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© 2008 American Society for Nutrition

Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

A Specific Blend of Intact Protein Rich in Aspartate Has Strong Postprandial Glucose Attenuating Properties in Rats1

Robert Hageman, Chantal Severijnen, Bert J. M. van de Heijning, Hetty Bouritius, Nick van Wijk, Katrien van Laere and Eline M. van der Beek*

Danone Research Centre for Specialised Nutrition, 6700 CA Wageningen, The Netherlands

* To whom correspondence should be addressed. E-mail: eline.vanderbeek{at}danone.com.


   ABSTRACT
TOP
 ABSTRACT
Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
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.


   Introduction
TOP
 ABSTRACT
 Introduction
Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
Epidemiological surveys and intervention studies have shown that postprandial hyperglycemia is a direct and independent risk factor for the development of complications in type 2 diabetes. In fact, postprandial glucose (Glu) spikes were considered to be even more relevant to the onset of cardiovascular complications than elevated fasting blood Glu concentrations (1–3).

Pharmaceutical treatment aims to improve overall glycemic control in type 2 diabetes by either suppressing hepatic Glu production or enhancing the conversion of excess Glu into lipids, which then can be stored in fat and muscle tissue (4,5). Otherwise, drugs address the insulin resistance or try to reduce postprandial plasma Glu concentrations by increasing the secretion of postprandial insulin or by enhancing insulin action in muscle, fat, and other tissues. Proper use of these drugs requires careful adaptation to the patient's conditions to avoid safety issues and adverse events (e.g. hypoglycemia due to overdosing).

Apart from and complementary to pharmaceuticals, low-glycemic nutritional products also can be and have been safely used to attenuate postprandial Glu concentrations in diabetics. Many human studies show that dietary protein (including peptides and amino acids) attenuates postprandial plasma Glu concentrations (6–11) resulting from the consumption of a Glu polymer. The question now arises which nutritional products, and in particular which proteins, should be included to induce normal postprandial Glu concentrations in diabetics.

When selecting a proper protein fraction in the product, several potential effects should be taken into consideration. Proteins may induce insulin secretion (12), in particular in combination with digestible carbohydrates, due to their incretin effect (13), their effect on gastric emptying, or to an effect of postprandial amino acids resulting from digestion and absorption of the proteinaceous fraction (9,14).

Also at the cellular concentration, amino acids may play a relevant role. The biosynthesis of ATP and the replenishment of substrates for ATP synthesis drives a network of cytosolic and mitochondrial metabolic pathways and enables normal cell functioning. Substrate cycling in various shuttles, for example the glycerol-phosphate shuttle and/or the aspartate/malate shuttle involved in the transport of reducing equivalents (NADH) across the mitochondrial membrane, is pivotal in this respect (15). Malfunctioning of such a shuttle system has important implications, because it directly compromises the cell's capacity to produce ATP and hence cell functioning (16). For example, in type 2 diabetes, the activity of NAD+/NADH shuttles is disturbed (17), which might lead to an impaired Glu-stimulated insulin secretion as shown in fetal islet β-cells (18). This disturbed shuttle activity may be due to an inappropriate availability or imbalance of cytosolic substrates required for a proper shuttle functioning. We hypothesized that in particular an imbalance of aspartate and glutamate ions at the cytosolic side of the mitochondrial membrane might be a reason for inappropriate availability of reducing equivalents to the mitochondrial respiratory chain and insulin resistance. To shed some light on these potential effects of dietary proteins on postprandial Glu concentrations, we tested several proteins with a different aspartate concentration.

Our previous studies in healthy rats showed that the addition of soy protein to a Glu load resulted consistently in reduced postprandial Glu concentrations compared with casein protein. In addition, many secondary health benefits are reported for soy protein elsewhere (19–21). Based on this, we decided to further study soy protein.

