Plasma glucose and insulin profiles in normal subjects ingesting diets of varying carbohydrate, fat, and protein content

Gestational hyperglycaemia impacts glucose control and insulin sensitivity in mouse offspring

Gestational diabetes mellitus (GDM) predisposes offspring to the development of obesity and type 2 diabetes. While GDM is studied in the context of maternal obesity and insulin resistance, the consequences of GDM in lean, insulin sensitive women for offspring health are unclear. This preclinical study investigated whether GDM in lean dams characterized by reduced insulin secretion affects offspring metabolic health. Lean GDM was induced by short-term 60% high-fat diet and low-dose streptozotocin injections before mating in mice. The control dams received only high-fat diet (HF) or low-fat diet (LF). Glucose homeostasis was studied in chow-fed offspring. GDM resulted in decreased birth weight, that resolved at postnatal day 15 (PN15). At PN100, higher postprandial glucose responses were found in GDM offspring, while insulin secretion was lower in both GDM and HF offspring. Female GDM offspring showed lower endogenous glucose production and increased liver insulin sensitivity at PN100 compared to controls. No differences in metabolic parameters were observed at PN200 and PN300. Prenatal exposure to elevated maternal glucose levels without maternal obesity modestly affected glucose regulation in mouse offspring during early adulthood. Future studies should clarify if a less favourable postnatal diet may further challenge metabolic health in offspring of GDM dams.

Manipulation of Post-Prandial Hyperglycaemia in Type 2 Diabetes: An Update for Practitioners

This review paper explores post-prandial glycemia in type 2 diabetes. Post-prandial glycemia is defined as the period of blood glucose excursion from immediately after the ingestion of food or drink to 4 to 6 hours after the end of the meal. Post-prandial hyperglycemia is an independent risk factor for cardiovascular disease with glucose "excursions" being more strongly associated with markers of oxidative stress than the fasting or pre-prandial glucose level. High blood glucose is a major promoter of enhanced free radical production and is associated with the onset and progression of type 2 diabetes. Oxidative stress impairs insulin action creating a vicious cycle where repeated post-prandial glucose spikes are key drivers in the pathogenesis of the vascular complications of type 2 diabetes, both microvascular and macrovascular. Some authors suggest post-prandial hyperglycemia is the major cause of death in type 2 diabetes. Proper management of post-prandial hyperglycemia could yield up to a 35% cut in overall cardiovascular events, and a 64% cut in myocardial infarction. The benefits of managing post-prandial hyperglycemia are similar in magnitude to those seen in type 2 diabetes patients receiving secondary prevention with statins - prevention which today is regarded as fundamental by all practitioners. Given all the evidence surrounding the impact of post-prandial glycemia on overall outcome, it is imperative that any considered strategy for the management of type 2 diabetes should include optimum dietary, pharma, and lifestyle interventions that address glucose excursion. Achieving a low post-prandial glucose response is key to prevention and progression of type 2 diabetes and cardiometabolic diseases. Further, such therapeutic interventions should be sustainable and must benefit patients in the short and long term with the minimum of intrusion and side effects. This paper reviews the current literature around dietary manipulation of post-prandial hyperglycemia, including novel approaches. A great deal of further work is required to optimize and standardize the dietary management of post-prandial glycemia in type 2 diabetes, including consideration of novel approaches that show great promise.

A mixed meal tolerance test predicts onset of type 2 diabetes in Southwestern Indigenous adults

BACKGROUND/OBJECTIVE

To identify predictors of incident type 2 diabetes using a mixed meal tolerance test (MMTT).

METHODS

Adult Indigenous Americans without diabetes (n = 501) from a longitudinal cohort underwent at baseline a 4-h MMTT, measures of body composition, an oral glucose tolerance test, an intravenous glucose tolerance test for acute insulin response (AIR), and a hyperinsulinemic-euglycemic clamp for insulin action (M). Plasma glucose responses from the MMTT were quantified by the total and incremental area under the curve (AUC/iAUC).

RESULTS

At follow-up (median time 9.6 [inter-quartile range: 5.6-13.5] years), 169 participants were diagnosed with diabetes. Unadjusted Cox proportional hazards models, glucose AUC180-min (HR: 1.98, 95% CI: 1.67, 2.34, p < 0.0001), AUC240-min (HR: 1.93, 95% CI: 1.62, 2.31, p < 0.0001), and iAUC180-min (HR: 1.43, 95% CI: 1.20, 1.71, p < 0.0001) were associated with an increased risk of diabetes. After adjustment for covariates (age, sex, body fat percentage, M, AIR, Indigenous American heritage) in three subsequent models, AUC180-min (HR: 1.44, 95% CI: 1.10, 1.88, p = 0.007) and AUC240-min (HR: 1.41, 95% CI: 1.09, 1.84, p < 0.01) remained associated with increased risk of diabetes.

CONCLUSIONS

Glucose responses to a mixed meal predicted the development of type 2 diabetes. This indicates that a mixed nutritional challenge provides important information on disease risk.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov identifier : NCT00340132, NCT00339482.

Differential Responders to a Mixed Meal Tolerance Test Associated with Type 2 Diabetes Risk Factors and Gut Microbiota-Data from the MEDGI-Carb Randomized Controlled Trial

The global prevalence of type 2 diabetes mellitus (T2DM) has surged in recent decades, and the identification of differential glycemic responders can aid tailored treatment for the prevention of prediabetes and T2DM. A mixed meal tolerance test (MMTT) based on regular foods offers the potential to uncover differential responders in dynamical postprandial events. We aimed to fit a simple mathematical model on dynamic postprandial glucose data from repeated MMTTs among participants with elevated T2DM risk to identify response clusters and investigate their association with T2DM risk factors and gut microbiota. Data were used from a 12-week multi-center dietary intervention trial involving high-risk T2DM adults, comparing high- versus low-glycemic index foods within a Mediterranean diet context (MEDGICarb). Model-based analysis of MMTTs from 155 participants (81 females and 74 males) revealed two distinct plasma glucose response clusters that were associated with baseline gut microbiota. Cluster A, inversely associated with HbA1c and waist circumference and directly with insulin sensitivity, exhibited a contrasting profile to cluster B. Findings imply that a standardized breakfast MMTT using regular foods could effectively distinguish non-diabetic individuals at varying risk levels for T2DM using a simple mechanistic model.

Colostrum insulin supplementation to neonatal Holstein bulls affects small intestinal histomorphology, mRNA expression, and enzymatic activity with minor influences on peripheral metabolism

The objectives of this study were to evaluate how varying colostral insulin concentrations influenced small intestinal development and peripheral metabolism in neonatal Holstein bulls. Insulin was supplemented to approximately 5× (70.0 μg/L; n = 16) or 10× (149.7 μg/L; n = 16) the basal colostrum insulin (12.9 μg/L; BI, n = 16) concentration to maintain equivalent macronutrient intake (crude fat: 4.1 ± 0.06%; crude protein: 11.7 ± 0.05%; and lactose: 1.9 ± 0.01%) among treatments. Colostrum was fed at 2, 14, and 26 h postnatal and blood metabolites and insulin concentration were measured at 0, 30, 60, 90, 120, 180, 240, 360, 480, and 600 min postprandial respective to the first and second colostrum meal. At 30 h postnatal, a subset of calves (n = 8/treatment) were killed to excise the gastrointestinal and visceral tissues. Gastrointestinal and visceral gross morphology and dry matter and small intestinal histomorphology, gene expression, and carbohydrase activity were assessed. Insulin supplementation tended to linearly reduce the glucose clearance rate following the first meal, whereas after the second meal, supplementation linearly increased the rate of glucose absorption and nonesterified fatty acid clearance rate, decreased the time to maximum glucose concentrations, and decreased the time to reach minimum nonesterified fatty acid concentrations. Additionally, insulin clearance rate was linearly increased by insulin supplementation following the second colostrum feeding. However, there were no overall differences between treatments in the concentrations of glucose, nonesterified fatty acids, or insulin in plasma or serum. With respect to macroscopic intestinal development, dry rumen tissue mass linearly decreased when insulin was supplemented in colostrum, and supplementation linearly increased duodenal dry tissue density (g dry matter/cm) while tending to increase duodenal dry tissue weight. Increasing the colostrum insulin concentration improved small intestinal histomorphological development in the distal small intestine, as ileal villi height and mucosal-serosal surface area index were increased by supplementing insulin. Lactase enzymatic activity linearly increased in the proximal jejunum while ileal isomaltase activity linearly decreased with insulin supplementation. These data indicate that changes in colostrum insulin concentrations rapidly affect gastrointestinal growth prioritization and carbohydrase activity. The changes in gastrointestinal ontology result in minor changes in postprandial metabolite availability and clearance.

