- Email: [email protected]
Combining protein and carbohydrate increases postprandial insulin levels but does not improve glucose response in patients with type 2 diabetes
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
Available online at www.sciencedirect.com
Metabolism www.metabolismjournal.com
Combining protein and carbohydrate increases postprandial insulin levels but does not improve glucose response in patients with type 2 diabetes Meidjie Ang a , Andreas S. Müller b , Florian Wagenlehner c , Adrian Pilatz c , Thomas Linn a,⁎ a b c
Medizinische Klinik und Poliklinik III, Justus-Liebig-Universität, 35392 Giessen, Germany Institut für Agrar- und Ernährungswissenschaften, Martin-Luther-Universität, Halle-Wittenberg, Germany Klinik für Urologie, Kinderurologie und Andrologie, Universitätsklinikum Giessen und Marburg GmbH, Giessen, Germany
A R T I C LE I N FO Article history:
AB S T R A C T Objective. A combined load of carbohydrate and protein stimulates insulin secretion.
Received 11 October 2011
However, results on postprandial glucose responses in type 2 diabetic (T2D) subjects have
Accepted 9 May 2012
been inconclusive. Therefore, we investigated the effects of co-ingestion of carbohydrate and protein on glucose and insulin responses in these subjects. Methods. After an overnight fast, 30 subjects consumed a drink containing 50 g of slowly-
Keywords:
digested isomaltulose (ISO), combined either with a mixture of 21 g whey/soy (ISO + WS) or
Isomaltulose
with 21 g casein (ISO + C) in a randomized order on separate days. In another experiment, the
Protein
subjects consumed a control drink containing only 50 g ISO.
Insulin action
Results. No significant differences in glucose responses were observed after ingestion of
Postprandial glucose metabolism
the drinks. Compared to ingestion of ISO alone, insulin response was ~ 190%–270% higher
Type 2 diabetes
(P < .001), whereas insulin action was lower (P < .01) after ingestion of ISO + WS and ISO + C. Plasma insulin levels increased more significantly (P < .001) after ingestion of ISO + WS compared to ISO + C and were positively correlated with total amino acid levels (P < .001). Insulin action, however, showed a greater decrease following ingestion of ISO + WS than ISO + C (P < .01). Conclusions. Combining carbohydrate with protein can elevate postprandial insulin levels, but decreases insulin action, and therefore does not improve glucose response in T2D subjects. Our results further suggest that different types of proteins (i.e., fastabsorbing whey/soy vs. slow-absorbing casein) differently modulate insulin response and insulin action. A fast-absorbing protein mixture reduces insulin action to a greater extent than a slow-absorbing protein, and therefore may not be recommended for glycemic control in T2D patients. © 2012 Elsevier Inc. All rights reserved.
Abbreviations: BCAA, branched-chain amino acid; BMI, body mass index; EAA, essential amino acid; HbA1c, glycated hemoglobin; HOMA-IR, homeostasis model assessment of insulin resistance; iAUC, incremental area under the curve; ISO, isomaltulose; ISO + C, isomaltulose combined with casein; ISO + WS, isomaltulose combined with whey and soy (ratio 1:1); SEM, standard error of the mean; SI, insulin sensitivity index; TAA, total amino acid; T2D, type 2 diabetic; rs, Spearman's correlation coefficient. ⁎ Corresponding author. Tel.: +49 641 985 42841; fax: +49 641 985 42849. E-mail address: [email protected] (T. Linn). 0026-0495/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.metabol.2012.05.008
1697
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
1.
Table 2 – Amino acid composition (g/100 g protein).
Introduction
Postprandial hyperglycemia plays an important role in the development of cardiovascular complications in patients with type 2 diabetes [1,2]. To reduce the incidence and progression of these complications, an optimal glycemic control strategy should be considered in the treatment [3,4]. Several reviews reported that nutrition and lifestyle interventions can be effective in delaying the onset of the disease [5–7]. Meta-analyses of randomized controlled trials reported that a low glycemic index diet has a clinically relevant effect on glycemic control [8,9]. The glycemic index, originally described by Jenkins et al. [10], is a ranking system that measures the extent to which carbohydrates affect postprandial blood glucose levels. Carbohydrates with a low glycemic index are usually slowlyabsorbed, producing delayed gradual rises in blood glucose and insulin levels. For example, isomaltulose (ISO) is an isomer of sucrose which is digested slower than other sugars such as sucrose or maltose [11]. Studies on blood glucose, fructose, and insulin levels after oral administration of ISO have generally confirmed its suitability for diabetic subjects [11–13]. The dietary macronutrients carbohydrates, proteins, and fats are usually ingested in a complex food matrix rather than in their pure form. As a consequence, interactions between the macronutrients may influence glycemic response. Understanding nutrient interdependencies is therefore important. For instance, food proteins alone already stimulate insulin release, whereas a notably additive effect on insulin release is triggered by the combined uptake of proteins with carbohydrates [14–18]. However, controversial results have been reported in regard to the effects of insulin stimulation on glucose homeostasis in type 2 diabetic (T2D) subjects. Some studies have shown a reduction of postprandial glucose response when proteins and carbohydrates were taken up in combination compared to the uptake of carbohydrates alone [14,17,18]. Other studies did not confirm this effect [15,16]. In this context, various proteins were studied and it remains to be clarified whether they have comparable and consistent effects on postprandial glucose. In animal studies, it was reported that a protein mixture of whey and soy has potent postprandial glucose-attenuating and insulin-stimulating effects. These were also observed when the proteins were simultaneously ingested with a slowrelease carbohydrate [19]. In the present study, an isonitro-
Table 1 – Patients’ characteristics (n = 30). Sex (female/male) Age (years) Body weight (kg) Height (m) BMI (kg/m2) HbA1c (%) HOMA-IR Diabetes duration (years) Metformin (female/male)
12/18 62.9 ± 1.3 85.6 ± 3.1 1.7 ± 0.02 29.0 ± 0.7 6.6 ± 0.1 4.0 ± 0.6 5.2 ± 2.6 8/11
BMI, body mass index; HbA1c, glycated hemoglobin; HOMA-IR, homeostasis model assessment of insulin resistance. Data are mean ± SEM.
Alanine Arginine Aspartic acid Cyst(e)ine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine
Whey/Soy
Casein
3.8 4.7 12.2 2.1 18.0 3.2 2.4 5.9 8.7 7.2 1.5 4.3 4.8 5.2 5.2 2.3 3.4 5.2
2.8 3.4 6.6 0.4 20.2 1.7 2.9 5.2 9.1 7.5 2.7 4.9 9.5 5.7 4.2 1.3 5.2 6.7
Whey/Soy (ratio 1:1).
genous mixture of whey and soy proteins, as well as casein, was used as protein sources. We investigated whether a combined load of protein and slowly digested ISO could reduce postprandial glucose response in T2D subjects.
2.
Subjects and methods
2.1.
Subjects
Thirty T2D subjects with good glycemic control (HbA1c < 7%, Table 1) were recruited from the University Hospital of Giessen, Germany and were treated with dietary advice and/or metformin. No other anti-diabetic medication was allowed. Metformin administration was stopped three days prior to the tests. Exclusion criteria include unstable or untreated proliferative retinopathy, clinically significant nephropathy, neuropathy, hepatic diseases, heart failure, uncontrolled hypertension, systemic treatment with corticosteroids, and insulin treatment. Prior to the study, all subjects underwent a thorough physical examination, as well as laboratory testing (blood cell count, liver and kidney chemistry, urine analysis, pregnancy test in premenopausal women, electrocardiography). The purpose was to exclude pregnancy and persons with medical conditions (e.g., cerebrovascular or coronary artery disease), which would complicate the evaluation of the tests. The study was conducted according to the guidelines set out in the Declaration of Helsinki and all procedures involving human subjects were approved by the Ethics Committee of the Justus Liebig University (Giessen, Germany). Written informed consent was obtained from all subjects.
2.2.
Study design
Each subject participated in 3 different experiments with a minimum 3-day washout period between two experiments. Subjects were randomized to ingest either a drink containing 50 g ISO with 21 g whey/soy (ratio 1:1) (ISO + WS) or a drink
1698
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
containing 50 g ISO with 21 g casein (ISO + C). In another experiment, the subjects were given a control drink containing only 50 g ISO. All experimental drinks were prepared from powder (Nutricia, Wageningen, Netherlands), dissolved in water. The amino acid composition of whey/soy and casein is listed in Table 2. To exclude any possible interactions, no other nutrients were added to the drinks.
calculated from 0 to 240 min, GE is glucose effectiveness, Doral is the dose of ingested carbohydrate per unit of body weight (mg/kg) and f is the fraction of ingested glucose that appears in the systemic circulation. GE was fixed at 0.024 dL/kg·min and f was set at 0.8 [22]. When glucose concentration falls below baseline, the equation becomes t
f ⋅Doral
AUC½ΔGðtÞ = GðtÞ00 −AUC½ΔGðtÞ = GðtÞ∞ t
2.3.
