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.

Effects of whey proteins on glycaemia and insulinaemia to an oral glucose load in healthy adults; a dose-response study.

BACKGROUND/OBJECTIVES: Whey proteins have insulinogenic properties and the effect appears to be mediated from a postprandial plasma amino-acid (AA) response. The aim was to study the possible dose-response relationship between whey intake and glycaemic-, insulinaemic- and plasma AA responses. SUBJECTS/METHODS: Twelve healthy volunteers participated in the study. They were provided three whey protein drinks, containing 4.5, 9 or 18 g protein as breakfast meals in random order. All meals contained 25 g available carbohydrates (glucose). The same amount of glucose in water was used as reference. RESULTS: Linear dose-response relations were found between whey protein intake and postprandial glycaemia, insulinaemia and plasma AAs. The two highest doses, 18 g and 9 g, significantly reduced postprandial glycaemia (incremental area under the curve (iAUC) 0-120 min; P ≤ 0.05). The 18 g dose significantly increased the insulin response (iAUC 0-120 min; P ≤ 0.05). All measured plasma AAs (15 in total), except glutamic acid, responded in a dose-dependent way, and the 9 and 18 g doses resulted in significantly higher plasma levels of AAs compared with the reference. CONCLUSIONS: Whey protein affects glycaemia, insulinaemia and plasma AAs to a glucose load in a dose-dependent manner. Comparatively low doses of whey protein (9 g) reduced postprandial glycaemia significantly when added to a carbohydrate-rich meal.

Impact of postprandial glycaemia on health and prevention of disease.

Postprandial glucose, together with related hyperinsulinemia and lipidaemia, has been implicated in the development of chronic metabolic diseases like obesity, type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). In this review, available evidence is discussed on postprandial glucose in relation to body weight control, the development of oxidative stress, T2DM, and CVD and in maintaining optimal exercise and cognitive performance. There is mechanistic evidence linking postprandial glycaemia or glycaemic variability to the development of these conditions or in the impairment in cognitive and exercise performance. Nevertheless, postprandial glycaemia is interrelated with many other (risk) factors as well as to fasting glucose. In many studies, meal-related glycaemic response is not sufficiently characterized, or the methodology with respect to the description of food or meal composition, or the duration of the measurement of postprandial glycaemia is limited. It is evident that more randomized controlled dietary intervention trials using effective low vs. high glucose response diets are necessary in order to draw more definite conclusions on the role of postprandial glycaemia in relation to health and disease. Also of importance is the evaluation of the potential role of the time course of postprandial glycaemia.

Effects on cognitive performance of modulating the postprandial blood glucose profile at breakfast.

BACKGROUND/OBJECTIVES: Considering the importance of glucose as a brain substrate, the postprandial rate of glucose delivery to the blood could be expected to affect cognitive functions. The purpose was to evaluate to what extent the rate of glucose absorption affected measures of cognitive performance in the postprandial period. In addition, cognitive performance was evaluated in relation to individual glucoregulation. SUBJECTS/METHODS: A white wheat bread (WWB) enriched with guar gum (G-WWB) with the capacity to produce a low but sustained blood glucose net increment was developed. The G-WWB was evaluated in the postprandial period after breakfast with respect to effects on cognitive function (working memory and selective attention (SA)) in 40 healthy adults (49-71 years, body mass index 20-29 kg/m(2)), using a high glycaemic index WWB for comparison in a randomised crossover design. RESULTS: The G-WWB improved outcome in the cognitive tests (SA test) in the later postprandial period (75-225 min) in comparison with the WWB (P<0.01). Subjects with better glucoregulation performed superior in cognitive tests compared with subjects with worse glucoregulation (P<0.05). CONCLUSIONS: Beneficial effects on cognitive performance were observed with the G-WWB in the late postprandial period. The positive effect is suggested to emanate from improved insulin sensitivity, possibly in a combination with an enhanced neural energy supply. The results highlight the importance of carbohydrate foods that induces a low but sustained blood glucose profile in enhancing postprandial cognitive functions.

A low glycaemic diet improves oral glucose tolerance but has no effect on ß-cell function in C57BL/6J mice.

