Effect of Dietary Glycemic Index on β-Cell Function in Prediabetes: A Randomized Controlled Feeding Study

The glycemic index (GI) reflects the relative ability of carbohydrates to raise blood glucose. We utilized a controlled feeding study to assess the impact of the dietary GI on β-cell function in adults with prediabetes (17F/18M, mean ± SEM: BMI 32.44 ± 0.94 kg/m², age 54.2 ± 1.57 years). Following a 2 week Control diet (GI = 55–58), participants were randomized to either a 4 week low GI (LGI: GI < 35, n = 17) or high GI (HGI: GI > 70, n = 18) diet (55% of energy from carbohydrate/30% fat/15% protein). The data from 4 h meal tolerance tests (MTTs) underwent mathematical modeling to assess insulin sensitivity, insulin secretion and β-cell function. Glucose concentrations during the MTT decreased on the LGI diet (p < 0.001) and trended to increase on the HGI diet (p = 0.14; LGI vs. HGI p < 0.001), with parallel changes in insulin and C-peptide concentrations. Total insulin secretion, adjusted for glucose and insulin sensitivity, increased on the LGI diet (p = 0.002), and trended lower on the HGI diet (p = 0.10; LGI vs. HGI p = 0.001). There was no significant diet effect on insulin sensitivity or other measures of β-cell function. Total insulin clearance increased on the LGI diet (p = 0.01; LGI vs. HGI p < 0.001). We conclude that short-term consumption of an LGI diet reduced glucose exposure and insulin secretion but had no impact on measures of β-cell function.     

Effect of a low-glycemic-index diet during pregnancy on obstetric outcomes

BACKGROUND: Pregnancy is a condition in which the glycemic index (GI) may be of particular relevance because maternal glucose is the main energy substrate for intrauterine growth. OBJECTIVE: The aim was to compare the effects of low-GI and conventional dietary strategies on pregnancy outcomes in healthy women. Compliance and acceptability were also investigated. DESIGN: The subjects were assigned alternately to receive dietary counseling that encouraged either low-GI (LGI) carbohydrate foods or high-fiber, moderate-to-high GI (HGI) foods and were studied 5 times between <16 wk gestation and delivery. Of the 70 women who met the inclusion criteria, 62 completed the study (32 in the LGI and 30 in the HGI groups). Primary outcomes were measures of fetal size. RESULTS: The mean diet GI fell significantly in the LGI group but not in the HGI group. Compared with the LGI group, women in the HGI group gave birth to infants who were heavier (3408 +/- 78 compared with 3644 +/- 90 g; P = 0.051) and had a higher birth centile (48 +/- 5 compared with 69 +/- 5; P = 0.005), a higher ponderal index (2.62 +/- 0.04 compared with 2.74 +/- 0.04; P = 0.03), and a higher prevalence of large-for-gestational age (3.1% compared with 33.3%; P = 0.01). Women in the LGI group found the diet easier to follow. CONCLUSION: Because birth weight and ponderal index may predict chronic disease in later life, a low-GI diet may favorably influence long-term outcomes.     

Beneficial effects of a 5-week low-glycaemic index regimen on weight control and cardiovascular risk factors in overweight non-diabetic subjects

The glycaemic index (GI) has been developed in order to classify food according to the postprandial glycaemic response. This parameter is of interest, especially for people prone to glucose intolerance; however, the effects of a low-GI (LGI) diet on body weight, carbohydrate and lipid metabolism remain controversial. We studied the effects of either a LGI or high-GI (HGI) diet on weight control and cardiovascular risk factors in overweight, non-diabetic subjects. The study was a randomized 5-week intervention trial. The thirty-eight subjects (BMI 27.3 (sem 0.2) kg/m2) followed an intervention diet in which usual starch was replaced ad libitum with either LGI or HGI starch. Mean body weight decrease was significant in the LGI group ( - 1.1 (sEM 0.3) kg, P = 0.004) and was significantly greater than in the HGI group ( - 0.3 (sEM 0.2) kg, P = 0.04 between groups). Hunger sensation scales showed a trend towards a decrease in hunger sensation before lunch and dinner in the LGI group when compared with the HGI group (P = 0.09). No significant increase in insulin sensitivity was noticed. The LGI diet also decreased total cholesterol by 9.6 % (P < 0.001), LDL-cholesterol by 8.6 % (P = 0.01) and both LDL-:HDL-cholesterol ratio (10.1 %, P = 0.003) and total:HDL-cholesterol ratio (8.5 %, P = 0.001) while no significant changes were observed in the HGI group. Lowering the GI of daily meals with simple dietary recommendations results in increased weight loss and improved lipid profile and is relatively easy to implement with few constraints. These potential benefits of consuming a LGI diet can be useful to develop practical dietetic advice.     