Analysis
Calculations
Homeostasis model assessment of insulin resistance (HOMAIR) was calculated with HOMA = (G0 ⋅ I0)/405 where G0 is the fasting plasma glucose (mg/dL) and I0 is the fasting plasma insulin (μU/mL) [20]. Plasma glucose and insulin curves were fitted using an equation described by Trujillo-Arriaga and Roman-Ramos [21]. Glucose, insulin, and amino acid responses were calculated as incremental areas under the curves (iAUCs) above the baseline level. Incremental AUCs were calculated using GraphPad Prism 5. Insulin action was assessed in the postprandial state using the oral glucose minimal model [22]. The model provides an insulin sensitivity index (SI, dL/kg·min per pmol/L), which is based on the total integrated AUCs of glucose and insulin concentrations assuming that the systemic glucose disposal equals the glucose entering the peripheral circulation. SIðoralÞ =
½ΔGðtÞ = GðtÞ f ⋅Doral AUCAUC −GE⋅AUC½ΔGðtÞ = GðtÞ ½ΔGðtÞ
AUC½ΔIðtÞ
−GE⋅AUC½ΔGðtÞ = GðtÞ ð2Þ
Plasma glucose concentrations were measured by the glucose hexokinase method (Bayer ADVIA, Germany). Plasma insulin concentrations were determined using a sandwich immunoassay based on a direct luminescence technique (Bayer ADVIA Centaur, Germany). Coefficients of variation for intra- and interassay precisions of glucose and insulin measurements were < 6%. Amino acids were determined by high performance liquid chromatography using the fluorometric detection after precolumn derivatization with ortho-phthaldialdehyde.
2.5.
0
AUC½ΔIðtÞ
Study protocol
Subjects were admitted to the Clinical Research Unit at 08:00 h after an overnight fast. Basal blood samples were drawn from the antecubital vein before the start of the study. Thereafter, the subjects consumed the drinks containing only ISO, ISO + WS or ISO + C within 5 min. Blood samples were taken at 15, 30, 45, 60, 75, and 90 min after ingestion of the drinks, subsequently at every 30 min until blood glucose levels returned to baseline. Blood samples were collected into lithium heparin-coated tubes for the measurement of glucose, insulin, and amino acids. They were immediately centrifuged at 2000 g for 10 min. Aliquots of plasma were analyzed for glucose and insulin concentrations. The remaining samples were frozen and stored at − 20 °C until the analysis of the amino acids.
2.4.
t
AUC½ΔGðtÞ00 −AUC½ΔGðtÞ∞ t
0
SIðoralÞ =
ð1Þ
where ΔG (mg/dL) and ΔI (pmol/L) are glucose and insulin concentrations above basal, ΔG(t) = G(t) − Gb, ΔI = I(t) − Ib. AUC is
t0 is the time when glucose concentration crosses the baseline level. SI measures the overall effect of insulin to stimulate glucose disposal and inhibit glucose production [23].
2.6.
Statistical analysis
All data are expressed as mean ± SEM. The Kolmogorov– Smirnov test was used to evaluate the normality of the data. Comparisons between the drinks at different time points were analyzed by using two-way repeated measures ANOVA with drink and time as within-subject factors. When the data violated the assumption of sphericity for homogeneity of variances, Greenhouse–Geisser correction was used. For nontime-dependent variables, one-way repeated measures ANOVA or Friedman test was used to analyze data set with or without normality of distribution, respectively. If the test revealed significant changes and the normality assumption was not violated, Bonferroni post hoc test was further applied for multiple comparisons between the drinks. For data set without normality of distribution, Wilcoxon signed-rank test with Bonferroni correction was chosen as post hoc test for multiple comparisons between the drinks. Spearman's correlation coefficient (rs) was used to assess the relationship between insulin and amino acids. Analysis was performed by using SPSS 16. Differences between means with an error probability of P < .05 were considered statistically significant. In case of Bonferroni corrections, the significance level was set at P < .05/number of comparisons.
3.
Results
3.1.
Plasma glucose and insulin concentrations
Fasting plasma glucose levels did not differ between the study days on which only ISO, ISO + WS, or ISO + C was ingested (P = .648, Table 3). After ingestion of ISO alone, ISO + WS, and ISO + C, plasma glucose concentrations increased significantly above the baseline level (P < .001) and reached peak values at ~ 75 min. Glucose responses did not differ following ingestion of the different drinks (P = .239, Fig. 1A). Accordingly, fasting plasma insulin levels did not differ between the days of ingestion of ISO alone, ISO + WS, and ISO + C (P = .525, Table 3). Plasma insulin concentrations increased from baseline (P < .001) to peak levels after ~ 90 min consumption of the different drinks. Insulin responses were ~ 270% and ~ 190% higher after ingestion of ISO + WS and ISO + C than after ingestion of ISO alone (P < .001). Following intake of ISO +
1699
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
Table 3 – Plasma glucose and insulin after ingestion of drinks containing only ISO, ISO + WS, and ISO + C in 30 type 2 diabetic patients. ISO
Plasma glucose Baseline (mmol/L) Peak (mmol/L) Peak time (min) Plasma insulin Baseline (pmol/L) Peak (pmol/L) Peak time (min) SI (10− 5 dL/kg·min per pmol/L)
ISO + WS
ISO + C
Overall P value
7.1 ± 0.2 11.2 ± 0.3 77.5 ± 4.0
7.2 ± 0.3 11.1 ± 0.4 78.5 ± 4.4
7.2 ± 0.3 10.9 ± 0.4 76.0 ± 4.0
.648 .656 .639
77.1 ± 2.9 212.4 ± 10.2 94.0 ± 4.1 16.3 ± 2.0
88.6 ± 11.2 571.9 ± 47.0 94.0 ± 7.3 5.9 ± 0.8
76.5 ± 11.8 445.4 ± 38.6 95.5 ± 10.0 10.4 ± 1.8
.525 <.001 .515 <.001
P value
a
ISO vs. ISO + WS ISO vs. ISO + C ISO + WS vs. ISO + C NA NA NA
NA NA NA
NA NA NA
NA <.001 NA <.001
NA <.001 NA .005
NA <.001 NA .003
iAUC (mmol/L.4h)
ISO, isomaltulose; ISO + WS, isomaltulose combined with whey/soy (ratio 1:1); ISO + C, isomaltulose combined with casein; SI, insulin sensitivity index; NA, not applicable (due to non-significant overall P value). Data are mean ± SEM. a A P value < .0167 was considered significant (Bonferroni adjustment for 3 comparisons).
WS, insulin response was ~ 30% higher compared to that observed following intake of ISO + C (P = .002, Fig. 1B).
3.2.
Net SI was lower after ingestion of ISO + WS and ISO + C than after ingestion of ISO alone (P < .001 and P = .005, respectively). Moreover, SI was lower following intake of ISO + WS compared to that following intake of ISO + C (P = .003, Table 3).
3.3.
Time (min)
B
Time (min)
iAUC (pmol/L.4h)
A
Fig. 1 – Plasma glucose and insulin after ingestion of drinks containing only ISO (grey), ISO + WS (black), and ISO + C (white) in 30 type 2 diabetic patients. (A) No significant drink effect (P = .704) or drink × time interaction (P = .411) was found for glucose concentrations. Glucose iAUCs were not significantly different between the drinks (P = .239). (B) A significant drink effect (P < .001) and drink × time interaction (P < .001) were found for insulin concentrations. Insulin iAUCs were significantly different between the drinks (P < .001). ISO, isomaltulose; ISO + WS, isomaltulose combined with whey/ soy (ratio 1:1); ISO + C, isomaltulose combined with casein; iAUC, incremental area under the curve; ns, non-significant. Data are mean ± SEM. **P = .002, ***P < .001.
Insulin action
Plasma amino acid concentrations
An overview of plasma amino acid concentrations at 0, 30 and 60 min is shown in Table 4. Total fasting plasma amino acid (TAA) concentrations did not differ on the study days when ISO + WS and ISO + C were ingested (P = .651). TAA levels increased from baseline (P < .001) and were higher after administration of ISO + WS compared to those following administration of ISO + C (P < .001). Similarly, fasting plasma concentrations of essential amino acid (EAA) and branchedchain amino acid (BCAA) did not differ on the ISO + WS and ISO + C study days (P = .221 and P = .141, respectively). EAA and BCAA levels increased from baseline (P < .001) and showed a pattern similar to those of TAA. Moreover, both EAA and BCAA levels were higher after administration of ISO + WS than after administration of ISO + C (P < .001). Plasma TAA concentrations positively correlated with plasma insulin levels in the 60 min postprandial period following ingestion of ISO + WS and ISO + C (rs = .690 and rs = .684, P < .001, respectively). Plasma TAA, EAA, and BCAA responses were ~ 54%, ~ 63%, and ~ 59%, respectively, higher after administration of ISO + WS than after administration of ISO + C (P < .001, Table 4). EAA and BCAA responses accounted for ~ 52%–55% and ~ 31%– 32% of increases in TAA response after ingestion of both drinks, respectively.
