Is glycaemic index (GI) a valid measure of carbohydrate quality?

Glycemic index, glycemic load, and common psychological disorders

BACKGROUND

Potential associations between dietary glycemic index (GI) and glycemic load (GL) with psychological disorders remain uncertain.

OBJECTIVE

We investigated the relations of dietary GI and GL with psychological distress, anxiety, and depression.

DESIGN

A total of 3363 nonacademic members of the staff of Isfahan University of Medical Sciences were included in this cross-sectional study. GI and GL were assessed by using a validated, self-administered, dish-based, semiquantitative food-frequency questionnaire. Validated Iranian versions of the Hospital Anxiety and Depression Scale and General Health Questionnaire-12 were used to assess anxiety, depression, and psychological distress.

RESULTS

After control for potential confounders, individuals in the top tertile of GI had greater odds of depression (OR: 1.44; 95% CI: 1.03, 2.02; P-trend = 0.03) and a trend for greater odds of anxiety (OR: 1.52; 95% CI: 0.97, 2.38; P trend = 0.06) compared with those in the first tertile. Higher GL values were linked to lower odds for mental disorders (OR: 0.66; 95% CI: 0.49, 0.90; P-trend = 0.009), depression (OR: 0.69; 95% CI: 0.51, 0.93; P-trend = 0.02), and psychological distress (OR: 0.67; 95% CI: 0.48, 0.92; P-trend = 0.01). Significant interactions were observed between GI and sex for depression (P = 0.01) and psychological distress (P = 0.046) in the crude model. In stratified analyses by sex, after control for potential confounders, a greater GI was linked to a higher odds of depression (OR: 1.52; 95% CI: 1.20, 1.94; P-trend = 0.001) and psychological distress (OR: 1.66; 95% CI: 1.28, 2.14; P-trend = 0.001) in women but not in men.

CONCLUSION

Our findings support a direct link between the odds of depression and dietary GI but inverse associations between GL and mental disorders, depression, and psychological distress. This trial was registered at clinicaltrials.gov as NCT02362113.

Glycemic index, glycemic load and glycemic response: An International Scientific Consensus Summit from the International Carbohydrate Quality Consortium (ICQC)

BACKGROUND AND AIMS

The positive and negative health effects of dietary carbohydrates are of interest to both researchers and consumers.

METHODS

International experts on carbohydrate research held a scientific summit in Stresa, Italy, in June 2013 to discuss controversies surrounding the utility of the glycemic index (GI), glycemic load (GL) and glycemic response (GR).

RESULTS

The outcome was a scientific consensus statement which recognized the importance of postprandial glycemia in overall health, and the GI as a valid and reproducible method of classifying carbohydrate foods for this purpose. There was consensus that diets low in GI and GL were relevant to the prevention and management of diabetes and coronary heart disease, and probably obesity. Moderate to weak associations were observed for selected cancers. The group affirmed that diets low in GI and GL should always be considered in the context of diets otherwise understood as healthy, complementing additional ways of characterizing carbohydrate foods, such as fiber and whole grain content. Diets of low GI and GL were considered particularly important in individuals with insulin resistance.

CONCLUSIONS

Given the high prevalence of diabetes and pre-diabetes worldwide and the consistency of the scientific evidence reviewed, the expert panel confirmed an urgent need to communicate information on GI and GL to the general public and health professionals, through channels such as national dietary guidelines, food composition tables and food labels.

Effect of ethnicity on glycaemic index: a systematic review and meta-analysis

Objectives:

Low glycaemic index (GI) foods are recommended to improve glycaemic control in diabetes; however, Health Canada considers that GI food labeling would be misleading and unhelpful, in part, because selected studies suggest that GI values are inaccurate due to an effect of ethnicity. Therefore, we conducted a systematic review and meta-analysis to compare the GI of foods when measured in Caucasians versus non-Caucasians.

Methods:

We searched MEDLINE, EMBASE and Cochrane databases for relevant articles. GI differences were aggregated using the generic inverse variance method (random effects model) and expressed as mean difference (MD) with 95% confidence intervals (95% CI). Study quality was assessed based on how well studies complied with official international GI methodology.

Results:

Review of 1288 trials revealed eight eligible studies, including 28 comparisons of GI among 585 non-Caucasians and 971 Caucasians. Overall, there was borderline significant evidence of higher GI in non-Caucasians than Caucasians (MD, 3.3 (95% CI, −0.1, 6.8); P=0.06) with significant heterogeneity (I², 46% P=0.005). The GI of eight types of rice was higher in non-Caucasians than Caucasians (MD, 9.5 (95% CI, 3.7, 23.1); P=0.001), but there was no significant difference for the other 20 foods (MD, 1.0 (95% CI, −2.5, 4.6); P=0.57). MD was significantly greater in the four low-quality studies (nine comparisons) than the four high-quality studies (19 comparisons; 7.8 vs 0.7, P=0.047).

