The relevance of the glycaemic index to our understanding of dietary carbohydrates

Diet and Glycemic Index in Children with Type 1 Diabetes

In children with type 1 diabetes, a healthy lifestyle is important to control postprandial glycemia and to avoid hyperglycemic peaks that worsen the inflammatory state of vessels and tissues. Glycemic index and glycemic load are two important indexes which assess the quality and quantity of foods consumed during meals. The main macronutrients of the diet have a different effect on postprandial blood glucose levels, so it is important that diabetic children consume foods which determine a slower and steadier glycemic peak. In this review, we present the results of the most recent studies carried out in the pediatric population with T1D, whose aim was to analyze the effects of low-glycemic-index foods on glycemic control. The results are promising and demonstrate that diets promoting low-glycemic-index foods guarantee a greater glycemic stability with a reduction in postprandial hyperglycemic peaks. However, one of the main limitations is represented by the poor adherence of children to a healthy diet. In order to obtain satisfactory results, a possibility might be to ensure a balanced intake of low-, moderate- and high-glycemic-index foods, preferring those with a low glycemic index and limiting the consumption of the high- and moderate-glycemic-index types.

Comparison of Glycemic Response to Carbohydrate Meals without or with a Plant-Based Formula of Kidney Bean Extract, White Mulberry Leaf Extract, and Green Coffee Extract in Individuals with Abdominal Obesity

Due to the rising prevalence of obesity and type 2 diabetes, a strategy that can positively influence diet quality in a simple way is being explored, since a low glycemic index (GI) diet is advised in the dietoprophylaxis and diet therapy of diabetes. Methods: Twenty-three women with abdominal obesity participated in the study. The postprandial glycemic response and glycemic index were determined after three carbohydrate meals (noodle soup, white rice, strawberry sorbet) without or with the addition of a plant-base supplement (extracts of kidney bean, white mulberry leaf, and green coffee) with a potentially hypoglycemic effect. For two products (instant noodle soup and white rice), the addition of the plant supplement resulted in a reduction in glicemic iAUC values (respectively, by: 17.1%, p = 0.005 and 5.3%; p = 0.03; 40.6%, p = 0.004 and 5.3%, p = 0.019). However, this effect was not observed for strawberry sorbet. The blood glucose concentrations 30 min after the consumption of instant noodle soup and white rice with the plant-based formula addition significantly affected the GI value of tested meals (p = 0.0086, r = 0.53; p = 0.0096, r = 0.53), which may indicate the effect of this plant supplement on enterohormone and/or insulin secretion. Conclusion: A formula containing kidney bean, white mulberry leaves, and green coffee extracts may therefore be a notable factor in lowering postprandial glycemia and the GI of carbohydrate foods. However, further research is needed to determine for which food groups and meals its use may be most effective.

Glycemic index of different varieties of yam as influenced by boiling, frying and roasting

Yam is one of the commonly consumed carbohydrate staples. The objective of this work was to investigate the effect of boiling, roasting, and frying on the glycemic index (GI) of white yam (Dioscorea rotundata), yellow yam (Dioscorea cayenesis), and water yam (Dioscorea alata). Yam tubers were obtained (peeled, sliced, washed) deep fried in vegetable oil for 35-40 min and boiled in water for about 35-45 min. Sliced unpeeled tubers were also roasted at about 120°C for 40-45 min. The cooked yam samples were fed to 10 healthy subjects aged between 20-50 years. A glucometer was used to measure the blood glucose concentrations of the test individuals before consuming the yam diets and after the 15th, 30th, 45th, 60th, 90th, and 120th min of consumption. The average incremental area under the curves (IAUC) obtained from the recorded blood glucose concentrations were used to calculate the GI of various yam diets. The GI of the yam diets were found to be in the following increasing order: White-yam-boiled (44.26%) < Water-yam-boiled (50.12%) < White-yam-roasted (50.62%) < Water-yam-roasted (54.04%) < White-yam-fried (59.13%) < Yellow-yam-fried (65.08%) < Water-yam-fried (69.16%) < Yellow-yam-roasted (70.62%) < Yellow-yam-boiled (75.18%). White yam diets relatively had lower GI compared to yellow yam and water yam. Boiling was found to give generally lower GI in the white and water yams and could therefore be applied in the preparation of lower GI diets for diabetics.