4.
Discussion
The present study shows that ingestion of ISO + WS or ISO + C substantially increased insulin but did not reduce glucose
1700
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
Table 4 – Plasma amino acid after ingestion of drinks containing ISO + WS and ISO + C in 30 type 2 diabetic patients. Amino acid
Alanine Arginine Asparagine Aspartic acid Citrulline Glutamine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Serine Taurine Threonine Tryptophan Tyrosine Valine TAA EAA BCAA
ISO + WS (μmol/L)
ISO + C (μmol/L)
ISO + WS vs. ISO + C
Baseline
30 min
60 min
Baseline
30 min
60 min
473 ± 20 79 ± 3 43 ± 1 10 ± 1 35 ± 2 457 ± 23 160 ± 19 208 ± 13 77 ± 2 88 ± 4 157 ± 6 177 ± 7 27 ± 2 64 ± 3 108 ± 4 106 ± 9 126 ± 5 59 ± 2 74 ± 4 280 ± 10 2811 ± 43 980 ± 29 526 ± 20
621 ± 32 116 ± 5 75 ± 4 13 ± 1 34 ± 2 500 ± 24 178 ± 16 231 ± 15 87 ± 2 166 ± 7 274 ± 12 270 ± 10 38 ± 2 84 ± 4 151 ± 6 115 ± 11 187 ± 8 76 ± 2 99 ± 5 372 ± 11 3687 ± 99 1467 ± 43 813 ± 28
676 ± 29 108 ± 5 75 ± 4 12 ± 1 35 ± 2 509 ± 23 175 ± 17 228 ± 18 91 ± 2 168 ± 7 266 ± 9 264 ± 9 36 ± 2 81 ± 4 147 ± 6 113 ± 11 195 ± 8 80 ± 3 99 ± 5 374 ± 10 3733 ± 91 1464 ± 37 807 ± 25
483 ± 20 76 ± 3 44 ± 1 10 ± 1 33 ± 2 463 ± 21 157 ± 14 211 ± 14 77 ± 2 86 ± 4 151 ± 6 173 ± 5 26 ± 1 64 ± 3 108 ± 4 112 ± 9 125 ± 5 60 ± 2 71 ± 3 265 ± 9 2793 ± 33 949 ± 25 501 ± 18
588 ± 27 96 ± 5 61 ± 2 11 ± 1 34 ± 2 495 ± 24 171 ± 16 221 ± 15 88 ± 2 131 ± 6 231 ± 10 235 ± 9 40 ± 2 81 ± 4 140 ± 6 124 ± 11 158 ± 6 68 ± 2 100 ± 5 343 ± 12 3416 ± 85 1288 ± 41 704 ± 27
631 ± 26 86 ± 4 56 ± 3 10 ± 1 34 ± 3 483 ± 25 171 ± 16 211 ± 16 88 ± 2 114 ± 5 195 ± 7 212 ± 6 35 ± 1 73 ± 4 129 ± 5 119 ± 10 152 ± 5 64 ± 2 90 ± 5 321 ± 9 3274 ± 76 1165 ± 28 630 ± 20
iAUC (μmol/L.1 h) 7501 ± 781 1528 ± 149 1430 ± 133 142 ± 23 32 ± 10 2187 ± 315 1164 ± 266 1030 ± 221 543 ± 47 3521 ± 263 5127 ± 424 4112 ± 291 455 ± 38 846 ± 73 1880 ± 194 690 ± 230 2846 ± 239 808 ± 72 1123 ± 121 4154 ± 343 40115 ± 3434 21878 ± 1640 12803 ± 1004
5526 ± 761 761 ± 130 698 ± 90 55 ± 9 68 ± 16 1451 ± 250 1004 ± 210 423 ± 105 491 ± 59 1795 ± 219 3048 ± 400 2456 ± 333 567 ± 81 654 ± 104 1280 ± 156 744 ± 192 1422 ± 165 354 ± 59 1135 ± 193 3198 ± 377 26055 ± 3326 13454 ± 1697 8042 ± 993
P value a,b
<.001 <.001 <.001 <.001 .035 .047 .798 <.001 .281 <.001 <.001 < .01 .097 .007 <.001 .827 <.001 <.001 .468 .002 <.001 <.001 <.001
ISO + WS, isomaltulose combined with whey/soy (ratio 1:1); ISO + C, isomaltulose combined with casein; iAUC, incremental area under the curve; TAA, total amino acid; EAA, essential amino acid; BCAA, branched-chain amino acid. Data are mean ± SEM. a For each individual amino acid, a P value < .0025 was considered significant (Bonferroni adjustment for 20 comparisons). b For TAA, EAA, and BCAA, a P value < .0167 was considered significant (Bonferroni adjustment for 3 comparisons).
response compared to the ingestion of ISO alone in T2D subjects. Based on our results the explanation for this observation is a reduced postprandial insulin action after ingestion of ISO + WS or ISO + C. In healthy subjects, shortterm elevations of plasma amino acids have been shown to decrease glucose uptake, inhibit glucose transport or muscle insulin signaling, and enhance endogenous glucose production [24,25]. Taken together it can be concluded that protein components of ISO + WS and ISO + C decreased the effects of insulin in T2D subjects. Reduced insulin action is counterbalanced by an increase in insulin secretion, thereby regulating plasma glucose levels. Differences in insulin responses following ingestion of ISO + WS or ISO + C were exclusively dependent on the protein compositions as displayed by their amino acid profiles (P < .001). Our results confirm a previous report on the stimulation of insulin by postprandial TAA levels [26]. Differences in the rise of plasma TAA concentrations are attributed to a faster absorption of whey compared to casein. While whey proteins are readily soluble in gastric juice, caseins tend to clot in the stomach due to precipitation by gastric acid [27]. Overall, postprandial individual amino acid responses were enhanced after ingestion of ISO + WS as opposed to ingestion of ISO + C. Our results confirm previous findings of marked increments of alanine, leucine, valine, lysine, isoleucine, and threonine following the meals containing whey in healthy subjects [28,29]. The highest increase was seen in the alanine response, despite the fact that glutamic acid is the most abundant. This could be explained by transamination of
glutamic acid to alanine during intestinal absorption [30], or increased conversion of glutamine to alanine due to substantial alterations of glutamine and alanine metabolism in type 2 diabetes [31]. The effects of ingestion of variable protein and carbohydrate combinations on glucose levels are discussed controversially. Non-diabetic probands often showed small, but significant absolute effects of total mean blood glucose when two carbohydrate/protein blends were compared [17,18], yet the shape of the glucose profiles did not differ [16]. In T2D subjects, the glucose responses were highly variable and the magnitude of glucose reduction was moderate at best [14,17,18]. Combining carbohydrate with casein reduced glucose responses, but glucose appearance rates [17] and plasma glucose levels [18] were identical compared to carbohydrate ingestion only. A reduced glucose response was further reported after whey intake for lunch, compared to a ham meal [32] without significant differences for breakfast with the same meals. Thus, no definitive conclusion on the glucose-lowering effect of protein can be drawn from these studies. Our study focused on the impact of protein ingestion on glucose and insulin responses, since study drinks contained only the macronutrients, carbohydrate and protein. By contrast, matrix and nutrient–nutrient interactions will interfere with the contribution of the components in meal studies. Impaired insulin action is a major feature of type 2 diabetes and was calculated using the oral minimal model in our study. This model provides an accurate measurement of insulin sensitivity after ingestion of a single protein load and
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
is as powerful as that obtained from an intravenous glucose tolerance test [23]. Insulin action was lower for ISO + WS compared to ISO + C drink, indicating that the type of ingested protein modulated insulin action. The fast-absorbing protein mixture whey/soy reduced insulin action to a greater extent than slow-absorbing casein. Interestingly, consumption of protein from animal sources (meat, milk/products, and cheese), but not from vegetables, was associated with a higher prevalence of diabetes [33]. Diets rich in protein may have long-term adverse effects on glycemic control, such as impaired suppression of hepatic glucose output by insulin, promotion of insulin resistance, and increased gluconeogenesis [34,35]. Dietary protein intake in diabetic patients usually ranges between 15% and 20% of total daily energy in most industrialized countries, which corresponds to 1.3–2.0 g/kg body weight and represents an intake that exceeds the recommended daily amount of 0.8 g/kg body weight. Recent epidemiological studies strongly indicate an association of higher intake of various proteins and increased risk of type 2 diabetes [33,36]. There are currently no guidelines addressing protein quality for the management of diabetes [37]. Our findings suggest that ingestion of fast-absorbing protein mixtures cannot be recommended for the glycemic control of T2D patients. Long-term effects of the consumption of proteins with different absorption rates remain to be established. In this study slowly absorbed ISO or the addition of ISO to both proteins increased glucose and insulin levels moderately. Incremental peak glucose and insulin levels were higher in previous studies with diabetic patients [14–18], but were similar after a lunch meal containing mashed potatoes and whey [32] compared to our study (~ 5–10 vs. ~ 3.5 mmol/L and ~ 500–1700 vs. ~ 120–380 pmol/L). Since the amounts of ingested carbohydrate (~ 45–60 g) and protein (~ 25–30 g) were comparable [14,15,18,32], part of the variation in publications may be explained by the differing carbohydrate sources (glucose, maltodextrin, or mashed potatoes). Altogether, modulating the type of carbohydrates in the diabetic diet was effective in controlling postprandial hyperglycemia. Results of metaanalyses support the use of low glycemic index foods in the metabolic control of diabetic patients [8,9]. In summary, a single drink containing ISO combined with whey/soy or casein elevated insulin levels, but reduced insulin action, and therefore did not improve glucose responses compared to the single drink of ISO alone. The whey/ soy drink increased insulin, which was associated with enhanced plasma amino acid levels, but concomitantly decreased insulin action compared to the casein drink. Thus, different types of proteins modulate insulin response and insulin action differently. A fast-absorbing protein reduces insulin action to a greater extent than a slow-absorbing protein. Our results suggest the importance of monitoring protein intake, as well as the type of protein, for the glycemic control of T2D patients.
