High Glycemic Index Meals Research Articles

Effect of the glycaemic index of pre-exercise carbohydrate meals on running performance

The aim of this study was to examine the effect of pre-exercise low and high glycaemic index (GI) carbohydrate meals on running performance. Eight endurance-trained male runners (mean age 33 years, s x =1.7; 63 ml · kg−1 · min−1, s x =1.8) completed two trials separated by at least 7 days in a counterbalanced design. Two hours before they were to run and after an overnight fast, each participant consumed an isocaloric meal containing either low (gi=37) or high (gi=77) GI carbohydrate foods (2.4 MJ; 65% carbohydrate; 15% protein; 20% fat) that provided 1.5 g carbohydrate per kilogram of body mass in random order. Each trial consisted of a 21-km performance run on a level treadmill. The participants were required to run at 70% during the first 5 km of the run. They subsequently completed the remaining 16 km in as short a time as possible. All participants achieved a faster performance time after the consumption of the low GI meal (low vs. high GI: 98.7 min, s x =2 vs. 101.5 min, s x =2; P<0.01). Blood glucose and serum free fatty acids concentrations were higher throughout the performance run in the low GI trial. Serum insulin concentrations were higher in the high GI trial during the postpandial resting period. However, there were no differences between trials in serum insulin or blood lactate concentrations throughout exercise. Compared with the high GI trial, carbohydrate oxidation was 9.5% lower and fat oxidation was 17.9% higher during exercise in the low GI trial. In conclusion, our results indicate that compared with an isocaloric high GI meal, the consumption of a low GI meal 2 h before a 21-km performance run is a more effective means of improving performance time.

Effects of the glycemic index of breakfast on metabolic responses to brisk walking in females

The aim of this study was to examine the metabolic responses during 1 h of brisk walking, 3 h after ingesting high glycemic index (HGI) and moderate glycemic index (MGI) breakfasts. Six females completed three treadmill walking trials (approximately 50% VO2 max), separated by at least 1 month. Three hours before walking, they ingested either water or a HGI or MGI breakfast. The MGI breakfast consisted of a mixture of an HGI breakfast cereal and low GI carbohydrate (CHO) foods. The GI values of the HGI and MGI meals were 77 and 51, respectively. The study took place in the School of Sport and Exercise Sciences at Loughborough University, Loughborough, UK. In the HGI and MGI trials, plasma glucose and serum insulin concentrations peaked 15 min into the postprandial period. At the onset of exercise, plasma insulin concentrations were twofold higher in the HGI (31.5+/-7.7 microl U l(-1)) than in the MGI trial (15.2+/-1.9 microl U l(-1)) (P<0.05). However, there were no differences in substrate utilization between the two CHO trials. These results suggest that although the addition of LGI CHO foods to an HGI breakfast cereal reduces the overall GI of the meal, the metabolic response to exercise is similar to that following a breakfast comprised entirely of HGI foods.

The Effect of Glycemic Index and Timing of Meal on Exercise to Fatigue

Pre-exercise meals have been studied in the past. In addition, the glycemic index (GI) of these meals has also been the subject of investigations. The timing of these meals may also have an impact on the efficacy of these pre-exercise meals to maintain blood glucose and to offset time to fatigue. PURPOSE: The purpose of this study was to investigate and describe the influence of pre-carbohydrate (low and high glycemic) feedings and timing of meal prior to exercise to fatigue. METHODS: Five individuals performed a peak bike test and four experimental trials, separated by 7 days. Upon arrival, subjects ingested 1g of carbohydrates (CHO) for every kilogram of body weight (BW) of a high glycemic index meal (H) or a low glycemic index meal (L) prior to exercise to fatigue. Subjects waited 30 or 60-minutes following each test meal, totaling four experimental conditions (H30, L30, H60, L60). These conditions were completed in a counterbalanced fashion. The exercise regiment was consistent following each meal; 90 minutes cycling at 70% peak oxygen consumption (VO2peak) followed by an all-out sprint until fatigue. The subjects, for the 60 minute trial, had blood draws taken at −30, 0, +10, +30, +60, +90-min, and fatigue. One less blood sample was taken from the subjects waiting 30 minutes (0, +10, +30, +60, +90-min, and fatigue). Heart rate was taken at rest, every 10 minutes of exercise, and at fatigue. VO2 and respiratory exchange ratio (RER) measurements were taken for the first 30 minutes of exercise and at 10 minutes surrounding each blood draw. RESULTS: No significant statistical differences (p>0.05) were found for any of the variables between trials (H30, L30, H60, L60) including blood glucose, blood lactate, RPE, RER, VO2, and performance time. CONCLUSION: The timing and GI of meals Time(min| used in this study did not effect time to fatigue. In addition, blood glucose levels remained essentially the same between conditions with no impact due to timing and/or GI.Figure