Effects of co-ingesting glucose and whey protein on blood glucose, plasma insulin and glucagon concentrations, and gastric emptying, in older men with and without type 2 diabetes

AIM

To investigate whether co-ingestion of dietary protein with, or before, carbohydrate may be a useful strategy to reduce postprandial hyperglycaemia in older men with type 2 diabetes (T2D).

MATERIALS AND METHODS

Blood glucose, plasma insulin and glucagon concentrations were measured for 180 minutes following ingestion of a drink containing 30 g of glucose (G; 120 kcal), 30 g of whey protein (120 kcal), 30 g of glucose plus 30 g of whey protein (GP; 240 kcal), or control (~2 kcal) in older men with T2D (n = 10, 77 ± 1 years; 31 ± 1.7 kg/m2 ) and without T2D (n = 10, 78 ± 2 years; 27 ± 1.4 kg/m2 ). Mixed model analysis was used.

RESULTS

GP versus G markedly reduced the increase in blood glucose concentrations (P < .001) and had a synergistic effect on the increase in insulin concentrations (P < .001), in men both with and without T2D. Glucose concentrations were higher in men with T2D compared with those without T2D, whereas insulin and glucagon concentrations were largely unaffected by the presence of T2D. Gastric emptying was faster in men with T2D than in those without T2D.

CONCLUSIONS

The ability of whey protein to reduce carbohydrate-induced, postprandial hyperglycaemia is retained in older men with T2D compared with those without T2D, and whey protein supplementation may be a useful strategy in the prevention and management of T2D in older people.

A Glucose-Only Model to Extract Physiological Information from Postprandial Glucose Profiles in Subjects with Normal Glucose Tolerance

BACKGROUND

Current mathematical models of postprandial glucose metabolism in people with normal and impaired glucose tolerance rely on insulin measurements and are therefore not applicable in clinical practice. This research aims to develop a model that only requires glucose data for parameter estimation while also providing useful information on insulin sensitivity, insulin dynamics and the meal-related glucose appearance (GA).

METHODS

The proposed glucose-only model (GOM) is based on the oral minimal model (OMM) of glucose dynamics and substitutes the insulin dynamics with a novel function dependant on glucose levels and GA. A Bayesian method and glucose data from 22 subjects with normal glucose tolerance are utilised for parameter estimation. To validate the results of the GOM, a comparison to the results of the OMM, obtained by using glucose and insulin data from the same subjects is carried out.

RESULTS

The proposed GOM describes the glucose dynamics with comparable precision to the OMM with an RMSE of 5.1 ± 2.3 mg/dL and 5.3 ± 2.4 mg/dL, respectively and contains a parameter that is significantly correlated to the insulin sensitivity estimated by the OMM (r = 0.7) Furthermore, the dynamic properties of the time profiles of GA and insulin dynamics inferred by the GOM show high similarity to the corresponding results of the OMM.

CONCLUSIONS

The proposed GOM can be used to extract useful physiological information on glucose metabolism in subjects with normal glucose tolerance. The model can be further developed for clinical applications to patients with impaired glucose tolerance under the use of continuous glucose monitoring data.

Discordance between postprandial plasma glucose measurement and continuous glucose monitoring

BACKGROUND

There has been growing interest in studying postprandial glucose responses using continuous glucose monitoring (CGM) in nondiabetic individuals. Accurate measurement of glucose responses to meals can facilitate applications such as precision nutrition and early detection of diabetes.

OBJECTIVES

We aimed to quantify the discordance between simultaneous postprandial glucose measurements made using plasma and CGM.

METHODS

We studied 10 nondiabetic older adults who randomly consumed 9 predefined meals of varying macronutrient compositions. Glucose was measured for 8 h after the meal by the CGM, blood samples for plasma collection were taken regularly, and plasma glucose was quantified using gold-standard laboratory measurement and a fingerstick blood glucose meter. The primary outcome measured was the mean absolute relative difference (MARD) of CGM and fingerstick measurements relative to the gold standard. Secondary outcomes were Bland-Altman statistics, Clarke Error Grid, and time in range metrics. Additional subgroup analyses were performed by stratifying the postprandial glucose measurements based on the macronutrient composition of the meals.

RESULTS

When compared against the gold-standard postprandial glucose measurements, the fingerstick meter was more accurate (MARD: 8.0%; 95% CI: 7.6%, 8.6%) than the CGM (MARD: 13.7%; 95% CI: 13.1%, 14.3%; P < 0.0001). After the meals, Bland-Altman analysis demonstrated that the CGM underestimated the 8-h gold-standard glucose rise by 12.8 mg/dL on average (P < 0.0001), whereas the fingerstick meter did so by 5.5 mg/dL on average (P < 0.0001). The CGM underestimated the time spent in the 70-180 mg/dL range (P = 0.002) and overestimated the time spent <70 mg/dL (P < 0.0001) compared with the other 2 methods.

CONCLUSIONS

We discovered discordance between gold standard, fingerstick, and CGM in measuring plasma glucose concentrations after a meal. Consequently, emerging applications of CGM in healthy individuals, such as precision nutrition and diabetes onset prediction, may need to account for these discordances.This trial was registered at clinicaltrials.gov as NCT04928872.

Comparative Effects of Co-Ingesting Whey Protein and Glucose Alone and Combined on Blood Glucose, Plasma Insulin and Glucagon Concentrations in Younger and Older Men

The ingestion of dietary protein with, or before, carbohydrate may be a useful strategy to reduce postprandial hyperglycemia, but its effect in older people, who have an increased predisposition for type 2 diabetes, has not been clarified. Blood glucose, plasma insulin and glucagon concentrations were measured for 180 min following a drink containing either glucose (120 kcal), whey-protein (120 kcal), whey-protein plus glucose (240 kcal) or control (~2 kcal) in healthy younger (n = 10, 29 ± 2 years; 26.1 ± 0.4 kg/m2) and older men (n = 10, 78 ± 2 years; 27.3 ± 1.4 kg/m2). Mixed model analysis was used. In both age groups the co-ingestion of protein with glucose (i) markedly reduced the increase in blood glucose concentrations following glucose ingestion alone (p < 0.001) and (ii) had a synergistic effect on the increase in insulin concentrations (p = 0.002). Peak insulin concentrations after protein were unaffected by ageing, whereas insulin levels after glucose were lower in older than younger men (p < 0.05) and peak insulin concentrations were higher after glucose than protein in younger (p < 0.001) but not older men. Glucagon concentrations were unaffected by age. We conclude that the ability of whey-protein to reduce carbohydrate-induced postprandial hyperglycemia is retained in older men and that protein supplementation may be a useful strategy in the prevention and management of type 2 diabetes in older people.

Metabolic Effects of an Oral Glucose Tolerance Test Compared to the Mixed Meal Tolerance Tests: A Narrative Review

The oral glucose tolerance test (OGTT) is recommended for assessing abnormalities in glucose homeostasis. Recognised as the gold standard test for diagnosing diabetes, the OGTT provides useful information about glucose tolerance. However, it does not replicate the process of absorption and digestion of complex foods, such as that which occurs with a mixed meal tolerance test (MMTT), an alternative that is still not well explored in the diagnosis of metabolic alterations. The MMTT could be an asset in detecting glucose homeostasis disorders, including diabetes since it has more similarities to the common dietary pattern, allowing early detection of subtle changes in metabolic homeostasis in response to combined nutrients. This alternative has the advantage of being more tolerable and pleasant to patients since it induces a more gradual increase in blood glucose, thus reducing the risk of rebound hypoglycemia and other related complications. The present article reviewed the clinical data available regarding the possibility of screening or diagnosing altered glucose homeostasis, including type 2 diabetes mellitus, with the MMTT.

