Effect of source of dietary fats on serum glucose,insulin, and gastric inhibitory polypeptide responses to mixed test meals in subjects with non-insulin dependent diabetes mellitus.

We recently demonstrated that normal subjects given mixed test meals of varying fatty acid composition showed significantly greater serum insulin responses to meals enriched with polyunsaturated fat as compared to those in which the fat content was derived from saturated fatty acids. To determine if a similar phenomenon occurs in subjects with non-insulin dependent diabetes mellitus (NIDDM), serum glucose, insulin, C-peptide, and gastric inhibitory polypeptide (GIP) responses to three mixed test meals of varying fatty acid composition were assessed in twelve subjects with NIDDM. Baseline means (+/? SEM) fasting serum glucose concentration was 205 +/? 15 mg/dl and mean glycosylated hemoglobin was 8.5 +/? 0.5%. Fatty acids in the test meals were either saturated fats, or polyunsaturated fats derived from vegetables or fish. Each test meal provided 40% of the subjects' calculated daily caloric requirement and contained approximately 45% carbohydrate, 40% fat, and 15% protein. No appreciable differences in serum glucose, insulin, and C-peptide responses occurred during the three mixed test meals. Although GIP values were higher in the saturated fat and the vegetable meals when compared to the fish meal, the differences did not reach statistical significance. The inability of NIDDM subjects to evoke a greater insulin response to polyunsaturated fatty acids than to saturated fatty acids suggests another pathogenetic factor contributing to their glucose intolerance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polyunsaturated fatty acids augment insulin secretion

Carbohydrate intolerance is positively correlated with animal fat consumption and is more common in beef eating populations. In contrast, individuals consuming diets comprised of polyunsaturated fats have a lower incidence of diabetes mellitus. To test the hypothesis that dietary fats may influence carbohydrate metabolism, serum glucose, insulin, and gastric inhibitory polypeptide (GIP) responses to three mixed test meals of varying fatty acid composition were assessed in 12 normal subjects. Fatty acids in the meals were either saturated fats or polyunsaturated fats derived from vegetables or fish. Each test meal provided 40% of a subject's calculated daily caloric requirement and contained approximately 45% carbohydrate, 40% fat, and 15% protein. Serum insulin responses were 62% higher (p less than 0.01) after the fish and 39% higher (p less than 0.01) after the vegetable meals compared to the saturated fat meal. No significant differences in insulin responses were observed between the vegetable and fish meals. Serum glucose concentration was slightly higher (p less than 0.02) during the fish meal than with the vegetable or saturated fat meals. The GIP levels were comparable following the fish and vegetable meals and were 25% lower than those observed with the saturated fat meal. These findings suggest that diets enriched with polyunsaturated fatty acids augment insulin secretion significantly more than a diet comprised primarily of saturated fatty acids. The mechanism for this increased insulin secretion is unknown but did not appear to be mediated through differences in serum glucose values or through the insulin-otrophic effects of GIP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Magnesium and lipids in cardiovascular disease.

Carbohydrate intolerance is positively correlated with animal fat consumption and is more common in beef eating populations. In contrast, individuals consuming diets comprised of polyunsaturated fats have a lower incidence of diabetes mellitus. To test the hypothesis that dietary fats may influence carbohydrate metabolism, serum glucose, insulin, and gastric inhibitory polypeptide (GIP) responses to three mixed test meals of varying fatty acid composition were assessed in 12 normal subjects. Fatty acids in the meals were either saturated fats or polyunsaturated fats derived from vegetables or fish. Each test meal provided 40% of a subject's calculated daily caloric requirement and contained approximately 45% carbohydrate, 40% fat, and 15% protein. Serum insulin responses were 62% higher (p less than 0.01) after the fish and 39% higher (p less than 0.01) after the vegetable meals compared to the saturated fat meal. No significant differences in insulin responses were observed between the vegetable and fish meals. Serum glucose concentration was slightly higher (p less than 0.02) during the fish meal than with the vegetable or saturated fat meals. The GIP levels were comparable following the fish and vegetable meals and were 25% lower than those observed with the saturated fat meal. These findings suggest that diets enriched with polyunsaturated fatty acids augment insulin secretion significantly more than a diet comprised primarily of saturated fatty acids. The mechanism for this increased insulin secretion is unknown but did not appear to be mediated through differences in serum glucose values or through the insulin-otrophic effects of GIP.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Influence of breakfasts with different nutrient contents on glucose, C peptide, insulin, glucagon, triglycerides, and GIP in non-insulin-dependent diabetics