Grain Dimension, Nutrition and Nutraceutical Properties of Black and Red Varieties of Rice in India

Traditional colored rice varieties in India are the source of carbohydrates, phytochemicals and minerals. They facilitate the growth of probiotics in intestine and protect human from many chronic diseases. The present study investigated the nutritional properties such as total sugars, digestible sugars, resistant sugars, hydrolysis index, glycemic index and total proteins of thirteen colored varieties of rice in India. Nutraceutical properties like anti diabetic and prebiotic activity were investigated by standard methods. Chak hao poreiton and mappillai samba grains were 6.3 mm in length. Lowest length of 5.1 mm was recorded in 60 m Kuruvai. Among the rice varieties, mappillai samba has high concentration of digestible starch of 91% and Chak hao poreiton had low concentration of 62%. Resistant starch was 38% in Chak hao poreiton and 8% in mappillai samba. Lowest glycemic index of 52 and 53 were recorded in karuthakar poha and Chak hao poreiton respectively. Anthocyanin extracted from Chak hao poreiton inhibited 24% of human pancreatic α-amylase activity. It significantly increased the probiotic number from 0.15 CFU/mL to 1.95 CFU/mL. The study revealed that the black rice variety, Chak hao poreiton was rich in resistant starch and exhibited low glycemic index. The anthocyanins from Chak hao poreiton possessed significant antidiabetic and prebiotic activity. Molecular docking studies revealed the interaction of anthocyanin with pancreatic α-amylase, β-glucosidase and GLUT1.

Effect of semolina pudding prepared from starch branching enzyme IIa and b mutant wheat on glycaemic response in vitro and in vivo: a randomised controlled pilot study

Refined starchy foods are usually rapidly digested, leading to poor glycaemic control, but not all starchy foods are the same. Complex carbohydrates like resistant starch (RS) have been shown to reduce the metabolic risk factors for chronic diseases such as hyperglycaemia and overweight. The aim of the project was to develop a semolina-based food made from a starch branching enzyme II (sbeIIa/b-AB) durum wheat mutant with a high RS content and to measure its glycaemic index using a double-blind randomised pilot study. We report here the amylose, RS and non-starch polysaccharide concentration of raw sbeIIa/b-AB and wild-type control (WT) semolina. We measured RS after cooking to identify a model food for in vivo testing. Retrograded sbeIIa/b-AB semolina showed a higher RS concentration than the WT control (RS = 4.87 ± 0.6 g per 100 g, 0.77 ± 0.34 g per 100 g starch DWB, respectively), so pudding was selected as the test food. Ten healthy participants consumed ∼50 g of total starch from WT and sbeIIa/b-AB pudding and a standard glucose drink. Capillary blood glucose concentrations were measured in the fasting and postprandial state (2 h): incremental area-under-the-curve (iAUC) and GI were calculated. We found no evidence of difference in GI between sbeIIa/b-AB pudding and the WT control, but the starch digestibility was significantly lower in sbeIIa/b-AB pudding compared to the WT control in vitro (C90 = 33.29% and 47.38%, respectively). Based on these results, novel sbeIIa/b-AB wheat foods will be used in future in vivo studies to test the effect of different RS concentrations and different food matrices on glycaemia.

Low glycaemic index diets for the prevention of cardiovascular disease

BACKGROUND

The glycaemic index (GI) is a physiological measure of the ability of a carbohydrate to affect blood glucose. Interest is growing in this area for the clinical management of people at risk of, or with, established cardiovascular disease. There is a need to review the current evidence from randomised controlled trials (RCTs) in this area. This is an update of the original review published in 2008.

OBJECTIVES

To assess the effect of the dietary GI on total mortality, cardiovascular events, and cardiovascular risk factors (blood lipids, blood pressure) in healthy people or people who have established cardiovascular disease or related risk factors, using all eligible randomised controlled trials.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase and CINAHL in July 2016. We also checked reference lists of relevant articles. No language restrictions were applied.

SELECTION CRITERIA

We selected RCTs that assessed the effects of low GI diets compared to diets with a similar composition but a higher GI on cardiovascular disease and related risk factors. Minimum trial duration was 12 weeks. Participants included were healthy adults or those at increased risk of cardiovascular disease, or previously diagnosed with cardiovascular disease. Studies in people with diabetes mellitus were excluded.