AIM: Clinical studies have suggested a role for dietary glycaemic index (GI) in body weight regulation and diabetes risk. Here, we investigated the long-term metabolic effects of low and high glycaemic diets using the C57BL/6J mouse model. METHODS: Female C57BL/6J mice were fed low or high glycaemic starch in either low-fat or medium-fat diets for 22 weeks. Oral and intravenous glucose tolerance tests were performed to investigate the effect of the experimental diets on glucose tolerance and insulin resistance. RESULTS: In this study, a high glycaemic diet resulted in impaired oral glucose tolerance compared to a low glycaemic diet. This effect was more pronounced in the group fed a medium-fat diet, suggesting that a lower dietary fat content ameliorates the negative effect of a high glycaemic diet. No effect on body weight or body fat content was observed in either a low-fat diet or a medium-fat diet. Static incubation of isolated islets did not show any differences in basal (3.3 mM glucose) or glucose-stimulated (8.6 and 16.7 mM glucose) insulin secretion between mice fed a low or high glycaemic diet. CONCLUSION: Together, our data suggest that the impaired glucose tolerance seen after a high glycaemic diet is not explained by altered ß-cell function.

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.

Muesli with 4 g oat beta-glucans lowers glucose and insulin responses after a bread meal in healthy subjects.

OBJECTIVE: To evaluate the impact of an extruded muesli product based on beta-glucan-rich oat bran on postprandial glycaemia and insulinaemia. SUBJECT/DESIGN: The study is divided in two series. Blood glucose and serum insulin responses were studied after subjects consuming test meals including a serving of muesli with 3 g (series 1) and 4 g (series 2) of beta-glucans, respectively. The muesli was a component in a single serving packet with muesli and yoghurt. This was served together with white wheat bread in the morning after an overnight fast. The compositions were standardized to contain 50 g available carbohydrates. As a reference meal a serving packet without beta-glucans was included. The study was performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. Nineteen and thirteen healthy volunteers with normal body mass index were recruited for series 1 and 2, respectively. RESULTS: Muesli with 3 g of beta-glucans, included in a mixed bread meal, gave no significant differences in glycaemic response compared to a reference meal without muesli and beta-glucans. In contrast, muesli with 4 g of beta-glucans significantly (P<0.05) lowered the glucose and insulin responses compared to the reference meal. CONCLUSIONS: Muesli enriched with 4 g of beta-glucans reduces postprandial glucose and insulin levels to a breakfast based on high glycaemic index products. A total of 4 g of beta-glucans from oats seems to be a critical level for a significant decrease in glucose and insulin responses in healthy people.

Dietary supplementation with beta-glucan enriched oat bran increases faecal concentration of carboxylic acids in healthy subjects.

BACKGROUND/OBJECTIVE: Carboxylic acids (CAs), especially butyric acid, have been suggested to counteract colonic diseases, such as ulcerative colitis and colon cancer. Colonic formation of CAs can be influenced by the diet, but the concentrations and pattern formed need to be evaluated for different food products in humans. To elucidate how the colonic concentration of CAs in healthy subjects is influenced by dietary supplementation with oat bran, and whether the concentration varies over time and during consecutive days. SUBJECTS/METHODS: Twenty-five healthy subjects (age 24+/-1.3) were recruited to the study. The subjects were given 40 g beta-glucan enriched oat bran per day, corresponding to 20 g dietary fibre, in 4 slices of bread. CAs were analysed in faeces during three consecutive days after 0, 4, 8 and 12 weeks on this diet. RESULTS: The concentration of acetic, propionic, butyric, isobutyric and isovaleric acid was higher (P<0.05-0.001) after 8 weeks on the oat bran diet as compared with values at entry, whereas that of lactic acid was lower (P<0.05). After 12 weeks, the concentrations of acetic, propionic and isobutyric acid were still higher and that of lactic acid lower. The variation between individuals was considerable, whereas in the same individuals there was little variation. CONCLUSIONS: Oat bran increased the faecal concentration of CAs after 8 weeks, indicating an increased concentration also in the distal colon. The concentration of all main acids increased, except for lactic acid, which decreased. Oat bran may therefore have a preventive potential adjunct to colonic diseases.