Author contributions MA carried out the data analysis and drafted the manuscript. ASM, FW, and AP contributed with valuable and
1701
critical discussion. TL coordinated the study and drafted the manuscript.
Funding TL is supported by grants from Nutricia Advanced Medical Nutrition (Wageningen, Netherlands) and the Dutch Ministry of Agriculture and Food Quality. TL, FW, and AP are supported by the LOEWE focus group MIBIE, an excellence initiative of the state government of Hessen (Germany).
Acknowledgments We thank the staff of the Clinical Research Unit for their technical assistance and the patients for their contribution to this study. We also thank Mirian Lansink and colleagues for contributing with the amino acid data and providing useful comments during the early development of the manuscript.
Conflict of interest None of the authors has personal or financial conflicts of interest.
REFERENCES
[1] DECODE Study Group, the European Diabetes Epidemiology Group. Glucose tolerance and cardiovascular mortality: comparison of fasting and 2-hour diagnostic criteria. Arch Intern Med 2001;161:397–405. [2] Milicevic Z, Raz I, Beattie SD, et al. Natural history of cardiovascular disease in patients with diabetes: role of hyperglycemia. Diabetes Care 2008;31(Suppl. 2):S155–60. [3] Del Prato S. In search of normoglycaemia in diabetes: controlling postprandial glucose. Int J Obes Relat Metab Disord 2002;26(Suppl. 3):S9–17. [4] Ceriello A, Colagiuri S. International Diabetes Federation guideline for management of postmeal glucose: a review of recommendations. Diabet Med 2008;25:1151–6. [5] Psaltopoulou T, Ilias I, Alevizaki M. The role of diet and lifestyle in primary, secondary, and tertiary diabetes prevention: a review of meta-analyses. Rev Diabet Stud 2010;7:26–35. [6] Thomas GN, Jiang CQ, Taheri S, et al. A systematic review of lifestyle modification and glucose intolerance in the prevention of type 2 diabetes. Curr Diabetes Rev 2010;6:378–87. [7] Walker KZ, O'Dea K, Gomez M, et al. Diet and exercise in the prevention of diabetes. J Hum Nutr Diet 2010;23: 344–52. [8] Brand-Miller J, Hayne S, Petocz P, et al. Low-glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials. Diabetes Care 2003;26: 2261–7. [9] Thomas DE, Elliott EJ. The use of low-glycaemic index diets in diabetes control. Br J Nutr 2010;104:797–802. [10] Jenkins DJ, Wolever TM, Taylor RH, et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981;34:362–6. [11] Lina BA, Jonker D, Kozianowski G. Isomaltulose (Palatinose): a review of biological and toxicological studies. Food Chem Toxicol 2002;40:1375–81.
1702
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
[12] Kawai K, Yoshikawa H, Murayama Y, et al. Usefulness of palatinose as a caloric sweetener for diabetic patients. Horm Metab Res 1989;21:338–40. [13] Holub I, Gostner A, Theis S, et al. Novel findings on the metabolic effects of the low glycaemic carbohydrate isomaltulose (Palatinose). Br J Nutr 2010;103:1730–7. [14] Gannon MC, Nuttall FQ, Neil BJ, et al. The insulin and glucose responses to meals of glucose plus various proteins in type II diabetic subjects. Metabolism 1988;37:1081–8. [15] Gannon MC, Nuttall FQ, Lane JT, et al. Metabolic response to cottage cheese or egg white protein, with or without glucose, in type II diabetic subjects. Metabolism 1992;41: 1137–45. [16] van Loon LJ, Kruijshoop M, Menheere PP, et al. Amino acid ingestion strongly enhances insulin secretion in patients with long-term type 2 diabetes. Diabetes Care 2003;26: 625–30. [17] Manders RJ, Wagenmakers AJ, Koopman R, et al. Co-ingestion of a protein hydrolysate and amino acid mixture with carbohydrate improves plasma glucose disposal in patients with type 2 diabetes. Am J Clin Nutr 2005;82:76–83. [18] Manders RJ, Koopman R, Sluijsmans WE, et al. Co-ingestion of a protein hydrolysate with or without additional leucine effectively reduces postprandial blood glucose excursions in Type 2 diabetic men. J Nutr 2006;136:1294–9. [19] Hageman R, Severijnen C, van de Heijning BJ, et al. A specific blend of intact protein rich in aspartate has strong postprandial glucose attenuating properties in rats. J Nutr 2008;138:1634–40. [20] Matthews DR, Hosker JP, Rudenski AS, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985;28:412–9. [21] Trujillo-Arriaga HM, Román-Ramos R. Fitting and evaluating the glucose curve during a quasi continuous sampled oral glucose tolerance test. Comput Biol Med 2008;38: 185–95. [22] Caumo A, Bergman RN, Cobelli C. Insulin sensitivity from meal tolerance tests in normal subjects: a minimal model index. J Clin Endocrinol Metab 2000;85:4396–402. [23] Cobelli C, Toffolo GM, Dalla Man C, et al. Assessment of betacell function in humans, simultaneously with insulin sensitivity and hepatic extraction, from intravenous and oral glucose tests. Am J Physiol Endocrinol Metab 2007;293: E1–15. [24] Krebs M, Krssak M, Bernroider E, et al. Mechanism of amino acid-induced skeletal muscle insulin resistance in humans. Diabetes 2002;51:599–605.
[25] Krebs M, Brehm A, Krssak M, et al. Direct and indirect effects of amino acids on hepatic glucose metabolism in humans. Diabetologia 2003;46:917–25. [26] Calbet JA, MacLean DA. Plasma glucagon and insulin responses depend on the rate of appearance of amino acids after ingestion of different protein solutions in humans. J Nutr 2002;132:2174–82. [27] Boirie Y, Dangin M, Gachon P, et al. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A 1997;94:14930–5. [28] Nilsson M, Stenberg M, Frid AH, et al. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr 2004;80: 1246–53. [29] Veldhorst MA, Nieuwenhuizen AG, Hochstenbach-Waelen A, et al. Dose-dependent satiating effect of whey relative to casein or soy. Physiol Behav 2009;96:675–82. [30] Joint FAO/WHO Expert Committee on Food Additives (JECFA). Toxicological evaluation of certain food additives. WHO Food Additives Series, No. 22. Geneva: Cambridge University Press; 1988. [31] Stumvoll M, Perriello G, Nurjhan N, et al. Glutamine and alanine metabolism in NIDDM. Diabetes 1996;45: 863–8. [32] Frid AH, Nilsson M, Holst JJ, et al. Effect of whey on blood glucose and insulin responses to composite breakfast and lunch meals in type 2 diabetic subjects. Am J Clin Nutr 2005;82:69–75. [33] Sluijs I, Beulens JW, van der ADL, et al. Dietary intake of total, animal, and vegetable protein and risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-NL Study. Diabetes Care 2010;33:43–8. [34] Linn T, Geyer R, Prassek S, et al. Effect of dietary protein intake on insulin secretion and glucose metabolism in insulin-dependent diabetes mellitus. J Clin Endocrinol Metab 1996;81:3938–43. [35] Linn T, Santosa B, Grönemeyer D, et al. Effect of long-term dietary protein intake on glucose metabolism in humans. Diabetologia 2000;43:1257–65. [36] Liese AD, Weis KE, Schulz M, et al. Food intake patterns associated with incident type 2 diabetes: the Insulin Resistance Atherosclerosis Study. Diabetes Care 2009;32: 263–8. [37] Mann JI, De Leeuw I, Hermansen K, et al. Evidence-based nutritional approaches to the treatment and prevention of diabetes mellitus. Nutr Metab Cardiovasc Dis 2004;14: 373–94.
