose tolerance test, cycling, green coffee bean extract

Document Type

Dissertation

Language

English

Degree Name

Physical Education, Sports and Exercise Science

Level of Degree

Doctoral

Department Name

Health, Exercise, and Sports Sciences

First Committee Member (Chair)

Mermier, Christine

Second Committee Member

Gibson, Ann

Third Committee Member

Kerksick, Chad

Fourth Committee Member

Conn, Carole

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