DATA COLLECTION AND ANALYSIS

Two reviewers independently screened and selected studies. Two review authors independently assessed risk of bias, evaluated the overall quality of the evidence using GRADE, and extracted data following the Cochrane Handbook for Systematic Reviews of Interventions. We contacted trial authors for additional information. Analyses were checked by a second reviewer. Continuous outcomes were synthesized using mean differences and adverse events were synthesized narratively.

MAIN RESULTS

Twenty-one RCTs were included, with a total of 2538 participants randomised to low GI intervention (1288) or high GI (1250). All 21 included studies reported the effect of low GI diets on risk factors for cardiovascular disease, including blood lipids and blood pressure.Twenty RCTs (18 of which were newly included in this version of the review) included primary prevention populations (healthy individuals or those at high risk of CVD, with mean age range from 19 to 69 years) and one RCT was in those diagnosed with pre-existing CVD (a secondary prevention population, with mean age 26.9 years). Most of the studies did not have an intervention duration of longer than six months. Difference in GI intake between comparison groups varied widely from 0.6 to 42.None of the included studies reported the effect of low GI dietary intake on cardiovascular mortality and cardiovascular events such as fatal and nonfatal myocardial infarction, unstable angina, coronary artery bypass graft surgery, percutaneous transluminal coronary angioplasty, and stroke. The unclear risk of bias of most of the included studies makes overall interpretation of the data difficult. Only two of the included studies (38 participants) reported on adverse effects and did not observe any harms (low-quality evidence).

AUTHORS' CONCLUSIONS

There is currently no evidence available regarding the effect of low GI diets on cardiovascular disease events. Moreover, there is currently no convincing evidence that low GI diets have a clear beneficial effect on blood lipids or blood pressure parameters.

The effect of food with different glycaemic index on the blood glucose level

Blood glucose levels are affected by many factors including the type of foods consumed, processing technology and cooking method. Hormone insulin lowers blood glucose to its constant level, while glucagon, growth hormone, adrenalin and glucocorticoids have the opposite effect. High steepness of the blood glucose level rise after meals may be unfavourable for the organism. Sugars are transferred into the blood at different speeds according to the type of food. Therefore the aim of this study was to confirm experimentally the effect of food on blood glucose levels in men and women of different ages. Two types of low, medium and high-glycaemic index (GI) foods were given to 4 men and 4 women of different age (from 35 to 65 years). All volunteers were healthy, slightly overweight, and without any regular sporting activity. None of them had any idea about their daily carbohydrates consumption and what the term glycaemic index meant. The volunteers came to the GI determination fasted in the morning. Their rise in blood glucose level was monitored by glucometer before the meal and after 1 and 2 hours of the consumption of baked potatoes (GI 85), white bread bun (GI 70), boiled potatoes (GI 64), rye bread (GI 62), potato dumplings (GI 52) and white cooked spaghetti (GI 41). Fasting blood sugar levels of volunteers highly depended on their age (p <0.0001) and gender (p <0.0001). The blood glucose values increased with age and were higher in men than in women. Significant influence of food GI on blood glucose levels in both men and women in all the age categories was observed (p <0.0001). An interaction between age and gender was also statistically highly significant (p <0.0001). One hour after consuming food the blood glucose values were significantly different from the values of fasting (p = 0.0035). The differences of these values did not depend on the age (p = 0.0574) and sex (p = 0.8256) of volunteers, but there was a significant difference on the GI value of food (p <0.0001). Significant interactions were also found in case of sex*age (p = 0.0002), age*GI (p <0.0001) and age*sex*GI (p <0.0001). Medium correlation was found between the GI values of food and the rise of blood glucose levels after 1 h (r = 0.6468). After the consumption of high-GI foods the values of glycaemia did not returned to their fasting levels even after 2 hours. There was still significant difference (p = 0.0032), but the values after 2 h were also statistically different from those after 1 hour (p <0.0001). The response to a particular type of consumed food depended on age (p = 0.0018) and especially the GI of foods.