To examine the influence of coingestion of fat and protein in a mixed meal on carbohydrate metabolism, subjects with non-insulin-dependent diabetes mellitus (NIDDM) received three different breakfasts varying in the amount of fat and protein (group 1) or only in the amount of fat (group 2). Compared with the changes after a standard breakfast, insulin increased after the protein-rich meal and decreased after the fat-rich meal in group 1. Glucose and gastric inhibitory polypeptide (GIP) remained constant. In contrast, only GIP showed a significant increase after a high-fat meal in group 2. Thus, in NIDDM subjects, glucose and insulin responses to different mixed meals do not appear to be exclusively mediated by GIP. Protein was confirmed as a potent stimulator of insulin secretion. Other factors, such as an altered beta-cell response in diabetics to GIP or other incretions, must be considered to explain the reported results.     

High saturated fatty acid intake induces insulin secretion by elevating gastric inhibitory polypeptide levels in healthy individuals

Insulin resistance is central to the etiology of the metabolic syndrome cluster of diseases. Evidence suggests that a high-fat diet is associated with insulin resistance, which may be modulated by dietary fatty acid composition. We hypothesized that high saturated fatty acid intake increases insulin and gastric inhibitory polypeptide (GIP) secretion. To clarify the effect of ingested fatty acid composition on glucose levels, we conducted an intervention study to investigate the insulin and plasma GIP responses in 11 healthy women, including a dietary control. Subjects were provided daily control meals (F-20; saturated fatty acids/monounsaturated fatty acids/polyunsaturated fatty acids [S/M/P] ratio, 3:4:3) with 20 energy (E) % fat, followed by 2 isoenergetic experimental meals for 7 days each. These meals comprised 60 E% carbohydrate, 15 E% protein, and 30 E% fat (FB-30; high saturated fatty acid meal; S/M/P, 5:4:1; F-30: reduced saturated fatty acid meal; S/M/P, 3:4:3). On the second day of the F-20 and the last day of F-30 and FB-30, blood samples were taken before and 30, 60, and 120 minutes after a meal tolerance test. The plasma glucose responses did not differ between F-20 and FB-30 or F-30. However, insulin levels were higher after the FB-30 than after the F-20 (P < .01). The GIP response after the FB-30 was higher than that after the F-30 (P < .05). In addition, the difference in the incremental GIP between FB-30 and F-30 correlated significantly and positively with that of the insulin. These results suggest that a high saturated fatty acid content stimulates postprandial insulin release via increased GIP secretion.     

Polyunsaturated fats enhance peripheral glucose utilization in rats

Carbohydrate intolerance is positively correlated with saturated fat consumption. In contrast, individuals consuming diets comprised of polyunsaturated fatty acids (PUFA) have a lower incidence of diabetes mellitus (DM). To test the hypothesis that dietary fats may influence insulin sensitivity, insulin-stimulated glucose utilization was estimated in vivo in rats consuming diets enriched with saturated fatty acids (SFA) (cocoa butter), monounsaturated fatty acid (MUFA) (olive oil), or PUFA derived from corn or fish sources. Each test meal provided (as percentage of calories) 45% carbohydrate, 39% fat, and 16% protein. The meals were consumed over an 8-week period. Metabolic clearance rate (MCR) for glucose was significantly higher (p less than 0.01; 5.69 +/- 0.46 and 5.18 +/- 0.29 ml/kg/min) for diets containing fish and corn oil sources, respectively, when compared to olive oil (4.34 +/- 0.32 ml/kg/min) and cocoa butter (4.61 +/- 0.11 ml/kg/min). Although the MCR between the fish and corn oil diets were not significantly different, the steady state plasma insulin concentration was lower during the fish oil meal (75 +/- 20 microU/ml) when compared to the corn meal (112 +/- 13 microU/ml). Fasting plasma insulin concentrations were significantly lower (p less than 0.01) following the PUFA diets compared to the other two diets. Fasting plasma glucose levels, despite being lower in the fish meal, were insignificantly different among the four test meals. Lastly, body weights were comparable among the four groups tested. These results suggest that diets enriched with PUFA enhance peripheral glucose utilization significantly more than diets comprised of MUFA or SFA sources.(ABSTRACT TRUNCATED AT 250 WORDS)     