Effects of GI vs content of cereal fibre of the evening meal on glucose tolerance at a subsequent standardized breakfast.

OBJECTIVE: To investigate if the improved glucose tolerance previously observed at breakfast following an evening meal with boiled barley kernels derives from colonic events related to the fermentation of the elevated amounts of indigestible carbohydrates present and/or from the low-GI features. SUBJECTS/METHODS: Twenty healthy volunteers aged 19-30 years. DESIGN: High-GI white wheat bread (WWB), WWB+barley dietary fibre (DF) corresponding to the DF content of barley kernels, low-GI spaghetti+ barley DF, spaghetti+double amounts of barley DF (2(*)DF), spaghetti+oat DF, or whole grain barley flour porridge, were provided as late evening meals. At a subsequent standardised WWB breakfast, B-glucose, s-insulin, p-SCFA, p-FFA, and breath hydrogen (H(2)) were measured. RESULTS: The B-glucose response (incremental areas under the curves (IAUC) 0-120 min and total areas under the curves 0-180 min) to the standardized breakfast was significantly lower after consuming spaghetti+2*DF in the evening compared with barley porridge (P=0.012). The spaghetti+2*DF meal also resulted in the highest breath H(2) excretion (P<0.02). The glucose IAUC (0-120 min) after the standardized breakfast was positively correlated to fasting p-FFA (r=0.29, P<0.02), and the total glucose area (0-180 min) was negatively correlated to the p-propionate level (0-30 min) (r=-0.24, P<0.02). CONCLUSIONS: The prolonged digestive and absorptive phase per se, like with a low-glycaemic index (GI) spaghetti evening meal, did not induce overnight benefits on glucose tolerance. Addition of barley DF in high amounts (2*DF) was required to improve overnight glucose tolerance. The correlations observed between glycaemia and p-propionate implicate colonic fermentation as a modulator of glucose tolerance through a mechanism leading to suppressed free fatty acids levels. It is proposed that the overnight benefits on glucose tolerance previously reported for boiled barley kernels is mediated through colonic fermentation of the prebiotic carbohydrates present in this product.

Glycaemic and satiating properties of potato products.

OBJECTIVE: To investigate glycaemic and satiating properties of potato products in healthy subjects using energy-equivalent or carbohydrate-equivalent test meals, respectively. SUBJECTS AND SETTING: Thirteen healthy subjects volunteered for the first study, and 14 for the second. The tests were performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. EXPERIMENTAL DESIGN AND TEST MEALS: All meals were served as breakfast in random order after an overnight fast. Study 1 included four energy-equivalent (1000 kJ) meals of boiled potatoes, french fries, or mashed potatoes; the latter varying in portion size by use of different amounts of water. The available carbohydrate content varied between 32.5 and 50.3 g/portion. Capillary blood samples were collected during 240 min for analysis of glucose, and satiety was measured with a subjective rating scale. Study 2 included four carbohydrate-equivalent meals (50 g available carbohydrates) of french fries, boiled potatoes served with and without addition of oil, and white wheat bread (reference). The energy content varied between 963 and 1534 kJ/portion. Capillary blood samples were collected during 180 min for analysis of glucose, and satiety was measured using a subjective rating scale. RESULTS: Study 1: boiled potatoes induced higher subjective satiety than french fries when compared on an energy-equivalent basis. The french fries elicited the lowest early glycaemic response and was less satiating in the early postprandial phase (area under the curve (AUC) 0-45 min). No differences were found in glycaemic or satiety response between boiled or mashed potatoes. Study 2: french fries resulted in a significantly lower glycaemic response (glycaemic index (GI)=77) than boiled potatoes either with or without addition of oil (GI=131 and 111, respectively). No differences were found in subjective satiety response between the products served on carbohydrate equivalence. CONCLUSIONS: Boiled potatoes were more satiating than french fries on an energy-equivalent basis, the effect being most prominent in the early postprandial phase, whereas no difference in satiety could be seen on a carbohydrate-equivalent basis. The lowered GI for french fries, showing a typical prolonged low-GI profile, could not be explained by the fat content per se.

