Influence of Fiber on Glycemic Index of Enteral Nutrition

By Visek, Jakub Zourek, Michal; Lacigova, Silvie; Rusavy, Zdenek

ABSTRACT. Background: Enteral nutrition is indicated in patients with malnutrition due to inadequate peroral intake. A number of these patients have diabetes mellitus or impaired glucose tolerance. The aim of the study was to evaluate the influence of fiber- enriched enteral nutrition on postprandial glycemia and insulinemia. Methods: Ten healthy volunteers consumed the following solutions: A. 50 g of glucose, B. enteral formula containing 50 g of saccharides, and C. enteral formula containing 50 g of saccharides enriched with 2.3 g of fiber/100 mL. Postprandial glycemia and insulinemia were measured in time period after administration of specified nutrition. Time courses of glycemia and insulinemia were used for calculation of areas under the curve (AUC). The glycemic (GlyI) and insulinemic (InsI) indices of the nutrition were subsequently derived from AUC. Every measurement was performed 3 times for given type of nutrition. Results: Results are presented as median and interquartile range. GlyI of enteral nutrition was 85.76 (82.71-87.82), GlyI of enteral nutrition with fiber was 84.61 (80.31-94.39). InsI of enteral nutrition was 114.15 (106.55-137.71); InsI of enteral nutrition with fiber was 104.10 (96.71-127.96). The GlyI and InsI results did not differ significantly. Addition of fiber into enteral nutrition did not influence postprandial glycemia in comparison with common enteral nutrition. Conclusions: Added fiber in polymerous enteral nutrition does not influence postprandial glycemia compared with polymerous enteral nutrition without fiber. (Journal of Parenteral and Enteral Nutrition 31:491-495, 2007) Enteral nutrition supports maintenance of functional gut barrier and positively modulates immune mechanisms in malnourished patients. Patients with impaired glucose tolerance, diabetic patients, and critically ill patients with insulin resistance count among those. It is acknowledged that hyperglycemia, especially postprandial, is associated with higher risk of micro- and macroangiopathy development in the long-term perspective.1 In the short-term perspective, it deteriorates the prognosis of critically ill patients,2,3 promotes dehydration, leads to elevated incidence of infectious complications, deteriorates rheologic properties of the blood, and decelerates wound healing.4

At present, enteral nutrition is well dispensed among patients, especially for its positive effects on the clinical state of patients, low number of complications, and also large selection of sip feedings on the market. Enterai nutrition is usually administered via a nasogastric or nasojejunal tube. In less severe cases, patients can sip special nutritionally defined enteral formulas several tunes a day. Classic enteral formulas designed for sipping contain a considerable amount of glucose in the form of maltodextrins, lipids, proteins, vitamins, and minerals. Low- residue liquid nutrition causes fast evacuation of the stomach, fast absorption of saccharides, and consequently fast increase of postprandial glycemia. Modern sip formulas are enriched with fiber that is resistant to hydrolysis by human digestive enzymes and thus shows minimal absorption from the gastrointestinal tract.5 It is fermented by colon bacteria to short-chain fatty acids that inhibit gluconeogenesis and lipid oxidation, which positively influences glycemic control.6 The positive effect of fiber also lies in prevention of colorectal carcinoma or cardiovascular diseases.7 Soluble viscose fiber is generally preferred in diabetic patients. It positively influences the glycemic control, produces feelings of satiety, and decreases the gastric emptying rate.8

Although there exist numerous recommendations regarding “diabetic diet” that are focused on normalization (reduction) of body weight,9 no recommendations regarding use of artificial nutrition in diabetic patients with malnutrition have been developed so far.