White vegetables: glycemia and satiety

The objective of this review is to discuss the effect of white vegetable consumption on glycemia, satiety, and food intake. White vegetables is a term used to refer to vegetables that are white or near white in color and include potatoes, cauliflowers, turnips, onions, parsnips, white corn, kohlrabi, and mushrooms (technically fungi but generally considered a vegetable). They vary greatly in their contribution to the energy and nutrient content of the diet and glycemia and satiety. As with other foods, the glycemic effect of many white vegetables has been measured. The results illustrate that interpretation of the semiquantitative comparative ratings of white vegetables as derived by the glycemic index must be context dependent. As illustrated by using the potato as an example, the glycemic index of white vegetables can be misleading if not interpreted in the context of the overall contribution that the white vegetable makes to the carbohydrate and nutrient composition of the diet and their functionality in satiety and metabolic control within usual meals. It is concluded that application of the glycemic index in isolation to judge the role of white vegetables in the diet and, specifically in the case of potato as consumed in ad libitum meals, has led to premature and possibly counterproductive dietary guidance.

Low glycaemic index diets and blood lipids: a systematic review and meta-analysis of randomised controlled trials

AIMS

Low glycaemic index (GI) diets are beneficial in the management of hyperglycemia. Cardiovascular diseases are the major cause of mortality in diabetes therefore it is important to understand the effects of GI on blood lipids. The aim was to systematically review randomised controlled trials (RCTs) of low GI diets on blood lipids.

DATA SYNTHESIS

We searched OVID Medline, Embase and Cochrane library to March 2012. Random effects meta-analyses were performed on twenty-eight RCTs comparing low- with high GI diets over at least 4 weeks (1272 participants; studies ranged from 6 to 155 participants); one was powered on blood lipids, 3 had adequate allocation concealment. Low GI diets significantly reduced total (-0.13 mmol/l, 95%CI -0.22 to -0.04, P = 0.004, 27 trials, 1441 participants, I(2) = 0%) and LDL-cholesterol (-0.16 mmol/l, 95%CI -0.24 to -0.08, P < 0.0001, 23 trials, 1281 participants, I(2) = 0%) compared with high GI diets and independently of weight loss. Subgroup analyses suggest that reductions in LDL-C are greatest in studies of shortest duration and greatest magnitude of GI reduction. Furthermore, lipid improvements appear greatest and most reliable when the low GI intervention is accompanied by an increase in dietary fibre. Sensitivity analyses, removing studies without adequate allocation concealment, lost statistical significance but retained suggested mean falls of ~0.10 mmol/l in both. There were no effects on HDL-cholesterol (MD -0.03 mmol/l, 95%CI -0.06 to 0.00, I(2) = 0%), or triglycerides (MD 0.01 mmol/l, 95%CI -0.06 to 0.08, I(2) = 0%).

CONCLUSIONS

This meta-analysis provides consistent evidence that low GI diets reduce total and LDL-cholesterol and have no effect on HDL-cholesterol or triglycerides.

Review: Starch Matrices and the Glycemic Response

Starch is the most important source of energy for humans, and it is present in many products derived from cereals, legumes and tubers. Interestingly, some of these food products can have different metabolic effects (e.g. change of postprandial blood glucose concentration) although the total amount of starch is the same. This review focuses on a microstructural perspective of the glycemic response, in search of an alternative and complementary explanation of this phenomenon. Several starch and food microstructures are responsible for the change in starch bioaccessibility. Aspects such as the characterization of the microstructure of starchy products and, its relation to the metabolic problem, the crucial role of the food matrix and other components in the ingested meal, and the gaps in our present knowledge are discussed.

Session 4: CVD, diabetes and cancer Diet, insulin resistance and diabetes: the right (pro)portions