Comparative Assessment of the Acute Effects of Whey, Rice and Potato Protein Isolate Intake on Markers of Glycaemic Regulation and Appetite in Healthy Males Using a Randomised Study Design

Global protein consumption has been increasing for decades due to changes in demographics and consumer shifts towards higher protein intake to gain health benefits in performance nutrition and appetite regulation. Plant-derived proteins may provide a more environmentally sustainable alternative to animal-derived proteins. This study, therefore, aimed to investigate, for the first time, the acute effects on glycaemic indices, gut hormones, and subjective appetite ratings of two high-quality, plant-derived protein isolates (potato and rice), in comparison to a whey protein isolate in a single-blind, triple-crossover design study with nine male participants (30.8 ± 9.3 yrs). Following a 12 h overnight fast, participants consumed an equal volume of the three isocaloric protein shakes on different days, with at least a one-week washout period. Glycaemic indices and gut hormones were measured at baseline, then at 30, 60, 120, 180 min at each visit. Subjective palatability and appetite ratings were measured using visual analogue scales (VAS) over the 3 h, at each visit. This data showed significant differences in insulin secretion with an increase in whey (+141.8 ± 35.1 pmol/L; p = 0.011) and rice (−64.4 ± 20.9 pmol/L; p = 0.046) at 30 min compared to potato protein. A significantly larger total incremental area under the curve (iAUC) was observed with whey versus potato and rice with p < 0.001 and p = 0.010, respectively. There was no significant difference observed in average appetite perception between the different proteins. In conclusion, this study suggests that both plant-derived proteins had a lower insulinaemic response and improved glucose maintenance compared to whey protein.

Postprandial responses of circulating energy homeostasis mediators to single macronutrient challenges: influence of obesity and sex hormones

We analysed the influence of obesity, sex and sex steroids on the postprandial responses of circulating energy homeostasis mediators and their receptors to different macronutrient challenges. Seventeen women with polycystic ovary syndrome (PCOS, 8 with obesity), 17 non-hyperandrogenic control women (8 with obesity) and 19 control men (9 with obesity) were submitted, on alternate days, to isocaloric (300 kcal) oral glucose, lipid and protein loads. We evaluated serum ghrelin, leptin, soluble leptin receptor and adiponectin levels and the leukocyte gene expression of ghrelin (GHRL) and its receptor (GHSR), leptin receptor (LEPR) and adiponectin receptor 1 (ADIPOR1) during the macronutrient challenges. The postprandial responses of circulating energy homeostasis mediators were entirely different than those of their related genes. After macronutrient loads the postprandial response of serum energy homeostasis mediators showed a generalized physiological decrease that was blunted in subjects with obesity but was not influenced by sex, sex hormones or PCOS. However, gene expression of GHRL, LEPR and ADIPOR1 showed a marked increase following the ingestion of glucose compared with lipids and proteins, regardless of obesity and sex steroids. The physiological decrease after macronutrient loads, that was deregulated in obesity, did not reflect the acute leukocyte gene expression mainly after glucose, and may suggest a possible role for ghrelin, leptin and adiponectin in the postprandial inflammatory process.

Impact of mixed meal tolerance test composition on measures of beta-cell function in type 2 diabetes

Background

Application of mixed meal tolerance tests (MMTT) to measure beta-cell function in long-term studies is limited by modification of the commercial products occurring over time. This study assessed the intra-individual reliability of MMTTs and compared the effects of liquid meals differing in macronutrient composition on the estimation of beta-cell function in type 2 diabetes (T2DM).

Methods

To test the reliability of MMTTs, 10 people with T2DM (age 58 ± 11 years, body mass index 30.0 ± 4.9 kg/m²) received Boost®high Protein 20 g protein three times. For comparing different meals, another 10 persons with T2DM (58 ± 5 years, 31.9 ± 5.3 kg/m²) ingested either Boost®high Protein 20 g protein or the isocaloric Boost®high Protein 15 g protein containing 35% less protein and 18% more carbohydrates. C-peptide, insulin and glucose release were assessed from the incremental area under the concentration time curve (iAUC) and the intra- and inter-individual variation of these parameters from the coefficients of variations (CV).

Results

Repetitive ingestion of one meal revealed intra-individual CVs for the iAUCs of C-peptide, insulin and glucose, which were at least 3-times lower than the inter-individual variation of these parameters (18.2%, 19.7% and 18.9% vs. 74.2%, 70.5% and 207.7%) indicating a good reliability. Ingestion of two different meals resulted in comparable intra-individual CVs of the iAUCs of C-peptide and insulin (16.9%, 20.5%).

Conclusion

MMTTs provide reliable estimation of beta-cell function in people with T2DM. Furthermore, moderate differences in the protein and carbohydrate contents in a standardized liquid meal do not result in relevant changes of C-peptide and insulin responses.

Trial registration: Clinicaltrials.gov, Identifier number: NCT01055093. Registered 22 January 2010 – Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/study/NCT01055093

Bayesian parameter estimation in the oral minimal model of glucose dynamics from non-fasting conditions using a new function of glucose appearance

BACKGROUND AND OBJECTIVE

The oral minimal model (OMM) of glucose dynamics is a prominent method for assessing postprandial glucose metabolism. The model yields estimates of insulin sensitivity and the meal-related appearance of glucose from insulin and glucose data after an oral glucose challenge. Despite its success, the OMM approach has several weaknesses that this paper addresses.

METHODS

A novel procedure introducing three methodological adaptations to the OMM approach is proposed. These are: (1) the use of a fully Bayesian and efficient method for parameter estimation, (2) the model identification from non-fasting conditions using a generalised model formulation and (3) the introduction of a novel function to represent the meal-related glucose appearance based on two superimposed components utilising a modified structure of the log-normal distribution. The proposed modelling procedure is applied to glucose and insulin data from subjects with normal glucose tolerance consuming three consecutive meals in intervals of four hours.

RESULTS

It is shown that the glucose effectiveness parameter of the OMM is, contrary to previous results, structurally globally identifiable. In comparison to results from existing studies that use the conventional identification procedure, the proposed approach yields an equivalent level of model fit and a similar precision of insulin sensitivity estimates. Furthermore, the new procedure shows no deterioration of model fit when data from non-fasting conditions are used. In comparison to the conventional, piecewise linear function of glucose appearance, the novel log-normally based function provides an improved model fit in the first 30 min of the response and thus a more realistic estimation of glucose appearance during this period. The identification procedure is implemented in freely accesible MATLAB and Python software packages.

CONCLUSIONS

We propose an improved and freely available method for the identification of the OMM which could become the future standardard for the oral minimal modelling method of glucose dynamics.

A Delayed Morning and Earlier Evening Time-Restricted Feeding Protocol for Improving Glycemic Control and Dietary Adherence in Men with Overweight/Obesity: A Randomized Controlled Trial

We determined the effects of time-restricted feeding (TRF; 8 h/d) versus extended feeding (EXF; 15 h/d) on 24-h and postprandial metabolism and subjective opinions of TRF in men with overweight/obesity. In a randomized crossover design, 11 sedentary males (age 38 ± 5 y; BMI: 32.2 ± 2.0 kg/m²) completed two isoenergetic diet protocols for 5 days, consuming meals at 1000, 1300 and 1700 h (TRF) or 0700, 1400 and 2100 h (EXF). On Day 5, participants remained in the laboratory for 24 h, and blood samples were collected at hourly (0700–2300 h) then 2-hourly (2300–0700 h) intervals for concentrations of glucose, insulin and appetite/incretin hormones. Structured qualitative interviews were conducted following completion of both dietary conditions and investigated thematically. Total 24-h area under the curve (AUC_total) [glucose] tended to be lower for TRF versus EXF (−5.5 ± 9.0 mmol/L/h, p = 0.09). Nocturnal glucose AUC was lower in TRF (−4.2 ± 5.8 mmol/L/h, p = 0.04), with no difference in waking glucose AUC or AUC_total for [insulin]. Attitudes towards TRF were positive with improved feelings of well-being. Barriers to TRF were work schedules, family commitments and social events. Compared to extended feeding, short-term TRF improved nocturnal glycemic control and was positively perceived in men with overweight/obesity.