Actual glycemia is defined by ratio of glucose absorbed into the circulation (rate of appearance) and glucose redistributed from blood to tissues (rate of disappearance). The redistribution of glucose from blood to tissues is driven particularly by insulin effect in target tissues. Postprandial glycemia is influenced especially by the composition and amount of ingested food. It predominantly depends on the form and amount of saccharides, presence of lipids, proteins, fiber, etc. It influences the rate of saccharide hydrolysis in the gastrointestinal tract and gastric emptying rate.10

In order to evaluate food according to its effect on postprandial glycemia, Jenkins invented a parameter, glycemic index (GlyI).11 This index expresses the ratio of the area under the curve (AUC) of glycemia after ingestion of food containing 50 g of saccharides to the AUC of glycemia after ingestion of 50 g of glucose or white bread.12 Food with GIyI <55 is considered to have low GIyI. Meta- analysis of studies showed that peaks of postprandial glycemia are significantly reduced by consumption of food with low GIyI. Improvements of insulin resistance and glycemic control were also observed. According to this analysis, a diet with low GIyI decreases glycosylated hemoglobin (HbAIc) by 7%-8% from its original value.13 According to the United Kingdom Prospective Study (UKPDS), decrease of HbAIc by 1% leads to mortality reduction in association with diabetes mellitus (DM) by 21%, myocardial infarction incidence decreases by 14%, and microvascular complications are reduced by 37%.14 Among food with low GIyI belong some vegetables and fruits, whole-wheat products, pasta, and legumes.

Low-Glyl food intake is not only accompanied by lower postprandial glycemia but also usually by lower insulin secretion.10 Insulinemic index (Insl) is used for insulin response assessment.15 It can be affected by other factors such as presence of lipids, proteins, and organic acids in food. At present, it is not routinely used; however, especially in hyperinsulinemic patients, it can represent another interesting parameter. Similar to GIyI, Insl expresses the ratio of the AUC of insulinemia after ingestion of food containing 50 g of saccharides to the AUC of insulinemia after ingestion of reference food (pure glucose or white bread).

Polymerous nutrition Nutridrink and Nutridrink MF (N.V. Nutricia, Zoetermeer, Netherlands) are formulas used for enterai nutrition and are administered in form of sipping. Their GIyI is not provided by the manufacturer. While Nutridrink MF is not specifically designed for diabetic patients, addition of fiber could presumably lead to lowering of GIyI and thus be suitable for diabetic patients.

Aim: To compare the influence of fiber in enterai nutrition on postprandial glycemia and insulinemia.

Methods: Ten healthy volunteers (5 men and 5 women) age 21-25 years were enrolled after approval by the local ethical committee of the Medical Faculty in Pilsen, Charles University in Prague, and signed informed consents were obtained. Physical examination and laboratory screening were performed before enrollment to eliminate any concomitant disease.

GIyI assessment11: A cannula was inserted into the antecubital vein for blood sampling during measurement at 7 AM after whole- night fasting. At 7:30 AM, the volunteer drank tested nutrition sample. It was either 50 g of glucose or enterai nutrition (Nutridrink) containing 50 g of saccharides (272 mL of solution) or enterai nutrition with fiber 2.3 g/100 mL (Nutridrink Multifibre) containing 50 g of saccharides (272 mL of solution). Each solution had equal volumes.

N.V. Nutricia provides the following fiber composition: nonstarch polysaccharides, nondigestible fructose poly- and oligosaccharides (inulin and fructooligosaccharides), resistant starch, and legnin. Unfortunately, further details and amounts of individual kinds of fiber are not available and usually are a part of trade secrets.

Blood samples were taken 10 minutes after ingestion (time O minutes) and then again at 15 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes, and 120 minutes. Vacuettes containing sodium fluoride were used for glycemia measurement. They were refrigerated throughout the experiment, and upon termination of the experiment they were immediately analyzed. Samples for insulinemia measurement (immunoreactive insulin, IRI) were centrifugea and plasma was frozen to -22[degrees]C for later analysis. For each formula, these measurements were repeated 3 times, with a 3-day spacing between the measurements for each volunteer. There were 9 measurements performed altogether with each volunteer, altogether 90 measurements of glycemic curves.

Levels of glycemia were assessed using glucose-oxidase method with Ebio plus machine (Eppendorf, Hamburg, Germany). Insulinemia or IRI was assessed by immunoradiometric method using commercial kit (Immunotech SA, Marseille, France).