In general, protein hydrolysates and amino acids are suggested to be absorbed at a faster rate than intact proteins (22,23) and might therefore enhance insulin secretion and peripheral Glu clearance even better (22). We therefore first tested the effects of soy protein chain length on the postprandial Glu and insulin response. Soy protein consists for ~12% of aspartate units; to improve its beneficial effects in diabetics even further, we prepared a 50:50 (wt:wt) mix of intact proteins, resulting in a protein aspartate content of ~14%, and tested the postprandial Glu response of this aspartate-rich protein blend compared with soy protein alone. By mixing the 2 proteins, we obtained a blend with a well-balanced amino acid composition (Table 1). Because nutritional products for diabetics may comprise low-glycemic, slow-release carbohydrates, we also tested if the benefits of the aspartate-rich protein blend persisted and were still effective in the presence of a low-glycemic, previously identified (24) carbohydrate designated modified high-amylose starch (mHAS).2


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  		TABLE 1 Amino acid composition of protein (blend) used in Expts. 1–3

 

   Materials and Methods
TOP
 ABSTRACT
 Introduction
 Materials and Methods
Results
 Discussion
 LITERATURE CITED
 
Rats

Male Wistar rats (HsdCpb: WU, Harlan) weighing 225–250 g on arrival, were pair-housed and kept in a temperature- (21 ± 1°C) and humidity- (55 ± 5%) controlled room under a light-dark schedule of 12:12 (lights on at 0500 h, = zeitgeber time 0). Rats had free access to a nonpurified AIN93-M-based diet (Teklad Global 18% Protein Rodent Diet, Harlan) (25) and tap water unless stated otherwise. All experiments were approved by the Animal Experiment Ethical Committee (DEC-Consult) and conducted according to their guidelines.

Surgical procedures

Following 2 wk of acclimatization, the rats were housed individually 2 d prior to surgery. All rats were equipped with an intragastric catheter for carbohydrate administration and a jugular vein catheter for stress-free blood sampling. Surgery was performed under O2/N2O/isoflurane anesthesia (IsoFlo, Abbott Laboratories). A jugular vein catheter (Silicon, 1.2-mm o.d., 0.60-mm i.d., Raumedics) was inserted into the heart via the right jugular vein according to the method of Steffens (26). The intragastric catheter (Silicon, 3.2-mm o.d., 1.5-mm i.d., Raumedics) was inserted and fixed into the antrum wall of the stomach. The opening of the intragastric catheter extended 0.5 cm into the stomach lumen (27). Tubings were tunneled subcutaneously, externalized on the top of the skull, and secured with dental cement and 2 screws. After surgery, buprenorfine (0.01 mL subcutaneously for 3 d, Schering-Plough) was injected for analgesia. The rats were allowed to recover for at least 1 wk after surgery and all rats had regained their preoperative weight before the experiments started. The body weight (BW) of the rats was monitored daily and did not change within the duration of the experiment.

Experimental protocol

At 1500 h (zeitgeber time 10) on the day of the experiment following 5 h of food deprivation, the rats received a bolus of 2.0 g available carbohydrate/kg BW alone or in combination with protein (2.5 g/kg BW) dissolved in tap water via the gastric cannula. Administered volumes were ~6–7 mL. At 1 min before and 5, 10, 15, 20, 30, 45, and 75 min after administration of the bolus, 200-µL blood samples were drawn and collected in ice-chilled, heparinized tubes. Blood samples were centrifuged at 2655 x g; 15 min at 4°C and plasma was stored at –80°C until assayed.

Experimental design

Three independent series of experiments were performed. Within 1 series, treatments were given in random order with a wash-out period of at least 1 wk in between.

    Expt. 1. Three protein sources containing different soy protein chain lengths were used to test the effects of protein chain length, each coadministered with Glu (D-(+)- Glu anhydrous mixed anomers; Sigma-Aldrich Chemie). Coingested intact soy protein (SI; Supro 1751 LN, Isolated Soy Protein, DuPont), soy protein hydrolysate (SH; Supro 1751 LN, hydrolyzed at our pilot plant facility), and soy protein amino acids (SAA; composition according to Supro 1751 LN; see Table 1) were tested compared with Glu; treatment designations are, respectively, GluSI, GluSH, GluSAA, and Glu.

    Expt. 2. To test the effects of adding an aspartate-enriched protein ({alpha}-lactalbumin) to soy protein, a 50:50 (wt:wt) blend of SI (Supro 1751 LN) with {alpha}-lactalbumin ({alpha}, BioPure, Davisco Foods) was used. L-Methionine (1%) was added to the blend to correct for the low methionine content (Rexim, F). Rapidly available maltodextrin (Malto; Glucidex DE19, Roquette, F) was coadministered as a carbohydrate source. The treatment designations in this experiment are, respectively, MaltoSI, MaltoSI{alpha}, and Malto.