Effects of GI and content of indigestible carbohydrates of cereal-based evening meals on glucose tolerance at a subsequent standardised breakfast.

OBJECTIVE: To evaluate the impact of four low-glycaemic index (GI) and one high-GI cereal-based evening meals on glucose tolerance at a subsequent standardised breakfast. DESIGN: Wheat kernels, barley kernels, spaghetti, spaghetti with added wheat bran and white wheat bread (WWB) were consumed in the evening in a random order at five different occasions. At the subsequent breakfast, blood glucose, serum insulin, plasma short chain fatty acid, plasma free fatty acid (FFA) and breath hydrogen were measured. SETTING: The study was performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. SUBJECTS: Fifteen healthy volunteers were recruited. One subject was later excluded owing to abnormal blood glucose values. RESULTS: The blood glucose response (0-120 min) to the standardised breakfast was significantly lower after consuming barley kernels in the evening compared with evening meals with WWB (P=0.019) or spaghetti+wheat bran (P=0.046). There were no significant differences in insulin concentrations at breakfast. Breath hydrogen excretion at breakfast was significantly higher after an evening meal with barley kernels compared with WWB, wheat kernels or spaghetti (P=0.026, 0.026 and 0.015, respectively), and the concentration of plasma propionate at breakfast was significantly higher following an evening meal with barley kernels compared with an evening meal with WWB (P=0.041). In parallel, FFA concentrations were significantly lower after barley kernels compared with WWB (P=0.042) or spaghetti evening meals (P=0.019). CONCLUSIONS: The improved glucose tolerance at breakfast, following an evening meal with barley kernels appeared to emanate from suppression of FFA levels, mediated by colonic fermentation of the specific indigestible carbohydrates present in this product, or, to the combination of the low-GI features and colonic fermentation.

A dietary exchange of common bread for tailored bread of low glycaemic index and rich in dietary fibre improved insulin economy in young women with impaired glucose tolerance.

OBJECTIVE: To study the possibility of improving blood lipids, glucose tolerance and insulin sensitivity in women with impaired glucose tolerance and a history of gestational diabetes by merely changing the glycaemic index (GI) and dietary fibre (DF) content of their bread. DESIGN: Randomized crossover study where test subjects were given either low GI/high DF or high GI/low DF bread products during two consecutive 3-week periods, separated by a 3-week washout period. An intravenous glucose tolerance test followed by a euglycaemic-hyperinsulinaemic clamp was performed on days 1 and 21 in both the high- and low-GI periods, to assess insulin secretion and insulin sensitivity. Blood samples were also collected on days 1 and 21 for analysis of fasting levels of glucose, insulin, HDL-cholesterol and triacylglycerols (TG). SETTING: Lund University, Sweden. SUBJECTS: Seven women with impaired glucose tolerance. RESULTS: The study shows that a modest dietary modification, confined to a lowering of the GI character and increasing cereal DF of the bread products, improved insulin economy as judged from the fact that all women lowered their insulin responses to the intravenous glucose challenge on average by 35% (0-60 min), in the absence of effect on glycaemia. No changes were found in fasting levels of glucose, insulin, HDL-cholesterol or TG. CONCLUSION: It is concluded that a combination of low GI and a high content of cereal DF has a beneficial effect on insulin economy in women at risk of developing type II diabetes. This is in accordance with epidemiological data, suggesting that a low dietary GI and/or increased intake of whole grain prevent against development of type II diabetes. SPONSORSHIP: Supported by grants from Cerealia Research Foundation.

Determination of glycaemic index; some methodological aspects related to the analysis of carbohydrate load and characteristics of the previous evening meal.