Excess energy intake and positive energy balance are associated with the development of obesity and insulin resistance, which is a key feature underlying the pathophysiology of type 2 diabetes. It is possible that dietary macronutrient intake may also be important, in particular increased levels of sugar and fat. High-fat energy-dense diets contribute to energy excess and obesity. Fat type is also a factor, with evidence suggesting that saturated fat intake is linked to insulin resistance. However, controversy exists about the role of carbohydrate in the development of diabetes. Epidemiological studies suggest that the risk of diabetes is unrelated to the total amount of carbohydrate, but that fibre intake and glycaemic load are important. Common dietary advice for the prevention of diabetes often advocates complex carbohydrates and restriction of simple carbohydrates; however, sugars may not be the main contributor to glycaemic load. Evidence continues to emerge in relation to the influence of dietary sugars intake on insulin resistance. In broader dietary terms fruit and vegetable intake may influence insulin resistance, possibly related to increased intake of fibre and micronutrients or displacement of other food types. There is also considerable debate about the most effective diet and appropriate macronutrient composition to facilitate weight loss. Recent evidence suggests comparable effects of diets with varying macronutrient profiles on weight loss, which is predominantly related to energy restriction. However, based on the results of diabetes prevention trials focusing on lifestyle measures, evidence favours low-fat diets as the preferred approach for weight loss and diabetes prevention.

A balanced diet is necessary for proper entrainment signals of the mouse liver clock

Background

The peripheral circadian clock in mice is entrained not only by light-dark cycles but also by daily restricted feeding schedules. Behavioral and cell culture experiments suggest an increase in glucose level as a factor in such feeding-induced entrainment. For application of feeding-induced entrainment in humans, nutrient content and dietary variations should be considered.

Principal Finding

To elucidate the food composition necessary for dietary entrainment, we examined whether complete or partial substitution of dietary nutrients affected phase shifts in liver clocks of mice. Compared with fasting mice or ad libitum fed mice, the liver bioluminescence rhythm advanced by 3–4 h on the middle day in Per2::luciferase knock-in mice that were administered a standard mouse diet, i.e. AIN-93M formula [0.6–0.85 g/10 g mouse BW] (composition: 14% casein, 47% cornstarch, 15% gelatinized cornstarch, 10% sugar, 4% soybean oil, and 10% other [fiber, vitamins, minerals, etc.]), for 2 days. When each nutrient was tested alone (100% nutrient), an insignificant weak phase advance was found to be induced by cornstarch and soybean oil, but almost no phase advance was induced by gelatinized cornstarch, high-amylose cornstarch, glucose, sucrose, or casein. A combination of glucose and casein without oil, vitamin, or fiber caused a significant phase advance. When cornstarch in AIN-93M was substituted with glucose, sucrose, fructose, polydextrose, high-amylose cornstarch, or gelatinized cornstarch, the amplitude of phase advance paralleled the increase in blood glucose concentration.

Conclusions

Our results strongly suggest the following: (1) balanced diets containing carbohydrates/sugars and proteins are good for restricted feeding-induced entrainment of the peripheral circadian clock and (2) a balanced diet that increases blood glucose, but not by sugar alone, is suitable for entrainment. These findings may assist in the development of dietary recommendations for on-board meals served to air travelers and shift workers to reduce jet lag-like symptoms.

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.

Effect of cereal test breakfasts differing in glycemic index and content of indigestible carbohydrates on daylong glucose tolerance in healthy subjects

BACKGROUND

Frequent hyperglycemic episodes are increasingly being associated with an increased risk of type 2 diabetes and cardiovascular disease.

OBJECTIVE

We studied the extent to which acute glycemia and glycemia after subsequent meals can be modulated by the characteristics of cereal foods, such as glycemic index (GI) and content of indigestible carbohydrates.

DESIGN

Twelve healthy subjects consumed test meals in a random order. In series 1, the test meals were consumed at breakfast, and postprandial blood glucose incremental areas under the curve (IAUCs) were calculated after the test breakfast, standardized lunch, and standardized dinner. In series 2, the subjects consumed test evening meals and IAUCs were calculated after a subsequent standardized breakfast. Breath hydrogen was measured as an indicator of colonic fermentation.

RESULTS

Barley or rye kernel breakfasts lowered the blood glucose IAUC (0-120 min) at breakfast, at a subsequent lunch, and the cumulative IAUCs (breakfast+lunch+dinner) when compared with white-wheat bread (P < 0.05). The lunch blood glucose IAUCs were positively correlated with breakfast IAUCs (r = 0.30, P < 0.05). Breath hydrogen excretion was negatively correlated with blood glucose IAUCs after lunch (r = -0.33, P < 0.05) and dinner (r = -0.22, P < 0.05). A barley kernel evening meal resulted in lower IAUCs (P < 0.05) and higher breath hydrogen (P < 0.001) after a subsequent breakfast compared with white-wheat bread.