Conclusions:

With the possible exception of rice, existing evidence suggests that GI values do not differ when measured in Caucasians versus non-Caucasians. To confirm these findings high-quality studies using a wide range of foods are required.

Glycemic responses, appetite ratings and gastrointestinal hormone responses of most common breads consumed in Spain. A randomized control trial in healthy humans

The present study was carried out to determine the glycemic index (GI), glycemic load (GL), insulinemic index (InI), appetite ratings and postprandial plasma concentrations of gastrointestinal hormones related to the control of food intake after the ingestion of the five most common breads consumed in Spain with different compositions and manufacturing processes. Twenty-two healthy adults participated in a randomized crossover study. The breads tested were Ordinary, Precooked-Frozen, Candeal-flour, Alfacar whites and Wholemeal. All breads portions were calculated to supply 50 g of available carbohydrates. In addition, 50 g of glucose was used as a reference. A linear mixed-effects model was used to compare data calculated for all breads with glucose load. The GI value varied from 61 for the Wholemeal, to Alfacar 68, Ordinary 76, and 78 and 86 for the Precooked-Frozen and Candeal-flour breads, respectively. Wholemeal and Alfacar had lower GI than glucose. All tested breads had a lower GL (ranged 9 to 18) compared with glucose. Wholemeal GL was similar to Alfacar, but lower than the other white breads. InI were significantly lower for all breads (ranged 68 to 73) compared with glucose, and similar among them. The intake of the Wholemeal bread led to a higher release of gastric inhibitory polypeptide compared with the Ordinary and Precooked breads and to a higher release of pancreatic polypeptide compared with the Precooked-Frozen bread. All breads affected appetite ratings similarly. In conclusion, based on GL, the Wholemeal bread would be expected to exert a favorable glycemic response.

Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 1: What to Look for and How to Recommend an Effective Fiber Therapy

Dietary fiber that is intrinsic and intact in fiber-rich foods (eg, fruits, vegetables, legumes, whole grains) is widely recognized to have beneficial effects on health when consumed at recommended levels (25 g/d for adult women, 38 g/d for adult men). Most (90%) of the US population does not consume this level of dietary fiber, averaging only 15 g/d. In an attempt to bridge this “fiber gap,” many consumers are turning to fiber supplements, which are typically isolated from a single source. Fiber supplements cannot be presumed to provide the health benefits that are associated with dietary fiber from whole foods. Of the fiber supplements on the market today, only a minority possess the physical characteristics that underlie the mechanisms driving clinically meaningful health benefits. The first part (current issue) of this 2-part series will focus on the 4 main characteristics of fiber supplements that drive clinical efficacy (solubility, degree/rate of fermentation, viscosity, and gel formation), the 4 clinically meaningful designations that identify which health benefits are associated with specific fibers, and the gel-dependent mechanisms in the small bowel that drive specific health benefits (eg, cholesterol lowering, improved glycemic control). The second part (next issue) of this 2-part series will focus on the effects of fiber supplements in the large bowel, including the 2 mechanisms by which fiber prevents/relieves constipation (insoluble mechanical irritant and soluble gel-dependent water-holding capacity), the gel-dependent mechanism for attenuating diarrhea and normalizing stool form in irritable bowel syndrome, and the combined large bowel/small bowel fiber effects for weight loss/maintenance. The second part will also discuss how processing for marketed products can attenuate efficacy, why fiber supplements can cause gastrointestinal symptoms, and how to avoid symptoms for better long-term compliance.

Changes in meal composition and duration affect postprandial endothelial function in healthy humans

Endothelial function, measured by flow-mediated dilatation (FMD), predicts cardiovascular events and is impaired postprandially. The objective of this study was to evaluate the effects of changes in composition or duration of ingestion of a meal, which slows gastric emptying and/or small intestinal nutrient exposure, on postprandial endothelial function. Twelve healthy subjects (6 male, 6 female; 33 ± 6 yr) were each studied on three occasions, in a randomized crossover design. After an overnight fast, subjects consumed a [(13)C]octanoic acid-labeled mashed potato meal ("meal 1"), or meal 1 mixed with 9 g guar ("meal 2") within 10 min, or meal 1 divided into 12 equal portions over 60 min ("meal 3"). Brachial artery FMD was measured every 30 min for 120 min. Blood glucose, serum insulin, and gastric emptying (breath test) were evaluated for 240 min. Data are means ± SE. Compared with meal 1, meal 2 was associated with slower gastric emptying (half-emptying time 285 ± 27 vs. 208 ± 15 min, P < 0.05), lower postprandial blood glucose and insulin (P < 0.001 for both), and a delayed, but more sustained, suppression of FMD (P < 0.001). After meal 3, both glycemic increment and reduction in FMD were less than after meal 2 (P < 0.05 for both). The decrement in FMD was directly related to the increment in blood glucose (r = 0.46, P = 0.02). We conclude that, in health, postprandial FMD is influenced by perturbation of gastric emptying and the duration of meal consumption, which also impact on glycemia.