Statistical Evaluation

Results are presented as median and interquartile range. Calculated AUC, GIyI, and Insl for both forms of enterai nutrition were tested for normality and were evaluated using Wilcoxon’s paired test. Ap value < .05 was considered significant.

FIGURE 1. Glycemia after ingestion of different types of solutions. Data show glycemia and areas under the curve (AUC) after ingestion of different types of solutions. Collected data of all (n = 10) patients. No significant differences were found between AUC of glycemia of the enterai formula and the enteral formula with fiber. RESULTS

Ten subjects underwent 90 GlyI and InsI examinations altogether. In the course of this period, no significant differences occurred in weight or lifestyle of the subjects.

GlyI of enteral nutrition was 85.76 (range, 82.71-87.82); GlyI of enteral nutrition with fiber was 84.61 (range, 80.31-94.39). InsI of enteral nutrition was 114.15 (range, 106.55-137.71); InsI of enteral nutrition with fiber was 104.10 (range, 96.71-127.96). No significant differences in GlyI or InsI were found between enteral nutrition and enteral nutrition with fiber. Figure 1 shows the course of glycemia after consumption of individual types of nutrition. Figure 2 demonstrates the course of insulinemia.

DISCUSSION

In our study we evaluated enteral nutrition administered in form of sipping, specifically common enteral nutrition (Nutridrink) and enteral nutrition enriched by fiber (Nutridrink Multifibre). We focused on comparison of both sip feedings regarding postprandial glycemia or more precisely the effect of fiber addition on postprandial glycemia. We chose GIyI and Insl as a method of evaluation.16 In contrast to the Hofman et al17 study, we did not prove any difference after administration of Nutridrink and Nutridrink Multifibre. Our conclusions are supported by results of a study18 with different kinds of enteral formulas, where adding fiber into the enteral formula did not yield any positive effect on glycemia either.

FIGURE 2. Insulinemia after ingestion of different types of solutions. Data show insulinemia and areas under the curve (AUC) after ingestion of different types of solutions. Collected data of all (n = 10) patients. No significant differences were found between AUC of insulinemia of the enteral formula and the enteral formula with fiber.

Different GIyI values to previous study are probably due to differences in methods used. In our study, original Jenkins’ methodology was used, where the whole AUC for 2 hours after ingestion of examined solution is used for the calculation as opposed to only its incremental part. At present, the method using only the incremental part may be more frequently used; on the other hand, it is criticized by some authors. As Pi-Sunyer19 argued, “glucose molecules are all the same and circulate in the bloodstream similarly.” All glucose molecules should be thus considered similar and the AUC for all of the available glucose should be calculated. As might be expected, if total AUC is used, the differences in GIyIs between foods are greatly reduced. Glycemie responses and subsequently the calculation of GIyI vary markedly, depending on how AUC is calculated. The method selected for this study takes into account the course of glycemia during the 2 hours after ingestion of the solution. The aim of our study was to evaluate the influence of fiber addition into a solution on postprandial glycemia. If we calculate GIyI only according to the incremental part of the curve, we get lower GIyI values; nonetheless, it is still valid to say that GIyI of enterai nutrition with and without fiber does not differ.

Furthermore, in the study by Hofman et al17 the measurements were not reiterated in volunteers for each given nutrition. Besides, we know from the literature and from our practical experience that GIyI shows considerably high intraindividual variability.12 It is therefore desirable to test the given meal in a volunteer repeatedly in few-day intervals and state the GIyI result as an average of 3 measurements. Intraindividual variability is probably higher than interindividual GIyI variability.12 The necessity of measurement repetition for limitation of intraindividual variability, associated time, and financial expense represents a great disadvantage of GIyI. Also, it does not matter whether the given meal is tested in diabetic patients or nondiabetic patients because the given subject represents a control for himself.11 For this reason, even though the assessed AUC can significantly differ, the resulting GIyI does not change by much. The results of our study should not thus be influenced by the fact that the measurement was performed in healthy volunteers. Finally, the Hofman et al study17 used solutions with 25 g saccharide content. However, as Jenkins et al11 described in their study, 25 g of saccharides can be insufficient for testing; therefore for GIyI testing it is generally recommended to use food with 50 g saccharide content.