Glycaemic index effects on fuel partitioning in humans

The purpose of this review was to examine the role of glycaemic index in fuel partitioning and body composition with emphasis on fat oxidation/storage in humans. This relationship is based on the hypothesis postulating that a higher serum glucose and insulin response induced by high-glycaemic carbohydrates promotes lower fat oxidation and higher fat storage in comparison with low-glycaemic carbohydrates. Thus, high-glycaemic index meals could contribute to the maintenance of excess weight in obese individuals and/or predispose obesity-prone subjects to weight gain. Several studies comparing the effects of meals with contrasting glycaemic carbohydrates for hours, days or weeks have failed to demonstrate any differential effect on fuel partitioning when either substrate oxidation or body composition measurements were performed. Apparently, the glycaemic index-induced serum insulin differences are not sufficient in magnitude and/or duration to modify fuel oxidation.

Almonds, Glycemic Index, Dietary Antioxidants and Risk Factors for Coronary Heart Disease

Background Low glycemic index (GI) diets may be of benefit in reducing risk of coronary heart disease (CHD) and diabetes, possibly by reducing postprandial glucose, insulin and oxidative stress. Objective To assess whether almonds reduce the glycemic response, insulinemia, and oxidative stress more than the same reduction by a low GI food (parboiled rice) without endogenous antioxidants. Methods Two studies were undertaken. The first study (n=10) assessed the dose-response effect of almonds in reducing postprandial glycemia. The second study (n=15) assessed a high GI meal (mashed potatoes) compared to two low GI meals (parboiled rice, almonds) on postprandial glucose, insulin and measures of oxidative stress. All meals contained 50g available carbohydrates and were balanced for protein and fat. Results The first study found that 60g almonds significantly reduced the glycemic response of white bread. In the second study, the glycemic responses (mean±SE) of the low GI almond (54.5±6.9, P<0.001) and rice (37.5±6.3, P<0.001) meals were significantly reduced compared to white bread, while the high GI potato (94.3±11.1, P=0.61) meal showed no significant difference. Insulin values reflected the glycemic responses. Protein thiols tended to be higher following the almond meal indicating less oxidative damage. Conclusion Low GI foods lower postprandial glycemic and insulinemic response curves, and tend to reduce oxidative stress. Preliminary data indicate that low GI foods as part of a healthy diet may reduce risk factors for CHD and diabetes. Support: Almond Board of California

The Metabolic Responses to High Carbohydrate Meals with Different Glycemic Indices Consumed during Recovery from Prolonged Strenuous Exercise

This study investigated the metabolic responses to high glycemic index (HGI) or low glycemic index (LGI) meals consumed during recovery from prolonged exercise. Eight male, trained athletes undertook 2 trials. Following an overnight fast, subjects completed a 90-min run at 70% VO(2max). Meals were provided 30 min and 2 h following cessation of exercise. The plasma glucose responses to both meals were greater in the HGI trial compared to the LGI trial (P < 0.05). Following breakfast, there were no differences in the serum insulin concentrations between the trials; however, following lunch, concentrations were higher in the HGI trial compared to the LGI trial (P < 0.05). This suggests that the glycemic index of the carbohydrates consumed during the immediate post-exercise period might not be important as long as sufficient carbohydrate is consumed. The high insulin concentrations following a HGI meal later in the recovery period could facilitate further muscle glycogen resynthesis.