CONCLUSIONS

Glucose tolerance at subsequent meals can be notably improved during the course of a whole day or overnight by choosing specific low-GI, whole-grain cereal products. A low GI may be sufficient to achieve a second-meal effect from breakfast to lunch. A specific indigestible carbohydrate mixture appears to be required to show benefits on glucose tolerance in a longer time frame (9.5 h), most likely mediated through colonic fermentation.

Effects of differences in postprandial glycaemia on cognitive functions in healthy middle-aged subjects

OBJECTIVE

To find useful methods for the studies of cognitive function during a postprandial period, and to use these methods to evaluate function after test meals differing in post meal glycaemia.

SUBJECTS/METHODS

Forty healthy volunteers aged 49-70 years were studied. A glucose solution (glucose 50 g) was provided through either a bolus or sipping regimen at breakfast to simulate a high-GI or a low-GI breakfast, respectively. Cognitive tests of working memory (WM) were performed at 35, 90, 120 and 150 min after commencing the breakfast, and a test of selective attention (SA) was performed at 170 min.

RESULTS

Subjects with higher glucose tolerance performed better in the cognitive tests (P<0.05). After entering glucose tolerance as covariate, the subjects performed better in the working memory test at 90 min (P<0.034) and in the selective attention test at 170 min (P<0.017) after the simulated low-glycaemic index (GI) breakfast compared with the simulated high-GI breakfast.

CONCLUSION

Possibly, the cognitive functions tested were enhanced by avoiding a sharp decline in blood glucose concentration and by maintaining a higher glycaemia in the late postprandial period, respectively. A low-GI diet is preferable in the prevention of the risk of cognitive decline as a result of less efficient glucose regulation.

Acceptability of lower glycemic index foods in the diabetes camp setting

OBJECTIVE

To determine the acceptability of lower glycemic index (GI) foods served at diabetes camp.

DESIGN

Crossover design of standard and lower GI menus.

SETTING

Three consecutive 5-day diabetes camp sessions.

PARTICIPANTS

140 youth, age 7-16, with type 1 or 2 diabetes.

INTERVENTION

A standard camp cycle menu was reformulated to include 2 1/2 days of standard foods and 2 1/2 days of lower GI foods.

MAIN OUTCOME MEASURES

Youth provided satisfaction ratings after meals and snacks using measures designed for this study. Observations of food consumption were conducted on a random sample of youth for each meal.

ANALYSIS

Descriptive analyses and t-tests were conducted to assess differences in satisfaction with and consumption of standard and lower GI foods.

RESULTS

Lower GI foods served at dinner and for snacks received satisfaction ratings equal to standard foods (dinner: 3.68 lower GI versus 3.79 standard, P = .30; snacks: 3.74 lower GI versus 3.79 standard, P = .60). Lower GI foods served at breakfast and lunch received lower, though very acceptable, ratings (breakfast: 3.76 lower GI versus 4.04 standard, P < .01; lunch: 3.64 lower GI versus 3.88 standard, P = .01). Consumption of all meals was acceptable. No differences occurred in the frequency of high or low blood sugars between standard and lower GI days.

CONCLUSIONS AND IMPLICATIONS

Higher quality carbohydrates may be provided to youth in institutional settings while maintaining sufficient levels of acceptability; specific findings are instructive for designing efforts to increase their consumption.

Dietary fibre, glycaemic response, and diabetes

The much publicised global trend in rising levels of obesity and diabetes has refuelled interest in the dietary intake of the macronutrients (fat, protein, and carbohydrates) necessary to maintain the state of normalcy (good health) of an individual. Both scientific and public attention have focused on the dietary mediation of chronic health syndromes, either through use of dietary supplements, or a review of the whole diet situation. Dietary supplements have been used extensively both as pharmacological supplements, food ingredients, in processed foods to aid weight control, and the regulation of glucose control for diabetic patients. Particular interest has focused on the use of dietary fibres, especially soluble dietary fibres (such as guar gum, locust bean gum, and psyllium fibres), resistant starch, and slowly digestible carbohydrates. These have been shown to alter food structure, texture, and viscosity, and hence the rate of starch degradation during digestion. Research has also illustrated an association between the rate of carbohydrate degradation during digestion, and the regulation of postprandial blood sugar and insulin levels. The current paper explores the potential use of dietary fibres in the treatment of obesity and diabetes.

