Insulin response to ingested protein in diabetes

Amino acid-stimulated insulin secretion: a path forward in type 2 diabetes

Qualitative and quantitatively appropriate insulin secretion is essential for optimal control of blood glucose. Beta-cells of the pancreas produce and secrete insulin in response to glucose and non-glucose stimuli including amino acids. In this manuscript, we review the literature on amino acid-stimulated insulin secretion in oral and intravenous in vivo studies, in addition to the in vitro literature, and describe areas of consensus and gaps in understanding. We find promising evidence that the synergism of amino acid-stimulated insulin secretion could be exploited to develop novel therapeutics, but that a systematic approach to investigating these lines of evidence is lacking. We highlight evidence that supports the relative preservation of amino acid-stimulated insulin secretion compared to glucose-stimulated insulin secretion in type 2 diabetes, and make the case for the therapeutic potential of amino acids. Finally, we make recommendations for research and describe the potential clinical utility of nutrient-based treatments for type 2 diabetes including remission services.

A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome

Equine metabolic syndrome (EMS) is characterized by an abnormal insulin response to a glycemic challenge but despite the known insulinotropic effects of certain amino acids, there is a paucity of data evaluating the impact of dietary protein on insulin dynamics in these horses. The objective was therefore to assess insulin and amino acid responses following intake of a high protein meal in healthy horses and those with EMS. Six mature horses diagnosed with EMS and six age-matched control horses without EMS were used. Horses were fed 2g/kg body mass (BM) of a high protein pellet (31% crude protein) at time 0 and 30min, for a total of 4g/kg BM, following an overnight fast. Blood samples collected during a 4h period were analysed for plasma glucose, insulin, amino acids and urea concentrations. Glucose concentrations were not different between groups (P=0.2). Horses with EMS had a 9-fold greater insulinemic response to the consumption of a high protein meal compared with controls (P=0.046). Post-prandial levels of histidine, citrulline, tyrosine, valine, methionine, isoleucine, leucine and ornithine were higher in horses with EMS (P<0.05). Baseline urea nitrogen concentrations were not significantly different between groups (P=0.1). Knowing that certain amino acids are insulin secretagogues, these results illustrate that consumption of a high protein meal caused a hyperinsulinemic response and affected amino acid dynamics in horses with EMS. These findings suggest that dietary protein content should be taken into consideration in the management of horses with insulin dysregulation.

Effects of acute ingestion of whey protein with or without prior aerobic exercise on postprandial glycemia in type 2 diabetics

PURPOSE

Acute protein co-ingestion or a single bout of aerobic exercise can attenuate postprandial glycemia, but their combined effect has not been investigated in type 2 diabetics.

METHODS

Using a randomised crossover design, male type 2 diabetics (n = 8) [mean (95% CI); age, 55.0 (45.2, 64.8) year; BMI, 33.7 (25.6, 41.8) kg·m^- 2; 2 h glucose 14.0 (12.5, 15.5) mM] completed (1) 75 g oral glucose tolerance test (OGTT) (CON); (2) OGTT supplemented with 0.33 g·kg BM^- 1 of whey protein concentrate (PRO); or OGTT supplemented with PRO but preceded by a bout of aerobic cycling exercise (PRO + EX). Postprandial venous blood samples were collected for glucose, insulin, C-peptide and glucagon.

RESULTS

Despite a fold-increase of 1.90 (1.26, 2.56; p < 0.05) in postprandial insulin compared to CON, PRO failed to attenuate postprandial glycemia measured by 2 h glucose area under the curve. During PRO + EX, plasma glucose was elevated by 1.51 (0.5, 2.5) mM and 1.3 (0.3, 2.3) mM at 15 and 30 min, respectively, compared to CON, but was lower by 1.60 (0.6, 2.6) mM and 1.5 (0.5, 2.5) mM at 90 and 120 min, respectively (all p < 0.01). The additive effect of exercise and protein ingestion resulted in a fold-increase of 1.67 (1.35, 2.00; p < 0.05) in postprandial glucagon compared to CON.

CONCLUSION

In type 2 diabetics, prior aerobic exercise altered the humoral response to co-ingestion of whey protein with a carbohydrate load, but neither protein ingestion alone nor when preceded by prior exercise attenuated postprandial glycemia.

The insulinotropic effect of a high-protein nutrient preload is mediated by the increase of plasma amino acids in type 2 diabetes

AIMS

Eating protein before carbohydrate reduces postprandial glucose excursions by enhancing insulin and glucagon-like peptide-1 (GLP-1) secretion in type 2 diabetes (T2D). We tested the hypothesis that this insulinotropic effect depends on the elevation of plasma amino acids (AA) after the digestion of food protein.