Available online at www.sciencedirect.com
Metabolism www.metabolismjournal.com
Combining protein and carbohydrate increases postprandial insulin levels but does not improve glucose response in patients with type 2 diabetes Meidjie Ang a , Andreas S. Müller b , Florian Wagenlehner c , Adrian Pilatz c , Thomas Linn a,⁎ a b c
Medizinische Klinik und Poliklinik III, Justus-Liebig-Universität, 35392 Giessen, Germany Institut für Agrar- und Ernährungswissenschaften, Martin-Luther-Universität, Halle-Wittenberg, Germany Klinik für Urologie, Kinderurologie und Andrologie, Universitätsklinikum Giessen und Marburg GmbH, Giessen, Germany
A R T I C LE I N FO Article history:
AB S T R A C T Objective. A combined load of carbohydrate and protein stimulates insulin secretion.
Received 11 October 2011
However, results on postprandial glucose responses in type 2 diabetic (T2D) subjects have
Accepted 9 May 2012
been inconclusive. Therefore, we investigated the effects of co-ingestion of carbohydrate and protein on glucose and insulin responses in these subjects. Methods. After an overnight fast, 30 subjects consumed a drink containing 50 g of slowly-
Keywords:
digested isomaltulose (ISO), combined either with a mixture of 21 g whey/soy (ISO + WS) or
Isomaltulose
with 21 g casein (ISO + C) in a randomized order on separate days. In another experiment, the
Protein
subjects consumed a control drink containing only 50 g ISO.
Insulin action
Results. No significant differences in glucose responses were observed after ingestion of
Postprandial glucose metabolism
the drinks. Compared to ingestion of ISO alone, insulin response was ~ 190%–270% higher
Type 2 diabetes
(P < .001), whereas insulin action was lower (P < .01) after ingestion of ISO + WS and ISO + C. Plasma insulin levels increased more significantly (P < .001) after ingestion of ISO + WS compared to ISO + C and were positively correlated with total amino acid levels (P < .001). Insulin action, however, showed a greater decrease following ingestion of ISO + WS than ISO + C (P < .01). Conclusions. Combining carbohydrate with protein can elevate postprandial insulin levels, but decreases insulin action, and therefore does not improve glucose response in T2D subjects. Our results further suggest that different types of proteins (i.e., fastabsorbing whey/soy vs. slow-absorbing casein) differently modulate insulin response and insulin action. A fast-absorbing protein mixture reduces insulin action to a greater extent than a slow-absorbing protein, and therefore may not be recommended for glycemic control in T2D patients. © 2012 Elsevier Inc. All rights reserved.
Abbreviations: BCAA, branched-chain amino acid; BMI, body mass index; EAA, essential amino acid; HbA1c, glycated hemoglobin; HOMA-IR, homeostasis model assessment of insulin resistance; iAUC, incremental area under the curve; ISO, isomaltulose; ISO + C, isomaltulose combined with casein; ISO + WS, isomaltulose combined with whey and soy (ratio 1:1); SEM, standard error of the mean; SI, insulin sensitivity index; TAA, total amino acid; T2D, type 2 diabetic; rs, Spearman's correlation coefficient. ⁎ Corresponding author. Tel.: +49 641 985 42841; fax: +49 641 985 42849. E-mail address: [email protected] (T. Linn). 0026-0495/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.metabol.2012.05.008
1697
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
1.
Table 2 – Amino acid composition (g/100 g protein).
Introduction
Postprandial hyperglycemia plays an important role in the development of cardiovascular complications in patients with type 2 diabetes [1,2]. To reduce the incidence and progression of these complications, an optimal glycemic control strategy should be considered in the treatment [3,4]. Several reviews reported that nutrition and lifestyle interventions can be effective in delaying the onset of the disease [5–7]. Meta-analyses of randomized controlled trials reported that a low glycemic index diet has a clinically relevant effect on glycemic control [8,9]. The glycemic index, originally described by Jenkins et al. [10], is a ranking system that measures the extent to which carbohydrates affect postprandial blood glucose levels. Carbohydrates with a low glycemic index are usually slowlyabsorbed, producing delayed gradual rises in blood glucose and insulin levels. For example, isomaltulose (ISO) is an isomer of sucrose which is digested slower than other sugars such as sucrose or maltose [11]. Studies on blood glucose, fructose, and insulin levels after oral administration of ISO have generally confirmed its suitability for diabetic subjects [11–13]. The dietary macronutrients carbohydrates, proteins, and fats are usually ingested in a complex food matrix rather than in their pure form. As a consequence, interactions between the macronutrients may influence glycemic response. Understanding nutrient interdependencies is therefore important. For instance, food proteins alone already stimulate insulin release, whereas a notably additive effect on insulin release is triggered by the combined uptake of proteins with carbohydrates [14–18]. However, controversial results have been reported in regard to the effects of insulin stimulation on glucose homeostasis in type 2 diabetic (T2D) subjects. Some studies have shown a reduction of postprandial glucose response when proteins and carbohydrates were taken up in combination compared to the uptake of carbohydrates alone [14,17,18]. Other studies did not confirm this effect [15,16]. In this context, various proteins were studied and it remains to be clarified whether they have comparable and consistent effects on postprandial glucose. In animal studies, it was reported that a protein mixture of whey and soy has potent postprandial glucose-attenuating and insulin-stimulating effects. These were also observed when the proteins were simultaneously ingested with a slowrelease carbohydrate [19]. In the present study, an isonitro-
Table 1 – Patients’ characteristics (n = 30). Sex (female/male) Age (years) Body weight (kg) Height (m) BMI (kg/m2) HbA1c (%) HOMA-IR Diabetes duration (years) Metformin (female/male)
12/18 62.9 ± 1.3 85.6 ± 3.1 1.7 ± 0.02 29.0 ± 0.7 6.6 ± 0.1 4.0 ± 0.6 5.2 ± 2.6 8/11
BMI, body mass index; HbA1c, glycated hemoglobin; HOMA-IR, homeostasis model assessment of insulin resistance. Data are mean ± SEM.
Alanine Arginine Aspartic acid Cyst(e)ine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine
Whey/Soy
Casein
3.8 4.7 12.2 2.1 18.0 3.2 2.4 5.9 8.7 7.2 1.5 4.3 4.8 5.2 5.2 2.3 3.4 5.2
2.8 3.4 6.6 0.4 20.2 1.7 2.9 5.2 9.1 7.5 2.7 4.9 9.5 5.7 4.2 1.3 5.2 6.7
Whey/Soy (ratio 1:1).
genous mixture of whey and soy proteins, as well as casein, was used as protein sources. We investigated whether a combined load of protein and slowly digested ISO could reduce postprandial glucose response in T2D subjects.
2.
Subjects and methods
2.1.
Subjects
Thirty T2D subjects with good glycemic control (HbA1c < 7%, Table 1) were recruited from the University Hospital of Giessen, Germany and were treated with dietary advice and/or metformin. No other anti-diabetic medication was allowed. Metformin administration was stopped three days prior to the tests. Exclusion criteria include unstable or untreated proliferative retinopathy, clinically significant nephropathy, neuropathy, hepatic diseases, heart failure, uncontrolled hypertension, systemic treatment with corticosteroids, and insulin treatment. Prior to the study, all subjects underwent a thorough physical examination, as well as laboratory testing (blood cell count, liver and kidney chemistry, urine analysis, pregnancy test in premenopausal women, electrocardiography). The purpose was to exclude pregnancy and persons with medical conditions (e.g., cerebrovascular or coronary artery disease), which would complicate the evaluation of the tests. The study was conducted according to the guidelines set out in the Declaration of Helsinki and all procedures involving human subjects were approved by the Ethics Committee of the Justus Liebig University (Giessen, Germany). Written informed consent was obtained from all subjects.
2.2.
Study design
Each subject participated in 3 different experiments with a minimum 3-day washout period between two experiments. Subjects were randomized to ingest either a drink containing 50 g ISO with 21 g whey/soy (ratio 1:1) (ISO + WS) or a drink
1698
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
containing 50 g ISO with 21 g casein (ISO + C). In another experiment, the subjects were given a control drink containing only 50 g ISO. All experimental drinks were prepared from powder (Nutricia, Wageningen, Netherlands), dissolved in water. The amino acid composition of whey/soy and casein is listed in Table 2. To exclude any possible interactions, no other nutrients were added to the drinks.
calculated from 0 to 240 min, GE is glucose effectiveness, Doral is the dose of ingested carbohydrate per unit of body weight (mg/kg) and f is the fraction of ingested glucose that appears in the systemic circulation. GE was fixed at 0.024 dL/kg·min and f was set at 0.8 [22]. When glucose concentration falls below baseline, the equation becomes t
f ⋅Doral
AUC½ΔGðtÞ = GðtÞ00 −AUC½ΔGðtÞ = GðtÞ∞ t
2.3.