    Expt. 3. Finally, the effects of a slowly vs. a rapidly available carbohydrate coinfused with the protein blend were tested. To evaluate these effects, the slowly digestible carbohydrate mHAS [Cargill, B; heat-treated to modify its functional properties as previously reported (24)] was compared with the rapidly available carbohydrate Malto (Glucidex DE19), both in combination with the protein blend (SI{alpha}). The treatment designations in this experiment are, respectively, Malto, mHAS, MaltoSI{alpha}, and mHASSI{alpha}.

    Plasma analyses. Glu concentrations in the plasma samples were determined colorimetrically (GOD-PAP, Roche Diagnostics). We analyzed insulin concentrations using a specific rat ELISA kit (DRG Diagnostics, Diagnostic System Laboratories Benelux) with a detection limit of 22.6 pmol/L. The insulin ELISA was performed in triplicate using serially diluted samples. Intra-assay variability was 4.6% and interassay variability was 4.8%.

Data processing

Data are expressed as means ± SEM. The basal concentration (t = –1 min) and maximal concentrations (peak) were determined for each trial, as well as the incremental area under the curve (iAUC). The latter was calculated as the sum of the AUC between each sampling time point above the basal concentration as measured at t = –1 until 45 min upon bolus administration.

Statistical analyses

The experiment had a randomized complete block design and was evaluated accordingly. The data obtained were evaluated using the statistical software package SPSS 15.0 (SPSS Benelux). All data were normally distributed and were analyzed using repeated-measures ANOVA. Differences in basal and peak concentration, and iAUC were tested using 1-way ANOVA. Post hoc analyses of significant effects were performed using multiple comparisons with post hoc LSD testing. Differences were considered significant at P < 0.05.


   Results
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
Discussion
 LITERATURE CITED
 
    Expt. 1. Intragastric administration of Glu in combination with either SI (GluSI), SH (GluSH), or SAA (GluSAA) significantly and equally attenuated the plasma Glu response compared with infusion of Glu alone (Fig. 1A). The addition of protein equally curtailed the duration of the Glu response compared with Glu alone; at 30 min, the Glu concentration did not differ from the basal value. The plasma insulin response was augmented and prolonged in the GluSI and GluSAA groups compared with Glu (Fig. 1B; Table 2). Baseline Glu and insulin concentrations did not differ among groups (Table 2). Maximal Glu concentrations attained (peaks) were not affected by protein addition, but in the insulin response, peaks were higher and prolonged and timing (peak time) was postponed with 5–10 min (Fig.1A,B; Table 2).


Figure 1
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  		FIGURE 1  Changes in plasma Glu (A) and insulin (B) in healthy rats after administration of Glu alone or in combination with SI, SH, or SAA (Expt. 1). Insets are iAUC of the plasma Glu and insulin responses during the first 45 min. Data are means ± SEM, n = 6. Means without a common letter differ, P < 0.05.

 

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  		TABLE 2 Expt. 1: Effects of intragastric administration of Glu alone or in combination with different soy protein chain lengths on the postprandial glycemic response in plasma of healthy rats1

 
The iAUC of the postprandial Glu response showed that all 3 soy protein chain lengths attenuated (P < 0.01) the response during the first 45 min by 40–50% compared with the response to Glu alone (Fig. 1A, inset). For insulin, the addition of soy protein increased the iAUC values compared with the Glu treatment; this was significant for the GluSI combination (P < 0.01,Fig. 1B, inset) but not for the others.

    Expt. 2. Intragastric infusion of either SI (MaltoSI) or a 50:50 mixture of SI and the whey-derived intact protein {alpha}-lactalbumin (MaltoSI{alpha}), both in combination with maltodextrin, tended to have a lower postprandial Glu response compared with the response to Malto alone (Fig. 2A). Again, the Glu response duration was curtailed and baseline concentrations were reached sooner (at 30 min). This Glu-lowering effect tended to be greater (P = 0.08) with MaltoSI{alpha} than with Malto alone. Correspondingly, the plasma insulin response tended to be greater (P = 0.14) and the maximal insulin concentrations attained were significantly higher in the MaltoSI{alpha} group than in the Malto group (Table 3). Peak time of the Glu response was not affected, but the peak time was delayed for 5 min in the insulin response. Moreover, the insulin response was higher and prolonged (Fig.2; Table 3). Again, baseline Glu and insulin concentrations were comparable among groups (Table 3).


