Livia S. A. Augustin

Effect of a Low–Glycemic Index or a High–Cereal Fiber Diet on Type 2 Diabetes: A Randomized Trial

CONTEXT Clinical trials using antihyperglycemic medications to improve glycemic control have not demonstrated the anticipated cardiovascular benefits. Low-glycemic index diets may improve both glycemic control and cardiovascular risk factors for patients with type 2 diabetes but debate over their effectiveness continues due to trial limitations. OBJECTIVE To test the effects of low-glycemic index diets on glycemic control and cardiovascular risk factors in patients with type 2 diabetes. DESIGN, SETTING, AND PARTICIPANTS A randomized, parallel study design at a Canadian university hospital research center of 210 participants with type 2 diabetes treated with antihyperglycemic medications who were recruited by newspaper advertisement and randomly assigned to receive 1 of 2 diet treatments each for 6 months between September 16, 2004, and May 22, 2007. INTERVENTION High-cereal fiber or low-glycemic index dietary advice. MAIN OUTCOME MEASURES Absolute change in glycated hemoglobin A(1c) (HbA(1c)), with fasting blood glucose and cardiovascular disease risk factors as secondary measures. RESULTS In the intention-to-treat analysis, HbA(1c) decreased by -0.18% absolute HbA(1c) units (95% confidence interval [CI], -0.29% to -0.07%) in the high-cereal fiber diet compared with -0.50% absolute HbA(1c) units (95% CI, -0.61% to -0.39%) in the low-glycemic index diet (P < .001). There was also an increase of high-density lipoprotein cholesterol in the low-glycemic index diet by 1.7 mg/dL (95% CI, 0.8-2.6 mg/dL) compared with a decrease of high-density lipoprotein cholesterol by -0.2 mg/dL (95% CI, -0.9 to 0.5 mg/dL) in the high-cereal fiber diet (P = .005). The reduction in dietary glycemic index related positively to the reduction in HbA(1c) concentration (r = 0.35, P < .001) and negatively to the increase in high-density lipoprotein cholesterol (r = -0.19, P = .009). CONCLUSION In patients with type 2 diabetes, 6-month treatment with a low-glycemic index diet resulted in moderately lower HbA(1c) levels compared with a high-cereal fiber diet. Trial Registration clinicaltrials.gov identifier: NCT00438698.

Viscous and nonviscous fibres, nonabsorbable and low glycaemic index carbohydrates, blood lipids and coronary heart disease

Viscous fibres such as guar, glucomannans, pectins, oat betaglucan and psyllium continue to be seen as hypocholesterolaemic. Nevertheless, in large cohort studies, ironically it is the insoluble cereal fibre that has been demonstrated to relate negatively to cardiovascular disease and diabetes, despite an absence of effect on fasting lipids or postprandial glycaemia. In general, resistant or nonabsorbable starch is lipid neutral, whereas some nonabsorbable sugars or oligosaccharides may raise serum cholesterol, possibly through providing more acetate after colonic fermentation by colonic microflora. On the other hand, fructo-oligosaccharides appear to reduce serum triglycerides for reasons that are not entirely clear. Of possibly greater recent interest have been the carbohydrates that are not so much resistant to absorption, but rather are slowly absorbed. They possess some of the features of dietary fibre in providing a substrate for colonic bacterial fermentation. In the small intestine, however, they form lente or sustained release carbohydrate. In the form of low glycaemic index foods, lente carbohydrate consumption has been shown to relate to improved blood lipid profiles in hyperlipidaemic individuals and improved glycaemic control in diabetes. In larger cohort studies, low glycaemic index foods or low glycaemic load diets have been associated with higher HDL-cholesterol levels and reduced incidence of diabetes and cardiovascular disease.

Physiological Effects of Resistant Starches on Fecal Bulk, Short Chain Fatty Acids, Blood Lipids and Glycemic Index

