Modifying effects of alcohol on the postprandial glucose and insulin responses in healthy subjects.

BACKGROUND: Moderate alcohol consumption associates with lower risk of type 2 diabetes, but in postprandial studies, alcohol induced impaired insulin sensitivity. The measurement of the glycemic index (GI) for beer has been considered challenging because of its low carbohydrate content. Therefore, imputed GI values from 36 to 95 on the basis of carbohydrate-rich beverages have been used for beer in epidemiologic studies. OBJECTIVES: We investigated the acute effects of alcohol on glucose and insulin responses and measured GIs and insulinemic indexes (IIs) of nonalcoholic and alcoholic beers. DESIGN: In a crossover design, 10 healthy volunteers were served beer with 4.5% alcohol by volume, nonalcoholic beer, and a glucose solution with alcohol once and the reference glucose solution twice. Each portion contained 25 g available carbohydrate, and the beer and glucose solution with alcohol contained 21 g alcohol. Capillary blood samples were collected up to 2 h after ingestion, and the incremental AUCs (IAUCs), GIs, and IIs were calculated. RESULTS: Compared with the reference glucose solution, the glucose solution with alcohol produced an 18% higher postprandial glucose IAUC (P = 0.03) and had no significant effect on the insulin IAUC. Compared with the reference glucose solution, beer had no significant effect on glucose or insulin IAUCs, and nonalcoholic beer tended to reduce the glucose IAUC (P = 0.06) but not the insulin IAUC. GIs of beer and nonalcoholic beer were 119 and 80, and IIs were 130 and 88, respectively. CONCLUSIONS: Alcohol increases the postprandial glucose response, probably through impaired insulin sensitivity. GI values published for alcohol-containing beers have underestimated the true glycemic effects.

Coffee does not modify postprandial glycaemic and insulinaemic responses induced by carbohydrates.

BACKGROUND: Strong epidemiological evidence suggests that coffee consumption is associated with lower risk of type 2 diabetes. In postprandial studies, however, caffeine consumption has been associated with impaired glucose regulation. AIM OF THE STUDY: To study the acute effects of coffee and caffeine-containing soft drinks on glycaemic and insulinaemic responses. DESIGN: Twelve healthy volunteers were served each test food once and the reference glucose solution twice, containing 50 g of available carbohydrates, after an overnight fast at 1-week intervals in a random order. Capillary blood samples were drawn at 15-30 min intervals for 2 h after each study meal. The incremental areas under the curve (IAUC), glycaemic index (GI) and insulinaemic index (II), were calculated to estimate the glycaemic and insulinaemic responses. RESULTS: Glucose and insulin responses of coffees with glucose containing 150 or 300 mg of caffeine did not differ from responses of pure glucose solution; the GIs were 104 and 103, and the IIs were 89 and 92, respectively. When a bun or sucrose and milk were consumed together with coffee, lower GI values and insulin responses were observed, reflecting the carbohydrate quality and protein content of the accompaniments. Sucrose-sweetened cola produced a high GI value of 90 and an II of 61. CONCLUSIONS: Coffee does not modify glycaemic and insulinaemic responses when ingested with a carbohydrate source. Therefore, there is no need to avoid coffee as a choice of beverage in GI testing.

Protein and fat modify the glycaemic and insulinaemic responses to a mashed potato-based meal.

Potatoes, especially mashed potatoes, are known to result in high glycaemic and insulinaemic responses. However, in most meals, potatoes are accompanied by other foods. The objective of the present study was to investigate how glycaemic and insulinaemic responses to a mashed potato meal changed when a high-fat food (rapeseed oil), a high-protein food (chicken breast) and/or salad were added to the meal. Healthy subjects (n 11) ingested the test meals once and the reference food (glucose solution) twice in a random order at 1-week intervals. Capillary blood samples were then drawn for 2 h, and glucose and insulin were analysed. The 2 h glycaemic responses to six mashed potato-containing meals varied more than twofold. The glycaemic index (GI) of pure mashed potato was 108, whereas combined with chicken breast, rapeseed oil and salad, it was only 54. The latter GI also differed considerably from its predicted value of 103, which was based on the individual GI of the components of the meal. The insulinaemic indices of the mashed potato-based meals varied between 94 and 148. Chicken breast in the meal increased the insulinaemic response, and rapeseed oil diminished it. However, the insulinaemic response to mashed potato with chicken breast and rapeseed oil was lower than that to mashed potato alone. In conclusion, the protein, fat and salad contents of a meal exert considerable influence on the glycaemic and insulinaemic responses to mashed potatoes. Furthermore, the estimation of the GI of a mixed meal by calculation is imprecise.

Impact of overweight and glucose tolerance on postprandial responses to high- and low-glycaemic index meals.

The beneficial effects of a low-glycaemic index (GI) meal on postprandial glucose and insulin levels have been demonstrated. However, limited data are available on the impact of overweight and glucose tolerance on postprandial responses to different GI meals. Our aim was to study the effects of physiological characteristics on postprandial glucose, insulin and lipid responses and the relative glycaemic response (RGR) of a low-GI (LGI) and a high-GI (HGI) meal. We recruited twenty-four normal-weight and twenty-four overweight subjects, twelve with normal glucose tolerance (NGT) and twelve with impaired glucose tolerance (IGT) in each group. Both test meals were consumed once and the glucose reference twice. Blood glucose and insulin were measured in the fasting state and over a 2 h period after each study meal, and TAG and NEFA were measured in the fasting state and over a 5 h period. The glucose responses of subjects with IGT differed significantly from those of subjects with NGT. The highest insulin responses to both meals were observed in overweight subjects with IGT. Physiological characteristics did not influence TAG or NEFA responses or the RGR of the meals. The LGI meal resulted in lower glucose (P < 0·001) and insulin (P < 0·001) responses, but higher TAG responses (P < 0·001), compared with the HGI meal. The GI of the meals did not affect the NEFA responses. In conclusion, the LGI meal causes lower glucose and insulin responses, but higher TAG responses, than the HGI meal. The RGR of the meals does not differ between normal-weight and overweight subjects with NGT or IGT.

Methodologic considerations in the measurement of glycemic index: glycemic response to rye bread, oatmeal porridge, and mashed potato.

BACKGROUND: Methodologic choices affect measures of the glycemic index (GI). The effects on GI values of blood sampling site, reference food type, and the number of repeat tests have been insufficiently determined. OBJECTIVE: The objective was to study the effect of methodologic choices on GI values. Comparisons were made between venous and capillary blood sampling and between glucose and white bread as the reference food. The number of tests needed for the reference food was assessed. Rye bread, oatmeal porridge, and instant mashed potato were used as the test foods. DESIGN: Twelve healthy volunteers were served each test food once and both reference foods 3 times at 1-wk intervals in a random order after they had fasted overnight. Capillary and venous blood samples were drawn at intervals for 3 h after each study meal. RESULTS: GIs and their CVs based on capillary samples were lower than those based on venous samples. Two tests of glucose solution as the reference provided stable capillary GIs for the test foods. The capillary GIs did not differ significantly when white bread was used as the reference 1, 2, or 3 times, but the variation was lower when tests were performed 2 and 3 times. Capillary GIs with white bread as the reference were 1.3 times as high as those with glucose as the reference. The capillary GIs of rye bread, oatmeal porridge, and mashed potato were 77, 74, and 80, respectively, with glucose as the reference. CONCLUSIONS: Capillary blood sampling should be used in the measurement of GI, and reference tests with glucose or white bread should be performed at least twice.