METHODS

In 16 T2D patients, we measured plasma AA levels through the course of two 75-g oral glucose tolerance tests (OGTT) preceded by either 500-ml water or a high-protein nutrient preload (50-g Parmesan cheese, one boiled egg, and 300-ml water). Changes in beta cell function were evaluated by measuring and modelling plasma glucose, insulin, and C-peptide through the OGTT. Changes in incretin hormone secretion were assessed by measuring plasma GLP-1.

RESULTS

Plasma AA levels were 24% higher after the nutrient preload (p < 0.0001). This increment was directly proportional to both the enhancement of beta cell function (r = 0.58, p = 0.02) and the plasma GLP-1 gradients (r = 0.57, p = 0.02) produced by the nutrient preload. Among single AA, glutamine showed the strongest correlation with changes in beta cell function (r = 0.61, p = 0.01), while leucine showed the strongest correlation with GLP-1 responses (r = 0.74, p = 0.001).

CONCLUSIONS

The elevation of circulating AA that occurs after a high-protein nutrient preload is associated with an enhancement of beta cell function and GLP-1 secretion in T2D. Manipulating the meal sequence of nutrient ingestion may reduce postprandial hyperglycaemia through a direct and GLP-1-mediated stimulation of insulin secretion by plasma AA.

TRIAL REGISTRATION NUMBER

NCT02342834.

Increase in insulin secretion and decrease in muscle degradation by fat-free milk intake are attenuated by physical exercise

BACKGROUND

Protein intake, particularly branched chain amino acids (BCAAs), and exercise have opposing actions on insulin secretion, but the same action on protein anabolism. We examined the effects of BCAA-rich fat-free milk intake and/or exercise on levels of insulin secretion and indices related to muscle protein metabolism in order to assess the potency of dietary and exercise therapies against metabolic and locomotive disorders.

METHODS

Eight adult female volunteers participated in all four 24 h experiments; control diet intake with or without exercise, and fat-free milk-containing diet intake with or without exercise. Fat-free milk was replaced with one-sixth of all foods in the control diet. Exercise was set at an equal-energy level as fat-free milk. Urine and fasting blood samples were collected for each experiment.

RESULTS

Urinary C-peptide immunoreactivity excretion and serum insulin levels were significantly higher, but urinary 3-methyl-histidine excretion levels were significantly lower with low urinary adrenaline and dopamine excretion in the fat-free milk-containing diet than in the control diet. These findings were reduced by exercise with high urinary adrenaline and noradrenaline excretion.

CONCLUSIONS

BCAA-rich fat-free milk intake enhanced insulin secretion and suppressed muscle protein degradation, but these effects are attenuated by exercise accompanied with increase in catecholamine secretion.

Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes

Presently, routine screening misses many cases of prediabetes and early type 2 diabetes (T2D). Therefore, better biomarkers are needed for a simple and early detection of abnormalities of glucose metabolism and prediction of future T2D. Possible candidates for this include plasma or serum amino acids because glucose and amino acid metabolism are closely connected. This review presents the available evidence of this connectivity and discusses its clinical implications. First, we examine the underlying physiological, pre-analytical, and analytical issues. Then, we summarize results of human studies that evaluate amino acid levels as markers for insulin resistance, prediabetes, and future incident T2D. Finally, we illustrate the interconnection of amino acid levels and metabolic syndrome with our own data from a deeply phenotyped human cohort. We also discuss how amino acids may contribute to the pathophysiology of T2D. We conclude that elevated branched-chain amino acids and reduced glycine are currently the most robust and consistent amino acid markers for prediabetes, insulin resistance, and future T2D. Yet, we are cautious regarding the clinical potential even of these parameters because their discriminatory power is insufficient and their levels depend not only on glycemia, but also on other components of the metabolic syndrome. The identification of more precise intermediates of amino acid metabolism or combinations with other biomarkers will, therefore, be necessary to obtain in order to develop laboratory tests that can improve T2D screening.

Increased Incretin But Not Insulin Response after Oral versus Intravenous Branched Chain Amino Acids

BACKGROUND/AIMS

Branched chain amino acids (BCAAs) are known to exert an insulinotropic effect. Whether this effect is mediated by incretins (glucagon like peptide 1 [GLP-1] or glucose-dependent insulinotropic peptide [GIP]) is not known. The aim of this study was to show whether an equivalent dose of BCAA elicits a greater insulin and incretin response when administered orally than intravenously (IV).