OBJECTIVE To assess the effects on fecal bulking, fecal short chain fatty acid (SCFA) production, blood lipids and glycemic indices of two different forms of resistant starch (RS2 and RS3) from a high-amylose cornstarch. METHODS Twenty-four healthy subjects (12 men; 12 women) consumed four supplements taken for 2 weeks in random order separated by 2-week washout periods. The supplements were a low-fiber (control) and supplements providing an additional 30 g dietary fiber as wheat bran (high-fiber control) or the equivalent amount of resistant starch analyzed gravimetrically as dietary fiber from RS2 or RS3. Four-day fecal collections and 12-hour breath gas collections were obtained at the end of each period. Fasting blood was taken at the beginning and end of each period. Glycemic indices of supplements were also assessed. RESULTS The wheat bran supplement increased fecal bulk 96+/-14 g/day compared with the low-fiber control (p<0.001) with the mean for both resistant starches also being greater (22+/-8 g/day) than the low-fiber control (p=0.013). On the resistant starch phases, the mean fecal butyrate:SCFA ratio, which has been suggested to have positive implications for colonic health, was significantly above the low-fiber control by 31+/-14% (p=0.035). Resistant starches did not alter serum lipids, urea or breath H2 or CH4. No significant differences in glycemic index were seen between the RS and control supplements. CONCLUSION The potential physiological benefits of the resistant starches studied appear to relate to colonic health in terms of effects on fecal bulk and SCFA metabolism.

Dietary glycemic index and glycemic load, and breast cancer risk: A case-control study

BACKGROUND Certain types of carbohydrates increase glucose and insulin levels to a greater extent than others. In turn, insulin may raise levels of insulin-like growth factors, which may influence breast cancer risk. We analyzed the effect of type and amount of carbohydrates on breast cancer risk, using the glycemic index and the glycemic load measures in a large case-control study conducted in Italy. PATIENTS AND METHODS Cases were 2,569 women with incident, histologically-confirmed breast cancer interviewed between 1991 and 1994. Controls were 2588 women admitted to the same hospital network for a variety of acute, non-neoplastic conditions. Average daily glycemic index and glycemic load were calculated from a validated 78-item food frequency questionnaire. RESULTS Direct associations with breast cancer risk emerged for glycemic index (odds ratio, OR for highest vs. lowest quintile = 1.4; P for trend <0.01) and glycemic load (OR = 1.3; P < 0.01). High glycemic index foods, such as white bread, increased the risk of breast cancer (OR = 1.3) while the intake of pasta, a medium glycemic index food, seemed to have no influence (OR = 1.0). Findings were consistent across different strata of menopausal status, alcohol intake, and physical activity level. CONCLUSIONS This study supports the hypothesis of moderate, direct associations between glycemic index or glycemic load and breast cancer risk and, consequently, a possible role of hyperinsulinemia/insulin resistance in breast cancer development.

Type 2 diabetes and the vegetarian diet

Based on what is known of the components of plant-based diets and their effects from cohort studies, there is reason to believe that vegetarian diets would have advantages in the treatment of type 2 diabetes. At present there are few data on vegetarian diets in diabetes that do not in addition have weight loss or exercise components. Nevertheless, the use of whole-grain or traditionally processed cereals and legumes has been associated with improved glycemic control in both diabetic and insulin-resistant individuals. Long-term cohort studies have indicated that whole-grain consumption reduces the risk of both type 2 diabetes and cardiovascular disease. In addition, nuts (eg, almonds), viscous fibers (eg, fibers from oats and barley), soy proteins, and plant sterols, which may be part of the vegetarian diet, reduce serum lipids. In combination, these plant food components may have a very significant impact on cardiovascular disease, one of the major complications of diabetes. Furthermore, substituting soy or other vegetable proteins for animal protein may also decrease renal hyperfiltration, proteinuria, and renal acid load and in the long term reduce the risk of developing renal disease in type 2 diabetes. The vegetarian diet, therefore, contains a portfolio of natural products and food forms of benefit for both the carbohydrate and lipid abnormalities in diabetes. It is anticipated that their combined use in vegetarian diets will produce very significant metabolic advantages for the prevention and treatment of diabetes and its complications.

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.

Glycemic index and glycemic load in endometrial cancer

Glycemic index (GI) and glycemic load (GL) are measures of the metabolic effects of dietary carbohydrates. The higher their value, the greater the glucose and insulin responses. Raised insulin levels are associated with endometrial cancer and with its risk factors including obesity, diabetes and hypertension. To study the role of the GI and GL we analyzed the data of two hospital‐based case–control studies on endometrial cancer conducted between 1988–98 in Italy and Switzerland, including a total of 410 women with incident, histologically confirmed endometrial cancer and 753 controls admitted for acute, non‐neoplastic diseases. A food frequency questionnaire was used to assess the subjects usual diet and to derive estimates of dietary GI and GL. The odds ratios (OR) of endometrial cancer, after adjustment for major risk factors, for the highest versus the lowest quintile of dietary GI and GL were 2.1 (95% confidence interval [CI] = 1.4–3.2) and 2.7 (95% CI = 1.8–4.2), respectively. The associations were stronger in older women, in those with higher body mass index and in hormone replacement therapy users. Our study supports the hypothesis of a direct association between GI and endometrial cancer risk.