A low glycemic index diet does not affect postprandial energy metabolism but decreases postprandial insulinemia and increases fullness ratings in healthy women

At present, it is difficult to determine whether glycemic index (GI) is an important tool in the prevention of lifestyle diseases, and long-term studies investigating GI with diets matched in macronutrient composition, fiber content, energy content, and energy density are still scarce. We investigated the effects of 2 high-carbohydrate (55%) diets with low GI (LGI; 79) or high GI (HGI; 103) on postprandial blood profile, subjective appetite sensations, energy expenditure (EE), substrate oxidation rates, and ad libitum energy intake (EI) from a corresponding test meal (LGI or HGI) after consuming the diets ad libitum for 10 wk. Two groups of a total of 29 healthy, overweight women (age: 30.5 ± 6.6 y; BMI: 27.6 ± 1.5 kg/m(2)) participated in the 10-wk intervention and a subsequent 4-h meal test. The breakfast test meals differed in GI but were equal in total energy, macronutrient composition, fiber content, and energy density. The LGI meal resulted in lower plasma glucose, serum insulin, and plasma glucagon-like peptide (GLP)-1 and higher plasma glucose-dependent insulinotropic polypeptide concentrations than the HGI meal (P ≤ 0.05). Ratings of fullness were slightly higher and the desire to eat something fatty was lower after the test meal in the LGI group (P < 0.05). Postprandial plasma GLP-2, plasma glucagon, serum leptin, plasma ghrelin, EE, substrate oxidation rates, and ad libitum EI at lunch did not differ between groups. In conclusion, postprandial glycemia, insulinemia, and subjective appetite ratings after a test meal were better after 10-wk ad libitum intake of a LGI compared to a HGI diet. EE and substrate oxidation rates were, however, not affected. These findings give some support to recommendations to consume a LGI diet.     

Impact of overweight and glucose tolerance on postprandial responses to high- and low-glycaemic index meals

The beneficial effects of a low-glycaemic index (GI) meal on postprandial glucose and insulin levels have been demonstrated. However, limited data are available on the impact of overweight and glucose tolerance on postprandial responses to different GI meals. Our aim was to study the effects of physiological characteristics on postprandial glucose, insulin and lipid responses and the relative glycaemic response (RGR) of a low-GI (LGI) and a high-GI (HGI) meal. We recruited twenty-four normal-weight and twenty-four overweight subjects, twelve with normal glucose tolerance (NGT) and twelve with impaired glucose tolerance (IGT) in each group. Both test meals were consumed once and the glucose reference twice. Blood glucose and insulin were measured in the fasting state and over a 2 h period after each study meal, and TAG and NEFA were measured in the fasting state and over a 5 h period. The glucose responses of subjects with IGT differed significantly from those of subjects with NGT. The highest insulin responses to both meals were observed in overweight subjects with IGT. Physiological characteristics did not influence TAG or NEFA responses or the RGR of the meals. The LGI meal resulted in lower glucose (P < 0·001) and insulin (P < 0·001) responses, but higher TAG responses (P < 0·001), compared with the HGI meal. The GI of the meals did not affect the NEFA responses. In conclusion, the LGI meal causes lower glucose and insulin responses, but higher TAG responses, than the HGI meal. The RGR of the meals does not differ between normal-weight and overweight subjects with NGT or IGT.     