Effect Of Glycemic Index Meal And Carbohydrate Solution On Immune Responses And Running Performance

Increasing evidence suggested that physical stress to immune system can be reduced by ingestion of carbohydrate (CHO) before and during prolonged exercise. However, little research has been undertaken to investigate the role of glycemic index (GI) on immune function and exercise performance. PURPOSE To investigate the effect of pre-exercise GI meal on the immune responses and endurance running performance. METHODS Eight endurance-trained male runners (Age: 28.6 ±2.7ys; Body mass: 61.9±1.71 kg; VO2max:58.5±1.6ml.kg−1min−1) completed three trials in a randomized order, separated by at least 7 days. Pre-exercise meal consisted of either high GI meal (GI=83, HGI), lower GI meal (GI=36, LGI) or control (CON) (low energy sugar-free jelly) was given to the subjects 2 hours before the performance run on a level treadmill, i.e., 5-km of run at 70% VO max followed by a 16-km self-paced run. The two GI meals were isocalaric (61.2% CHO; 14.1% protein; 24.7% fat) and provided 1.5 g CHO.kg−1 BM. During each trial, 2ml.kg−1BM of 6.6% CHO-electrolyte solution was consumed immediate pre-exercise and every 2.5-km afterward. Venous blood samples were collected before the meals (PRE-2h), immediately before the exercise (PRE-ex), 15min (POST-0.25h) and 60min after exercise (POST-1h) respectively and were assayed for plasma cytokines, cortisol, glucose and insulin. RESULTS There was no difference in time to complete the 21-km run between LGI and HGI (92.4 ± 6.7minvs 91.5 ± 6.3min, NS) but difference was observed between the HGI and CON (91.5 ± 6.3min vs 93.6 ± 6.0min, P<0.05). No overshooting response of tumour necrosis factor alpha (TNF-D) after exercise was detected in all trials. The concentration of interleukin 6 (IL-6) increased by more than 100 times at POST-0.25h in all trials and returned to the PRE-ex level on LGI but not on CON (P<0.05) and HGI (P<0.01). In contrast, the interleukin 2 (IL-2) concentrations decreased at POST-0.25h on CON only (P<0.001) and returned to baseline level by POST-1h in all trials. The blood glucose concentrations in HGI did not return to the pre-diet level by the POST-1h when compared with CON and LGI. Cortisol levels increased during the post exercise period and were lower on LGI but not on HGI when compared to CON (P<0.05) at the POST-1h. CONCLUSIONS The results suggested that running performance was improved when CHO-electrolyte solution was consumed during the run after the pre-exercise HGI meal when compared with CON. However, pre-exercise LGI meal attenuated the increases in cortisol and hastened the recovery of the increased IL-6 to normal value when compared with HGI and CON at POST-1h.

Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise

The aim of this study was to compare the effect of preexercise breakfast containing high- and low-glycemic index (GI) carbohydrate (CHO) (2.5g CHO/kg body mass) on muscle glycogen metabolism. On two occasions, 14 days apart, seven trained men ran at 71% maximal oxygen uptake for 30 min on a treadmill. Three hours before exercise, in a randomized order, subjects consumed either isoenergetic high- (HGI) or low-GI (LGI) CHO breakfasts that provided (per 70 kg body mass) 3.43 MJ energy, 175 g CHO, 21 g protein, and 4 g fat. The incremental areas under the 3-h plasma glucose and serum insulin response curves after the HGI meal were 3.9- (P < 0.05) and 1.4-fold greater (P < 0.001), respectively, than those after the LGI meal. During the 3-h postprandial period, muscle glycogen concentration increased by 15% (P < 0.05) after the HGI meal but remained unchanged after the LGI meal. Muscle glycogen utilization during exercise was greater in the HGI (129.1 +/- 16.1 mmol/kg dry mass) compared with the LGI (87.9 +/- 15.1 mmol/kg dry mass; P < 0.01) trial. Although the LGI meal contributed less CHO to muscle glycogen synthesis in the 3-h postprandial period compared with the HGI meal, a sparing of muscle glycogen utilization during subsequent exercise was observed in the LGI trial, most likely as a result of better maintained fat oxidation.