METHODS

Eighteen healthy, male subjects participated in 3 tests: IV application of BCAA solution, oral ingestion of BCAA and placebo in an equivalent dose (30.7 ± 1.1 g). Glucose, insulin, C-peptide, glucagon, GLP-1, GIP, valine, leucine and isoleucine concentrations were measured.

RESULTS

Rise in serum BCAA was achieved in both BCAA tests, with incremental areas under the curve (iAUC) being 2.1 times greater for IV BCAA compared with those of the oral BCAA test (p < 0.0001). Oral and IV BCAA induced comparable insulin response greater than placebo (240 min insulin iAUC: oral 3,411 ± 577 vs. IV 2,361 ± 384 vs. placebo 961.2 ± 175 pmol/L, p = 0.0006). Oral BCAA induced higher GLP-1 (p < 0.0001) and GIP response (p < 0.0001) compared with the IV or placebo. Glucose levels declined significantly (p < 0.001) in the same pattern during both BCAA tests with no change in the placebo group.

CONCLUSIONS

An equivalent dose of BCAA elicited a comparable insulin and greater incretin response when administered orally and not when administered through IV. We conclude that insulinotropic effects of BCAA are partially incretin dependent.

Algorithms to Improve the Prediction of Postprandial Insulinaemia in Response to Common Foods

Dietary patterns that induce excessive insulin secretion may contribute to worsening insulin resistance and beta-cell dysfunction. Our aim was to generate mathematical algorithms to improve the prediction of postprandial glycaemia and insulinaemia for foods of known nutrient composition, glycemic index (GI) and glycemic load (GL). We used an expanded database of food insulin index (FII) values generated by testing 1000 kJ portions of 147 common foods relative to a reference food in lean, young, healthy volunteers. Simple and multiple linear regression analyses were applied to validate previously generated equations for predicting insulinaemia, and develop improved predictive models. Large differences in insulinaemic responses within and between food groups were evident. GL, GI and available carbohydrate content were the strongest predictors of the FII, explaining 55%, 51% and 47% of variation respectively. Fat, protein and sugar were significant but relatively weak predictors, accounting for only 31%, 7% and 13% of the variation respectively. Nutritional composition alone explained only 50% of variability. The best algorithm included a measure of glycemic response, sugar and protein content and explained 78% of variation. Knowledge of the GI or glycaemic response to 1000 kJ portions together with nutrient composition therefore provides a good approximation for ranking of foods according to their “insulin demand”.

Metabolic changes in serum metabolome in response to a meal

PURPOSE

The change in serum metabolic response from fasting state to postprandial state provides novel insights into the impact of a single meal on human metabolism. Therefore, this study explored changes in serum metabolite profile after a single meal.

METHODS

Nineteen healthy postmenopausal women with normal glucose tolerance participated in the study. They received a meal consisting of refined wheat bread (50 g carbohydrates, 9 g protein, 4.2 g fat and 2.7 g dietary fibre), 40 g cucumber and 300 mL noncaloric orange drink. Blood samples were collected at fasting and five postprandial time points. Metabolic profile was measured by nuclear magnetic resonance and targeted liquid chromatography-mass spectrometry. Changes over time were assessed with multivariate models and ANOVA, with baseline as control.

RESULTS

The metabolomic analyses demonstrated alterations in phospholipids, amino acids and their breakdown products, glycolytic products, acylcarnitines and ketone bodies after a single meal. More specifically, phosphatidylcholines, lysophosphatidylcholines and citrate displayed an overall declining pattern, while leucine, isoleucine, methionine and succinate increased initially but declined thereafter. A sharp decline in acylcarnitines and ketone bodies and increase in glycolytic products postprandially suggest a switch in the body's energy source from β-oxidation to glycolysis. Moreover, individuals with relatively high postprandial insulin responses generated a higher postprandial leucine responses compared to participants with lower insulin responses.

CONCLUSIONS

The study demonstrated complex changes from catabolic to anabolic metabolism after a meal and indicated that the extent of postprandial responses is different between individuals with high and low insulin response.

Slow and fast dietary proteins differentially modulate postprandial metabolism

The quality of dietary proteins is influenced by their content and composition of amino acids and bioavailability. Recent data suggest that the digestion and absorption kinetics of proteins influences the effects of protein ingestion on the metabolic processes. Slowly and fast-digested dietary proteins differentially modulate postprandial protein and glucose metabolism. This is an important factor for defining the physiological outcome and application for nutritional purposes of different dietary protein sources.