No difference in body weight decrease between a low-glycemic-index and a high-glycemic-index diet but reduced LDL cholesterol after 10-wk ad libitum intake of the low-glycemic-index diet

BACKGROUND: The role of glycemic index (GI) in appetite and body-weight regulation is still not clear. OBJECTIVE: The objective of the study was to investigate the long-term effects of a low-fat, high-carbohydrate diet with either low glycemic index (LGI) or high glycemic index (HGI) on ad libitum energy intake, body weight, and composition, as well as on risk factors for type 2 diabetes and ischemic heart disease in overweight healthy subjects. DESIGN: The study was a 10-wk parallel, randomized, intervention trial with 2 matched groups. The LGI or HGI test foods, given as replacements for the subjects' usual carbohydrate-rich foods, were equal in total energy, energy density, dietary fiber, and macronutrient composition. Subjects were 45 (LGI diet: n = 23; HGI diet: n = 22) healthy overweight [body mass index (in kg/m(2)): 27.6 +/- 0.2] women aged 20-40 y. RESULTS: Energy intake, mean (+/- SEM) body weight (LGI diet: -1.9 +/- 0.5 kg; HGI diet: -1.3 +/- 0.3 kg), and fat mass (LGI diet: -1.0 +/- 0.4 kg; HGI diet: -0.4 +/- 0.3 kg) decreased over time, but the differences between groups were not significant. No significant differences were observed between groups in fasting serum insulin, homeostasis model assessment for relative insulin resistance, homeostasis model assessment for beta cell function, triacylglycerol, nonesterified fatty acids, or HDL cholesterol. However, a 10% decrease in LDL cholesterol (P < 0.05) and a tendency to a larger decrease in total cholesterol (P = 0.06) were observed with consumption of the LGI diet as compared with the HGI diet. CONCLUSIONS: This study does not support the contention that low-fat LGI diets are more beneficial than HGI diets with regard to appetite or body-weight regulation as evaluated over 10 wk. However, it confirms previous findings of a beneficial effect of LGI diets on risk factors for ischemic heart disease.     

Use of low-glycaemic index bread to reduce 24-h blood glucose: implications for dietary advice to non-diabetic and diabetic subjects

The present study investigated the effect of a simple dietary change on 24-h blood glucose. In a randomized cross-over design, 10 healthy subjects were prescribed a low-glycaemic-index (LGI) diet and a high-glycaemic-index (HGI) diet. The diets were identical with the exception of the type of bread consumed (LGI or HGI). Glucose concentrations over 24 h were measured using a continuous glucose monitoring system. The LGI diet resulted in a lower mean glucose response compared with the HGI diet over 24 h (P=0.135), during the day (P=0.171) and at night (P=0.100). Similarly, the 24-h, daytime and overnight incremental area under the curve for glucose following the LGI diet was consistently lower than following the HGI diet (P=0.093, P=0.132 and P=0.061, respectively). The results demonstrate how a very simple dietary change can favourably alter overall blood glucose concentrations. Such small modifications to the diet, if adopted in the long term, could improve glucose control and consequently reduce the risk of chronic disease in both diabetic and non-diabetic individuals.     

The effect of low glycemic index diet on body weight status and blood pressure in overweight adolescent girls: a randomized clinical trial

Although several studies have assessed the influence of the glycemic index on body weight and blood pressure among adults, limited evidence exists for the pediatric age population. In the current study, we compared the effects of low glycemic index (LGI) diet to the healthy nutritional recommendation (HNR)-based diet on obesity and blood pressure among adolescent girls in pubertal ages. This 10-week parallel randomized clinical trial comprised of 50 overweight or obese and sexually mature girls less than 18 years of age years, who were randomly assigned to LGI or HNR-based diet. Macronutrient distribution was equivalently prescribed in both groups. Blood pressure, weight and waist circumference were measured at baseline and after intervention. Of the 50 participants, 41 subjects (include 82%) completed the study. The GI of the diet in the LGI group was 42.67 ± 0.067. A within-group analysis illustrated that in comparison to the baseline values, the body weight and body mass index (not waist circumference and blood pressure) decreased significantly after the intervention in both groups (P = 0.0001). The percent changes of the body weight status, waist circumference and blood pressure were compared between the two groups and the findings did not show any difference between the LGI diet consumers and those in the HNR group. In comparison to the HNR, LGI diet could not change the weight and blood pressure following a 10-week intervention. Further longitudinal studies with a long-term follow up should be conducted in this regard.     