OBJECTIVES: To determine the possible differences in glycaemic index (GI) depending on (1) the analytical method used to calculate the 'available carbohydrate' load, that is, using carbohydrates by difference (total carbohydrate by difference, minus dietary fibre (DF)) as available carbohydrates vs available starch basis (total starch minus resistant starch (RS)) of a food rich in intrinsic RS and (2) the effect of GI characteristics and/or the content of indigestible carbohydrates (RS and DF) of the evening meal prior to GI testing the following morning. DESIGN: Blood glucose and serum insulin responses were studied after subjects consuming (1) two levels of barley kernels rich in intrinsic RS (15.2%, total starch basis) and (2) after a standard breakfast following three different evening meals varying in GI and/or indigestible carbohydrates: pasta, barley kernels and white wheat bread, respectively. SUBJECTS: Healthy adults with normal body mass index. RESULTS: (1) Increasing the portion size of barley kernels from 79.6 g (50 g 'available carbohydrates') to 93.9 g (50 g available starch) to adjust for its RS content did not significantly affect the GI or insulin index (11). (2) The low GI barley evening meal, as opposed to white wheat bread and pasta evening meals, reduced the postprandial glycaemic and insulinaemic (23 and 29%, respectively, P < 0.05) areas under the curve at a standardized white bread breakfast fed the following morning. CONCLUSION: (1) Increasing portion size to compensate for the considerable portion of RS in a low GI barley product had no significant impact on GI or II. However, for GI testing, it is recommended to base carbohydrate load on specific analyses of the available carbohydrate content. (2) A low GI barley evening meal containing high levels of indigestible carbohydrates (RS and DF) substantially reduced the GI and II of white wheat bread determined at a subsequent breakfast meal.

Vinegar dressing and cold storage of potatoes lowers postprandial glycaemic and insulinaemic responses in healthy subjects.

OBJECTIVE: To investigate the effects of cold storage and vinegar addition on glycaemic and insulinaemic responses to a potato meal in healthy subjects. SUBJECTS AND SETTING: A total of 13 healthy subjects volunteered for the study, and the tests were performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. Experimental design and test meals:The study included four meals; freshly boiled potatoes, boiled and cold stored potatoes (8 degrees C, 24 h), boiled and cold stored potatoes (8 degrees C, 24 h) with addition of vinaigrette sauce (8 g olive oil and 28 g white vinegar (6% acetic acid)) and white wheat bread as reference. All meals contained 50 g available carbohydrates and were served as a breakfast in random order after an overnight fast. Capillary blood samples were collected at time intervals during 120 min for analysis of blood glucose and serum insulin. Glycaemic (GI) and insulinaemic indices (II) were calculated from the incremental areas using white bread as reference. RESULTS: Cold storage of boiled potatoes increased resistant starch (RS) content significantly from 3.3 to 5.2% (starch basis). GI and II of cold potatoes added with vinegar (GI/II=96/128) were significantly reduced by 43 and 31%, respectively, compared with GI/II of freshly boiled potatoes (168/185). Furthermore, cold storage per se lowered II with 28% compared with the corresponding value for freshly boiled potatoes. CONCLUSION: Cold storage of boiled potatoes generated appreciable amounts of RS. Cold storage and addition of vinegar reduced acute glycaemia and insulinaemia in healthy subjects after a potato meal. The results show that the high glycaemic and insulinaemic features commonly associated with potato meals can be reduced by use of vinegar dressing and/or by serving cold potato products.

Vinegar supplementation lowers glucose and insulin responses and increases satiety after a bread meal in healthy subjects.

OBJECTIVE: To investigate the potential of acetic acid supplementation as a means of lowering the glycaemic index (GI) of a bread meal, and to evaluate the possible dose-response effect on postprandial glycaemia, insulinaemia and satiety. SUBJECTS AND SETTING: In all, 12 healthy volunteers participated and the tests were performed at Applied Nutrition and Food Chemistry, Lund University, Sweden. INTERVENTION: Three levels of vinegar (18, 23 and 28 mmol acetic acid) were served with a portion of white wheat bread containing 50 g available carbohydrates as breakfast in randomized order after an overnight fast. Bread served without vinegar was used as a reference meal. Blood samples were taken during 120 min for analysis of glucose and insulin. Satiety was measured with a subjective rating scale. RESULTS: A significant dose-response relation was seen at 30 min for blood glucose and serum insulin responses; the higher the acetic acid level, the lower the metabolic responses. Furthermore, the rating of satiety was directly related to the acetic acid level. Compared with the reference meal, the highest level of vinegar significantly lowered the blood glucose response at 30 and 45 min, the insulin response at 15 and 30 min as well as increased the satiety score at 30, 90 and 120 min postprandially. The low and intermediate levels of vinegar also lowered the 30 min glucose and the 15 min insulin responses significantly compared with the reference meal. When GI and II (insulinaemic indices) were calculated using the 90 min incremental area, a significant lowering was found for the highest amount of acetic acid, although the corresponding values calculated at 120 min did not differ from the reference meal. CONCLUSION: Supplementation of a meal based on white wheat bread with vinegar reduced postprandial responses of blood glucose and insulin, and increased the subjective rating of satiety. There was an inverse dose-response relation between the level of acetic acid and glucose and insulin responses and a linear dose-response relation between acetic acid and satiety rating. The results indicate an interesting potential of fermented and pickled products containing acetic acid.