New Insight into Diabetes Management: From Glycemic Index to Dietary Insulin Index

BACKGROUND

Despite efforts to control hyperglycemia, diabetes management is still challenging. This may be due to focusing on reducing hyperglycemia and neglecting the importance of hyperinsulinemia; while insulin resistance and resultant hyperinsulinemia preceded diabetes onset and may contribute to disease pathogenesis.

OBJECTIVE

The present narrative review attempts to provide a new insight into the management of diabetes by exploring different aspects of glycemic index and dietary insulin index.

RESULTS

The current data available on this topic is limited and heterogeneous. Conventional diet therapy for diabetes management is based on reducing postprandial glycemia through carbohydrate counting, choosing foods with low-glycemic index and low-glycemic load. Since these indicators are only reliant on the carbohydrate content of foods and do not consider the effects of protein and fat on the stimulation of insulin secretion, they cannot provide a comprehensive approach to determine the insulin requirements.

CONCLUSION

Selecting foods based on carbohydrate counting, glycemic index or glycemic load are common guides to control glycemia in diabetic patients, but neglect the insulin response, thus leading to failure in diabetes management. Therefore, paying attention to insulinemic response along with glycemic response seems to be more effective in managing diabetes.

Influence of macronutrient composition of commercial diets on circulating leptin and adiponectin concentrations in overweight dogs

Leptin and adiponectin play important roles in obesity‐related inflammation and comorbidities. Previous research suggests that alterations in dietary macronutrient composition can modify circulating leptin and adiponectin concentrations in people, but limited research on this subject has been performed in dogs. This study investigated the effects of commercial high protein (HP), high fat (HF) and high carbohydrate medium protein (HCMP) diets on baseline (T₋₁) concentrations, post‐prandial peak concentrations and total release in a ten‐hour time span of leptin and adiponectin in dogs, when compared to a maintenance high carbohydrate low protein (HCLP) diet. Thirty‐six overweight dogs were fed the HCLP diet in a one‐week control period, after which the animals were assigned to one of three groups. In three four‐week periods, each group was fed all test diets in a different sequence. At the last day of each period, blood was sampled at one hour before feeding (T₋₁) and at three (T₃), six (T₆) and nine (T₉) hours after feeding. Feeding caused peak leptin concentrations at T₆ and T₉ (p < .001). No significant post‐prandial change in adiponectin concentrations was found (p = .056). The HP diet resulted in lower leptin peak concentrations (p = .004) and AUC_T−1–T9 (p = .01), but none of the diets influenced baseline leptin concentrations (p = .273). Baseline adiponectin concentrations were lower for the HF diet (p = .018) and HCMP (p < .001), and the HP, HF and HCMP AUC_T−1–T9 (p < .001) were lower compared with the HCLP diet. Female dogs had lower adiponectin baseline concentrations (p = .041) and AUC_T−1–T9 (p = .023) than male dogs. In conclusion, the HP diet was associated with the lowest post‐prandial peak leptin concentration and the least decrease in adiponectin release, suggesting that a HP diet may improve immune‐metabolic health and post‐prandial satiety in overweight dogs.

Regulation of GLUT4 translocation in an in vitro cell model using postprandial human serum ex vivo

NEW FINDINGS

What is the research question? This study used a new experimental model, in which culture medium is conditioned with human serum ex vivo, to investigate nutrient-mediated regulation of GLUT4 translocation in skeletal muscle cells in vitro. What is the main finding and importance? Human serum stimulated GLUT4 translocation, an effect differentially modulated by whether the culture medium was conditioned with serum from fasted subjects or with serum collected after feeding of intact or hydrolysed whey protein. Conditioning cell culture medium with human serum ex vivo represents a new approach to elucidate the effects of ingesting specific nutrients on skeletal muscle cell metabolism.

ABSTRACT

Individual amino acids, amino acid mixtures and protein hydrolysates stimulate glucose uptake in many experimental models. To replicate better in vitro the dynamic postprandial response to feeding in vivo, in the present study we investigated the effects of culture media conditioned with fasted and postprandial human serum on GLUT4 translocation in L6-GLUT4myc myotubes. Serum samples were collected from healthy male participants (n = 8) at baseline (T0), 60 (T60) and 120 min (T120) after the ingestion of 0.33 g (kg body mass)^-1 of intact (WPC) or hydrolysed (WPH) whey protein and an isonitrogenous non-essential amino acid (NEAA) control. L6-GLUT4myc myotubes were starved of serum and amino acids for 1 h before incubation for 1 h in medium containing 1% postprandial human serum, after which GLUT4 translocation was determined via colorimetric assay. Medium conditioned with fasted human serum at concentrations of 5-20% increased cell surface GLUT4myc abundance. Incubation with serum collected after the ingestion of WPH increased cell surface GLUT4myc at T60 relative to T0 [mean (lower, upper 95% confidence interval)]; [1.13 (1.05, 1.22)], whereas WPC [0.98 (0.90, 1.07)] or NEAA [1.02 (0.94, 1.11)] did not. The differential increases in cell surface GLUT4myc abundance were not explained by differences in serum concentrations of total, essential and branched-chain amino acids or insulin, glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP). Using a new ex vivo, in vitro approach, cell culture medium conditioned with postprandial serum after the ingestion of a whey protein hydrolysate increased GLUT4 translocation in skeletal muscle cells.

Physiological hyperinsulinemia caused by acute hyperglycemia minimizes renal sodium loss by direct action on kidneys

This study used acute, renal artery insulin infusion in conscious rats to test the hypothesis that hyperinsulinemia attenuates glucose-induced natriuresis by a direct renal mechanism. We reported previously that hyperinsulinemia was required to prevent ad libitum eating or an acute glucose bolus from causing excessive renal sodium loss. Rats were instrumented with renal artery, aortic, and femoral vein catheters and Data Sciences International blood pressure telemeters and were housed in metabolic cages. Insulin was clamped chronically at normal levels in two groups [vehicle infused (irV) and insulin infused (irI)] by administering streptozotocin and then infusing insulin intravenously 24 h/day to maintain normal blood glucose. Bolus glucose administration was used as a meal substitute to produce hyperglycemia that was not different between groups, and urinary sodium excretion (UNaV) was measured over the next 4 h. In the irV and control (C) rats, vehicle was infused in the renal artery during that period, whereas insulin was infused in the renal artery of the irI rats. Plasma insulin increased significantly in C rats but not in either of the clamped groups. UNaV in the irV rats, which could not increase circulating insulin levels, was approximately threefold greater than in C rats, similar to our previous report. However, allowing the kidney of irI rats to experience hyperinsulinemia via the renal artery insulin infusion completely prevented this, with no blood pressure differences. These data support our hypothesis that meal-induced increases in plasma insulin are a major component of normal sodium homeostasis, and that this occurs by direct action of insulin on the kidney.

The Synergism in Hormonal and Cellular Changes in Male Mice on Long Term High Fat Exposure

OBJECTIVE

To determine the hormonal changes that occur as a result of the long-term intake of a very-high-fat diet (VHFD) that leads to simultaneous changes in the islets of Langerhans and adipocyte cell size.

METHODS

Male mice were fed with a normal chow diet (ND, n = 15) and a VHFD (n = 30) for 2, 12, and 24 weeks. Body weight, food intake, caloric intake (fat [saturated and unsaturated], protein, and carbohydrate), hormone levels (leptin and insulin), and islet of Langerhans/adipocyte size were quantitatively recorded.

RESULTS

In VHFD-fed animals, body weight showed a significant percent increase within the first 12 weeks and then plateaued with time. VHFD-fed animals consumed significantly less food than ND at all time periods, indicating that it was the quality of food and not the quantity that caused this increase in body weight. Male mice on VHFD showed a significant increase in leptin and insulin levels, along with accompanying growth in islet and adipocyte size within the first 12 weeks, which plateaued as the mice aged. The increases in the islet and adipocyte size in VHFD-fed animals were similar to the analogous increases in hormonal levels (2 vs. 12 vs. 24 weeks). These results, therefore, suggest that in diet-induced obesity changes, shifts in hormonal levels works hand-in-hand with metabolic adjustments at the cellular level to combat the effect of fat.