Improved recovery from prolonged exercise following the consumption of low glycemic index carbohydrate meals

This study examined the effects of the glycemic index (GI) of post-exercise carbohydrate (CHO) intake on endurance capacity the following day. Nine active males participated in 2 trials. On day 1, subjects ran for 90 min at 70% VO(2max)(R1). Thereafter, they were supplied with either a high GI (HGI) or low GI (LGI) CHO diet which provided 8 g CHO/kg body mass (BM). On day 2, after an overnight fast, subjects ran to exhaustion at 70% VO(2max)(R2). Time to exhaustion during R2 was longer in the LGI trial (108.9 +/- 7.4 min) than in the HGI trial (96.9 +/- 4.8 min) (P < 0.05). Fat oxidation rates and free fatty acid concentrations were higher in the LGI trial than the HGI trial (P < 0.05). The results suggest that the increased endurance capacity was largely a consequence of the increased fat oxidation following the LGI recovery diet.     

Pre-Operative Modification of Dietary Glycemic Index Improves Pre but Not Post-Operative Indices of Insulin Resistance in Patients Undergoing Coronary Artery Bypass Graft Surgery

Background: Improving insulin sensitivity in coronary artery bypass grafting (CABG) patients may translate into improved glycemic control and postoperative outcomes. The implementation of a low glycemic index (LGI) diet in the pre-operative period may improve insulin sensitivity and subsequently impact on the development of post-operative insulin resistance. The aim of this study was to determine whether a short term LGI diet would reduce postoperative insulin resistance.

Methods: Eleven non-diabetic patients referred for elective CABG surgery were randomized to consume either a high glycemic index (HGI)(5) or LGI (6) diet for three weeks prior to their surgery. Outcomes, including insulin sensitivity (SITT, HOMA), were measured at baseline, preoperatively and postoperatively.

Results: Substitution of HGI or LGI foods resulted in an average 8.6 unit increase, or 11.0 unit decrease, respectively, in glycemic index. Insulin sensitivity (HOMA) improved significantly in the LGI group preoperatively compared to the HGI group (p = 0.018). Insulin sensitivity (SITT) was significantly reduced postoperatively in both groups, but no significant difference was found between groups. There was a trend in the LGI group towards improved glycemic control which warrants further investigation.

Conclusion: A preoperative LGI diet presents a non-invasive cardio-protective opportunity warranting clinical trial.     

Glycaemic index of meals affects appetite sensation but not energy balance in active males

Background

Foods with low glycaemic index (LGI) are reported to suppress appetite mainly in overweight population but have not been investigated in athletic adults.

Objective

The aim of this study was to compare the short-term effects of LGI and high GI (HGI) meals over a day on subsequent subjective appetite sensation, energy intake, energy expenditure, energy balance and resting metabolic rate in physically active males.

Methods

This cross-sectional randomized crossover study included 14 active males (mean ± SD; age 34.5 ± 8.9 years, body mass index 22.8 ± 2.1 kg m^?2) to consume LGI and HGI meals on two separate days. On each trial day, participants consumed a breakfast in the laboratory and then left with a packed lunch, dinner and snacks. Appetite scores, energy intake and expenditure were assessed.

Results

The area under the curve for appetite scores of the HGI trial was significantly smaller than that of the LGI trial during the laboratory period (p = 0.027) and throughout the day (p = 0.009). No significant differences in energy intake, energy expenditure, energy balance and resting metabolic rate were found between groups, between the trial days and between the corresponding post-trial days.

Conclusions

These results show that frequent ingestion of the HGI meals, contrary to the previous reports, suppresses appetite more than that of LGI meals, but did not affect energy balance in physically active normal-weight males.     

The influence of the glycaemic index of breakfast and lunch on substrate utilisation during the postprandial periods and subsequent exercise