Fiber-enriched enterai nutrition was originally used for improvement of gastric functions and reduction of diarrhea incidence as a complication of enterai nutrition.18 Fiber was believed to affect postprandial glycemie profiles due to its positive effect on the gastric emptying rate. Although our study did not prove any effect of fiber on lowering postprandial glycemia, enterai nutrition with fiber still has its advantages. Fiber optimizes stool production and regulates its frequency; it supports bowel peristalsis; improves absorption of nutrients, water, and electrolytes; maintains colon microflora in an optimal state; and prevents bacterial translocation from the intestine and serves as energy substrate for colonocytes.7

The fiber content does not always correlate with GIyI. For example, GIyI of whole-wheat bread with fiber is higher than GIyI of pasta with lower fiber content. Yet generally it is acknowledged that food with higher fiber content has lower GIyI.20 Whether food artificially enriched with fiber shows the same effect is still questioned. Peters and Davidson21 did not demonstrate any change in postprandial glycemia after addition of soy polysaccharides to enterai nutrition. We can find a possible parallel in a study with gluten-free bread.22 In this study, higher GIyI was found after consumption of bread made of a gluten-free flour in contrast to bread made of regular flour. This effect, however, was not reversible upon secondary addition of gluten into gluten-free flour. Gluten in flour presumably acts as a mechanical barrier that encases starch molecules and limits the access possibility of hydrolases.

Continuous administration of fiber-enriched enterai nutrition provides the amount of fiber corresponding to general diet recommendations (20-30 g of fiber per day).23 Fiber content in enterai nutrition can be insufficient to influence postprandial glycemia in bolus administration; however, we do not know what effects on glycemie profiles or insulin sensitivity this type of nutrition may have in long-term continuous administration. It is not even possible to say for sure whether different fiber composition would influence postprandial glycemia. A study focused on this phenomenon would be worthwhile.

Diabetes-specific formulas with additional low GIyl as oral supplements and tube feedings are associated with improved glycemie control compared with standard formulas. Lower GIyI was assessed in diabetesspecific clinical nutrition products. Contents of this nutrition differed in higher proportion of lipids, monounsaturated fatty acids, and fiber. It is therefore evident that a positive effect on glycemie response cannot be ascribed to the fiber itself.

Insl11 is used for classification of meals regarding insulin secretion. Insl is used less commonly than with GIyI as Insl usually closely correlates with the results of GIyI measurements. In our case, we proved that Insl of enterai nutrition does not change significantly by mere addition of fiber. Our results suggest that AUC of insulinemia of enterai nutrition is higher than AUC when administering a glucose solution. We explain this phenomenon by the presence of other nutrition components, such as lipids and proteins in solutions.24

SUMMARY

In summary, this study shows that Insl of the polymerous enterai nutrition is higher than in glucose solution. Moreover, it shows that mere addition of fiber with the composition described above as in the polymerous enterai nutrition does not influence postprandial glycemia. Despite the fact that fiber plays an important role in nutrition not only in critically ill and diabetic patients, it does not suffice to produce a positive influence on postprandial glycemia by itself.

ACKNOWLEDGMENTS

The study was supported by scientific grant MSM 0021620814 of the Medical Faculty in Pilsen, Charles University in Prague.

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Jakub Visek, MD; Michal Zourek, MD; Silvie Lacigova, MD, PhD; and Zdenek Rusavy, MD, PhD

From the Diabetologic Centre, Department of Medicine I, Charles University Hospital, Pilsen, Czech Republic

Received for publication February 20, 2007.

Accepted for publication June 12, 2007.

Correspondence: Jakub Visek, Department of Medicine I, Charles University Hospital, Alej Svobody 80, 304 60 Plzen, Czech Republic. Electronic mail may be sent to visekj@fnplzen.cz.

Copyright American Society for Parenteral and Enteral Nutrition Nov/ Dec 2007

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