Role of proteins in insulin secretion and glycemic control

Dietary proteins are essential for the life of all animals and humans at all stages of the life cycle. They serve many structural and biochemical functions and have significant effects on health and wellbeing. Dietary protein consumption has shown an upward trend in developed countries in the past two decades primarily due to greater supply and affordability. Consumption is also on the rise in developing countries as affluence is increasing. Research shows that proteins have a notable impact on glucose homeostasis mechanisms, predominantly through their effects on insulin, incretins, gluconeogenesis, and gastric emptying. Since higher protein consumption and impaired glucose tolerance can be commonly seen in the same population demographics, a thorough understanding of the former's role in glucose homeostasis is crucial both toward the prevention and management of the latter. This chapter reviews the current state of the art on proteins, amino acids, and their effects on blood glucose and insulin secretion.

Low-protein diet improves blood and urinary glucose levels and renal manifestations of diabetes in C57BLKS-db/db mice

PURPOSE

Dietary protein content is related clinically to the development of diabetic nephropathy. Here, we investigated how dietary protein content (12-24 % energy) within the range used by humans affected renal manifestations including the expressions of genes involved in the renin-angiotensin (RA) system in control and diabetic mice. Moreover, we examined the effects of dietary protein content on HbA1c and urinary glucose.

METHODS

Control (CT) and leptin receptor-deficient obese (db) mice, 5 weeks old, were fed the diets below. Under ad libitum conditions, mice were fed 12, 18, and 24 % energy from protein (L-, M-, and H-diets) for 8 weeks. Under pair-feeding conditions, db mice were supplied H-diet (db-Hp) to the equivalent energy to that consumed by db-L mice. Renal manifestations and values related to glucose and insulin were examined biochemically and pathologically.

RESULTS

Under ad libitum conditions, db mice consumed food and water dose dependently of the dietary protein content, although they were consumed similarly by CT mice. CT-L mice showed lower urinary albumin and kidney weight, in association with lower mRNA levels of angiotensinogen and renin, than CT-H mice. Under pair-feeding conditions, db-L mice showed a lower ratio of kidney/body weight, HbA1(C), and urinary glucose, and a higher β-cell distribution rate in the pancreas than db-Hp mice.

CONCLUSIONS

Low-protein intake in the range used by humans may relieve renal manifestations through the suppressed expression of genes in the renal RA system of CT mice. On the other hand, in db mice, low-protein intake improved hyperglycemia and the renal manifestations of diabetes.

Slow versus fast proteins in the stimulation of beta-cell response and the activation of the entero-insular axis in type 2 diabetes

BACKGROUND

We tested whether ingestion of whey protein can induce greater post-prandial amino acid (AA) levels in the plasma and a higher beta-cell response than casein ingestion in type 2 diabetes mellitus patients.

METHODS

The study was designed as a double-blind, randomized, and controlled cross-over clinical trial. Twelve post-absorptive type 2 diabetic subjects who were withdrawn from their usual hypoglycemic therapy were studied. A medium calorie (approximately 6 kcal/kg BW), high protein (approximately 50% of total kcal) mixed meal, containing whey protein, casein, or a free amino acid (FREE AA) mixture matching the casein AA composition, was randomly administered on three different occasions.

RESULTS

Following ingestion of whey protein, plasma concentrations of total, branched chain, and essential AA were 25-50% greater than after ingestion of casein (p < 0.0001), and were similar to those observed after the FREE AA meal. With whey protein, C-peptide, insulin, and pro-insulin concentrations were greater by 12-40% (p < 0.02 or less) than with casein, and similar to those with FREE AA. Glucagon-like polypeptide 1 (GLP-1) response tended to be lower with casein than with whey protein. Glucose-dependent insulinotropic polypeptide (GIP) response was greater with either whey protein or casein than with FREE AA. Post-prandial glucose concentrations were similar after whey protein and casein ingestion, but lower after the FREE AA meal.

CONCLUSIONS

In type 2 diabetes, the ingestion of a fast-absorbable protein results in a greater post-prandial aminoacidemia and a higher beta-cell secretion than the ingestion of a 'slow' protein. Whether these changes can be maintained chronically in combination with hypoglycemic therapy, possibly also resulting in better glycemic control, remains to be established.

Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition

Background

Over the past several years our research group has taken a systematic, comprehensive approach to determining the effects on body function (hormonal and non-hormonal) of varying the amounts and types of proteins, carbohydrates and fats in the diet. We have been particularly interested in the dietary management of type 2 diabetes. Our objective has been to develop a diet for people with type 2 diabetes that does not require weight loss, oral agents, or insulin, but that still controls the blood glucose concentration. Our overall goal is to enable the person with type 2 diabetes to control their blood glucose by adjustment in the composition rather than the amount of food in their diet.

Methods

This paper is a brief summary and review of our recent diet-related research, and the rationale used in the development of diets that potentially are useful in the treatment of diabetes.