The Effects of Pre-Exercise High Carbohydrate Meals with Different Glycemic Indices on Blood Leukocyte Redistribution, IL-6, and Hormonal Responses during a Subsequent Prolonged Exercise

The purpose of this study was to determine the effect of pre-exercise high carbohydrate meals with high glycemic index (HGI) or low glycemic index (LGI) on blood leukocyte redistribution during subsequent endurance exercise. Eight male subjects performed a 90-min run on a treadmill at 70 % VO2max 3 h after ingesting an isocaloric HGI or LGI meal with GI values of 77 and 37, respectively. Blood counts of leukocytes, and neutrophils and the neutrophil/lymphocyte ratio were significantly lower in LGI than HGI at 90 min of exercise (P < 0.05). The plasma glucose concentrations were significantly higher in LGI than HGI between 15 min and 45 min of exercise. There were, however, no differences in plasma cortisol, growth hormone, and interleukin-6 concentrations between trials. Thus, the GI of a pre-exercise meal influences leukocyte trafficking and plasma glucose but has limited effects on circulating stress hormone and cytokine responses to exercise.

Low Glycemic Index Pre-exercise Meal Attenuates Blood Leukocyte Redistribution During Subsequent Exercise

1761 Carbohydrate ingestion during prolonged strenuous exercise attenuates the leukocytosis and subsequent neutrophilia and lymphopenia by maintaining plasma glucose concentration and minimizing stress hormone responses. Ingestion of a low glycemic index (LGI) meal before exercise has been demonstrated to better maintain plasma glucose levels during subsequent submaximal exercise compared with a high glycemic index (HGI) meal. PURPOSE: To determine whether the redistribution of leukocytes during endurance exercise is affected by the glycemic index of a preexercise high carbohydrate meal. METHODS: Eight male subjects (age 27.5 ± 1.5 yrs, body mass 72.1 ± 1.6 kg, height 1.77 ± 0.02 m, VO2max 60.7 ± 1.3 mL·kg−1·min−1; mean ± S.E.M.) performed two 90-min runs on a treadmill at 70% VO2max three hours after ingesting a HGI or LGI meal. Each isocaloric test meal contained 2 g·kg−1 body mass of carbohydrate and the glycemic index values were 77 and 37, respectively. Trials were separated by at least 7 days in counterbalanced order. Results were analysed using a two-factor (trial × time) repeated measures ANOVA with post hoc comparison as appropriate. RESULTS: Blood leukocyte and neutrophil counts were significantly lower in LGI than HGI at 90-min of exercise (8.70 ± 0.80 vs. 10.12 ± 0.94 and 4.75 ± 0.63 vs. 6.47 ± 0.77 × 109·L−1; both P < 0.05). The ratio of neutrophils/lymphocytes was significantly lower in LGI than HGI at 90-min (1.57 ± 0.17 vs. 2.28 ± 0.27, P < 0.05). Plasma glucose concentrations were significantly higher in LGI than HGI at 15-min and 45-min of exercise. However, there were no significant differences in plasma cortisol, human growth hormone and interleukin-6 concentrations between trials. CONCLUSION: Ingestion of a LGI meal 3 h before submaximal exercise attenuates the increase in circulating leukocyte and neutrophil counts, and better maintains plasma glucose concentration during subsequent exercise when compared with ingestion of a HGI meal. However, it seems to have limited effects on circulating stress hormone and cytokine responses to exercise.