The amount and types of fatty acids acutely affect insulin,glycemic and gastrointestinal peptide responses but not satiety in metabolic syndrome subjects

Purpose

Limited clinical evidence is available on the effects of amount and types of dietary fats on postprandial insulinemic and gastrointestinal peptide responses in metabolic syndrome subjects. We hypothesized that meals enriched with designated: (1) amount of fats (50 vs 20 g), (2) fats with differing fatty acid composition (saturated, SFA; monounsaturated, MUFA or n-6 polyunsaturated fatty acids, PUFA) would affect insulinemic and gastrointestinal peptide releases in metabolic syndrome subjects.

Methods

Using a randomized, crossover and double-blinded design, 15 men and 15 women with metabolic syndrome consumed high-fat meals enriched with SFA, MUFA or n-6 PUFA, or a low-fat/high-sucrose (SUCR) meal. C-peptide, insulin, glucose, gastrointestinal peptides and satiety were measured up to 6 h.

Results

As expected, SUCR meal induced higher C-peptide (45 %), insulin (45 %) and glucose (49 %) responses compared with high-fat meals regardless of types of fatty acids (P < 0.001). Interestingly, incremental area under the curve (AUC_0-120min) for glucagon-like peptide-1 was higher after SUCR meal compared with MUFA (27 %) and n-6 PUFA meals (23 %) (P = 0.01). AUC_0-120min for glucose-dependent insulinotropic polypeptide was higher after SFA meal compared with MUFA (23 %) and n-6 PUFA meals (20 %) (P = 0.004). Significant meal x time interaction (P = 0.007) was observed for ghrelin, but not cholecystokinin and satiety.

Conclusions

The amount of fat regardless of the types of fatty acids affects insulin and glycemic responses. Both the amount and types of fatty acids acutely affect the gastrointestinal peptide release in metabolic syndrome subjects, but not satiety.

     

Differential effects of saturated and monounsaturated fatty acids on postprandial lipemia and incretin responses in healthy subjects.

BACKGROUND: Elevations of postprandial triacylglycerol-rich plasma lipoproteins and suppressions of HDL-cholesterol concentrations are considered potentially atherogenic. Long-term studies have shown beneficial effects of monounsaturated fatty acids (eg, oleic acid) on fasting lipid and lipoprotein concentrations in humans. A direct stimulatory effect of oleic acid on the secretion of glucagon-like peptide 1 (GLP-1) was shown in animal studies. OBJECTIVE: We compared the postprandial responses of glucose, insulin, fatty acids, triacylglycerol, gastric inhibitory polypeptide (GIP), and GLP-1 to test meals rich in saturated and monounsaturated fatty acids. DESIGN: Ten young, lean, healthy persons ingested 3 meals: an energy-free soup consumed with 50 g carbohydrate (control meal), the control meal plus 100 g butter, and the control meal plus 80 g olive oil. Triacylglycerol and retinyl palmitate responses were measured in total plasma, in a chylomicron-rich fraction, and in a chylomicron-poor fraction. RESULTS: No significant differences in glucose, insulin, or fatty acid responses to the 2 fat-rich meals were seen. Plasma triacylglycerol responses were highest after the butter meal, with chylomicron triacylglycerol rising 2.5-5-fold. Retinyl palmitate responses were higher and more prolonged after the butter meal than after the control and olive oil meals, whereas both postprandial HDL-cholesterol concentrations and GLP-1 and GIP responses were higher after the olive oil meal than after the butter meal. CONCLUSIONS: Olive oil induced lower triacylglycerol concentrations and higher HDL-cholesterol concentrations than butter, without eliciting differences in concentrations of glucose, insulin, or fatty acids. Furthermore, olive oil induced higher concentrations of GLP-1 and GIP than did butter, which may point to a relation between fatty acid composition, incretin responses, and triacylglycerol metabolism in the postprandial phase.     