Analysis
Calculations
Homeostasis model assessment of insulin resistance (HOMAIR) was calculated with HOMA = (G0 ⋅ I0)/405 where G0 is the fasting plasma glucose (mg/dL) and I0 is the fasting plasma insulin (μU/mL) [20]. Plasma glucose and insulin curves were fitted using an equation described by Trujillo-Arriaga and Roman-Ramos [21]. Glucose, insulin, and amino acid responses were calculated as incremental areas under the curves (iAUCs) above the baseline level. Incremental AUCs were calculated using GraphPad Prism 5. Insulin action was assessed in the postprandial state using the oral glucose minimal model [22]. The model provides an insulin sensitivity index (SI, dL/kg·min per pmol/L), which is based on the total integrated AUCs of glucose and insulin concentrations assuming that the systemic glucose disposal equals the glucose entering the peripheral circulation. SIðoralÞ =
½ΔGðtÞ = GðtÞ f ⋅Doral AUCAUC −GE⋅AUC½ΔGðtÞ = GðtÞ ½ΔGðtÞ
AUC½ΔIðtÞ
−GE⋅AUC½ΔGðtÞ = GðtÞ ð2Þ
Plasma glucose concentrations were measured by the glucose hexokinase method (Bayer ADVIA, Germany). Plasma insulin concentrations were determined using a sandwich immunoassay based on a direct luminescence technique (Bayer ADVIA Centaur, Germany). Coefficients of variation for intra- and interassay precisions of glucose and insulin measurements were < 6%. Amino acids were determined by high performance liquid chromatography using the fluorometric detection after precolumn derivatization with ortho-phthaldialdehyde.
2.5.
0
AUC½ΔIðtÞ
Study protocol
Subjects were admitted to the Clinical Research Unit at 08:00 h after an overnight fast. Basal blood samples were drawn from the antecubital vein before the start of the study. Thereafter, the subjects consumed the drinks containing only ISO, ISO + WS or ISO + C within 5 min. Blood samples were taken at 15, 30, 45, 60, 75, and 90 min after ingestion of the drinks, subsequently at every 30 min until blood glucose levels returned to baseline. Blood samples were collected into lithium heparin-coated tubes for the measurement of glucose, insulin, and amino acids. They were immediately centrifuged at 2000 g for 10 min. Aliquots of plasma were analyzed for glucose and insulin concentrations. The remaining samples were frozen and stored at − 20 °C until the analysis of the amino acids.
2.4.
t
AUC½ΔGðtÞ00 −AUC½ΔGðtÞ∞ t
0
SIðoralÞ =
ð1Þ
where ΔG (mg/dL) and ΔI (pmol/L) are glucose and insulin concentrations above basal, ΔG(t) = G(t) − Gb, ΔI = I(t) − Ib. AUC is
t0 is the time when glucose concentration crosses the baseline level. SI measures the overall effect of insulin to stimulate glucose disposal and inhibit glucose production [23].
2.6.
Statistical analysis
All data are expressed as mean ± SEM. The Kolmogorov– Smirnov test was used to evaluate the normality of the data. Comparisons between the drinks at different time points were analyzed by using two-way repeated measures ANOVA with drink and time as within-subject factors. When the data violated the assumption of sphericity for homogeneity of variances, Greenhouse–Geisser correction was used. For nontime-dependent variables, one-way repeated measures ANOVA or Friedman test was used to analyze data set with or without normality of distribution, respectively. If the test revealed significant changes and the normality assumption was not violated, Bonferroni post hoc test was further applied for multiple comparisons between the drinks. For data set without normality of distribution, Wilcoxon signed-rank test with Bonferroni correction was chosen as post hoc test for multiple comparisons between the drinks. Spearman's correlation coefficient (rs) was used to assess the relationship between insulin and amino acids. Analysis was performed by using SPSS 16. Differences between means with an error probability of P < .05 were considered statistically significant. In case of Bonferroni corrections, the significance level was set at P < .05/number of comparisons.
3.
Results
3.1.
Plasma glucose and insulin concentrations
Fasting plasma glucose levels did not differ between the study days on which only ISO, ISO + WS, or ISO + C was ingested (P = .648, Table 3). After ingestion of ISO alone, ISO + WS, and ISO + C, plasma glucose concentrations increased significantly above the baseline level (P < .001) and reached peak values at ~ 75 min. Glucose responses did not differ following ingestion of the different drinks (P = .239, Fig. 1A). Accordingly, fasting plasma insulin levels did not differ between the days of ingestion of ISO alone, ISO + WS, and ISO + C (P = .525, Table 3). Plasma insulin concentrations increased from baseline (P < .001) to peak levels after ~ 90 min consumption of the different drinks. Insulin responses were ~ 270% and ~ 190% higher after ingestion of ISO + WS and ISO + C than after ingestion of ISO alone (P < .001). Following intake of ISO +
1699
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
Table 3 – Plasma glucose and insulin after ingestion of drinks containing only ISO, ISO + WS, and ISO + C in 30 type 2 diabetic patients. ISO
Plasma glucose Baseline (mmol/L) Peak (mmol/L) Peak time (min) Plasma insulin Baseline (pmol/L) Peak (pmol/L) Peak time (min) SI (10− 5 dL/kg·min per pmol/L)
ISO + WS
ISO + C
Overall P value
7.1 ± 0.2 11.2 ± 0.3 77.5 ± 4.0
7.2 ± 0.3 11.1 ± 0.4 78.5 ± 4.4
7.2 ± 0.3 10.9 ± 0.4 76.0 ± 4.0
.648 .656 .639
77.1 ± 2.9 212.4 ± 10.2 94.0 ± 4.1 16.3 ± 2.0
88.6 ± 11.2 571.9 ± 47.0 94.0 ± 7.3 5.9 ± 0.8
76.5 ± 11.8 445.4 ± 38.6 95.5 ± 10.0 10.4 ± 1.8
.525 <.001 .515 <.001
P value
a
ISO vs. ISO + WS ISO vs. ISO + C ISO + WS vs. ISO + C NA NA NA
NA NA NA
NA NA NA
NA <.001 NA <.001
NA <.001 NA .005
NA <.001 NA .003
iAUC (mmol/L.4h)
ISO, isomaltulose; ISO + WS, isomaltulose combined with whey/soy (ratio 1:1); ISO + C, isomaltulose combined with casein; SI, insulin sensitivity index; NA, not applicable (due to non-significant overall P value). Data are mean ± SEM. a A P value < .0167 was considered significant (Bonferroni adjustment for 3 comparisons).
WS, insulin response was ~ 30% higher compared to that observed following intake of ISO + C (P = .002, Fig. 1B).
3.2.
Net SI was lower after ingestion of ISO + WS and ISO + C than after ingestion of ISO alone (P < .001 and P = .005, respectively). Moreover, SI was lower following intake of ISO + WS compared to that following intake of ISO + C (P = .003, Table 3).
3.3.
Time (min)
B
Time (min)
iAUC (pmol/L.4h)
A
Fig. 1 – Plasma glucose and insulin after ingestion of drinks containing only ISO (grey), ISO + WS (black), and ISO + C (white) in 30 type 2 diabetic patients. (A) No significant drink effect (P = .704) or drink × time interaction (P = .411) was found for glucose concentrations. Glucose iAUCs were not significantly different between the drinks (P = .239). (B) A significant drink effect (P < .001) and drink × time interaction (P < .001) were found for insulin concentrations. Insulin iAUCs were significantly different between the drinks (P < .001). ISO, isomaltulose; ISO + WS, isomaltulose combined with whey/ soy (ratio 1:1); ISO + C, isomaltulose combined with casein; iAUC, incremental area under the curve; ns, non-significant. Data are mean ± SEM. **P = .002, ***P < .001.
Insulin action
Plasma amino acid concentrations
An overview of plasma amino acid concentrations at 0, 30 and 60 min is shown in Table 4. Total fasting plasma amino acid (TAA) concentrations did not differ on the study days when ISO + WS and ISO + C were ingested (P = .651). TAA levels increased from baseline (P < .001) and were higher after administration of ISO + WS compared to those following administration of ISO + C (P < .001). Similarly, fasting plasma concentrations of essential amino acid (EAA) and branchedchain amino acid (BCAA) did not differ on the ISO + WS and ISO + C study days (P = .221 and P = .141, respectively). EAA and BCAA levels increased from baseline (P < .001) and showed a pattern similar to those of TAA. Moreover, both EAA and BCAA levels were higher after administration of ISO + WS than after administration of ISO + C (P < .001). Plasma TAA concentrations positively correlated with plasma insulin levels in the 60 min postprandial period following ingestion of ISO + WS and ISO + C (rs = .690 and rs = .684, P < .001, respectively). Plasma TAA, EAA, and BCAA responses were ~ 54%, ~ 63%, and ~ 59%, respectively, higher after administration of ISO + WS than after administration of ISO + C (P < .001, Table 4). EAA and BCAA responses accounted for ~ 52%–55% and ~ 31%– 32% of increases in TAA response after ingestion of both drinks, respectively.
4.