Figure 2
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  		FIGURE 2  Changes in plasma Glu (A) and insulin (B) in healthy rats after administration of Malto alone or in combination with protein to healthy rats (Expt. 2). Insets are iAUC of the plasma Glu and insulin responses during the first 45 min. Data are means ± SEM, n = 10. Means without a common letter differ, P < 0.05.

 

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  		TABLE 3 Expt. 2: Effects of intragastric administration of Malto alone or in combination with different protein sources on the postprandial glycemic response in plasma of healthy rats1

 
The iAUC of the first 45 min of the postprandial Glu response tended to be reduced (P = 0.08) by the addition of intact soy and {alpha}-lactalbumin to Malto (Fig. 2, inset). The 2 protein-administered groups, MaltoSI and MaltoSI{alpha}, did not differ. In this series of experiments, the iAUC value of the insulin response to the infusion of the protein combination soy/{alpha}-lactalbumin (MaltoSI{alpha}) was not significantly elevated compared with either pure soy protein (MaltoSI) or Malto alone.

    Expt. 3. Infusion of a slow-release carbohydrate, such as mHAS, induced as expected a significantly smaller Glu and insulin response than Malto (Fig. 3). mHASSI{alpha} further decreased the magnitude and curtailed the duration of the postprandial Glu response, whereas the insulinotropic feature remained equally strong when compared with infusion of carbohydrate alone (Fig. 3; Table 4). The MaltoSI{alpha} confirmed the effects shown in Fig. 2, but its stimulating effects on insulin release were even more pronounced in this experiment. In both protein groups, plasma Glu concentrations were below basal for some time and coincided with the augmented insulin response; this below-basal period was shorter for mHAS than for Malto. Baseline Glu and insulin concentrations were similar among groups; peak insulin concentrations doubled in the protein-carbohydrate groups (MaltoSI{alpha} and mHASSI{alpha}) compared with carbohydrate alone (Malto and mHAS; Table 4). The timing of the Glu response peak shifted to the left in the mHAS groups only and the insulin response peaks were delayed in the rapidly available Malto groups only (Fig. 3).


Figure 3
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  		FIGURE 3  Changes in plasma Glu (A) and insulin (B) in healthy rats after administration of Malto alone or in combination with protein to healthy rats (Expt. 3). Insets are iAUC of the plasma Glu and insulin responses during the first 45 min. Data are means ± SEM, n = 14. Means without a common letter differ, P < 0.05.

 

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  		TABLE 4 Expt. 3: Effects of intragastric administration of Malto or mHAS alone or in combination with intact soy and {alpha}-lactalbumin on the postprandial glycemic response in plasma of healthy rats1

 
The iAUC of the postprandial Glu concentrations (Fig. 3, inset) showed that the addition of the aspartate-enriched protein blend to the 2 different carbohydrates resulted in a significant reduction of the response during the first 45 min by ~60% for Malto and 90% for mHAS. Furthermore, the iAUC of the postprandial insulin response in both protein groups showed a significantly enhanced increase compared with carbohydrate infusion alone, i.e. ~100% for MaltoSI{alpha} and 200% for mHASSI{alpha}. The load of mHAS combined with the protein blend (mHASSI{alpha}) resulted in 60% of the insulin response to Malto but showed only 6% of its Glu response.


   Discussion
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
LITERATURE CITED
 
The combined ingestion of digestible carbohydrate and protein has been shown to synergistically lower the postprandial Glu response both in healthy subjects (28,29) and type 2 diabetics (6,11). The present study confirms this specifically for an aspartate-rich intact protein blend of soy and the whey-derived protein {alpha}-lactalbumin in healthy rats and shows its lowering effect on postprandial glycemia and a stimulating effect on insulin secretion.

We and others (6,14,30,31) previously screened various protein sources for these effects and found soy protein to perform very well in this respect. For this reason and because beneficial effects have been attributed to soy protein compared with casein with regard to hypertension and cholesterol concentrations (32), both potential problems for diabetics, we used soy protein as a starting point for our experiments to find an improved protein blend for diabetics.