Glucose and insulin responses in healthy women after intake of composite meals containing cod-, milk-, and soy protein

OBJECTIVE: To evaluate the metabolic effect of three different kinds of dietary proteins as part of composite meals with similar macronutrient composition in healthy subjects. DESIGN: A randomised meal study. SETTING: Metabolic ward. SUBJECTS AND METHODS: In total, 17 healthy women, 30-65 years old, consumed three meals in randomised order. The meals consisted of foodstuffs with similar nutrient composition but different types of protein (cod, cottage cheese, or soy protein isolate). The distribution of energy from protein, fat and carbohydrates was 33, 26, and 41 energy percent, respectively. Total amount of energy was 2300 kJ. Blood samples were drawn for assay of B-glucose, S-insulin, S-free fatty acids, S-triglycerides, and C-peptide in the fasting state and at seven times (20, 40, 60, 90, 120, 180, and 240 min) after starting to eat the test meal. RESULTS: The blood glucose response after the cod protein meal differed from that of the soy protein meal, with a larger area under the curve (AUC) calculated up to 120 min. The serum insulin response after the milk protein meal differed from that of the cod protein meal with a larger AUC calculated up to 240 min. The insulin/C-peptide and the insulin/glucose ratios differed between the meals; the insulin/C-peptide ratio was higher after the milk protein meal compared to the cod, and soy protein meal at 120 min. The insulin/glucose ratio was lower after the cod protein meal compared to the milk, and soy protein meals at 120 min. The results showed that the metabolic responses differed after meals with similar macronutrient composition containing cod-, milk-, or soy protein.     

Acute effects of meal fatty acid composition on insulin sensitivity in healthy post-menopausal women

Postprandial plasma insulin concentrations after a single high-fat meal may be modified by the presence of specific fatty acids although the effects of sequential meal ingestion are unknown. The aim of the present study was to examine the effects of altering the fatty acid composition in a single mixed fat-carbohydrate meal on glucose metabolism and insulin sensitivity of a second meal eaten 5 h later. Insulin sensitivity was assessed using a minimal model approach. Ten healthy post-menopausal women underwent four two-meal studies in random order. A high-fat breakfast (40 g fat) where the fatty acid composition was predominantly saturated fatty acids (SFA), n-6 polyunsaturated fatty acids (PUFA), long-chain n-3 PUFA or monounsaturated fatty acids (MUFA) was followed 5 h later by a low-fat, high-carbohydrate lunch (5.7 g fat), which was identical in all four studies. The plasma insulin response was significantly higher following the SFA meal than the other meals after both breakfast and lunch (P<0.006) although there was no effect of breakfast fatty acid composition on plasma glucose concentrations. Postprandial insulin sensitivity (SI(Oral)) was assessed for 180 min after each meal. SI(Oral) was significantly lower after lunch than after breakfast for all four test meals (P=0.019) following the same rank order (SFA < n-6 PUFA < n-3 PUFA < MUFA) for each meal. The present study demonstrates that a single meal rich in SFA reduces postprandial insulin sensitivity with 'carry-over' effects for the next meal.     

Butter differs from olive oil and sunflower oil in its effects on postprandial lipemia and triacylglycerol-rich lipoproteins after single mixed meals in healthy young men

Accumulation of postprandial triacylglycerol-rich lipoproteins is generated by assimilation of ingested dietary fat and has been increasingly related to atherogenic risk. Nevertheless, the influence of different kinds of dietary fatty acids on postprandial lipid metabolism is not well established, except for (n-3) polyunsaturated long-chain fatty acids. Our goal was to evaluate the effects of test meals containing a common edible fat source of saturated (butter), monounsaturated (olive oil) or (n-6) polyunsaturated (sunflower oil) fatty acids on postprandial lipid and triacylglycerol-rich lipoprotein responses. After a 12-h fast, 10 healthy young men ingested mixed meals containing 0 g (control) or 40 g fat, provided as butter, olive oil or sunflower oil in a random order. Fasting and postmeal blood samples were collected for 7 h. The no-fat test meal did not elicit any change over baseline except for plasma phospholipids, insulin and nonesterified fatty acids. Conversely, the three fat-containing meals elicited bell-shaped postprandial changes (P < 0.05) in serum triacylglycerols, free and esterified cholesterol, and nonesterified fatty acids. The butter meal induced a lower postprandial rise of triacylglycerols in serum and chylomicrons (incremental AUC, mmol.h/L: 0.72) than the two unsaturated oils (olive oil: 1.6, sunflower oil: 1.8), which did not differ. Circulating chylomicrons were smaller after the butter meal than after the two vegetable oil meals. The in vitro susceptibility of circulating chylomicrons to hydrolysis by postheparin plasma was higher after sunflower oil than after butter or olive oil. We conclude that butter results in lower postprandial lipemia and chylomicron accumulation in the circulation of young men than olive or sunflower oils after consumption of a single mixed meal.     