CONCLUSION

Thus, mechanisms like hormonal resistance, changes in adiposity, islet size, and caloric intake with prolonged exposure to high fat are probably defensive mechanisms employed to protect against diabetes. In order to understand these complicated and nuanced effects of high fat and to comprehend the underlying mechanism associated with it, it is important to focus on long-term studies that emphasize the synergy between cellular and hormonal changes, in addition to an analysis of individual components.

The Effect of a Diet Moderately High in Protein and Fiber on Insulin Sensitivity Measured Using the Dynamic Insulin Sensitivity and Secretion Test (DISST)

Evidence shows that weight loss improves insulin sensitivity but few studies have examined the effect of macronutrient composition independently of weight loss on direct measures of insulin sensitivity. We randomised 89 overweight or obese women to either a standard diet (StdD), that was intended to be low in fat and relatively high in carbohydrate (n = 42) or to a relatively high protein (up to 30% of energy), relatively high fibre (>30 g/day) diet (HPHFib) (n = 47) for 10 weeks. Advice regarding strict adherence to energy intake goals was not given. Insulin sensitivity and secretion was assessed by a novel method—the Dynamic Insulin Sensitivity and Secretion Test (DISST). Although there were significant improvements in body composition and most cardiometabolic risk factors on HPHFib, insulin sensitivity was reduced by 19.3% (95% CI: 31.8%, 4.5%; p = 0.013) in comparison with StdD. We conclude that the reduction in insulin sensitivity after a diet relatively high in both protein and fibre, despite cardiometabolic improvements, suggests insulin sensitivity may reflect metabolic adaptations to dietary composition for maintenance of glucose homeostasis, rather than impaired metabolism.

Satiety and memory enhancing effects of a high-protein meal depend on the source of protein

OBJECTIVE

High- protein diets have become increasingly popular with various touted benefits. However, the extent to which protein quantity and source affects cognitive functioning through altering postprandial amino acid profiles has not been investigated. Further, whether all protein sources are similarly anorexigenic is uncertain. The objective of this study was to determine the influence of protein level and source on Barnes maze performance, satiety and plasma amino acid levels in male Sprague-Dawley rats.

METHODS

Rats were entrained to a meal-feeding schedule consisting of a 30 minutes meal, equivalent to 20% of average daily intake, one hour into the dark phase then ad libitum access to food for 5 h. On test days, rats received one of three isocaloric diets as their first meal, hereafter referred to as Egg White (EW), Wheat Gluten (WG), or Basal, and then were measured for cognitive performance, feeding behavior, or plasma amino acid levels via jugular catheter. Percentage energy from protein was 35% for both EW and WG and 20% for Basal with equal amounts provided by EW and WG proteins.

RESULTS

Rats provided EW performed similarly to Basal on the Barnes maze, whereas WG performed worse. EW increased satiety, whereas WG reduced satiety relative to Basal. Both EW and WG increased postprandial concentrations of large neutral and branched chain amino acids relative to Basal, but in EW, concentrations were slower to peak, and peaked to a higher level than WG.

DISCUSSION

Results demonstrate the importance of protein source for cognition and satiety enhancing effects of a high-protein meal.

A data driven nonlinear stochastic model for blood glucose dynamics

The development of adequate mathematical models for blood glucose dynamics may improve early diagnosis and control of diabetes mellitus (DM). We have developed a stochastic nonlinear second order differential equation to describe the response of blood glucose concentration to food intake using continuous glucose monitoring (CGM) data. A variational Bayesian learning scheme was applied to define the number and values of the system's parameters by iterative optimisation of free energy. The model has the minimal order and number of parameters to successfully describe blood glucose dynamics in people with and without DM. The model accounts for the nonlinearity and stochasticity of the underlying glucose-insulin dynamic process. Being data-driven, it takes full advantage of available CGM data and, at the same time, reflects the intrinsic characteristics of the glucose-insulin system without detailed knowledge of the physiological mechanisms. We have shown that the dynamics of some postprandial blood glucose excursions can be described by a reduced (linear) model, previously seen in the literature. A comprehensive analysis demonstrates that deterministic system parameters belong to different ranges for diabetes and controls. Implications for clinical practice are discussed. This is the first study introducing a continuous data-driven nonlinear stochastic model capable of describing both DM and non-DM profiles.

Metabolic effects of Foofoo corn on healthy volunteers: influence of some traditional Cameroonian sauces

Background

Little data to guide diet prescription exists about the foods most frequently consumed in Africa. Moreover, the sauce accompanying a meal can significantly alter the metabolic effects of food. Our work was to study the influence of sauces on the metabolic effects of foofoo corn (Zea mays), one of the most commonly consumed foods in several countries in sub-Saharan Africa with a wide range of sauces.

Methods

Our study population consisted of ten healthy volunteers (five men, five women), aged from 21 to 28 years, with mean BMI of 23.9 (SD 1.9) kg/m². The study involved seven visits of three hours each, conducted every 2 days, including one devoted to the oral glucose tolerance test (OGTT) and six visits to the consumption of each of 6 meals tested, standardized to 75 g of carbohydrate intake. Blood samples were collected at 0, 15, 30, 60, 90, 120 and 180 min after consumption of meals for blood glucose and triglycerides levels. The glucose area under the curve of each tested meal, was used to calculate its glycemic index, using the OGTT as the reference. The accompanying sauces tested with foofoo corn were: okra sauce (Abelmoschus esculentus), the so-called yellow sauce (Elaeis guinensis), the pistachio sauce (Pistacia vera), the nkui (Triumpheta pentandra), ndolé (Vernonia amygdalima) and cabbage (Brassica oleracea).

Results

All meals had generally a low glycemic index, with a maximum of 22.59 % for okra and cabbage, followed by ndolè (20.18 %), the yellow sauce (13.10 %), pistachio sauce (11.60 %), and nkui (5.27 %). There was a difference in the effects of the diets on triglyceride levels only at 180 min (p = 0.03).

Conclusion

Whatever the accompanying sauce, foofoo corn has a low glycemic index. Some sauces, such as nkui give it a very low glycemic index and may be of great interest in diet prescription for patients with various metabolic disorders such as diabetes and obesity.

Postprandial glycaemic and insulinaemic responses in adults after consumption of dairy desserts and pound cakes containing short-chain fructo-oligosaccharides used to replace sugars

The present studies aimed to evaluate the glycaemic and insulinaemic responses, in healthy adults, to short-chain fructo-oligosaccharides (scFOS) from sucrose used to replace sugars in foods. Two study populations aged 18-50 years were recruited and they consumed dairy desserts or pound cakes containing either standard sugar content or scFOS to replace 30 % of the sugar content. For each study, the two products were tested once under a double-blind and cross-over design with at least 7 d between the two tests. Glucose and insulin were measured using standard methods in blood samples collected with a venous catheter for 120 min during a kinetic test. For the dairy desserts, replacing 30 % of the sugars with scFOS significantly reduced postprandial glycaemic (AUC0-120 min; P = 0·020) and insulinaemic (AUC0-120 min; P = 0·003) responses. For the pound cakes, the glycaemic response was not altered (AUC0-120 min; P =  0·322) while the insulinaemic response tended to be lower (AUC0-120 min; P = 0·067). This study showed that scFOS can be used to replace sugars with the benefit of lowering the postprandial glycaemic response without increasing the insulinaemic response. The effect might be modulated by other parameters (e.g. fat content) of the food matrices.