Glucose and insulin responses to porridge and gruel meals intended for infants.

OBJECTIVE: The objective was to determine the glycaemic index (GI) and insulinaemic index (II) of some common products intended for infants; that is, three commercial porridges and one gruel. Also, the influence of added fruit components to porridge on postprandial metabolic responses was studied by comparing corresponding data with a matched model product without fruit. DESIGN: The volunteers were served the test products in random order following an overnight fast. A white bread was included as a reference product. Capillary blood samples were collected before and during 3 h after the meals. SETTING: The study was performed at the Department of Applied Nutrition and Food Chemistry, Lund University, Sweden. SUBJECTS: A total of 10 healthy volunteers, six men and four women, aged 24-41 y, with normal body mass indices, were recruited. RESULTS: The GIs (67-75) of the commercial porridges and gruel were significantly lower than for the white bread reference (P < 0.05). In contrast, the GI (79) of the model product (porridge without fruit) could not be distinguished from the reference. The IIs (112-149) for the commercial products and model products, respectively, were not significantly different from the reference. CONCLUSIONS: : The commercial porridges and gruel gave unexpectedly low GIs. In contrast, high IIs were noted. The inconsistency between GI and II could probably be explained by the insulinotrophic effect of the milk component in the products. The fruit and fruit juice added to some of the products had only minor effect on postprandial glycaemia. SPONSORSHIP: The Swedish Council for Forestry and Agricultural Research.

Glycaemic index methodology.

The glycaemic index (GI) concept was originally introduced to classify different sources of carbohydrate (CHO)-rich foods, usually having an energy content of >80 % from CHO, to their effect on post-meal glycaemia. It was assumed to apply to foods that primarily deliver available CHO, causing hyperglycaemia. Low-GI foods were classified as being digested and absorbed slowly and high-GI foods as being rapidly digested and absorbed, resulting in different glycaemic responses. Low-GI foods were found to induce benefits on certain risk factors for CVD and diabetes. Accordingly it has been proposed that GI classification of foods and drinks could be useful to help consumers make 'healthy food choices' within specific food groups. Classification of foods according to their impact on blood glucose responses requires a standardised way of measuring such responses. The present review discusses the most relevant methodological considerations and highlights specific recommendations regarding number of subjects, sex, subject status, inclusion and exclusion criteria, pre-test conditions, CHO test dose, blood sampling procedures, sampling times, test randomisation and calculation of glycaemic response area under the curve. All together, these technical recommendations will help to implement or reinforce measurement of GI in laboratories and help to ensure quality of results. Since there is current international interest in alternative ways of expressing glycaemic responses to foods, some of these methods are discussed.

Determination of the glycaemic index of foods: interlaboratory study.