Trans monounsaturated fatty acids and saturated fatty acids have similar effects on postprandial flow-mediated vasodilation

OBJECTIVE: Several studies suggest that a fatty meal impairs flow-mediated vasodilation (FMD), a measure of endothelial function. We tested whether the impairment was greater for trans fats than for saturated fats. We did this because we previously showed that replacement of saturated fats by trans fats in a controlled diet decreased FMD after 4 weeks. DESIGN: We fed 21 healthy men two different test meals with 0.9-1.0 g fat/kg body weight in random order: one rich in saturated fatty acids (Sat), mainly from palm kernel fat, and one rich in trans fatty acids (Trans) from partially hydrogenated soy bean oil. The study was performed in our metabolic ward. We had complete data for both diets of 21 men. RESULTS: FMD increased from a fasting value of 2.3+/-2.0% of the baseline diameter to 3.0+/-1.7% after the Sat test meal (95% CI for change -0.33, 1.70) and from 2.7+/-2.3 to 3.1+/-2.0% after the Trans test meal (95% CI for change -0.57, 1.29). The increase after the Sat meal was 0.22 (-1.18-1.61) FMD% higher than after the Trans meal. Serum triacylglycerols increased by 0.46+/-0.36 mmol/l after the Sat test meal and by 0.68+/-0.59 mmol/l after the Trans test meal; a difference of 0.23 (0.07, 0.39) mmol/l. Serum HDL-cholesterol was hardly affected by the test meals. The activity of serum paraoxonase, an esterase bound to HDL, increased slightly after the two test meals but the difference between meals was not significant. CONCLUSION: FMD was not impaired and not different after test meals with saturated or trans fatty acids. Thus, differences in long-term effects of these fats are not caused by differences in acute effects on the vascular wall.     

Postprandial lipid and carbohydrate responses after the ingestion of a casein-enriched mixed meal

BACKGROUND: Postprandial lipemia is markedly modulated when carbohydrates are added to a fatty meal. The effect of added protein is less known, however, and the data are controversial. OBJECTIVE: We investigated the effects of casein added to various fat-rich meals in the absence and presence of oligosaccharides. DESIGN: Four different test meals were given to 24 healthy volunteers: 1) fat alone, consisting of 3 g cream/kg body wt; 2) fat plus 75 g oligosaccharides; 3) fat plus 50 g sodium caseinate; and 4) a combination of all 3 components. Blood samples were taken before the meals and 1, 2, 3, 4, 5, 6, 7, and 8 h thereafter. The variables measured were serum free fatty acids, arginine, glucose, insulin, and C-peptide as well as triacylglycerol in serum, in chylomicrons, and in VLDL. Gastric emptying was monitored with the use of a (13)C breath test. RESULTS: Addition of oligosaccharides resulted in the known delay and reduction in postprandial lipemia. Casein caused additional effects: chylomicrons were further reduced and delayed, independently of gastric emptying. C-peptide and insulin, as expressed by their areas under the curves, were raised not only during the early response to the glucose load but also in the postabsorptive state. Concentrations of free fatty acids, which were markedly suppressed by 24% after oligosaccharides alone, were lowered a further 20% after the addition of casein. CONCLUSIONS: Casein added to a fatty meal lowers free fatty acids markedly in the postprandial and postabsorption phases, probably via its insulinotropic activity. Postprandial lipemia is also moderately reduced.     