Low glycaemic index diets for coronary heart disease

BACKGROUND

The glycaemic index (GI) is a physiological measure of the ability of a carbohydrate to affect blood glucose. Interest is growing in the low GI carbohydrate concept for the clinical management of people at risk of, or with established coronary heart disease. There is a need to review the current evidence from controlled trials in this area.

OBJECTIVES

The primary objective is to review the current evidence from RCTs that assess the relationship between the consumption of low glycaemic index diets and the effects on coronary heart disease and on risk factors for coronary heart disease.

SEARCH STRATEGY

We searched CENTRAL (Issue 4, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and CINAHL (1982 to 2003). We also contacted experts in the field.

SELECTION CRITERIA

We selected randomised controlled trials that assessed the effects of low glycaemic index diets, over a minimum of 4 weeks, on coronary heart disease (CHD) and risk factors. Participants included were adults who carry at least one major risk factor for coronary heart disease such as abnormal lipids, diabetes or being overweight.

DATA COLLECTION AND ANALYSIS

Two of our research team independently assessed trial quality and extracted data. Authors of the included studies were contacted for additional information when this was appropriate.

MAIN RESULTS

Fifteen randomised controlled trials met the inclusion criteria. No studies found reported the effect of low glycaemic index diets on CHD mortality or CHD events and morbidity. All fifteen included studies report the effect of low glycaemic index diets on major risk factors for CHD. Meta-analysis detected limited and weak evidence of a relationship between low glycaemic index diets and slightly lower total cholesterol, compared with higher glycaemic index diets. There is also limited and weak evidence of a small reduction in HbA1c after 12 weeks on low glycaemic index diets but not at 4 to 5 weeks. There is no evidence that low glycaemic index diets have an effect on LDL cholesterol or HDL cholesterol, triglycerides, fasting glucose or fasting insulin levels.

REVIEWERS' CONCLUSIONS

The evidence from randomised controlled trials showing that low glycaemic index diets reduces coronary heart disease and CHD risk factors is weak. Many of the trials identified were short-term, of poor quality and conducted on small sample sizes. There is a need for well designed, adequately powered, randomised controlled studies, of greater than 12 weeks duration to assess the effects of low glycaemic index diets for CHD.

Effects of Acute Chromium Supplementation on Postprandial Metabolism in Healthy Young Men

BACKGROUND

Chromium (Cr) potentiates the action of insulin in the cell and improves glucose tolerance after long-term supplementation.

OBJECTIVE

We hypothesized that Cr may also have acute effects and might be beneficial in lowering the glycemic index of a meal.

METHODS

We studied the effects of short-term Cr supplementation using a randomized crossover design. Thirteen apparently healthy, non-smoking young men of normal body mass index performed three trials each separated by one week. Test meals, providing 75 g of available carbohydrates, consisted of white bread with added Cr (400 or 800 microg as Cr picolinate) or placebo.

RESULTS

After addition of 400 and 800 microg Cr incremental area under the curve (AUC) for capillary glucose was 23% (p = 0.053) and 20% (p = 0.054), respectively, lower than after the white bread meal. These differences reached significance if the subjects were divided into responders (n = 10) and non-responders (n = 3). For the responders AUC after 400 and 800 microg Cr was reduced by 36% and 30%, respectively (Placebo 175 +/- 22, Cr400 111 +/- 14 (p < 0.01), Cr800 122 +/- 15 mmol. min/L (p < 0.01)). Glycemia was unchanged after addition of Cr in the non-responders. Responders and non-responders differed significantly in their nutrient intake and eating pattern, and total serum iron concentration tended to be lower in the responder group (p = 0.07).

CONCLUSIONS

Acute chromium supplementation showed an effect on postprandial glucose metabolism in most but not all subjects. The response to Cr may be influenced by dietary patterns.

Increased consumption of refined carbohydrates and the epidemic of type 2 diabetes in the United States: an ecologic assessment

BACKGROUND

Type 2 diabetes is an epidemic that is affecting an ever-increasing proportion of the US population. Although consumption of refined carbohydrates has increased and is thought to be related to the increased risk of type 2 diabetes, the ecologic effect of changes in the quality of carbohydrates in the food supply on the risk of type 2 diabetes remains to be quantified.