The present study investigated the effects of mixed high-carbohydrate (CHO) meals (breakfast and lunch) with different glycaemic indices (GI) on substrate metabolism during rest throughout the postprandial periods and during subsequent exercise. Nine recreationally active males completed two trials, high glycaemic index (HGI) and low glycaemic index (LGI), separated by 7 d in a randomised crossover design. In each trial, participants consumed breakfast and lunch, both of which were followed by a 3 h resting postprandial period. Following this, participants completed a 60 min run at 70 % of V O2max. The plasma glucose and serum insulin concentrations following both meals were significantly higher in the HGI trial than in the LGI trial (P<0.05). Serum insulin concentrations remained higher throughout the postprandial period following lunch in the HGI trial compared with the LGI trial (P<0.05). The total amount of fat oxidised was higher during the 3 h rest following lunch in the LGI trial than in the HGI trial (P<0.01) and subsequently CHO oxidation was lower (P<0.005). No significant differences in substrate utilisation were observed throughout the subsequent run. At 45 and 60 min, plasma glucose concentrations were higher in the LGI trial v. the HGI trial (P<0.05). The results of the present study provide further support that the GI concept can be successfully applied to mixed meals. The results also suggest that meals composed of LGI CHO may be more beneficial for maintaining a favourable metabolic milieu during the postprandial periods. Furthermore, during subsequent exercise, plasma glucose concentrations were better maintained following the LGI CHO meals.     

High-Protein or Low Glycemic Index Diet—Which Energy-Restricted Diet Is Better to Start a Weight Loss Program?

Background: To date, no crossover studies have compared the effects of high-protein (HP) and low glycemic index (LGI) diets applied as starting energy-restricted diets. Methods: Thirty-five overweight or obese volunteers with sedentary lifestyles aged 41.4 ± 11.0 years, with body mass index (BMI) of 33.6 ± 4.2 kg/m², without diabetes, completed an 8-week randomized crossover study of an energy-restricted diet (reduction of 30%; approximately 600 kcal/day). The anthropometric parameters, body composition, 24 h blood pressure, and basic metabolic profile were measured at baseline and after completing the two 4-week diets; i.e., the HP (protein at 30% of the daily energy intake) or LGI diet, followed by the opposite diet. All subjects maintained food diaries and attended six counselling sessions with a clinical dietitian. Results: The final weight loss was not significantly different when the HP diet was used first but was associated with a greater loss of fat mass: 4.6 kg (5.8; 3.0 kg) vs. 2.2 (4.5; 0.8); p < 0.025, preserved muscle mass, and reduced LDL-cholesterol. Conclusions: A short-term HP diet applied as a jump-start diet appeared to be more beneficial than an LGI diet, as indicated by the greater fat mass loss, preservation of muscle mass, and better effects on the lipid profile.     

Increased homocysteinemia is associated with beneficial effects on body weight after long-term high-protein, low-fat diet in rats

ObjectiveDiets rich in protein are often used for weight loss in obese patients, but their long-term effects are not fully understood. Homocysteine (Hcy) is considered to be a risk factor for cardiovascular diseases, and its levels are influenced by diet, particularly the protein and fat content. We studied the effect of diets with varying fat/protein content on body weight and composition, food intake, Hcy, B vitamins, leptin, and several pro-inflammatory cytokines.MethodsFor 2 mo, Long-Evans rats were fed either a low protein/high fat (LP), a standard control (C), or a high protein/low fat (HP) diet containing 5, 15, or 40% protein, respectively, and normal carbohydrate content (55% of total energy).ResultsThe HP rats ingested 12 to 15% fewer calories (P < 0.001), gained less weight (P < 0.04), and were less fatty (P < 0.01) than the other groups. Plasma Hcy was increased in HP rats compared to C (+23%) and LP (+29%) rats (P < 0.03). It was positively correlated with protein intake (r = 0.386; P < 0.01). No obvious signs of inflammation were observed in any of the groups. Hcy increase was related directly to decrease in plasma folate (r = ?0.372; P < 0.02).ConclusionThese data confirm the beneficial effects of HP diets on body weight but bring attention to the control of folate allowance to limit the adverse effects of elevated Hcy. Ingestion of folate-rich foods or even folate supplementation should be considered when using these HP diets over the long term for weight loss.     