The degree of fat saturation does not alter glycemic,insulinemic or satiety responses to a starchy staple in healthy men

Inclusion of fat reduces the glycemic response to a carbohydate meal, although the effect of different types of fat on glycemic, insulinemic and satiety responses is unclear. Ten healthy men received 50-g carbohydrate portions of mashed potato with isoenergetic amounts of butter (saturated fatty acid), Sunola oil (monounsaturated fatty acid) or sunflower oil (PUFA) and two 50-g glucose loads on separate days. Capillary blood was collected at regular intervals for 2 h. Satiety ratings were assessed by use of a rating scale. The glycemic index (GI), insulin index (II) and satiety index (SI) scores were calculated. Energy intakes from a meal consumed ad libitum at 2 h and for the remainder of the day were quantified. The GI values ranged from 68 +/- 8 to 74 +/- 10 and the II values ranged from 113 +/- 10 to 122 +/- 17, but there was no effect of fat type. SI scores and subsequent energy intake did not differ among the test meals. Substitution of unsaturated fats for saturated fatty acids had no acute benefits on postprandial glycemia, insulin demand or short-term satiety in young men.     

Insulin response and glycemic effects of meals in non-insulin-dependent diabetes

Glycemic and hormonal responses to two breakfast mixed meals were studied in six obese subjects with NIDDM. The study evaluated a high-glycemic-effect (HGE) and a low-glycemic-effect (LGE) meal, each with approximately 600 kcal and 12% protein, 15% fat, and 73% carbohydrate. Plasma insulin and counterregulatory hormones were measured at baseline and at 30-min intervals for 5 h after meals. Mean fasting plasma glucose and insulin concentrations were similar before both studies: for the LGE meal, 11.9 +/- 1.8 mmol/L and 261.9 +/- 50.1 pmol/L; for the HGE meal, 11.9 +/- 2.0 mmol/L and 262.6 +/- 43.1 pmol/L. Peak plasma glucose concentrations were approximately 25% lower with the LGE meal and the area under the glucose curve was 63% of that obtained for the HGE meal (p less than 0.05). Although the integrated insulin responses of the two meals did not differ, the peak occurred 60 min earlier in the LGE meal (p less than 0.05). The LGE meal may produce a lower glycemic response, in part because of earlier insulin secretion.     

Food glycemic index, as given in glycemic index tables, is a significant determinant of glycemic responses elicited by composite breakfast meals

BACKGROUND: Recent studies have concluded that the carbohydrate content and glycemic index (GI) of individual foods do not predict the glycemic and insulinemic effects of mixed meals. We hypothesized that these conclusions may be unwarranted because of methodologic considerations. OBJECTIVE: The aim was to ascertain whether the GI and carbohydrate content of individual foods influence glucose and insulin responses elicited by realistic mixed meals in normal subjects. DESIGN: With the use of a crossover design, we determined the glucose and insulin responses of 6 test meals in 16 subjects in Sydney and the glucose responses of 8 test meals in 10 subjects in Toronto and then the results were pooled. The 14 different test meals varied in energy (220-450 kcal), protein (0-18 g), fat (0-18 g), and available carbohydrate (16-79 g) content and in GI (35-100; values were rounded). RESULTS: The glucose and insulin responses of the Sydney test meals varied over a 3-fold range (P < 0.001), and the glucose responses of the Toronto test meals varied over a 2.4-fold range (P < 0.001). The glucose responses were not related to the fat or protein content of the test meal. Carbohydrate content (P = 0.002) and GI (P = 0.022) alone were related to glucose responses; together they accounted for 88% of the variation in the glycemic response (P < 0.0001). The insulin response was significantly related to the glucose response (r = 0.94, P = 0.005). CONCLUSIONS: When properly applied in realistic settings, GI is a significant determinant of the glycemic effect of mixed meals in normal subjects. For mixed meals within the broad range of nutrient composition that we tested, carbohydrate content and GI together explained approximately 90% of the variation in the mean glycemic response, with protein and fat having negligible effects.     

Differential effects of saturated and monounsaturated fats on postprandial lipemia and glucagon-like peptide 1 responses in patients with type 2 diabetes