OBJECTIVE

The objective was to examine the correlation between consumption of refined carbohydrates and the prevalence of type 2 diabetes in the United States.

METHODS

In this ecologic correlation study, the per capita nutrient consumption in the United States between 1909 and 1997 obtained from the US Department of Agriculture was compared with the prevalence of type 2 diabetes obtained from the Centers for Disease Control and Prevention.

RESULTS

In a univariate analysis, a significant correlation with diabetes prevalence was observed for dietary fat (r = 0.84, P < 0.001), carbohydrate (r = 0.55, P < 0.001), protein (r = 0.71, P < 0.001), fiber (r = 0.16, P = 0.03), corn syrup (r = 0.83, P < 0.001), and total energy (r = 0.75, P < 0.001) intakes. In a multivariate nutrient-density model, in which total energy intake was accounted for, corn syrup was positively associated with the prevalence of type 2 diabetes (beta = 0.0132, P = 0.038). Fiber (beta = -13.86, P < 0.01) was negatively associated with the prevalence of type 2 diabetes. In contrast, protein (P = 0.084) and fat (P = 0.79) were not associated with the prevalence of type 2 diabetes when total energy was controlled for.

CONCLUSIONS

Increasing intakes of refined carbohydrate (corn syrup) concomitant with decreasing intakes of fiber paralleled the upward trend in the prevalence of type 2 diabetes observed in the United States during the 20th century.

The implementation of nutritional advice for people with diabetes

These consensus-based recommendations emphasize the practical implementation of nutritional advice for people with diabetes, and describe the provision of services required to provide the information. Important changes from previous recommendations include greater flexibility in the proportions of energy derived from carbohydrate and monounsaturated fat, further liberalization in the consumption of sucrose, more active promotion of foods with a low glycaemic index, and greater emphasis on the provision of nutritional advice in the context of wider lifestyle changes, particularly physical activity. Monounsaturated fats are now promoted as the main source of dietary fat because of their lower susceptibility to lipid peroxidation and consequent lower atherogenic potential. Consumption of sucrose for patients who are not overweight can be increased up to 10% of daily energy provided that this is eaten in the context of a healthy diet and distributed throughout the day [corrected]. Evidence is presented for the effectiveness of advice provided by trained dieticians. The increasing evidence for the importance of good metabolic control and the growing requirement for measures to prevent Type 2 diabetes in an increasingly obese population will require major expansion of dietetic services if the standards in National Service Frameworks are to be successfully implemented.

Sugars, insulin sensitivity, and the postprandial state

Since insulin resistance was first associated with type 2 diabetes and later with cardiovascular disease and hypertension, there has been considerable interest in the role of dietary and environmental factors. Sucrose and fructose have been a particular research focus. Research on animals, particularly rodents, has shown a clear and consistent effect of high-sucrose and high-fructose diets in decreasing insulin sensitivity. Experiments in humans have produced very conflicting results, with limited evidence for a negative effect on insulin sensitivity at higher intakes of fructose or sucrose (generally > 30% of daily energy from sucrose and > 15% of daily energy from fructose). Observation studies in humans have not shown a link between sucrose consumption and insulin sensitivity independent of other dietary factors. This is in contrast with several small studies that showed an improvement in insulin sensitivity after subjects followed dietary advice to lower the glycemic index of their food choices (where sugars were not a target for change). However, the pattern of postprandial glucose and insulin responses elicited by sucrose and fructose differs substantially from that elicited by starches, with lower troughs elicited by sucrose and fructose 2-3 h after eating. These differences in the pattern of postprandial responses offer a potential explanation for the conflicting results on insulin sensitivity, with the possibility that increases in insulin exposure may affect insulin sensitivity through down-regulation of insulin action.

Glycemic index and disease

It has been suggested that foods with a high glycemic index are detrimental to health and that healthy people should be told to avoid these foods. This paper takes the position that not enough valid scientific data are available to launch a public health campaign to disseminate such a recommendation. This paper explores the glycemic index and its validity and discusses the effect of postprandial glucose and insulin responses on food intake, obesity, type 1 diabetes, and cardiovascular disease. Presented herein are the reasons why it is premature to recommend that the general population avoid foods with a high glycemic index.