Carbohydrate quality, weight change and incident obesity in a Mediterranean cohort: the SUN Project

BACKGROUND/OBJECTIVES

To evaluate the association between the carbohydrate quality index (CQI) and weight change or incident overweight/obesity (body mass index ⩾25 kg/m(2)) in the 'Seguimiento Universidad de Navarra (SUN)' cohort.

SUBJECTS/METHODS

A total of 8741 participants who were initially free of overweight/obesity were followed up for a median of 7.9 years. We evaluated at baseline the CQI according to four criteria: dietary fiber intake, glycemic index, whole grains/total grains ratio and solid carbohydrates/total carbohydrates ratio. Subjects were classified into quintiles according to CQI. Weight was recorded at baseline and updated every 2 years during follow-up.

RESULTS

Increasing CQI of diet was not significantly associated with lower weight gain, although participants in the highest quintile had the lowest average crude weight gain (+211 g/year). We observed 1862 incident cases of overweight/obesity during follow-up. CQI was significantly associated (P for trend 0.006) with a lower risk of overweight/obesity; adjusted odds ratio for the fourth and fifth quintiles were 0.81 (95% confidence interval (CI): 0.66-0.99) and 0.74 (95% CI: 0.60-0.92), respectively.

CONCLUSIONS

In this Mediterranean cohort, CQI showed a significant inverse association with the incidence of overweight/obesity, which highlights that carbohydrate intake guidelines related to obesity prevention should be focused on improving the CQI of the diet.

The CHANGE study: a healthy-lifestyles intervention to improve rural children's diet quality

BACKGROUND

Despite the high rates of overweight and obesity among rural children, there have been limited interventions reported to improve the diet quality of rural, low-income children in the United States.

OBJECTIVE

Our aim was to evaluate students' diet quality at baseline and after implementing the CHANGE (Creating Healthy, Active and Nurturing Growing-Up Environments) study, a 2-year (2007-2009) randomized, controlled, community- and school-based intervention to prevent unhealthy weight gain among rural school-aged children.

DESIGN

We used a school and community-based group randomized, controlled design.

PARTICIPANTS/SETTING

Data were collected in eight rural communities in California, Kentucky, Mississippi, and South Carolina (one elementary school per community). Children in grades 1 to 6 participated in the study (n=432; mean age=8.65 years ± 1.6 years). Students' diets were assessed at baseline (spring or early fall 2008) and post intervention (spring 2009) using the Block Food Screener for ages 2 to 17 years.

STATISTICAL ANALYSES

Mixed-model analysis of variance was used to examine the effect of the CHANGE study intervention on students' diets. Results were adjusted for corresponding baseline dietary values, sex, age, grade, race/ethnicity, and state, with school included as a random effect nested within condition.

RESULTS

At the end of 1 year, students enrolled in the CHANGE study intervention schools consumed significantly more vegetables (0.08 cups/1,000 kcal/day; P=0.03) and combined fruits and vegetables (0.22 cups/1,000 kcal/day; P<0.05) compared with students in control schools. Students in the intervention schools also showed a reduction in the average daily dietary glycemic index (GI=-1.22; P<0.05) and a trend toward more fruit consumption (0.15 cups/1,000 kcal/day; P=0.07). There were no significant differences in students' consumption of whole grains, legumes, dairy, potatoes/potato products, saturated fat, added sugars, or dietary fiber consumption.

CONCLUSIONS

The CHANGE study enhanced some aspects of rural students' dietary intake. Implementing similar interventions in rural America can be promising to support vegetable consumption.

Health Canada's evaluation of the use of glycemic index claims on food labels

The glycemic index (GI) is a system that ranks foods according to the blood glucose-increasing potential of servings of foods that provide the same amount of available carbohydrate. The GI was originally developed as a tool for carbohydrate exchange in the dietary management of glycemia in persons with diabetes, and studies have generally supported modest benefits of low-GI diets in this population. Despite inconsistent results for the utility of the GI in the nondiabetic population, there is some interest in its universal application on food labels to assist consumers in making food choices that would help them meet their dietary goals. The objective of this review was to evaluate the usefulness of including the GI values of foods as part of the information on food labels in Canada. Health Canada's assessment identified 3 areas of concern with respect to GI labeling: 1) the GI measure has poor accuracy and precision for labeling purposes; 2) as a ratio, the GI does not vary in response to the amount of food consumed and the partial replacement of available carbohydrates with unavailable carbohydrates, whereas the glycemic response does; and 3) an unintended focus on the GI for food selection could lead to food choices that are inconsistent with national dietary guidelines. Hence, Health Canada's current opinion is that the inclusion of the GI value on the label of eligible food products would be misleading and would not add value to nutrition labeling and dietary guidelines in assisting consumers to make healthier food choices.