BACKGROUND: Postprandial lipemia is important in the development of coronary artery disease because of elevated postprandial triacylglycerol-rich plasma lipoproteins and suppressed HDL-cholesterol concentrations. We showed in healthy subjects a possible association between postprandial lipid metabolism and the responses of the duodenal incretin hormones glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide after meals rich in saturated and monounsaturated fatty acids (oleic acid), respectively. OBJECTIVE: The objective was to compare the postprandial responses (8 h) of glucose, insulin, fatty acids, triacylglycerol, gastric inhibitory polypeptide, and GLP-1 to saturated- and monounsaturated-rich test meals. DESIGN: Twelve overweight patients with type 2 diabetes ingested 3 meals randomly: an energy-free soup with 50 g carbohydrate (control meal), the control meal plus 100 g butter, and the control meal plus 80 g olive oil. Triacylglycerol responses were measured in total plasma and in a chylomicron-rich and a chylomicron-poor fraction. RESULTS: No significant differences in the glucose, insulin, or fatty acid responses to the 2 fat-rich meals were seen. The plasma triacylglycerol and chylomicron triacylglycerol responses were highest after the butter meal. HDL-cholesterol concentrations decreased significantly after the butter meal but did not change significantly after the olive oil meal. GLP-1 responses were highest after the olive oil meal. CONCLUSIONS: Olive oil induced lower triacylglycerol concentrations and higher HDL-cholesterol concentrations than did butter, without eliciting significant changes in glucose, insulin, or fatty acids. Furthermore, olive oil induced higher concentrations of GLP-1, which may indicate a relation between fatty acid composition, incretin responses, and triacylglycerol metabolism postprandially in patients with type 2 diabetes.     

Effects of n-3 fatty acids on postprandial triacylglycerol and hormone concentrations in normal subjects.

The present study reports results from two investigations to determine effects of a 6-week period of moderate n-3 fatty acid supplementation (2.7 g/d) on fasting and on postprandial triacylglycerol and metabolic hormone concentrations in response to standard test meals. In the first study postprandial responses were followed for 210 min after an early morning test meal challenge; in the second study responses to an evening test meal were followed during the evening and overnight for a total period of 12 h. In both studies postprandial triacylglycerol responses to the test meals were significantly reduced after compared with before fish-oil supplementation. In the second study the triacylglycerol peak response seen between 200 and 400 min in subjects studied before supplementation with fish oils was almost completely absent in the same subjects after 6 weeks of n-3 fatty acid supplementation. Analysis of fasting concentrations of metabolites and hormones was carried out on the combined data from the two studies. There were no significant differences in total, low-density-lipoprotein- or high-density-lipoprotein-cholesterol concentrations during fish-oil supplementation, although there was considerable individual variation in cholesterol responses to the supplement. Concentrations of Apo-B and Apo-A1 were unchanged during supplementation with fish oils. Fasting and early morning postprandial GIP concentrations were lower in subjects taking fish oils, possibly due to acute effects of fish-oil capsules taken on the evening before the studies. In both studies fasting insulin and glucose and postprandial insulin concentrations remained unchanged following fish-oil supplementation. The results do not support the view that triacylglycerol-lowering effects of n-3 fatty acids are due to modulation of insulin secretion mediated via the enteroinsular axis. Further studies are required to determine the precise mechanism by which fish oils reduce both fasting and postprandial triacylglycerol concentrations.     

Effect of whey on blood glucose and insulin responses to composite breakfast and lunch meals in type 2 diabetic subjects

BACKGROUND: Whey proteins have insulinotropic effects and reduce the postprandial glycemia in healthy subjects. The mechanism is not known, but insulinogenic amino acids and the incretin hormones seem to be involved. OBJECTIVE: The aim was to evaluate whether supplementation of meals with a high glycemic index (GI) with whey proteins may increase insulin secretion and improve blood glucose control in type 2 diabetic subjects. DESIGN: Fourteen diet-treated subjects with type 2 diabetes were served a high-GI breakfast (white bread) and subsequent high-GI lunch (mashed potatoes with meatballs). The breakfast and lunch meals were supplemented with whey on one day; whey was exchanged for lean ham and lactose on another day. Venous blood samples were drawn before and during 4 h after breakfast and 3 h after lunch for the measurement of blood glucose, serum insulin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1). RESULTS: The insulin responses were higher after both breakfast (31%) and lunch (57%) when whey was included in the meal than when whey was not included. After lunch, the blood glucose response was significantly reduced [-21%; 120 min area under the curve (AUC)] after whey ingestion. Postprandial GIP responses were higher after whey ingestion, whereas no differences were found in GLP-1 between the reference and test meals. CONCLUSIONS: It can be concluded that the addition of whey to meals with rapidly digested and absorbed carbohydrates stimulates insulin release and reduces postprandial blood glucose excursion after a lunch meal consisting of mashed potatoes and meatballs in type 2 diabetic subjects.