The effect of coingestion of fat on the glucose, insulin, and gastric inhibitory polypeptide responses to carbohydrate and protein

The postprandial response of gastric inhibitory polypeptide to various dietary fats in man

Gastric Inhibitory Polypeptide (GIP) is secreted in response to oral glucose, amino acid, and fats. In the presence of hyperglycemia, GIP augments nutrient stimulated insulin secretion. Studies looking at the effect of fat on GIP release, however, have focused primarily on corn oil, a polyunsaturated fat. To determine if other fats give similar GIP results to those with corn oil, nine normal subjects underwent four tolerance tests with fats derived from saturated (cocoa butter), monounsaturated (olive oil), or polyunsaturated (corn oil and fish oil) sources. Fifty grams of each triglyceride rich fat were ingested and serum cholesterol, triglyceride, glucose, insulin, and GIP levels were determined over a 180-minute period. Serum cholesterol, triglyceride, glucose, and insulin levels were similar following each fat tolerance test. GIP concentrations, however, were significantly lower (P less than 0.01) with the fish oil, when compared to the other fats studied. Similar GIP responses were observed with olive oil and corn oil, but both were higher than with the cocoa butter. These findings suggest that the source of fatty acids affect GIP secretion. The reason for these differences in serum GIP responses is uncertain, but is not readily explained by changes in serum glucose, insulin, or triglyceride concentrations. Since GIP augments nutrient stimulated insulin release 1-3 hours postprandially, the source of dietary fat consumed as part of a mixed meal could ultimately influence pancreatic beta cell insulin secretion.

The glycemic index: similarity of values derived in insulin-dependent and non-insulin-dependent diabetic patients

To see whether relative differences in the glycemic responses to different foods were similar in insulin-dependent (IDDM) and non-insulin-dependent diabetic patients (NIDDM) we determined the glycemic index (GI) of a total of 20 foods and mixed test meals in groups of IDDM and NIDDM volunteers. The mean GI values ranged from 32 in NIDDM and 41 in IDDM (pearled barley) to 105 in NIDDM and 111 in IDDM (bread with cheese and tomato). The correlation between the mean GI values in IDDM and NIDDM was highly significant (r = 0.927, p less than 0.001). The mean GI values for 15 of the 20 test meals was greater in IDDM than in NIDDM (mean of GI for all 20 foods, 76 in IDDM compared with 68 in NIDDM, p less than 0.005). However, the difference in GI between IDDM and NIDDM was t statistically significant for 19 of the 20 individual test meals. Greater within-individual variability of glycemic responses in IDDM probably accounts for the slightly greater mean GI value seen in IDDM compared with NIDDM. The addition of 32 g cheddar cheese to four foods which were also fed without cheese had no significant effect on the GI in NIDDM (mean GI of 68 without cheese compared with 72 for the meals with cheese), but had a small effect in IDDM where the mean GI was increased from 72 to 87 (p less than 0.05). However, despite small increases in glycemic response to foods with added cheese, the relative differences between foods were unaffected by the addition of cheese in both IDDM and NIDDM. It is concluded that mean GI values for foods are very similar in IDDM and NIDDM patients.

Post-prandial glucose and insulin responses to different types of spaghetti and bread

The glycemic response following ingestion of carbohydrate in various forms is different. The factors involved are not fully elucidated. In this study the glycemic and insulin responses to 50 g of carbohydrate in the form of white bread (WB), semolina bread (SB), white spaghetti (WS) and wholemeal spaghetti (BS) were compared in ten noninsulin-dependent diabetics. The responses were assessed by calculating the area under the curve. WB and SB had significantly higher glycemic responses compared with WS and BS (P less than 0.01). There was no difference in glycemic response between either form of bread, or either type of spaghetti. Similarly WB and SB had greater insulin responses than WS and BS (P less than 0.05). There was no difference in insulin response between WB and SB but BS had a greater response than WS (P less than 0.01) attributed to the higher protein content of BS. Thus, in this study the physical form of the food was a major factor influencing the glycemic response, and other factors such as particle size and fibre content had negligible effects.