Discussion
The present study shows that ingestion of ISO + WS or ISO + C substantially increased insulin but did not reduce glucose
1700
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
Table 4 – Plasma amino acid after ingestion of drinks containing ISO + WS and ISO + C in 30 type 2 diabetic patients. Amino acid
Alanine Arginine Asparagine Aspartic acid Citrulline Glutamine Glutamic acid Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Serine Taurine Threonine Tryptophan Tyrosine Valine TAA EAA BCAA
ISO + WS (μmol/L)
ISO + C (μmol/L)
ISO + WS vs. ISO + C
Baseline
30 min
60 min
Baseline
30 min
60 min
473 ± 20 79 ± 3 43 ± 1 10 ± 1 35 ± 2 457 ± 23 160 ± 19 208 ± 13 77 ± 2 88 ± 4 157 ± 6 177 ± 7 27 ± 2 64 ± 3 108 ± 4 106 ± 9 126 ± 5 59 ± 2 74 ± 4 280 ± 10 2811 ± 43 980 ± 29 526 ± 20
621 ± 32 116 ± 5 75 ± 4 13 ± 1 34 ± 2 500 ± 24 178 ± 16 231 ± 15 87 ± 2 166 ± 7 274 ± 12 270 ± 10 38 ± 2 84 ± 4 151 ± 6 115 ± 11 187 ± 8 76 ± 2 99 ± 5 372 ± 11 3687 ± 99 1467 ± 43 813 ± 28
676 ± 29 108 ± 5 75 ± 4 12 ± 1 35 ± 2 509 ± 23 175 ± 17 228 ± 18 91 ± 2 168 ± 7 266 ± 9 264 ± 9 36 ± 2 81 ± 4 147 ± 6 113 ± 11 195 ± 8 80 ± 3 99 ± 5 374 ± 10 3733 ± 91 1464 ± 37 807 ± 25
483 ± 20 76 ± 3 44 ± 1 10 ± 1 33 ± 2 463 ± 21 157 ± 14 211 ± 14 77 ± 2 86 ± 4 151 ± 6 173 ± 5 26 ± 1 64 ± 3 108 ± 4 112 ± 9 125 ± 5 60 ± 2 71 ± 3 265 ± 9 2793 ± 33 949 ± 25 501 ± 18
588 ± 27 96 ± 5 61 ± 2 11 ± 1 34 ± 2 495 ± 24 171 ± 16 221 ± 15 88 ± 2 131 ± 6 231 ± 10 235 ± 9 40 ± 2 81 ± 4 140 ± 6 124 ± 11 158 ± 6 68 ± 2 100 ± 5 343 ± 12 3416 ± 85 1288 ± 41 704 ± 27
631 ± 26 86 ± 4 56 ± 3 10 ± 1 34 ± 3 483 ± 25 171 ± 16 211 ± 16 88 ± 2 114 ± 5 195 ± 7 212 ± 6 35 ± 1 73 ± 4 129 ± 5 119 ± 10 152 ± 5 64 ± 2 90 ± 5 321 ± 9 3274 ± 76 1165 ± 28 630 ± 20
iAUC (μmol/L.1 h) 7501 ± 781 1528 ± 149 1430 ± 133 142 ± 23 32 ± 10 2187 ± 315 1164 ± 266 1030 ± 221 543 ± 47 3521 ± 263 5127 ± 424 4112 ± 291 455 ± 38 846 ± 73 1880 ± 194 690 ± 230 2846 ± 239 808 ± 72 1123 ± 121 4154 ± 343 40115 ± 3434 21878 ± 1640 12803 ± 1004
5526 ± 761 761 ± 130 698 ± 90 55 ± 9 68 ± 16 1451 ± 250 1004 ± 210 423 ± 105 491 ± 59 1795 ± 219 3048 ± 400 2456 ± 333 567 ± 81 654 ± 104 1280 ± 156 744 ± 192 1422 ± 165 354 ± 59 1135 ± 193 3198 ± 377 26055 ± 3326 13454 ± 1697 8042 ± 993
P value a,b
<.001 <.001 <.001 <.001 .035 .047 .798 <.001 .281 <.001 <.001 < .01 .097 .007 <.001 .827 <.001 <.001 .468 .002 <.001 <.001 <.001
ISO + WS, isomaltulose combined with whey/soy (ratio 1:1); ISO + C, isomaltulose combined with casein; iAUC, incremental area under the curve; TAA, total amino acid; EAA, essential amino acid; BCAA, branched-chain amino acid. Data are mean ± SEM. a For each individual amino acid, a P value < .0025 was considered significant (Bonferroni adjustment for 20 comparisons). b For TAA, EAA, and BCAA, a P value < .0167 was considered significant (Bonferroni adjustment for 3 comparisons).
response compared to the ingestion of ISO alone in T2D subjects. Based on our results the explanation for this observation is a reduced postprandial insulin action after ingestion of ISO + WS or ISO + C. In healthy subjects, shortterm elevations of plasma amino acids have been shown to decrease glucose uptake, inhibit glucose transport or muscle insulin signaling, and enhance endogenous glucose production [24,25]. Taken together it can be concluded that protein components of ISO + WS and ISO + C decreased the effects of insulin in T2D subjects. Reduced insulin action is counterbalanced by an increase in insulin secretion, thereby regulating plasma glucose levels. Differences in insulin responses following ingestion of ISO + WS or ISO + C were exclusively dependent on the protein compositions as displayed by their amino acid profiles (P < .001). Our results confirm a previous report on the stimulation of insulin by postprandial TAA levels [26]. Differences in the rise of plasma TAA concentrations are attributed to a faster absorption of whey compared to casein. While whey proteins are readily soluble in gastric juice, caseins tend to clot in the stomach due to precipitation by gastric acid [27]. Overall, postprandial individual amino acid responses were enhanced after ingestion of ISO + WS as opposed to ingestion of ISO + C. Our results confirm previous findings of marked increments of alanine, leucine, valine, lysine, isoleucine, and threonine following the meals containing whey in healthy subjects [28,29]. The highest increase was seen in the alanine response, despite the fact that glutamic acid is the most abundant. This could be explained by transamination of
glutamic acid to alanine during intestinal absorption [30], or increased conversion of glutamine to alanine due to substantial alterations of glutamine and alanine metabolism in type 2 diabetes [31]. The effects of ingestion of variable protein and carbohydrate combinations on glucose levels are discussed controversially. Non-diabetic probands often showed small, but significant absolute effects of total mean blood glucose when two carbohydrate/protein blends were compared [17,18], yet the shape of the glucose profiles did not differ [16]. In T2D subjects, the glucose responses were highly variable and the magnitude of glucose reduction was moderate at best [14,17,18]. Combining carbohydrate with casein reduced glucose responses, but glucose appearance rates [17] and plasma glucose levels [18] were identical compared to carbohydrate ingestion only. A reduced glucose response was further reported after whey intake for lunch, compared to a ham meal [32] without significant differences for breakfast with the same meals. Thus, no definitive conclusion on the glucose-lowering effect of protein can be drawn from these studies. Our study focused on the impact of protein ingestion on glucose and insulin responses, since study drinks contained only the macronutrients, carbohydrate and protein. By contrast, matrix and nutrient–nutrient interactions will interfere with the contribution of the components in meal studies. Impaired insulin action is a major feature of type 2 diabetes and was calculated using the oral minimal model in our study. This model provides an accurate measurement of insulin sensitivity after ingestion of a single protein load and
M E TAB O LI S M CL I NI CA L A N D EX P ER IM EN T AL 6 1 (2 0 1 2) 1 69 6 –1 7 02
is as powerful as that obtained from an intravenous glucose tolerance test [23]. Insulin action was lower for ISO + WS compared to ISO + C drink, indicating that the type of ingested protein modulated insulin action. The fast-absorbing protein mixture whey/soy reduced insulin action to a greater extent than slow-absorbing casein. Interestingly, consumption of protein from animal sources (meat, milk/products, and cheese), but not from vegetables, was associated with a higher prevalence of diabetes [33]. Diets rich in protein may have long-term adverse effects on glycemic control, such as impaired suppression of hepatic glucose output by insulin, promotion of insulin resistance, and increased gluconeogenesis [34,35]. Dietary protein intake in diabetic patients usually ranges between 15% and 20% of total daily energy in most industrialized countries, which corresponds to 1.3–2.0 g/kg body weight and represents an intake that exceeds the recommended daily amount of 0.8 g/kg body weight. Recent epidemiological studies strongly indicate an association of higher intake of various proteins and increased risk of type 2 diabetes [33,36]. There are currently no guidelines addressing protein quality for the management of diabetes [37]. Our findings suggest that ingestion of fast-absorbing protein mixtures cannot be recommended for the glycemic control of T2D patients. Long-term effects of the consumption of proteins with different absorption rates remain to be established. In this study slowly absorbed ISO or the addition of ISO to both proteins increased glucose and insulin levels moderately. Incremental peak glucose and insulin levels were higher in previous studies with diabetic patients [14–18], but were similar after a lunch meal containing mashed potatoes and whey [32] compared to our study (~ 5–10 vs. ~ 3.5 mmol/L and ~ 500–1700 vs. ~ 120–380 pmol/L). Since the amounts of ingested carbohydrate (~ 45–60 g) and protein (~ 25–30 g) were comparable [14,15,18,32], part of the variation in publications may be explained by the differing carbohydrate sources (glucose, maltodextrin, or mashed potatoes). Altogether, modulating the type of carbohydrates in the diabetic diet was effective in controlling postprandial hyperglycemia. Results of metaanalyses support the use of low glycemic index foods in the metabolic control of diabetic patients [8,9]. In summary, a single drink containing ISO combined with whey/soy or casein elevated insulin levels, but reduced insulin action, and therefore did not improve glucose responses compared to the single drink of ISO alone. The whey/ soy drink increased insulin, which was associated with enhanced plasma amino acid levels, but concomitantly decreased insulin action compared to the casein drink. Thus, different types of proteins modulate insulin response and insulin action differently. A fast-absorbing protein reduces insulin action to a greater extent than a slow-absorbing protein. Our results suggest the importance of monitoring protein intake, as well as the type of protein, for the glycemic control of T2D patients.