Dairy foods and dairy proteins in the management of type 2 diabetes: a systematic review of the clinical evidence

Type 2 diabetes mellitus (T2DM) is a growing public health concern affecting hundreds of millions of people worldwide and costing the global economy hundreds of billions of dollars annually. This chronic disease damages the blood vessels and increases the risk of other cardiometabolic ailments such as cardiovascular disease and stroke. If left unmanaged it can also lead to nerve damage, kidney damage, blindness, and amputation. For the most part, many of these symptoms can be prevented or reduced through simple dietary modifications and proper nutrition. Therefore, identifying relatively inexpensive and easily implementable dietary modifications for the prevention and management of T2DM is of considerable value to human health and healthcare modalities around the globe. Protein-rich dairy products have consistently been shown in epidemiologic studies to be beneficial for reducing the risk of developing T2DM. The clinical evidence regarding both dairy foods and dairy proteins (i.e., casein and whey protein) have shown promise for improving insulin secretion in individuals with T2DM. However, the clinical research on dairy protein supplementation in subjects with T2DM has been limited to acute studies. These studies have been mostly descriptive and have not been focused on important T2DM endpoints such as prevention, management, or treatment. Long-term studies are clearly needed to help researchers and medical professionals better understand the effects of consistent dairy protein intake on the metabolic health of humans with T2DM.

Differential acute postprandial effects of processed meat and isocaloric vegan meals on the gastrointestinal hormone response in subjects suffering from type 2 diabetes and healthy controls: a randomized crossover study

BACKGROUND

The intake of meat, particularly processed meat, is a dietary risk factor for diabetes. Meat intake impairs insulin sensitivity and leads to increased oxidative stress. However, its effect on postprandial gastrointestinal hormone (GIH) secretion is unclear. We aimed to investigate the acute effects of two standardized isocaloric meals: a processed hamburger meat meal rich in protein and saturated fat (M-meal) and a vegan meal rich in carbohydrates (V-meal). We hypothesized that the meat meal would lead to abnormal postprandial increases in plasma lipids and oxidative stress markers and impaired GIH responses.

METHODS

In a randomized crossover study, 50 patients suffering from type 2 diabetes (T2D) and 50 healthy subjects underwent two 3-h meal tolerance tests. For statistical analyses, repeated-measures ANOVA was performed.

RESULTS

The M-meal resulted in a higher postprandial increase in lipids in both groups (p<0.001) and persistent postprandial hyperinsulinemia in patients with diabetes (p<0.001). The plasma glucose levels were significantly higher after the V-meal only at the peak level. The plasma concentrations of glucose-dependent insulinotropic peptide (GIP), peptide tyrosine-tyrosine (PYY) and pancreatic polypeptide (PP) were higher (p<0.05, p<0.001, p<0.001, respectively) and the ghrelin concentration was lower (p<0.001) after the M-meal in healthy subjects. In contrast, the concentrations of GIP, PYY and PP were significantly lower after the M-meal in T2D patients (p<0.001). Compared with the V-meal, the M-meal was associated with a larger increase in lipoperoxidation in T2D patients (p<0.05).

CONCLUSION/INTERPRETATION

Our results suggest that the diet composition and the energy content, rather than the carbohydrate count, should be important considerations for dietary management and demonstrate that processed meat consumption is accompanied by impaired GIH responses and increased oxidative stress marker levels in diabetic patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01572402.

Estimating insulin demand for protein-containing foods using the food insulin index

BACKGROUND/OBJECTIVE

The Food Insulin Index (FII) is a novel algorithm for ranking foods on the basis of insulin responses in healthy subjects relative to an isoenergetic reference food. Our aim was to compare postprandial glycemic responses in adults with type 1 diabetes who used both carbohydrate counting and the FII algorithm to estimate the insulin dosage for a variety of protein-containing foods.

SUBJECTS/METHODS

A total of 11 adults on insulin pump therapy consumed six individual foods (steak, battered fish, poached eggs, low-fat yoghurt, baked beans and peanuts) on two occasions in random order, with the insulin dose determined once by the FII algorithm and once with carbohydrate counting. Postprandial glycemia was measured in capillary blood glucose samples at 15-30  min intervals over 3 h. Researchers and participants were blinded to treatment.

RESULTS

Compared with carbohydrate counting, the FII algorithm significantly reduced the mean blood glucose level (5.7±0.2  vs 6.5±0.2 mmol/l, P=0.003) and the mean change in blood glucose level (-0.7±0.2 vs 0.1±0.2 mmol/l, P=0.001). Peak blood glucose was reached earlier using the FII algorithm than using carbohydrate counting (34±5 vs 56±7 min, P=0.007). The risk of hypoglycemia was similar in both treatments (48% vs 33% for FII vs carbohydrate counting, respectively, P=0.155).

CONCLUSIONS

In adults with type 1 diabetes, compared with carbohydrate counting, the novel FII algorithm improved postprandial hyperglycemia after consumption of protein-containing foods.

A tripeptide Diapin effectively lowers blood glucose levels in male type 2 diabetes mice by increasing blood levels of insulin and GLP-1

The prevalence of type 2 diabetes (T2D) is rapidly increasing worldwide. Effective therapies, such as insulin and Glucagon-like peptide-1 (GLP-1), require injections, which are costly and result in less patient compliance. Here, we report the identification of a tripeptide with significant potential to treat T2D. The peptide, referred to as Diapin, is comprised of three natural L-amino acids, GlyGlyLeu. Glucose tolerance tests showed that oral administration of Diapin effectively lowered blood glucose after oral glucose loading in both normal C57BL/6J mice and T2D mouse models, including KKay, db/db, ob/ob mice, and high fat diet-induced obesity/T2D mice. In addition, Diapin treatment significantly reduced casual blood glucose in KKay diabetic mice in a time-dependent manner without causing hypoglycemia. Furthermore, we found that plasma GLP-1 and insulin levels in diabetic models were significantly increased with Diapin treatment compared to that in the controls. In summary, our findings establish that a peptide with minimum of three amino acids can improve glucose homeostasis and Diapin shows promise as a novel pharmaceutical agent to treat patients with T2D through its dual effects on GLP-1 and insulin secretion.

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.

Digestion kinetics of potato protein isolates in vitro and in vivo

Recently, an industrial process was developed to isolate native protein fractions from potato: a high (HMW) and a low (LMW) molecular weight fraction. Digestion kinetics of HMW and LMW was studied in vitro and in vivo and compared with reference proteins. Under simulated conditions, highest digestion was found for whey protein, followed by soy, pea, HMW, casein and LMW. Ingestion of 20 g of proteins by eight healthy subjects (following a randomized, double-blind, cross-over design) induced a slow and moderate increase with HMW and LMW, while a peaked and high increase with whey protein, in postprandial plasma amino acid levels. Casein gave a similar profile as HMW, with higher levels. Contrary to whey and casein, HMW and LMW did not result in any changes in plasma insulin or glucose levels. This study provides insights in digestion of native potato protein isolates to assist their use as protein sources in food applications.

Should the amounts of fat and protein be taken into consideration to calculate the lunch prandial insulin bolus? Results from a randomized crossover trial

BACKGROUND

Concerning continuous subcutaneous insulin infusion (CSII), there are controversial results related to changes in glycemic response according to the meal composition and bolus design. Our aim is to determine whether the presence of protein and fat in a meal could involve a different postprandial glycemic response than that obtained with only carbohydrates (CHs).

SUBJECTS AND METHODS

This was a crossover, randomized clinical trial. Seventeen type 1 diabetes (T1D) patients on CSII wore a blinded continuous glucose monitoring system sensor for 3 days. They ingested two meals (meal 1 vs. meal 2) with the same CH content (50 g) but different fat (8.9 g vs. 37.4 g) and protein (3.3 g vs. 28.9 g) contents. A single-wave insulin bolus was used, and the interstitial glucose values were measured every 30 min for 3 h. We evaluated the different postprandial glycemic response between meal 1 and meal 2 by using mixed-effects models.

RESULTS

The postmeal glucose increase was 22 mg/dL for meal 1 and 31 mg/dL for meal 2. In univariate analysis, at different times not statistically significant differences in glucose levels between meals occurred. In mixed-model analysis, a time×meal interaction was found, indicating a different response between treatments along the time. However, most of the patients remained in the normoglycemic range (70-180 mg/dL) during the 3-h postmeal period (84.4% for meal 1 and 93.1% for meal 2).