The effect of guar gum and level and source of dietary fat on glucose tolerance in growing pigs

Six growing pigs (30-75 kg) were fed on semi-purified diets containing either 30 g maize oil/kg diet (LFM), 30 g soya-bean oil-tallow mixture (1:1, w/w)/kg diet (LFST) or 160 g soya-bean oil-tallow mixture (1:1, w/w)/kg diet (HFST) without and with the addition of guar gum (40 g/kg diet). Plasma glucose and insulin concentrations following twice daily feeding at 09.00 and 21.00 h were measured, during 24 h periods, in blood sampled from a permanent indwelling vena cava catheter. The source and level of dietary fat had no significant effect on pre-prandial plasma glucose or insulin concentrations except for insulin with diet LFST in the morning (P less than 0.05). Addition of guar gum to the diets had no significant effect on pre-prandial plasma glucose and insulin levels. The peak post-prandial plasma glucose and insulin levels were not significantly affected by dietary fat. The addition of guar gum, however, significantly reduced (P less than 0.05) the peak post-prandial plasma glucose concentration with diets LFM and LFST and also the peak plasma insulin concentration for all diets except for diet HFST in the morning. The time taken to reach the peak post-prandial plasma glucose and insulin concentrations was not significantly affected by dietary fat but it was increased by the addition of guar gum, although the differences were not always significant.

Influence of ingested load on postprandial insulin secretion. Rôle of gastric inhibitory polypeptide (GIP)

Two standard mixed meals including the same ingredients, and with different caloric values were ingested by 10 normal subjects. The plasma gastric inhibitory polypeptide (GIP) and immunoreactive insulin (IRI) as well as blood glucose (BG) were assayed during these meals at 0 (beginning of the meal) and after 30, 60, 120 and 180 min. BG was not significantly different between the two meals. At 30 min, the GIP peak was significantly higher in the case of the meal with the highest caloric (HC) value (499.5 +/- 112.0 vs. 273.4 +/- 57.5 pg/ml). Insulin was higher as well, although not in a significant way. At 120 min, the IRI was significantly higher (63.0 +/- 9.8 vs. 34.4 +/- 6.2 microU/ml) in the case of the HC meal. The HC meal induced a significantly higher insulinogenic index (0.29 +/- 0.05 vs. 0.14 +/- 0.07 mU litre g-1 ml-1). Integrated IRI and GIP responses of the HC meal were significantly higher than those of the meal with the lowest caloric value (IRI : 7.9 +/- 1.1 vs. 4.9 +/- 0.6 mU ml-1 180 min-1; GIP : 53.3 +/- 20.5 vs. 28.2 +/- 9.9 ng ml-1 180 min-1). The early (30 min) augmentation of IRI secretion after the ingestion of a larger meal is related to the insulinotropic action of the enhanced GIP secretion. The reasons for the late IRI increase are not obvious from this experiment. They might be of neural, nutrient, and/or intestinal origin.

Does a vegetarian diet reduce the occurrence of diabetes?

We propose the hypothesis that a vegetarian diet reduces the risk of developing diabetes. Findings that have generated this hypothesis are from a population of 25,698 adult White Seventh-day Adventists identified in 1960. During 21 years of follow-up, the risk of diabetes as an underlying cause of death in Adventists was approximately one-half the risk for all US Whites. Within the male Adventist population, vegetarians had a substantially lower risk than non-vegetarians of diabetes as an underlying or contributing cause of death. Within both the male and female Adventist populations, the prevalence of self-reported diabetes also was lower in vegetarians than in non-vegetarians. The associations observed between diabetes and meat consumption were apparently not due to confounding by over- or under-weight, other selected dietary factors, or physical activity. All of the associations between meat consumption and diabetes were stronger in males than in females.

Effect of Acarbose on the production of hydrogen and methane and on hormonal parameters in young adults under standardized low-fibre mixed diets

Short and middle term effects of Acarbose were studied in volunteers on a standardized, low-fibre, mixed diet for the development of tolerance phenomena with gas exhalations and some peptide hormone levels as main parameters. Both hydrogen and methane were measured quantitatively as diurnal profiles. Acarbose caused an about 20-fold increase of H2 exhalation and had only moderate effects on methane production, indicating the presence of fermentable carbohydrates in the large bowel. Methanogenic individuals exhaled significantly less H2 than did non-methanogenic subjects. Changes in blood glucose, serum insulin, GIP, gastrin, and plasma glucagon, caused by Acarbose, reflected delayed glucose absorption and were plausible within the regulatory framework of carbohydrate assimilation. When the Acarbose regime was maintained for 5 weeks on a controlled diet, abdominal sensations like e.g. meteorism declined remarkably while carbohydrate fermentation remained high and lowered GIP was sustained. Thus functional responses of the gastro-intestinal tract to altered carbohydrate supplies, elicited by Acarbose, were found by 3 independent parameters: anaerobic gas production, peptide hormone levels, and subjective abdominal sensations. The objective parameters seem to remain constant in the longer run, while subjective parameters show long-term adaptation.