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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.

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.

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.

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., (Published online 8 March 2006.)

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.

Background: Foods with a low glycemic index are increasingly being acknowledged as beneficial in relation to the insulin resistance syndrome. Certain organic acids can lower the glycemic index of bread products. However, the possible effect of acids in fermented milk products on the glycemic index and on insulinemic characteristics has not been addressed. The metabolic effects of fermented milk or pickled products used as additives to mixed meals have also not been addressed., Objectives: One objective was to characterize the glycemic and insulinemic responses after intake of regular or fermented milk products (study 1). In addition, the acute metabolic effect of fermented milk (yogurt) and pickled cucumber as supplements to a traditional breakfast based on a high-glycemic index bread was evaluated (study 2)., Design: Ten healthy volunteers were served different breakfast meals after an overnight fast. Capillary blood samples were collected before and during 2 (study 1) or 3 (study 2) h after the meal. White-wheat bread was used as a reference meal in both studies., Results: The lactic acid in the fermented milk products did not lower the glycemic and insulinemic indexes. Despite low glycemic indexes of 15-30, all of the milk products produced high insulinemic indexes of 90-98, which were not significantly different from the insulinemic index of the reference bread. Addition of fermented milk (yogurt) and pickled cucumber to a breakfast with a high-glycemic index bread significantly lowered postprandial glycemia and insulinemia compared with the reference meal. In contrast, addition of regular milk and fresh cucumber had no favorable effect on the metabolic responses., Conclusions: Milk products appear insulinotropic as judged from 3-fold to 6-fold higher insulinemic indexes than expected from the corresponding glycemic indexes. The presence of organic acids may counteract the insulinotropic effect of milk in mixed meals.

Accumulating data indicate that a diet characterized by low glycaemic-index (GI) foods not only improves certain metabolic ramifications of insulin resistance, but also reduces insulin resistance per se. Epidemiological data also suggest a protective role against development of non-insulin-dependent diabetes mellitus and cardiovascular disease. A major disadvantage in this connection is the shortage of low-GI foods, and many common starchy staple foods, such as bread products, breakfast cereals and potato products, have a high GI. Studies in our laboratory show that it is possible to significantly lower the GI of starchy foods, for example by choice of raw material and/or by optimizing the processing conditions. Such low-GI foods may or may not influence glucose tolerance at a subsequent meal. Consequently, certain low-GI breakfasts capable of maintaining a net increment in blood glucose and insulin at the time of the next meal significantly reduced post-prandial glycaemia and insulinaemia following a standardized lunch meal, whereas others had no 'second-meal' impact. These results imply that certain low-GI foods may be more efficient in modulating metabolism in the long term. Although the literature supports a linear correlation between the GI and insulinaemic index (II) of foods, this is not always the case. Consequently, milk products elicited elevated IIs, indistinguishable from a white bread reference meal, despite GIs in the lower range. This inconsistent behaviour of milk products has not been acknowledged, and potential metabolic consequences remain to be elucidated.