Improved Recovery from Prolonged Exercise Following the Consumption of Low Glycaemic Index Carbohydrate Meals

0157 A single bout of endurance exercise stimulates lipolysis and enhances fat oxidation in humans. An increased rate of fat oxidation is beneficial during exercise as it spares muscle glycogen. Consuming high glycaemic index (HGI) carbohydrates (CHO) after exercise is the recommended method of increasing the rate of muscle glycogen resynthesis. However, the increase in the insulin response following the consumption of HGI CHO suppresses fatty acid metabolism. PURPOSE: To examine whether low glycaemic index (LGI) CHO meals during 24h recovery from prolonged exercise result in a greater rate of fat oxidation and a better endurance capacity during exercise the following day than the consumption of HGI meals. METHODS: Nine recreationally active males (age 22.4 ± 0.6 years; body mass (BM) 79.4 ± 4.1kg; VO2 max 61.0 ± 2.2 ml•kg−1•min−1) took part in this study. Each subject participated in two trials separated by 7 days in a randomised cross-over design. The experimental protocol was completed over two days. On day 1, subjects completed a 90min treadmill run at 70% VO2max (R1). Thereafter, they were supplied with a recovery diet which consisted of either HGI or LGI CHO and provided 8g CHO• kgBM-1. On day 2, after an overnight fast, subjects ran to exhaustion at 70% VO2max (R2). RESULTS: Only eight subjects completed both performance runs (R2). Run time to exhaustion during R2 was longer in the LGI trial (108.9 ± 7.4min) than in the HGI trial (96.9 ± 4.8min) (p<0.05). Average RER values were higher in the HGI trial compared to the LGI trial (p<0.05). Fat oxidation rates and Free fatty acid concentrations were higher in the LGI trial than the HGI trial (p<0.05). CONCLUSION: The results of the study suggest that the increased endurance capacity during R2 was largely a consequence of the greater fat oxidation, and possibly glycogen sparing, following the consumption of the LGI meals.

Insulin is not mandatory for postprandial decrease of human plasma ghrelin

Ghrelin is the most powerful peripheral orexigenic hormone in mammalian physiology. Ghrelin plasma concentrations increase prior to meal onset, but decrease postprandially. We and others reported previously that insulin reduces circulating ghrelin levels and might therefore be a driving force for postprandial suppression of ghrelin. To test the influence of insulin on postprandial ghrelin regulation, a patient with type 1 diabetes with complete insulin deficiency received a low glycemic index meal and subsequently an additional high glycemic index meal in the absence of insulin substitution. Subsequently, a subcutaneous injection of 0,08 IU Lispro Insulin per kg bodyweight was given. Results were compared to those of a healthy control subject matched for sex, age and BMI, who was undergoing the same test series (without Lispro bolus) in the presence of endogenous postprandial insulin secretion. A substantial decrease of plasma ghrelin levels was observed in the insulin deficient patient following low glycemic index carbohydrate load (27% plasma ghrelin decrease). The subsequent exposure to a high glycemic index meal resulted in a slight additional reduction of ghrelin levels (32% from baseline), while Lispro bolus did not induce further changes of circulating ghrelin (27% of baseline at termination). This postprandial response was comparable to that of the healthy control subject (33% reduction after the first meal, 40% after the second meal).

Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycemic index food.

This study examined the effect of delaying the ingestion of carbohydrate on muscle glycogen storage following prolonged exhaustive exercise. Six endurance trained men cycled on two separate occasions at a workload corresponding to 70% VO2max for 2 h followed by four "all-out" 30-s sprints. Following exercise, subjects were fed five high glycemic index (HGI) meals over a 24-h period, with the first three being fed either at 0-4 h (IT) or 2-6 h (DT) at 2-h intervals. Muscle biopsies were taken immediately after exercise and at 8 and 24 h post-exercise and analyzed for glycogen and glucose-6-phosphate. Blood samples were obtained prior to and at 30, 60, and 90 min after each meal and analyzed for glucose and insulin. No differences were observed in the incremental glucose and insulin areas after each meal when IT and DT were compared. In addition, no differences were observed in muscle glycogen or glucose-6-phosphate any time in the two trials. These data indicate that delayed feeding of a HGI meal by 2 h has no effect on the rate of muscle glycogen resynthesis at 8 and 24 h post-exercise, providing that sufficient carbohydrate is ingested during the recovery period.