CONCLUSIONS

The presence of balanced amounts of protein and fat determined a different glycemic response from that obtained with only CH up to 3 h after eating. The clinical relevance of this finding remains to be elucidated.

Insulinotropic and muscle protein synthetic effects of branched-chain amino acids: potential therapy for type 2 diabetes and sarcopenia

The loss of muscle mass and strength with aging (i.e., sarcopenia) has a negative effect on functional independence and overall quality of life. One main contributing factor to sarcopenia is the reduced ability to increase skeletal muscle protein synthesis in response to habitual feeding, possibly due to a reduction in postprandial insulin release and an increase in insulin resistance. Branched-chain amino acids (BCAA), primarily leucine, increases the activation of pathways involved in muscle protein synthesis through insulin-dependent and independent mechanisms, which may help counteract the "anabolic resistance" to feeding in older adults. Leucine exhibits strong insulinotropic characteristics, which may increase amino acid availability for muscle protein synthesis, reduce muscle protein breakdown, and enhance glucose disposal to help maintain blood glucose homeostasis.

Glycaemic index methodology

The glycaemic index (GI) concept was originally introduced to classify different sources of carbohydrate (CHO)-rich foods, usually having an energy content of >80 % from CHO, to their effect on post-meal glycaemia. It was assumed to apply to foods that primarily deliver available CHO, causing hyperglycaemia. Low-GI foods were classified as being digested and absorbed slowly and high-GI foods as being rapidly digested and absorbed, resulting in different glycaemic responses. Low-GI foods were found to induce benefits on certain risk factors for CVD and diabetes. Accordingly it has been proposed that GI classification of foods and drinks could be useful to help consumers make 'healthy food choices' within specific food groups. Classification of foods according to their impact on blood glucose responses requires a standardised way of measuring such responses. The present review discusses the most relevant methodological considerations and highlights specific recommendations regarding number of subjects, sex, subject status, inclusion and exclusion criteria, pre-test conditions, CHO test dose, blood sampling procedures, sampling times, test randomisation and calculation of glycaemic response area under the curve. All together, these technical recommendations will help to implement or reinforce measurement of GI in laboratories and help to ensure quality of results. Since there is current international interest in alternative ways of expressing glycaemic responses to foods, some of these methods are discussed.

The effect of α- or β-casein addition to waxy maize starch on postprandial levels of glucose, insulin, and incretin hormones in pigs as a model for humans

BACKGROUND

Starch is a main source of glucose and energy in the human diet. The extent to which it is digested in the gastrointestinal tract plays a major role in variations in postprandial blood glucose levels. Interactions with other biopolymers, such as dairy proteins, during processing can influence both the duration and extent of this postprandial surge.

OBJECTIVE

To evaluate the effect of the addition of bovine α- or β-casein to waxy maize starch on changes in postprandial blood glucose, insulin, and incretin hormones [glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1)] in 30 kg pigs used as an animal model for humans.

DESIGN

Gelatinised starch, starch gelatinised with α-casein, and starch gelatinised with β-casein were orally administered to trained pigs (n = 8) at a level of 60 g of available carbohydrate. Pre- and postprandial glucose measurements were taken every 15 min for the first hour and every 30 min thereafter up to 180 min. Insulin, GIP, and GLP-1 levels were measured in plasma samples up to 90 min postprandial.

RESULTS

Starch gelatinised with α-casein had a significantly (p < 0.05) lower peak viscosity on pasting and resulted in significantly lower glucose release at 15, 30, and 90 min postprandial compared to starch gelatinised with β-casein. During the first 45-min postprandial, the area under the glucose curve (AUC) for starch gelatinised with α-casein was significantly (p < 0.05) lower than that for starch gelatinised with β-casein. There was also a significant (p < 0.05) difference at T30 in GIP levels in response to the control compared to starch gelatinised with α- or β-casein. Significant (p < 0.05) increases in several free amino acid concentrations were observed on ingestion of either α- or β-casein gelatinised with starch at 30 and 90 min postprandial compared to starch alone. In addition, plasma levels of six individual amino acids were increased on ingestion of starch gelatinised with α-casein compared to ingestion of starch gelatinised with β-casein.

CONCLUSION

The presence of casein fractions (α- or β-casein) in gelatinised waxy maize starch affects swelling characteristics, viscosity, and subsequent in vivo digestion as determined by glucose levels in blood postprandial.

The individual and combined effects of glycemic index and protein on glycemic response, hunger, and energy intake

Although high protein and low glycemic index (GI) foods are thought to promote satiety, little is known about the effects of GI, protein, and their interaction on hunger and energy intake several hours following a mixed meal. This study investigated the long term effects of GI, protein, and their combined effects on glucose, insulin, hunger, and energy intake in healthy, sedentary, overweight, and obese adults (BMI of 30.9 ± 3.7 kg/m(2)). Sixteen individuals participated separately in four testing sessions after an overnight fast. The majority (75%) were non-Hispanic Blacks. Each consumed one of four breakfast meals (high GI/low protein, high GI/high protein, low GI/low protein, low GI/high protein) in random order. Visual analog scales (VAS) and blood samples were taken at baseline, 15 min, and at 30 min intervals over 4 h following the meal. After 4 h, participants were given the opportunity to consume food ad libitum from a buffet style lunch. Meals containing low GI foods produced a smaller glucose (P < 0.002) and insulin (P = 0.0001) response than meals containing high GI foods. No main effects for protein or interactions between GI and protein were observed in glucose or insulin responses, respectively. The four meals had no differential effect on observed energy intake or self-reported hunger, satiety, and prospective energy intake. Low GI meals produced the smallest postprandial increases in glucose and insulin. There were no effects for GI, protein, or their interaction on appetite or energy intake 4 h after breakfast.

Effects of meal size and composition on incretin, alpha-cell, and beta-cell responses

The incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate postprandial insulin release from the beta-cells. We investigated the effects of 3 standardized meals with different caloric and nutritional content in terms of postprandial glucose, insulin, glucagon, and incretin responses. In a randomized crossover study, 18 subjects with type 2 diabetes mellitus and 6 healthy volunteers underwent three 4-hour meal tolerance tests (small carbohydrate [CH]-rich meal, large CH-rich meal, and fat-rich meal). Non-model-based and model-based estimates of beta-cell function and incremental areas under the curve of glucose, insulin, C-peptide, glucagon, GLP-1, and GIP were calculated. Mixed models and Friedman tests were used to test for differences in meal responses. The large CH-rich meal and fat-rich meal resulted in a slightly larger insulin response as compared with the small CH-rich meal and led to a slightly shorter period of hyperglycemia, but only in healthy subjects. Model-based insulin secretion estimates did not show pronounced differences between meals. Both in healthy individuals and in those with diabetes, more CH resulted in higher GLP-1 release. In contrast with the other meals, GIP release was still rising 2 hours after the fat-rich meal. The initial glucagon response was stimulated by the large CH-rich meal, whereas the fat-rich meal induced a late glucagon response. Fat preferentially stimulates GIP secretion, whereas CH stimulates GLP-1 secretion. Differences in meal size and composition led to differences in insulin and incretin responses but not to differences in postprandial glucose levels of the well-controlled patients with diabetes.

A high protein low fat meal does not influence glucose and insulin responses in obese individuals with or without type 2 diabetes

BACKGROUND

When substituted for carbohydrate in a meal, dietary protein enhances glycaemic control in subjects with type 2 diabetes (DM2). It is unknown whether the effect is a result of increased protein or reduced carbohydrate. The present study aimed to compare the effects of two meals differing in protein to fat ratios on post-prandial glucose and insulin responses.

METHODS

This was a crossover, blind study in which obese subjects with (n = 23) and without (n = 26) DM2 consumed two meals in random order with equal amounts of energy (3.1 MJ, 741 kcal), fibre and carbohydrates and a 1-week washout period. Meals were a high protein, low fat (30% protein, 51% carbohydrates, 19% fat) meal and a low protein, high fat (15% protein, 51% carbohydrates, 34% fat) meal. Subjects were matched for age and body mass index. Plasma glucose and insulin were measured at fasting, 30, 60, 90, 120 min post-prandially. Insulin resistance and insulin sensitivity were assessed.