Currently, controversial data appear in the literature on the effects and the use of protein hydrolysates and whether their digestive properties are superior to intact proteins (23,33–35). By partially hydrolyzing the proteins, they are expected to become more effective insulin secretagogues. Differences in rate of digestion have also been suggested to explain the differences in effect of casein and whey proteins or their hydrolysates on their effect on the postprandial Glu profile as induced by digestible carbohydrates (34,36,37). We found, in contrast, that partially hydrolyzed soy protein appeared to be initially equally effective in promoting insulin release as SI, i.e. both had a similar steepness in the rise of insulin concentrations (Fig. 1), but intact protein had a higher and more sustained insulin release. If the rate of absorption would be indeed slower for intact soy compared with the hydrolyzed form, the involvement of an additional mechanism, such as an effect of the protein on incretin release, e.g. GIP, could then explain the observed extra insulin output (31). We did not assess incretin concentrations or the rate of protein absorption in this study, but SI resulted in an equivalent postprandial Glu response to its hydrolysate or constituting amino acids. The reason why remains to be established.

Because previous studies demonstrated contrasting results [e.g. (36) vs. (14,37,38)], likely due to at least in part to mixed comparisons of different protein forms and sources, a systematic comparison of matched sets of different protein forms of 1 source would be required to make valid and meaningful recommendations on the proper protein (length) to be used in clinical nutrition.

In Expt. 2, we investigated whether the properties of SI might be further improved by adding a second protein source. As explained above, we investigated the effect of adding 50 weight % of intact {alpha}-lactalbumin–enriched whey protein to SI. Both proteins sources are palatable, have acceptable technological properties during manufacture of specialized liquid nutrition for diabetics, and have been shown to be highly potent in promoting exercise-stimulated muscle protein synthesis, a feature relevant to (pre-)diabetics, because these patients have been shown to have markedly elevated muscle protein breakdown rates (39,40). Another important reason to choose {alpha}-lactalbumin was to determine whether the inclusion of another aspartate-rich protein also resulted in an improvement of the postprandial Glu response.

At the cellular concentration, and especially for the pancreatic β-cell, dietary protein is not only a source of amino acids that can affect insulin release but also a source of amino acids that can function as gluconeogenic precursors or as anaplerotic agents to drive the Krebs cycle and several substrate cycling shuttles. The proper functioning of the 2 main substrate shuttle systems for transporting reducing agents (NADH) over the mitochondrial membrane, the malate-aspartate and the glycerol-phosphate shuttle, is vital to an adequate ATP production by the cell, allowing normal cell functioning. Because the oxidative phosphorylation and the tricarboxylic acid cycle, both occurring in the mitochondrion, provide the cell with the bulk of its ATP, an imparted flux of reducing equivalents to the mitochondrion would greatly restrain the energy supply of the cell. In β-cells, shuttle malfunction leads to a disturbed rate of insulin release and NADH shuttles are vital for Glu-induced insulin release or even synthesis (16).

Apart from being active in β-cells, the malate-aspartate shuttle is active in hepatocytes, adipocytes, and muscle cells, all involved in Glu homeostasis. The replenishment of cycling substrates in the diet may restore shuttle functioning and hence alleviate the compromised insulin secretion, as convincingly shown for aspartate in isolated β-cells obtained from diabetic rats (41). Pancreatic islets isolated from diabetic animals or immature Glu-irresponsive fetuses have indeed a disturbed NADH shuttle function (17,18). Furthermore, shuttle function resumption restores the cell's redox status and homeostasis in general, which affects many other vital functions and enzyme systems in general (15) and may affect the action of Glu transporters and insulin receptors, directly and/or indirectly.

The protein sources we have applied, soy and {alpha}-lactalbumin-enriched whey, were both rich in aspartate (see Table 1). This amino acid is able to restore shuttle functioning, because it can serve as a shuttling substrate or as a precursor in this respect (15,42,43). Aspartate might thus even ameliorate the ketoacidotic status of a diabetic situation. In a recent study in diabetic GK rats, we showed that consumption for 14 d of either a diet containing the soy/{alpha}-lactalbumin blend or an aspartate supplementation to a casein-containing diet, both compared with a plain casein diet, resulted in proportionally lower fasting Glu and fructosamine concentrations, whereas insulin concentrations remained unchanged (44).

The postprandial Glu response is directly related to the carbohydrate source used as shown in the present study; the response to Glu or Malto alone (compare Figs. 1 and 2) is different. The low glycemic response of the slow-release carbohydrate mHAS is also evident (Fig. 3), and as identified previously (24). Yet, irrespective of the carbohydrate source used, the addition of protein shows similar effects on the postprandial response of both plasma Glu and insulin concentrations, which are decreased and increased, respectively, compared with carbohydrate alone. The magnitude of the postprandial Glu response (reflected in the iAUC) is decreased in 2 ways: not only is the height attained decreased, but the response duration and the time to return to baseline concentrations is also curtailed. The reverse is true for the insulin response; concentrations attained are higher, peak time is delayed, and the response duration is extended.