Results

We determined that, of the carbohydrates present in the diet, absorbed glucose is largely responsible for the food-induced increase in blood glucose concentration. We also determined that dietary protein increases insulin secretion and lowers blood glucose. Fat does not significantly affect blood glucose, but can affect insulin secretion and modify the absorption of carbohydrates. Based on these data, we tested the efficacy of diets with various protein:carbohydrate:fat ratios for 5 weeks on blood glucose control in people with untreated type 2 diabetes. The results were compared to those obtained in the same subjects after 5 weeks on a control diet with a protein:carbohydrate:fat ratio of 15:55:30. A 30:40:30 ratio diet resulted in a moderate but significant decrease in 24-hour integrated glucose area and % total glycohemoglobin (%tGHb). A 30:20:50 ratio diet resulted in a 38% decrease in 24-hour glucose area, a reduction in fasting glucose to near normal and a decrease in %tGHb from 9.8% to 7.6%. The response to a 30:30:40 ratio diet was similar.

Conclusion

Altering the diet composition could be a patient-empowering method of improving the hyperglycemia of type 2 diabetes without weight loss or pharmacologic intervention.

Metabolic response of people with type 2 diabetes to a high protein diet

Background

One of the major interests in our laboratory has been to develop a scientific framework for dietary advice for patients with diabetes. Knowledge regarding the metabolic consequences and potential effects on health of protein in people with type 2 diabetes has been a particular interest.

Results

We recently have completed a study in which dietary protein was increased from 15% to 30% of total food energy. The carbohydrate content was decreased from 55% to 40%, i.e. dietary protein replaced part of the carbohydrate. This resulted in a significant decrease in total glycohemoglobin, a decrease in postprandial glucose concentrations and a modest increase in insulin concentration. Renal function was unchanged.

Currently we also are determining the metabolic response to a diet in which the carbohydrate content is further decreased to 20% of total food energy. The %tGHb decrease was even more dramatic than with the 40% carbohydrate diet.

Conclusion

From these data we conclude that increasing the protein content of the diet at the expense of carbohydrate can reduce the 24-hour integrated plasma glucose concentration, at least over a 5-week period of time. The reduction was similar to that of oral agents. Renal function was not affected significantly. Thus, increasing the protein content of the diet with a corresponding decrease in the carbohydrate content potentially is a patient empowering way of reducing the hyperglycemia present with type 2 diabetes mellitus, independent of the use of pharmaceutical agents.

Effect of insulin and energy restriction on the thermic effect of protein in type 2 diabetes mellitus

OBJECTIVE

The objective of this study was to test whether the thermic effect of oral protein is blunted in poorly controlled type 2 diabetes and is corrected by normalization of glycemia with insulin and 28 days of a very-low-energy diet.

RESEARCH METHODS AND PROCEDURES

Resting energy expenditure (REE) and the thermic effect of 90 g of oral protein were measured, using indirect calorimetry, in nine (five women and four men) obese diabetic people [weight, 108 +/- 10 kg; waist circumference, 123 +/- 8 cm; body mass index, 40 +/- 3 kg/m(2)] who were hyperglycemic on day 8 or euglycemic with insulin on day 16 of a weight-maintaining diet and euglycemic on day 28 of a very low energy diet (VLED). Results were compared with those of seven (six women and one man) weight- and body mass index-matched obese nondiabetic subjects with a waist circumference of 111 +/- 6 cm. Substrates and hormonal responses were determined concurrently.

RESULTS

Fasting glucose was normalized in the diabetic subjects with insulin from day 9 of VLED onward. Weight decreased in both groups by 9.9 +/- 0.9 kg with VLED. REE was 8 +/- 2% lower with insulin treatment and decreased by another 14 +/- 3% with VLED in the diabetic and by 15 +/- 1% in the nondiabetic subjects by week 4. After the protein meal, the thermic response was significantly (p < 0.05) less with hyperglycemia than with insulin-induced euglycemia, as percentage above REE (15.3 +/- 1.4 compared with 21.2 +/- 1.5%), as percentage of the energy content of the meal (19.5 +/- 1.5 compared with 25.2 +/- 1.7%), as kilocalories per 405 minutes (86 +/- 5 compared with 110 +/- 7), and less than in nondiabetic obese controls (21.0 +/- 2.2% above REE, 24.4 +/- 1.7% of energy of meal). After the VLED, the thermic effect of protein was significantly higher in both groups only as percentage above REE. The initial glucagon response was greater with hyperglycemia compared with euglycemia and post-VLED but not compared with the nondiabetic subjects. Hyperglycemia was associated with 21 +/- 4% greater urinary urea nitrogen excretion and urinary glucose losses of 134 +/- 50 mmol/d.