RESULTS

There was no significant meal effect on glucose and insulin responses within groups. Glucose response was higher in diabetic (120 min 11 +/- 0.7 mmol L(-1)) compared to nondiabetic (120 min 5 +/- 0.2; P < 0.001) subjects. Diabetic subjects had significantly higher insulin resistance (P < 0.001) and lower insulin sensitivity (P < 0.001) than nondiabetics. Although peak insulin levels, 60 min post-prandially, did not differ between groups (81 +/- 9 pmol L(-1) for diabetic versus 79 +/- 7 pmol L(-1) for nondiabetic subjects), they were achieved much later, 90 min post-prandially, in diabetic, (99 +/- 8 pmol L(-1)) compared to nondiabetic (63 +/- 7 pmol L(-1), P = 0.002) subjects.

CONCLUSIONS

Manipulating protein to fat ratio in meals does not affect post-prandial plasma blood glucose or insulin responses in obese people with and without DM2.

Classical and model-based estimates of beta-cell function during a mixed meal vs. an OGTT in a population-based cohort

This study compared classical and model-based beta-cell responses during an oral glucose tolerance test (OGTT) and a meal tolerance test (MTT) in a population-based cohort. Individuals with normal glucose metabolism (NGM, n=161), impaired glucose metabolism (IGM, n=19) and type 2 diabetes mellitus (DM, n=20) underwent a 75 g-OGTT and an MTT (75 g carbohydrates, 50 g fat, 24 g proteins). Classical estimates of beta-cell function (insulinogenic index and the ratio of areas under insulin and glucose curves) were calculated. Mathematical modelling was used to determine beta-cell glucose sensitivity, rate sensitivity and potentiation. Insulin sensitivity was characterized by three surrogate estimates. Both classical and model-based estimates of beta-cell function were higher during MTT than during OGTT (P<0.05). Regarding the model-based parameters, especially beta-cell sensitivity was increased following MTT as compared with OGTT (P<0.05). Both during OGTT and MTT, across most parameters describing beta-cell function, the largest reduction in beta-cell response occurred between IGM and DM, while the largest reduction in insulin sensitivity occurred between NGM and IGM. We conclude that beta-cell response is stronger after a mixed meal than after an OGTT with equal carbohydrate quantity, both for classical and model-based parameters. The higher response was mostly explained by higher beta-cell sensitivity during the meal.

A specific blend of intact protein rich in aspartate has strong postprandial glucose attenuating properties in rats

Three studies were carried out to help define an optimal protein blend for use in a nutritional product for diabetic patients. To this end, we tested the effects of coinfusions of combinations of different types of carbohydrates and proteins on the postprandial glycemic plasma response in healthy rats. Expt. 1 compared the effects of administering different forms of soy protein (intact protein, its hydrolysate, or an equivalent amount of the same amino acids), all in combination with a fixed amount of glucose (Glu), on postprandial Glu and insulin plasma concentrations. Intact soy protein (SI) had stronger insulinogenic properties compared with its hydrolysate but was equally potent in reducing the postprandial Glu response. In Expt. 2, we compared the effect of replacing 50% of the SI with the whey-derived protein alpha-lactalbumin when coingested with maltodextrin as the carbohydrate source. Only the specific aspartate-rich blend of SI and alpha-lactalbumin significantly improved the postprandial Glu response. In Expt. 3, we studied the effect of using the blend of SI and alpha-lactalbumin combined with a slowly digestible carbohydrate. The protein blend was still capable of significantly decreasing the postprandial Glu response even when a slow-release carbohydrate source was included. Combining this aspartate-rich protein blend with a slow-release carbohydrate might therefore lead to a low-glycemic nutritional product beneficial for dietary management in diabetic patients.

Protein in optimal health: heart disease and type 2 diabetes

Diets with increased protein and reduced carbohydrates have been shown to improve body composition, lipid and lipoprotein profiles, and glycemic regulations associated with treatment of obesity and weight loss. Derived from these outcomes, high-protein, low-carbohydrate diets are also being examined for treatment of heart disease, metabolic syndrome, and type 2 diabetes. High-protein, low-carbohydrate diets have been found to have positive effects on reducing risk factors for heart disease, including reducing serum triacylglycerol, increasing HDL cholesterol, increasing LDL particle size, and reducing blood pressure. These diets appear particularly attractive for use with individuals exhibiting the atherogenic dyslipidemia of metabolic syndrome. High-protein, low-carbohydrate diets have also been investigated for treatment of type 2 diabetes with positive effects on glycemic regulation, including reducing fasting blood glucose, postprandial glucose and insulin responses, and the percentage of glycated hemoglobin. Specific effects of increasing protein compared with reducing carbohydrates have not been extensively investigated. Additional research is needed to determine specific levels of protein, carbohydrate, and fat for optimum health of individuals who differ in age, physical activity, and metabolic phenotypes.

Metabolic effects of amino acid mixtures and whey protein in healthy subjects: studies using glucose-equivalent drinks

BACKGROUND

Milk protein, in particular the whey fraction, has been shown to display insulinotrophic properties in healthy persons and persons with type 2 diabetes. In parallel to the hyperinsulinemia, a pronounced postprandial rise of certain amino acids and of glucose-dependent insulinotrophic polypeptide (GIP) was observed in plasma.

OBJECTIVE

The objective of the study was to determine to what extent the insulinotrophic properties of whey could be simulated by specific amino acid mixtures.

DESIGN

Twelve healthy volunteers were served drinks consisting of pure glucose (reference drink) or glucose supplemented with free amino acids or whey proteins (test drinks).

RESULTS

A test drink with the branched-chain amino acids isoleucine, leucine, and valine resulted in significantly higher insulin responses than did the glucose reference. A drink containing glucose and leucine, isoleucine, valine, lysine, and threonine mimicked the glycemic and insulinemic responses seen after whey ingestion. With consumption of this drink, the glucose area under the curve (AUC) was 44% smaller (P < 0.05) and the insulin AUC was 31% larger (NS) than with consumption of the reference drink. With consumption of the whey drink, the AUCs were 56% smaller (glucose; P < 0.05) and 60% larger (insulin; P < 0.05), respectively, than with the reference drink. The whey drink was accompanied by an 80% greater GIP response (P < 0.05), whereas the drinks containing free amino acids did not significantly affect GIP secretion.

CONCLUSION

A mixture of leucine, isoleucine, valine, lysine, and threonine resulted in glycemic and insulinemic responses closely mimicking those seen after whey ingestion in the absence of an additional effect of GIP and glucagon-like peptide 1.

Towards understanding of glycaemic index and glycaemic load in habitual diet: associations with measures of glycaemia in the Insulin Resistance Atherosclerosis Study

Epidemiologic studies have applied the glycaemic index (GI) and glycaemic load (GL) to assessments of usual dietary intake. Results have been inconsistent particularly for the association of GI or GL with diabetes incidence. We aimed to advance understanding of the GI and GL as applied to food frequency questionnaires (FFQ) by evaluating GI and GL in relation to plasma measures of glycaemia. Included were 1255 adults at a baseline examination (1994–6) and 813 who returned for the 5-year follow-up examination. Usual diet, at both examinations, was assessed by a validated FFQ. GI and GL were evaluated in relation to average fasting glucose (two measures at each examination) and 2h post-75g glucose load plasma glucose (baseline and follow-up), and glycated haemoglobin (A1c; follow-up only); using generalized linear models. Correlation coefficients (r) for GI and GL related to measures of glycaemia, adjusted for total energy intake, ranged from −0·004 to 0·04 (all NS) for both examinations. Adjustment for potential confounders, for fasting glucose in models for 2h glucose (to model incremental glucose) and for average fasting glucose in models for A1c (to account, in part, for overnight endogenous glucose production) also did not materially alter findings, nor did inclusion of data from both examinations together in linear mixed models. The present results call into question the utility of GI and GL to reflect glycaemic response to food adequately, when used in the context of usual diet. Further work is needed to quantify usual dietary exposures relative to glucose excursion and associated chronic glycaemia and other metabolic parameters.