In a recent clinical study with healthy volunteers, we confirmed these effects of the protein blend when coingested with the low-glycemic carbohydrate isomaltulose: the glycemic index was 23.6 ± 5.9 compared with 29.7 ± 4.4 for isomaltulose alone. Combining isomaltulose with casein was not effective (glycemic index was 28.3 ± 3.6), again demonstrating the beneficial effects of the blend of intact soy and whey-derived {alpha}-lactalbumin (Mirian Lansink, Danone Research, Centre for Specialised Nutrition, personal communication).

In summary, we showed that an aspartate-rich blend of SI and {alpha}-lactalbumin has beneficial effects on postprandial Glu control in healthy rats. Preliminary data in diabetic rats indicate that long-term use might result in an improved Glu control and insulin economy. The mechanism is speculative but might involve a general restoration of redox status and homeostasis by the resumption of malate-aspartate shuttle activity due to dietary aspartate replenishment. This may lead to an improved overall cellular energy supply and insulin release capacity in particular. Furthermore, intact soy protein was the most insulinogenic, an effect more likely due to an enhanced incretin release rather than a direct β-cell stimulatory effect of amino acids.

The soy/{alpha}-lactalbumin protein blend retains its positive effects on glycemic control when combined with a previously identified slow-release carbohydrate. This combination is very well suited to be included in low-glycemic liquid products beneficial for dietary management in diabetics.


   ACKNOWLEDGMENTS
 
The authors thank Mirian Lansink, Dianne Delsing, and Arie Nieuwenhuizen for their valuable scientific input and Dustin Schetters for his practical assistance.


   FOOTNOTES
 
1 Author disclosures: R. Hageman, C. Severijnen, B. J. M. van de Heijning, H. Bouritius, N. van Wijk, K. van Laere, and E. M. van der Beek, no conflicts of interest. Back

2 Abbreviations used: BW, body weight; GluSAA, glucose + soy amino acids; GluSH, glucose + soy protein hydrolysate; GluSI, glucose + intact soy protein; iAUC, incremental area under the curve; Malto, maltodextrin; MaltoSI, maltodextrin + intact soy protein; MaltoSI{alpha}, maltodextrin + intact soy protein + {alpha}-lactalbumin; mHAS, modified high amylose starch; mHASSI{alpha}, mHAS + intact soy protein + {alpha}-lactalbumin. Back

Manuscript received 30 May 2008. Initial review completed 16 June 2008. Revision accepted 1 July 2008.


   LITERATURE CITED
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 

1. Ceriello A. Postprandial hyperglycemia and diabetes complications: is it time to treat? Diabetes. 2005;54:1–7.[Abstract/Free Full Text]

2. Ceriello A, Hanefeld M, Leiter L, Monnier L, Moses A, Owens D, Tajima N, Tuomilehto J. Postprandial glucose regulation and diabetic complications. Arch Intern Med. 2004;164:2090–5.[Abstract/Free Full Text]

3. Heine RJ, Balkau B, Ceriello A, Del Prato S, Horton ES, Taskinen MR. What does postprandial hyperglycaemia mean? Diabet Med. 2004;21:208–13.[CrossRef][Medline]

4. Bell DS. Type 2 diabetes mellitus: what is the optimal treatment regimen? Am J Med. 2004;116 Suppl 5A:S23–9.

5. Raptis SA, Dimitriadis GD. Oral hypoglycemic agents: insulin secretagogues, alpha-glucosidase inhibitors and insulin sensitizers. Exp Clin Endocrinol Diabetes. 2001;109 Suppl 2:S265–87.[Medline]

6. Gannon MC, Nuttall FQ, Lane JT, Burmeister LA. Metabolic response to cottage cheese or egg white protein, with or without glucose, in type II diabetic subjects. Metabolism. 1992;41:1137–45.[CrossRef][Medline]

7. Gannon MC, Nuttall FQ, Neil BJ, Westphal SA. The insulin and glucose responses to meals of glucose plus various proteins in type II diabetic subjects. Metabolism. 1988;37:1081–8.[CrossRef][Medline]

8. Gannon MC, Nuttall JA, Nuttall FQ. The metabolic response to ingested glycine. Am J Clin Nutr. 2002;76:1302–7.[Abstract/Free Full Text]