DISCUSSION

This study shows a blunted thermic effect of protein in obese hyperglycemic type 2 diabetic subjects compared with matched nondiabetic subjects that can be corrected with insulin- or energy restriction-induced euglycemia.

The origins of western obesity: a role for animal protein?

A reduced propensity to oxidize fat, as indicated by a relatively high fasting respiratory quotient, is a major risk factor for weight gain. Increased insulin secretion works in various ways to impede fat oxidation and promote fat storage. The substantial 'spontaneous' weight loss often seen with very-low-fat dietary regimens may reflect not only a reduced rate of fat ingestion, but also an improved insulin sensitivity of skeletal muscle that down-regulates insulin secretion. Reduction of diurnal insulin secretion may also play a role in the fat loss often achieved with exercise training, low-glycemic-index diets, supplementation with soluble fiber or chromium, low-carbohydrate regimens, and biguanide therapy. The exceptional leanness of vegan cultures may reflect an additional factor - the absence of animal protein. Although dietary protein by itself provokes relatively little insulin release, it can markedly potentiate the insulin response to co-ingested carbohydrate; Western meals typically unite starchy foods with an animal protein-based main course. Thus, postprandial insulin secretion may be reduced by either avoiding animal protein, or segregating it in low-carbohydrate meals; the latter practice is a feature of fad diets stressing 'food combining'. Vegan diets tend to be relatively low in protein, legume protein may be slowly absorbed, and, as compared to animal protein, isolated soy protein provokes a greater release of glucagon, an enhancer of fat oxidation. The low insulin response to rice may mirror its low protein content. Minimizing diurnal insulin secretion in the context of a low fat intake may represent an effective strategy for achieving and maintaining leanness.

High beta-glucan oat bran and oat gum reduce postprandial blood glucose and insulin in subjects with and without type 2 diabetes

The aim of the current study was to characterize the effects of isolated and native sources of beta-glucan, oat gum, and oat bran, respectively, when incorporated into a complete meal. Fasting control subjects and subjects with Type 2 diabetes were fed porridge meals containing either wheat farina, wheat farina plus oat gum or oat bran. Blood samples were collected for 3 h after the test meals and plasma glucose and insulin were measured. Oat bran and wheat farina plus oat gum meals reduced the postprandial plasma glucose excursions and insulin levels when compared with the control wheat farina meal in both control and Type 2 diabetic subjects. This study shows that both the native cell wall fibre of oat bran and isolated oat gum, when incorporated into a meal, act similarly by lowering postprandial plasma glucose and insulin levels. A diet rich in beta-glucan may therefore be of benefit in the regulation of postprandial plasma glucose levels in subjects with Type 2 diabetes.

Postprandial glucose and insulin responses to various tropical fruits of equivalent carbohydrate content in non-insulin-dependent diabetes mellitus

The plasma glucose and insulin responses were determined in 10 NIDDM female patients following the ingestion of tropical fruit containing 25 g of carbohydrate. The five tropical fruits were pineapple, mango, banana, durian and rambutan. Blood was drawn at 0, 30, 60, 120 and 180 min, respectively. The results showed that the glucose-response curves to mango and banana were significantly less than those to rambutan, durian and pineapple (P less than 0.05). Only the glucose area after mango ingestion was significantly less than the glucose areas of the other fruits (P less than 0.05). The insulin response curve and insulin area after durian ingestion was statistically greater than after ingestion of the others. We concluded that after mango ingestion, the glucose area was lower than it had been after rambutan, durian and pineapple ingestion and the insulin area was lower than that after durian ingestion of equivalent carbohydrate content in type 2 (NIDDM) diabetes.

Dose-kinetics of pancreatic alpha- and beta-cell responses to a protein meal in normal subjects

A protein meal is well known to induce a prompt secretion of insulin and glucagon. However, the data regarding the dose-response relationship between the protein meal and the insulin and glucagon responses are sparse. This study assessed the effects of ingestion of protein meals of varying amounts on plasma glucose [S], insulin [I], and glucagon [G] concentrations in eight normal subjects. Protein meals were administered after an overnight fast in a randomized sequence at intervals of 10 days in four different quantities: 250 mg/kg body weight (BW) (A), 500 mg/kg BW (B), 1 g/kg BW (C), and 2 g/kg BW (D). Mean S levels were not significantly altered following A, B, or C, although significant decreases in S responses were noted after C and D as reflected by absolute changes (delta) and/or the cumulative responses (CR) and the areas under the curve (sigma). Mean I increased promptly to peak concentration by 30 minutes, although in individual subjects the peak was achieved either at 30 or 60 minutes following all protein meals. The increase was progressively greater and the return was delayed with increasing quantities resulting in progressive elevations in delta I and percent increase from basal concentration (%), as well as CRI and sigma I. G increased following all protein meals as well. The mean peak G concentrations were achieved by 90 minutes, although in individual subjects the peak G was reached at 90 or 120 minutes, a significant delay in comparison to the peak I levels. G returned to base line only following ingestion of A during the study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of glycemic response and insulin requirements after mixed meals of equal carbohydrate content in healthy, type-1, and type-2 diabetic man