Author contributions MA carried out the data analysis and drafted the manuscript. ASM, FW, and AP contributed with valuable and
1701
critical discussion. TL coordinated the study and drafted the manuscript.
Funding TL is supported by grants from Nutricia Advanced Medical Nutrition (Wageningen, Netherlands) and the Dutch Ministry of Agriculture and Food Quality. TL, FW, and AP are supported by the LOEWE focus group MIBIE, an excellence initiative of the state government of Hessen (Germany).
Acknowledgments We thank the staff of the Clinical Research Unit for their technical assistance and the patients for their contribution to this study. We also thank Mirian Lansink and colleagues for contributing with the amino acid data and providing useful comments during the early development of the manuscript.
Conflict of interest None of the authors has personal or financial conflicts of interest.
REFERENCES
[1] DECODE Study Group, the European Diabetes Epidemiology Group. Glucose tolerance and cardiovascular mortality: comparison of fasting and 2-hour diagnostic criteria. Arch Intern Med 2001;161:397–405. [2] Milicevic Z, Raz I, Beattie SD, et al. Natural history of cardiovascular disease in patients with diabetes: role of hyperglycemia. Diabetes Care 2008;31(Suppl. 2):S155–60. [3] Del Prato S. In search of normoglycaemia in diabetes: controlling postprandial glucose. Int J Obes Relat Metab Disord 2002;26(Suppl. 3):S9–17. [4] Ceriello A, Colagiuri S. International Diabetes Federation guideline for management of postmeal glucose: a review of recommendations. Diabet Med 2008;25:1151–6. [5] Psaltopoulou T, Ilias I, Alevizaki M. The role of diet and lifestyle in primary, secondary, and tertiary diabetes prevention: a review of meta-analyses. Rev Diabet Stud 2010;7:26–35. [6] Thomas GN, Jiang CQ, Taheri S, et al. A systematic review of lifestyle modification and glucose intolerance in the prevention of type 2 diabetes. Curr Diabetes Rev 2010;6:378–87. [7] Walker KZ, O'Dea K, Gomez M, et al. Diet and exercise in the prevention of diabetes. J Hum Nutr Diet 2010;23: 344–52. [8] Brand-Miller J, Hayne S, Petocz P, et al. Low-glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials. Diabetes Care 2003;26: 2261–7. [9] Thomas DE, Elliott EJ. The use of low-glycaemic index diets in diabetes control. Br J Nutr 2010;104:797–802. [10] Jenkins DJ, Wolever TM, Taylor RH, et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981;34:362–6. [11] Lina BA, Jonker D, Kozianowski G. Isomaltulose (Palatinose): a review of biological and toxicological studies. Food Chem Toxicol 2002;40:1375–81.
1702
M ET AB O LI S M CL I NI CA L A N D EX PE R IM EN T AL 6 1 (2 0 1 2) 1 69 6–1 70 2
[12] Kawai K, Yoshikawa H, Murayama Y, et al. Usefulness of palatinose as a caloric sweetener for diabetic patients. Horm Metab Res 1989;21:338–40. [13] Holub I, Gostner A, Theis S, et al. Novel findings on the metabolic effects of the low glycaemic carbohydrate isomaltulose (Palatinose). Br J Nutr 2010;103:1730–7. [14] Gannon MC, Nuttall FQ, Neil BJ, et al. The insulin and glucose responses to meals of glucose plus various proteins in type II diabetic subjects. Metabolism 1988;37:1081–8. [15] Gannon MC, Nuttall FQ, Lane JT, et al. Metabolic response to cottage cheese or egg white protein, with or without glucose, in type II diabetic subjects. Metabolism 1992;41: 1137–45. [16] van Loon LJ, Kruijshoop M, Menheere PP, et al. Amino acid ingestion strongly enhances insulin secretion in patients with long-term type 2 diabetes. Diabetes Care 2003;26: 625–30. [17] Manders RJ, Wagenmakers AJ, Koopman R, et al. Co-ingestion of a protein hydrolysate and amino acid mixture with carbohydrate improves plasma glucose disposal in patients with type 2 diabetes. Am J Clin Nutr 2005;82:76–83. [18] Manders RJ, Koopman R, Sluijsmans WE, et al. Co-ingestion of a protein hydrolysate with or without additional leucine effectively reduces postprandial blood glucose excursions in Type 2 diabetic men. J Nutr 2006;136:1294–9. [19] Hageman R, Severijnen C, van de Heijning BJ, et al. A specific blend of intact protein rich in aspartate has strong postprandial glucose attenuating properties in rats. J Nutr 2008;138:1634–40. [20] Matthews DR, Hosker JP, Rudenski AS, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985;28:412–9. [21] Trujillo-Arriaga HM, Román-Ramos R. Fitting and evaluating the glucose curve during a quasi continuous sampled oral glucose tolerance test. Comput Biol Med 2008;38: 185–95. [22] Caumo A, Bergman RN, Cobelli C. Insulin sensitivity from meal tolerance tests in normal subjects: a minimal model index. J Clin Endocrinol Metab 2000;85:4396–402. [23] Cobelli C, Toffolo GM, Dalla Man C, et al. Assessment of betacell function in humans, simultaneously with insulin sensitivity and hepatic extraction, from intravenous and oral glucose tests. Am J Physiol Endocrinol Metab 2007;293: E1–15. [24] Krebs M, Krssak M, Bernroider E, et al. Mechanism of amino acid-induced skeletal muscle insulin resistance in humans. Diabetes 2002;51:599–605.
[25] Krebs M, Brehm A, Krssak M, et al. Direct and indirect effects of amino acids on hepatic glucose metabolism in humans. Diabetologia 2003;46:917–25. [26] Calbet JA, MacLean DA. Plasma glucagon and insulin responses depend on the rate of appearance of amino acids after ingestion of different protein solutions in humans. J Nutr 2002;132:2174–82. [27] Boirie Y, Dangin M, Gachon P, et al. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A 1997;94:14930–5. [28] Nilsson M, Stenberg M, Frid AH, et al. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr 2004;80: 1246–53. [29] Veldhorst MA, Nieuwenhuizen AG, Hochstenbach-Waelen A, et al. Dose-dependent satiating effect of whey relative to casein or soy. Physiol Behav 2009;96:675–82. [30] Joint FAO/WHO Expert Committee on Food Additives (JECFA). Toxicological evaluation of certain food additives. WHO Food Additives Series, No. 22. Geneva: Cambridge University Press; 1988. [31] Stumvoll M, Perriello G, Nurjhan N, et al. Glutamine and alanine metabolism in NIDDM. Diabetes 1996;45: 863–8. [32] Frid AH, Nilsson M, Holst JJ, et al. Effect of whey on blood glucose and insulin responses to composite breakfast and lunch meals in type 2 diabetic subjects. Am J Clin Nutr 2005;82:69–75. [33] Sluijs I, Beulens JW, van der ADL, et al. Dietary intake of total, animal, and vegetable protein and risk of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-NL Study. Diabetes Care 2010;33:43–8. [34] Linn T, Geyer R, Prassek S, et al. Effect of dietary protein intake on insulin secretion and glucose metabolism in insulin-dependent diabetes mellitus. J Clin Endocrinol Metab 1996;81:3938–43. [35] Linn T, Santosa B, Grönemeyer D, et al. Effect of long-term dietary protein intake on glucose metabolism in humans. Diabetologia 2000;43:1257–65. [36] Liese AD, Weis KE, Schulz M, et al. Food intake patterns associated with incident type 2 diabetes: the Insulin Resistance Atherosclerosis Study. Diabetes Care 2009;32: 263–8. [37] Mann JI, De Leeuw I, Hermansen K, et al. Evidence-based nutritional approaches to the treatment and prevention of diabetes mellitus. Nutr Metab Cardiovasc Dis 2004;14: 373–94.