9. Gannon MC, Nuttall JA, Nuttall FQ. Oral arginine does not stimulate an increase in insulin concentration but delays glucose disposal. Am J Clin Nutr. 2002;76:1016–22.[Abstract/Free Full Text]

10. Nuttall FQ, Gannon MC, Jordan K. The metabolic response to ingestion of proline with and without glucose. Metabolism. 2004;53:241–6.[CrossRef][Medline]

11. Nuttall FQ, Mooradian AD, Gannon MC, Billington C, Krezowski P. Effect of protein ingestion on the glucose and insulin response to a standardized oral glucose load. Diabetes Care. 1984;7:465–70.[Abstract]

12. Gannon MC, Nuttall FQ. Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition. Nutr Metab (Lond). 2006;3:16.[CrossRef][Medline]

13. Karamanlis A, Chaikomin R, Doran S, Bellon M, Bartholomeusz FD, Wishart JM, Jones KL, Horowitz M, Rayner CK. Effects of protein on glycemic and incretin responses and gastric emptying after oral glucose in healthy subjects. Am J Clin Nutr. 2007;86:1364–8.[Abstract/Free Full Text]

14. van Loon LJ, Saris WH, Verhagen H, Wagenmakers AJ. Plasma insulin responses after ingestion of different amino acid or protein mixtures with carbohydrate. Am J Clin Nutr. 2000;72:96–105.[Abstract/Free Full Text]

15. Bender K, Newsholme P, Brennan L, Maechler P. The importance of redox shuttles to pancreatic beta-cell energy metabolism and function. Biochem Soc Trans. 2006;34:811–4.[Medline]

16. Eto K, Tsubamoto Y, Terauchi Y, Sugiyama T, Kishimoto T, Takahashi N, Yamauchi N, Kubota N, Murayama S, et al. Role of NADH shuttle system in glucose-induced activation of mitochondrial metabolism and insulin secretion. Science. 1999;283:981–5.[Abstract/Free Full Text]

17. Novelli M, Fabregat ME, Fernandez-Alvarez J, Gomis R, Masiello P. Metabolic and functional studies on isolated islets in a new rat model of type 2 diabetes. Mol Cell Endocrinol. 2001;175:57–66.[Medline]

18. Tan C, Tuch BE, Tu J, Brown SA. Role of NADH shuttles in glucose-induced insulin secretion from fetal beta-cells. Diabetes. 2002;51:2989–96.[Abstract/Free Full Text]

19. Hasler CM. The cardiovascular effects of soy products. J Cardiovasc Nurs. 2002;16:50–63.[Medline]

20. Tovar AR, Torre-Villalvazo I, Ochoa M, Elias AL, Ortiz V, Aguilar-Salinas CA, Torres N. Soy protein reduces hepatic lipotoxicity in hyperinsulinemic obese Zucker fa/fa rats. J Lipid Res. 2005;46:1823–32.[Abstract/Free Full Text]

21. Torre-Villalvazo I, Tovar AR, Ramos-Barragan VE, Cerbon-Cervantes MA, Torres N. Soy protein ameliorates metabolic abnormalities in liver and adipose tissue of rats fed a high fat diet. J Nutr. 2008;138:462–8.[Abstract/Free Full Text]

22. 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.[Abstract/Free Full Text]

23. Ziegler F, Ollivier JM, Cynober L, Masini JP, Coudray-Lucas C, Levy E, Giboudeau J. Efficiency of enteral nitrogen support in surgical patients: small peptides v non-degraded proteins. Gut. 1990;31:1277–83.[Abstract/Free Full Text]

24. Severijnen C, Abrahamse E, van der Beek EM, Buco A, van de Heijning BJ, van Laere K, Bouritius H. Sterilization in a liquid of a specific starch makes it slowly digestible in vitro and low glycemic in rats. J Nutr. 2007;137:2202–7.[Abstract/Free Full Text]

25. Reeves PG, Nielsen FH, Fahey GC. AIN-93 purified diets for laboratory rodents: final report of the American Institute of Nutrition ad hoc writing committee on the reformulation of the AIN-76A rodent diet. J Nutr. 1993;123:1939–51.[Abstract/Free Full Text]

26. Steffens A. A method for frequent sampling of blood and continuous infusion of fluids in the rat without disturbing the animal. Physiol Behav. 1969;4:833–6.[CrossRef]