The postprandial insulin requirements after three mixed meals of equal carbohydrate and energy content were assessed in 10 type-1 and 12 type-2 diabetics by a glucose-controlled insulin infusion system. These were compared with the glycemic response to the same meals of 10 healthy individuals (glycemic index). In type-1 diabetics, we found the highest insulin requirements after consumption of a continental breakfast (low fibre, low protein, high fat). Ten percent less insulin was infused after milk (low fat, high protein) and 30% less after an English breakfast (high fibre, high protein). Type-2 diabetics showed no significant differences in insulin requirements between the three test meals. The glycemic response in healthy individuals had no relation to these insulin requirements. Continental and English breakfast had a similar glycemic effect, whereas milk produced only 30% of the blood glucose response observed after the continental breakfast. These results indicate that neither the carbohydrate content (exchange lists) nor the glycemic index enable prediction of postprandial insulin requirements in insulin-deficient diabetes. For this purpose, we propose the insulin-need index, elaborated by testing whole meals in closed-loop experiments with type-1 diabetics.

Modulation of postprandial glycaemia and insulinaemia by cellulose in mixed nutrient combinations

The present study was designed to examine the effect of cellulose (CL) on postprandial glycaemia and insulinaemia when ingested with glucose (G), casein (CS) and maize oil (CO) in various combinations. The study was conducted on five healthy male volunteers, on each of whom five meal tolerance tests were performed. The meals were isoenergetic and consisted of G; G and CL; G, CS and CL; G, CO and CL; G, CS, CO and CL. The meals were administered after an overnight fast. In addition to a fasting venous blood sample, blood was collected 0.5, 1.0, 1.5 and 2.0 h after ingestion for measurement of serum glucose and insulin levels. The glycaemic response to G + CS + CL and G + CS + CO + CL was significantly lower, while the insulinaemic response to G + CL was significantly higher than that to G. Addition of CL to G did not alter the glycaemic response, but accentuated the insulinaemic response. Further addition of CS in isoenergetic meals attenuated the glycaemic response, which may be because of a reduction in the amount of G in the meals. Like CS, CL also seemed to have an insulinotropic effect. The mechanism of the insulinotropic effect of CL cannot be deduced from the present study, but it is possible that like G, CL also stimulates gastric inhibitory peptide (GIP) secretion from the duodenum, which in turn stimulates insulin secretion.

The effect of ingestion of meat on hepatic extraction of insulin and glucagon and hepatic glucose output in conscious dogs

The effect of ingestion of protein on hepatic extraction of insulin and glucagon and hepatic glucose output were investigated in conscious dogs. The ingestion of meat stimulated both insulin and glucagon secretion but the glucagon response was much more rapid and greater than that of insulin. Secretion of glucagon demonstrated a biphasic pattern while insulin release was monophasic. The fractional hepatic extraction of glucagon increased gradually from the basal value of 15 +/- 3% to a peak of 36 +/- 5% at 90 min, and that of insulin increased from the basal level of 41 +/- 2% to 54 +/- 4% at 45 and 60 min. The increased hepatic extraction of glucagon and insulin after meat ingestion may be explained by neural or hormonal signals from the gut. The blood glucose and hepatic glucose output did not increase significantly despite the significant decrease of the portal vein insulin to glucagon molar ratio as well as the significant decrease of the molar ratio of the hepatic uptake of these hormones. The absence of greater hepatic glucose production despite the augmented glucagon secretion and decreased portal vein insulin to glucagon molar ratio could reflect down regulation by glucagon.