Associations of Glycemic Index and Load With Coronary Heart Disease Events: A Systematic Review and Meta-Analysis of Prospective Cohorts

Background Glycemic index (GI) and glycemic load (GL) have been associated with coronary heart disease (CHD) risk in some but not all cohort studies. We therefore assessed the association of GI and GL with CHD risk in prospective cohorts. Methods and Results We searched MEDLINE, EMBASE, and CINAHL (through April 5, 2012) and identified all prospective cohorts assessing associations of GI and GL with incidence of CHD. Meta-analysis of observational studies in epidemiology (MOOSE) methodologies were used. Relative measures of risk, comparing the group with the highest exposure (mean GI of cohorts=84.4 GI units, range 79.9 to 91; mean GL of cohorts=224.8, range 166 to 270) to the reference group (mean GI=72.3 GI units, range 68.1 to 77; mean GL=135.4, range 83 to 176), were pooled using random-effects models, expressed as relative risk (RR) with heterogeneity assessed by χ2 and quantified by I2. Subgroups included sex and duration of follow-up. Ten studies (n=240 936) were eligible. Pooled analyses showed an increase in CHD risk for the highest GI quantile compared with the lowest, with RR=1.11 (95% confidence interval [CI] 0.99 to 1.24) and for GL, RR=1.27 (95% CI 1.09 to 1.49), both with evidence of heterogeneity (I2>42%, P<0.07). Subgroup analyses revealed only a significant modification by sex, with the female cohorts showing significance for GI RR=1.26 (95% CI 1.12 to 1.41) and for GL RR=1.55 (95% CI 1.18 to 2.03). Conclusions High GI and GL diets were significantly associated with CHD events in women but not in men. Further studies are required to determine the relationship between GI and GL with CHD in men.

The Effect of Wheat Bran Particle Size on Laxation and Colonic Fermentation

OBJECTIVE Due to perceived inferior fecal bulking ability, finely ground wheat bran is not recommended for treatment of colonic disorders, despite possible short chain fatty acid generation with potential benefits for colonic mucosal health. We therefore tested the effects of very fine particle size wheat bran on colonic function. METHODS Two studies, each with three phases, were undertaken in healthy subjects in a randomized crossover design. In one study (metabolic, n=23) subjects took three diets containing either an additional 19 g/d dietary fiber with mean particle size (MPS) 50 microm or 758 microm in bread or a control low fiber bread. In the other study where the supplement was provided as a breakfast cereal (ad libitum, n=24) the respective wheat bran MPS were 692 microm and 1158 microm and the control was low fiber. Fecal collections were obtained during the last week of each diet. In the metabolic study, fecal short chain fatty acids were measured and 12-hour breath gas collections obtained. RESULTS In both studies, wheat bran supplements significantly increased fecal bulk compared to the control (p<0.004), with no significant differences between brans of different particle size and no differences in fecal water content. However, higher fecal butyrate concentrations (p<0.007), butyrate output and breath CH4 levels (p=0.025) were seen on the low MPS wheat bran compared to the other two treatments, suggesting increased bacterial fermentation. CONCLUSIONS Fine MPS wheat bran is an effective fecal bulking agent and may have added advantages if increased butyrate concentrations promote colonic mucosal integrity.

Glycemic index and load and risk of upper aero-digestive tract neoplasms (Italy)

Background: The ability of dietary carbohydrates to affect blood glucose and insulin levels by dietary carbohydrates is best measured by the glycemic index (GI) and glycemic load (GL) which have been directly associated with risk of several chronic conditions, including cancer. Patients and methods: Three case–control studies were conducted between 1992 and 2000 in Italy. The first one included 598 hospital patients with incident, histologically confirmed oral and pharyngeal cancer and 1491 controls admitted to the same hospital networks for acute, non-neoplastic diseases; the second study included 304 subjects with squamous cell oesophageal cancer and 743 controls; the third one included 460 cases with laryngeal cancer and 1088 controls. All subjects were interviewed using a validated food frequency questionnaire. Results: The odds ratios (OR) of upper aero-digestive tract neoplasms for the highest versus the lowest quintile of dietary GI and GL were 1.5 (95% confidence interval [CI]: 1.1–2.0) and 1.8 (95% CI: 1.1–2.9), respectively. The associations were in the same direction for various cancer sites. The ORs were apparently stronger in women, in those with high body mass index and reporting low alcohol consumption. Conclusions: This study supports the hypothesis that high dietary GI and GL are associated with cancers of the upper aero-digestive tract.