27. Strubbe JH, Keyser J, Dijkstra T, Prins AJ. Interaction between circadian and caloric control of feeding behavior in the rat. Physiol Behav. 1986;36:489–93.[CrossRef][Medline]

28. Krezowski PA, Nuttall FQ, Gannon MC, Bartosh NH. The effect of protein ingestion on the metabolic response to oral glucose in normal individuals. Am J Clin Nutr. 1986;44:847–56.[Abstract/Free Full Text]

29. Nuttall FQ, Gannon MC, Wald JL, Ahmed M. Plasma glucose and insulin profiles in normal subjects ingesting diets of varying carbohydrate, fat, and protein content. J Am Coll Nutr. 1985;4:437–50.[Abstract]

30. Claessens M, Calame W, Siemensma AD, van Baak MA, Saris WH. The effect of different protein hydrolysate/carbohydrate mixtures on postprandial glucagon and insulin responses in healthy subjects. Eur J Clin Nutr. Epub 2007. Doi: 10.1038/sj.ejcn.1602896.

31. Nilsson M, Stenberg M, Frid AH, Holst JJ, Bjorck IM. 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.[Abstract/Free Full Text]

32. Anthony TG, McDaniel BJ, Knoll P, Bunpo P, Paul GL, McNurlan MA. Feeding meals containing soy or whey protein after exercise stimulates protein synthesis and translation initiation in the skeletal muscle of male rats. J Nutr. 2007;137:357–62.[Abstract/Free Full Text]

33. Monchi M, Rerat AA. Comparison of net protein utilization of milk protein mild enzymatic hydrolysates and free amino acid mixtures with a close pattern in the rat. J Parenter Enteral Nutr. 1993;17:355–63.[Abstract/Free Full Text]

34. Silk DB, Chung YC, Berger KL, Conley K, Beigler M, Sleisenger MH, Spiller GA, Kim YS. Comparison of oral feeding of peptide and amino acid meals to normal human subjects. Gut. 1979;20:291–9.[Abstract/Free Full Text]

35. Silk DB, Grimble GK, Rees RG. Protein digestion and amino acid and peptide absorption. Proc Nutr Soc. 1985;44:63–72.[CrossRef][Medline]

36. Claessens M, Saris WH, van Baak MA. Glucagon and insulin responses after ingestion of different amounts of intact and hydrolysed proteins. Br J Nutr. 2008;100:61–9.[Medline]

37. Manders RJ, Praet SF, Meex RC, Koopman R, de Roos AL, Wagenmakers AJ, Saris WH, van Loon LJ. Protein hydrolysate/leucine co-ingestion reduces the prevalence of hyperglycemia in type 2 diabetic patients. Diabetes Care. 2006;29:2721–2.[Free Full Text]

38. Manders RJ, Wagenmakers AJ, Koopman R, Zorenc AH, Menheere PP, Schaper NC, Saris WH, van Loon LJ. 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.[Abstract/Free Full Text]

39. Charlton M, Nair KS. Protein metabolism in insulin-dependent diabetes mellitus. J Nutr. 1998;128:S323–7.[Medline]

40. Carl GF, Hoffman WH, Blankenship PR, Litaker MS, Hoffman MG, Mabe PA. Diabetic ketoacidosis depletes plasma tryptophan. Endocr Res. 2002;28:91–102.[Medline]

41. Song DK, Ahn YH, Bae JH, Park WK, Hong YS, Ho WK, Earm YE. Evidence of enhancement of malate-aspartate shuttle activity in beta cells of streptozotocin-induced non-insulin-dependent diabetic rats. Metabolism. 2000;49:92–6.[Medline]

42. Newsholme P, Bender K, Kiely A, Brennan L. Amino acid metabolism, insulin secretion and diabetes. Biochem Soc Trans. 2007;35:1180–6.[Medline]

43. Sener A, Best L, Malaisse-Lagae F, Malaisse WJ. The stimulus-secretion coupling of amino acid-induced insulin release: metabolism of L-asparagine in pancreatic islets. Arch Biochem Biophys. 1984;229:155–69.[Medline]

44. Severijnen C, van der Beek EM, Hageman R, van Laere K, van de Heijning BJ. Amelioration of fasting plasma glucose levels in diabetic rats after two weeks on an aspartate-rich diet. 25th International Symposium on Diabetes and Nutrition; 2007; Kuopio, Finland.





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