OBJECTIVE: Practical use of the glycaemic index (GI), as recommended by the FAO/WHO, requires an evaluation of the recommended method. Our purpose was to determine the magnitude and sources of variation of the GI values obtained by experienced investigators in different international centres. DESIGN: GI values of four centrally provided foods (instant potato, rice, spaghetti and barley) and locally obtained white bread were determined in 8-12 subjects in each of seven centres using the method recommended by FAO/WHO. Data analysis was performed centrally. SETTING: University departments of nutrition. SUBJECTS: Healthy subjects (28 male, 40 female) were studied. RESULTS: The GI values of the five foods did not vary significantly in different centres nor was there a significant centrexfood interaction. Within-subject variation from two centres using venous blood was twice that from five centres using capillary blood. The s.d. of centre mean GI values was reduced from 10.6 (range 6.8-12.8) to 9.0 (range 4.8-12.6) by excluding venous blood data. GI values were not significantly related to differences in method of glucose measurement or subject characteristics (age, sex, BMI, ethnicity or absolute glycaemic response). GI values for locally obtained bread were no more variable than those for centrally provided foods. CONCLUSIONS: The GI values of foods are more precisely determined using capillary than venous blood sampling, with mean between-laboratory s.d. of approximately 9.0. Finding ways to reduce within-subject variation of glycaemic responses may be the most effective strategy to improve the precision of measurement of GI values.

Milk as a supplement to mixed meals may elevate postprandial insulinaemia.

OBJECTIVE: The objective was to evaluate the impact of milk added to a high-glycaemic index (GI) white bread meal vs a low-GI spaghetti meal, respectively, on postprandial glucose and insulin responses in healthy subjects. DESIGN: The volunteers were served the bread or spaghetti meals with either milk (200 or 400 ml, respectively) or water (400 ml) following an overnight fast. Capillary blood samples were collected before and during 3 h after the meals. SETTING: The study was performed at the Department of Applied Nutrition and Food Chemistry, Lund University, Sweden. SUBJECTS: Ten healthy volunteers, seven men and three women, aged 22-30 y, with normal body mass indices, were recruited. RESULTS: There was no difference in postprandial glucose area under curve (AUC) with and without added milk in the case of the high-GI bread meals. As could be expected, glucose AUC after the bread meal+water was higher than after the spaghetti meal+water. Milk added at 200 or 400 ml to the spaghetti meal did not affect glucose AUC. However, a significantly higher insulin AUC was seen with the bread meal with 400 ml milk (+65%) and the spaghetti meal with 200 ml or 400 ml milk (+300%), respectively, compared with corresponding test meal with water CONCLUSIONS: The addition of milk to a low-GI spaghetti meal may significantly increase the postprandial insulinaemia. Even an ordinary amount of milk (200 ml) increased the insulin AUC to a low-GI spaghetti meal to the same level as seen with white bread. The mechanism for the insulinotrophic effect of milk is not known, and the potential long-term metabolic consequences need to be elucidated. SPONSORSHIP: Swedish Dairy Association.

Content of short-chain fatty acids in the hindgut of rats fed processed bean (Phaseolus vulgaris) flours varying in distribution and content of indigestible carbohydrates.

Red kidney beans (Phaseolus vulgaris) processed to differ in distribution and content of indigestible carbohydrates were used to study hindgut fermentability and production of short-chain fatty acids (SCFA). Bean flours with low or high content of resistant starch (RS), mainly raw and physically-inaccessible starch, were obtained by milling the beans before or after boiling. Flours containing retrograded starch and with a high or low content of oligosaccharides were prepared by autoclaving followed by freeze-drying with or without the boiling water. Six diets were prepared from these flours yielding a total concentration of indigestible carbohydrates of 90 or 120 g/kg (dry weight basis). The total fermentability of the indigestible carbohydrates was high with all diets (80-87 %). Raw and physically-inaccessible starch was more readily fermented than retrograded starch (97-99 % v. 86-95 %; ). Non-starch glucans were fermented to a lesser extent than RS, but the fermentability was higher in the case of autoclaved (50-54 %) than boiled beans (37-41 %). The distribution between acetic, propionic and butyric acid in the caecum was similar for all diets, with a comparatively high percentage of butyric acid (approximately 18). However, with diets containing the high amounts of RS, the butyric acid concentration was significantly higher in the distal colon than in the proximal colon ( and for the high- and low-level diets respectively), whereas it remained constant, or decreased along the colon in the case of the other diets. Furthermore, the two diets richest in RS also promoted the highest percentages of butyric acid in the distal colon (24 and 17 v. 12 and 12-16 for the high- and low-level diets respectively).