Comparison of a low-fat/low-glycemic index diet to a low-fat only diet in the treatment of adults with hypercholesterolemia

The Low Glycemic Index and Cholesterol study was a 12-week randomized clinical trial comparing the effects on serum lipids of a novel low-fat/low-glycemic index (GI) diet with those of a low-fat only diet in adults with hypercholesterolemia. Sixty-two subjects (men and women) with elevated serum low-density lipoprotein cholesterol were randomized to one of the two dietary interventions. The low-GI intervention included substituting low-GI carbohydrates for high-GI carbohydrates. Dietary assessment and serum lipid measurements were performed at baseline (BL), 4 weeks (FV4), and 12 weeks (FV12). In the low-fat/low-GI group, dietary GI and glycemic load significantly decreased between the BL and FV4 and BL and FV12 time intervals; however, there were no significant differences in lipid values between the two groups at any time point. Importantly, whereas high-density lipoprotein cholesterol was unchanged in the low-fat/low-GI group over the 12 weeks, it decreased 5 mg/dL (11.4%) in the low-fat only group (P = .05).     

The influence of high-carbohydrate meals with different glycaemic indices on substrate utilisation during subsequent exercise

The present study was designed to examine the effects of mixed high-carbohydrate meals with different glycaemic indices (GI) on substrate utilization during subsequent exercise. Nine healthy male recreational runners (age 26.8 (sem 1.1) years, body mass 74.7 (sem 2.4) kg, VO2max 58.1 (sem 1.7) ml/kg per min) completed three trials: high-glycaemic-index meal (HGI), low-glycaemic-index meal (LGI) and fasting (FAST), separated by 7 d. The test meals contained 2 g carbohydrate/kg body mass, they were isoenergetic and the GI values were 77.4, 36.9 and 0.0 respectively. In each trial, subjects consumed the test meal 3 h before performing a 60 min run at 65 % VO2max on a motorized treadmill. Ingestion of the HGI and LGI resulted in hyperglycaemia and hyperinsulinaemia during the postprandial period compared with the FAST (P<0.05). The incremental area under the curve for plasma glucose was 2-fold higher for HGI compared with LGI (108.7 v. 48.9 mmol/l per min). In contrast, plasma non-esterified fatty acid concentrations were significantly lower following HGI and LGI compared with FAST (P<0.05). During the subsequent submaximal exercise, plasma glucose declined to below the fasting value in HGI compared with LGI and FAST (P<0.05). The estimated total fat oxidation was significantly higher for the LGI than the HGI during exercise (P<0.05). In summary, both pre-exercise carbohydrate meals resulted in lower rates of fat oxidation during subsequent exercise than when subjects performed exercise in the fasting state. However, the LGI resulted in a higher rate of fat oxidation during exercise than following the consumption of the HGI.     

An 18-mo randomized trial of a low-glycemic-index diet and weight change in Brazilian women

BACKGROUND: Despite interest in the glycemic index diets as an approach to weight control, few long-term evaluations are available. OBJECTIVE: The objective was to investigate the long-term effect of a low-glycemic-index (LGI) diet compared with that of a high-glycemic-index (HGI) diet; all other dietary components were equal. DESIGN: After a 6-wk run-in, we randomly assigned 203 healthy women [body mass index (in kg/m2): 23-30] aged 25-45 y to an LGI or an HGI diet with a small energy restriction. The primary outcome measure was weight change at 18 mo. Secondary outcomes included hunger and fasting insulin and lipids. RESULTS: Despite requiring a run-in and the use of multiple incentives, only 60% of the subjects completed the study. The difference in glycemic index between the diets was approximately 35-40 units (40 compared with 79) during all 18 mo of follow-up, and the carbohydrate intake from energy remained at approximately 60% in both groups. The LGI group had a slightly greater weight loss in the first 2 mo of follow-up (-0.72 compared with -0.31 kg), but after 12 mo of follow-up both groups began to regain weight. After 18 mo, the weight change was not significantly different (P = 0.93) between groups (LGI: -0.41 kg; HGI: -0.26 kg). A greater reduction was observed in the LGI diet group for triacylglycerol (difference = -16.4 mg/dL; P = 0.11) and VLDL cholesterol (difference = -3.7 mg/dL; P = 0.03). CONCLUSIONS: Long-term weight changes were not significantly different between the HGI and LGI diet groups; therefore, this study does not support a benefit of an LGI diet for weight control. Favorable changes in lipids confirmed previous results.     