Insulinopenia in impaired glucose tolerance preservation of insulin response to I.V. arginine and tolbutamide

Immunoreactive insulin (IRI) response to successive i.v. injections of glucose (0.3 g/kg), arginine (5 g) and tolbutamide (20 mg/kg) was measured in 11 non-obese patients with mild glucose intolerance and 11 control subjects. In 3 of the patients the IRI response to i.v. arginine and subsequent i.v. glucose was also measured. The mean peak IRI level following glucose was grossly diminished in the patients compared to controls but peak IRI levels following arginine and tolbutamide were similar in the two groups. Administering arginine prior to glucose in the 3 patients tested resulted in a lowering of the IRI response to arginine but no increase in the IRI response to glucose. The decreased IRI response to i.v. glucose associated with an adequate response to i.v. arginine and tolbutamide in these patients suggests a failure of the B-cell sensor mechanism for glucose and may provide a physiological explanation for the recognized value of restricting carbohydrate relative to protein in the treatment of this condition. Any defect in the sensor mechanism for arginine appears quantitatively much less severe than that to glucose.

Factors governing insulin and glucagon responses during normal meals

An experimental model is described which can be used to study substrate and hormone responses to normal meals administered in very near normal circumstances. After 500, 300 and 125 calorie meals, the relative proportion of fat or protein content did not influence the plasma glucose except for minor differences between the high protein-high fat meals. The insulin response to such meals was correlated positively with the increment in glucose but reduction of protein content below 8 g caused a signficant reduction in the increment in plasma insulin per unit increase in plasma glucose. Alterations in protein content above 8 g made no difference. Fat content of the meal did not significantly alter the insulin response. No evidence was obtained for a major component of insulin release attributable to either bulk or preabsorption phenomena such as sight or smell. It is concluded that a significant accentuation of the insulin response to meals is dependent on a minimum amount of protein and that this is probably mediated by one of the gastro-intestinal hormones. Glucagon release is dependent on protein and carbohydrate content of the meal and is independent of the fat content. There may also be an early stimulation of glucagon release, regardless of content, which may also be hormonally mediated.

Effect of protein ingestion on splanchnic and leg metabolism in normal man and in patients with diabetes mellitus

The inter-organ flux of substrates after a protein-rich meal was studied in seven healthy subjects and in eight patients, with diabetes mellitus. Arterial concentrations as well as leg and splanchnic exchange of amino acids, carbohydrate substrates, free fatty acids (FFA), and ketone bodies were examined in the basal state and for 3 h after the ingestion of lean beef (3 g/kg body wt). Insulin was withheld for 24 h before the study in the diabetic patients. In the normal subjects, after protein ingestion, there was a large amino acid release from the splanchnic bed predominantly involving the branched chain amino acids. Valine, isoleucine, and leucine accounted together for more than half of total splanchnic amino acid output. Large increments were seen in the arterial concentrations of the branched chain amino acids (100-200%) and to a smaller extent for other amino acids. Leg exchange of most amino acids reverted from a basal net outut to a net uptake after protein feeding which was most marked for the branched chain amino acids. The latter accounted for more than half of total peripheral amino acid uptake...

Reactive hypoglycemia

The hypoglycemoses include a large category of distinctly unique entities. Guidelines for a clinical, physiological approach to these disorders is presented. Within this diagnostic spectrum of hypoglycemia lies the reactive hypoglycemic disorders that are characterized by their postprandial onset, adrenergic mediated symptoms, and relatively benign causes. The spectrum of reactive hypoglycemia includes early alimentary-reactive hypoglycemia, late diabetic-reactive hypoglycemia, hormonal deficiency states, and idiopathic hypoglycemia. A new postprandial hypoglycemic disorder, fructose 1-6 diphosphatase, can be added to this list. The frequent sampling of blood-glucose values in the postprandial state will frequently lead to the finding of a biochemically low blood-glucose value of below 50 ml/100 ml, and these individuals show no hypothalamic-pituitary-adrenal stress to the low blood sugar and do not manifest adrenergic symptoms. Their low blood-glucose value simply reflects the transition in intermediary metabolism between the fed and fasting state and provides a biochemical marker of this event. We refer to this asymptomatic biochemical event as transitional low blood-glucose state. It has no clinical implication and may frequently be confused with the bona fide reactive hypoglycemic disorders. Using a symptomatic, counter-regulatory model to define hypoglycemia as a bona fide disorder, findings are presented in patients with the varying types of reactive hypoglycemia, and their results are compared to normal controls and to a weight-matched and disease patient controls. Abnormalities in insulin secretion are discussed as relating to the pathophysiology causal in the hypoglycemia. An approach to therapy is presented based upon the classification of the patient as to the type of hypoglycemia and their abnormalities in insulin secretion.

Proteins and insulin release: a dual role of amino-acids and intestinal hormones

In two subjects concurrent infusion of amino-acids and the hormones secretin and pancreozymin provoked much higher plasma insulin levels than did administration of amino-acids or hormones individually. It is suggested that this may be a physiological phenomenon, augmenting the release of insulin from the pancreas after a meal containing protein.