The Effect of a Low-Glycemic Diet vs a Standard Diet on Blood Glucose Levels and Macronutrient Intake in Children with Type 1 Diabetes

A low-glycemic index (GI) diet may lower postprandial hyperglycemia and decrease the risk for postabsorptive hypoglycemia in people with type 1 diabetes. However, insufficient evidence exists on the efficacy of a low-GI diet to support practice recommendations. The goal of this study was to examine the blood glucose response to and the macronutrient composition of low-GI meals vs usual meals consumed ad libitum at home in children with type 1 diabetes. A within-subject, crossover design was employed. Twenty-three participants were recruited between June and August 2006. Participants wore a continuous blood glucose monitoring system and completed diet diaries on 2 days. On 1 day, participants consumed their usual meal; on another day, participants consumed low-GI meals ad libidum. Order of the 2 days was counterbalanced. The mean GI was 34±6 for the low-GI day and 57±6 for the usual meal day (P<0.0001). During the low-GI day, mean daytime blood glucose values (125±28 mg/dL [6.9±1.5 nmol/L] vs 185±58 mg/dL [10.3±3.2 nmol/L], P<0.001), blood glucose area above 180 mg/dL (4,486±6,138 vs 26,707±25,038, P<0.006), and high blood glucose index (5.1±5.1 vs 13.6±7.6, P<0.001) were lower compared to the usual mean day. During the low-GI day, subjects consumed more fiber (24.5±12.3 g vs 14.5±6.1 g, P<0.007) and less fat (45.7±12.2 g vs 76.8±32.4 g, P<0.005); however, there were no differences in energy, carbohydrate, or protein intake. In this pilot study, a low-GI diet was associated with improved diet quality and a reduction in hyperglycemia.     

Effect of glycemic index and fructose content in lunch on substrate utilization during subsequent brisk walking

The purpose of the present study was to investigate the effect of glycemic index (GI) and fructose content in lunch on substrate utilization during subsequent brisk walking. Ten healthy young males completed 3 main trials in a counterbalanced crossover design. They completed 60 min of brisk walking at approximately 50% maximal oxygen consumption after consuming a standard breakfast and 1 of 3 lunch meals, i.e., a low GI meal without fructose (LGI), a low GI meal that included fructose beverage (LGIF), or a high GI meal (HGI). The 3 lunch meals were isocaloric and provided 1.0 g·kg?1 carbohydrate. Substrate utilization was measured using indirect respiratory calorimetry method. Blood samples were collected at certain time points. During the 2-h postprandial period after lunch, the incremental area under the blood response curve values of glucose and insulin were higher (p < 0.05) in the HGI trial than those in the LGI and LGIF trials (HGI vs. LGI and LGIF: glucose, 223.5 ± 24.4 vs. 92.5 ± 10.4 and 128.0 ± 17.7 mmol·min·L?1; insulin, 3603 ± 593 vs. 1425 ± 289 and 1888 ± 114 mU·min·L?1). During brisk walking, decreased carbohydrate oxidation was observed (p < 0.05) in the LGI trial than in the LGIF and HGI trials (LGI vs. LGIF and HGI: 60.8 ± 4.0 vs. 68.1 ± 6.0 and 74.4 ± 4.7 g). No difference was found in fat oxidation among the 3 trials (LGI vs. LGIF vs. HGI: 21.6 ± 2.3 vs. 19.2 ± 2.3 vs. 16.4 ± 2.2 g). It appeared that fructose content was an important influencing factor when considering the effect of different GI lunch meals on substrate utilization during subsequent moderate intensity exercise.     

A low glycemic index meal before exercise improves endurance running capacity in men

This study investigated the effects of ingesting a low (LGI) or high (HGI) glycemic index carbohydrate (CHO) meal 3 h prior to exercise on endurance running capacity. Eight male recreational runners undertook two trials (LGI or HGI) which were randomized and separated by 7 d. After an overnight fast (12 h) the subjects ingested either a LGI or HGI meal 3 h prior to running at 70% VO2max until exhaustion. The meals contained 2 g/kg body mass CHO and were isocaloric and iso-macronutrient with calculated GI values 77 and 37 for the HGI and LGI respectively. The run times for the LGI and HGI trials were 108.8 +/- 4.1 min and 101.4 +/- 5.2 min respectively (P = 0.038). Fat oxidation rates were higher during exercise after the LGI meal than after the HGI meal (P < 0.05). In summary, ingestion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal.