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American Journal of Clinical Nutrition, Vol. 69, No. 3, 556-563, March 1999
© 1999 American Society for Clinical Nutrition

Original Research Communications

Composition of enteral diets and meals providing optimal absorption rates of nutrients in mini pigs1,2,3

Eckhard Weber and Hans J Ehrlein


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Commercial enteral diets differ widely in nutrient composition. It is unknown whether the nutrient composition of the diets influences intestinal absorption.

Objective: The objective of this study was to investigate the effects of different enteral diets providing 60% of energy as carbohydrate, protein, or fat or 33.3% of energy from each nutrient on intestinal absorption in mini pigs.

Design: Kinetics of nutrient absorption were determined by perfusing a 150-cm jejunal segment. The kinetics of absorption were used to determine optimal relations between the absorption and recovery of each nutrient. From these data, the optimal nutrient composition of the diets providing complete absorption of the macronutrients in the shortest intestinal length was evaluated. Absorption of nutrients was further determined after oral administration of 4 corresponding meals.

Results: With all enteral diets, the absorption of nutrients displayed saturation kinetics. Absorption rates of carbohydrate were significantly larger than those of fat and protein. Consequently, the amounts of nutrients remaining unabsorbed per unit length of jejunum differed among the macronutrients. After administration of various test meals, the length of the small intestine required for complete absorption of the nutrients depended on the composition of the meals. The shortest intestinal length for complete absorption was needed for a diet providing 48% of energy as carbohydrate, 23% as protein, and 29% as fat. This composition closely matched the nutritional requirements.

Conclusion: The nutrient composition of diets can optimize intestinal absorption. This may be especially important in patients with malabsorption or short-bowel syndrome.

Key Words: Enteral nutrition • macronutrients • short-bowel syndrome • intestinal absorption • nutrient requirements • malabsorption • meal composition • pigs


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The nutrient composition of diets for enteral nutrition varies greatly (1) and it is unknown whether intestinal absorption is influenced by the composition of enteral diets. Because carbohydrate, protein, and fat are absorbed by different transport mechanisms, it is likely that the capacity for absorption of these macronutrients also differs. Thus, the composition of a diet might contribute to optimal conditions for absorption, which could be important in patients with impaired digestion and absorption. Enteral feeding of intensive care patients is often associated with gastrointestinal sequelae (2–5). Although the genesis of disturbances may be multifactorial, adjusting the dietary composition to the maximal capacity of intestinal absorption of each nutrient may be beneficial. In patients with short-bowel syndrome, limitations of intestinal absorption play an important role in management of the disease (6–8). Clinical studies in these patients with either high-carbohydrate or high-fat diets did not reveal clear-cut results regarding intestinal secretion and absorption of total energy (6, 9, 10). However, in studies of patients, experimental conditions are usually complex and systematic investigations are difficult to perform. We hypothesized that the intestinal capacity for the absorption of carbohydrate, protein, and fat differs and that there is a definite composition of macronutrients providing optimal conditions for intestinal absorption.

The aim of the present study was to elucidate effects of the composition of enteral diets and test meals on the intestinal absorption of nutrients. In mini pigs, a jejunal test segment was perfused with enteral diets of different compositions to determine the intestinal absorptive capacity of the macronutrients. By means of absorption kinetics, we evaluated which macronutrient composition was optimal for providing complete absorption of the macronutrients in the shortest length of the small intestine. The results were verified by administering test meals with corresponding compositions and calculating the length of the small intestine required for the complete absorption of nutrients.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Experiments were performed in 4 Troll female mini pigs weighing 45–60 kg (Medical Service, Munich, Germany). The animals were adapted to a diet providing 33.3% of energy as carbohydrate, 33.3% as protein, and 33.3% as fat. The study protocol was approved by the local animal care committee of the Regierungspräsidium, Stuttgart, Germany. Surgical procedures were performed under general anesthesia. Three cannulas were implanted into the proximal jejunum 1, 2, and 3.65 m distal to the ligament of Treitz and exteriorized through the right abdominal wall. The experiments were started 2 wk after the surgery.

Two sets of experiments were performed. In the first set, absorption of nutrients was measured by perfusing a 150-cm length of jejunum with different enteral diets. In the second set of experiments, gastric delivery of nutrients and intestinal absorption were determined after feeding test meals with the same compositions as the enteral diets.

Enteral diet experiments
Four enteral diets that differed in nutrient composition were used: a diet containing equal amounts of energy (33.3%) as carbohydrate, protein, and fat (diet E); a diet rich (60%) in carbohydrate (diet C); a diet rich (60%) in protein (diet P); and a diet rich (60%) in fat (diet F). The compositions of the diets are summarized in Table 1Go. The carbohydrate consisted of maltodextrin (C-pur 1934; Cerestar, Krefeld, Germany). It was composed of 1.5% glucose, 35% maltose, 21% maltotriose, and 42.5% oligosaccharides. The protein consisted of hydrolyzed whey protein (Hyprol 8080; Quest International, Zwijndrecht, Netherlands) and was composed of 15% amino acids, 50% di- and tripeptides, 30% oligopeptides, and 5% polypeptides. The fat component consisted of a commercial emulsion of triacylglycerol (Lipovenös 10%; Fresenius, Bad Homburg, Germany). This emulsion was hydrolyzed in vitro by pancreatic enzymes (P-1750; Sigma Chemical Co, St Louis) after addition of cholesterol (C-3292; Sigma) and bile salts (B-8756; Sigma). During the hydrolysis at 37°C, the pH was kept at 7.0 by titration with 0.3 mol NaOH/L (Titrator D3; Metrohm, Herisau, Switzerland). The hydrolyzed fat solution contained 48.7% free fatty acids, 24.7% monoacylglycerol, 13.1% diacylglycerol, and 13.5% triacylglycerol. The energy density of the 4 enteral diets was 1673.6 kJ/L. This energy density was observed in the chyme entering the jejunum after meals. The diets were nearly isoosmotic (Table 1Go). Cobalt-EDTA (5 mg/L) was added as a nonabsorbable marker.


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  		TABLE 1. Composition of enteral diets1
 
Test meal experiments
Four different test meals were used. The nutrient composition of the meals corresponded to that of the enteral diets (Table 2Go). The meals had a volume of 1 L and an energy density of 4184 kJ/L. The nutrients consisted of maize starch, milk protein, and soy oil. Cobalt-EDTA (100 mg/L) was added as a nonabsorbable marker.


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  		TABLE 2. Composition of test meals1
 
Experimental procedures
Perfusion studies of jejunal segment
During the enteral diet experiments, animals were positioned with a hammock. After the 3 cannulas were opened, a balloon catheter was inserted into the middle cannula. One of the enteral diets was infused into the jejunal segment located between the middle and distal cannulas over 105 min. The effluent of the enteral diet was collected at the distal cannula in 15-min intervals. The initial 45 min served as an equilibration period. Absorption of nutrients was measured during the subsequent 60-min test period. The enteral diets were infused at perfusion rates between 2.5 and 20 mL/min, resulting in corresponding jejunal loads of total energy as follows: diet E at 4.18, 7.53, 15.06, 22.59, 25.1, and 30.12 kJ/min, and diets C, P, and F at 4.18, 8.36, 12.54, 16.72, 25.08, and 33.44 kJ/min. The energy load for carbohydrate, protein, and fat varied between 0.84 and 20.06 kJ/min. At the onset of the test period, a meal was administered to induce postprandial conditions. The meal was drained by the proximal cannula as it emptied from the stomach. At the end of the test period, infusion of the enteral diet was stopped and the jejunal segment was perfused with saline for 30 min for marker recovery.

Gastric delivery of nutrients and absorption after test meals
In a separate series of experiments, the gastric delivery of nutrients to the jejunum and intestinal absorption were determined after ingestion of the different test meals. The effluent from the proximal cannula was collected in 5-min intervals over 90 min. Small samples were taken for analysis and replaced by a solution of corresponding composition. In the subsequent 5-min interval the substituted chyme was returned to the jejunum via the distal cannula to maintain the feedback control of gastric emptying.

Analysis of nutrients and marker
Concentrations of carbohydrate, protein, and fat and the concentration of the nonabsorbable marker were determined in the enteral diets, in test meals, and in the effluents of the jejunal cannulas. For measurement of protein, small samples of the enteral diet, jejunal effluent, or test meal were freeze-dried (Lyovac GT2; Amsco/Finn-Aqua, Tuusula, Finland). Protein content was measured with an automatic nitrogen analyzer (macro N; Heraeus, Hanau, Germany). The concentration of carbohydrate was measured enzymatically with a commercial starch test (Boehringer Mannheim, Mannheim, Germany). For determination of fat, small samples of the enteral diet, jejunal effluent, or test meal were hydrolyzed with 8 mol HCl/L. From the neutralized and dried residues, the fat content was extracted with petroleum ether with use of automatic extraction equipment (Soxtherm; Gerhardt, Bonn, Germany). Concentrations of the nonabsorbable marker were measured by atomic absorption spectrometry (Perkin-Elmer, Ueberlingen, Germany). To convert amounts of nutrients (g) to energy (kJ), the following energy values for carbohydrate, protein, and fat were used: 16.15, 19.92, and 39.92 kJ/g, respectively, with the enteral diets and 17.57, 22.68, and 38.24 kJ/g, respectively, with the test meals.

Nutrient absorption
Nutrient absorption was measured as the difference between the infused and recovered nutrients according to the equation described by Modigliani et al (11):


(1)

With an increasing load, the jejunal absorption of nutrients showed saturation kinetics. The Km and Vmax values were calculated according to Michaelis-Menten kinetics:


(2)
where Vmax is the maximal absorption rate [kJ/(min{bullet}m)], S is the jejunal load of nutrients (kJ/min), and Km is the load (kJ/min) at the half-maximal absorption rate.

Gastric delivery of nutrients after meals
The gastric delivery of nutrients into the proximal jejunum was determined by multiplying the volume of the effluent of the proximal cannula by the concentration of nutrients. To determine the flow of exogenous protein, the endogenous secretion of protein by the stomach and the proximal gut was excluded by using the equation


(3)

Calculation of intestinal absorption of nutrients after meals
Because the measurement of absorption required steady state conditions, the intestinal absorption of nutrients after ingestion of a meal could be determined only indirectly. The kinetics determined by the perfusion experiments were used to calculate the absorption of nutrients delivered after the meals into the proximal jejunum.

Calculation of intestinal length required for complete absorption
The kinetics determined by the perfusion experiments were further used to calculate the length of the small intestine required for complete absorption of each nutrient delivered after meals from the stomach into the jejunum. Assuming that the absorption rate did not markedly change within the proximal half of the small intestine, the amounts of nutrients being absorbed and remaining unabsorbed in each subsequent meter of the jejunum were determined. In the pigs, the mean length of the small intestine between the pylorus and ileocecal sphincter was 9.7 ± 1.1 m.

Statistics
In each animal, 2 experiments were performed with each enteral diet and perfusion rate and with each test meal, with the exception that the perfusion rate of 4.18 kJ/min with solution E was used only once in each pig. Mean values were calculated from the data of the 2 experiments. Data are presented as grand means ± SDs for the 4 pigs, calculated from the mean values of the 2 experiments in each pig.

The kinetics of intestinal absorption were determined from mean values of a 60-min period using 6 different perfusion rates. To test the goodness of fit of the Michaelis-Menten kinetics, coefficients of multiple correlation (R) were estimated by using the t statistic (n = 6 perfusion rates). In addition, the kinetic parameters Vmax and Km were tested for fixed effects of diets and nutrients as well as for random effects of animals by using analysis of variance (ANOVA; n = 4 pigs). Differences in Vmax and Km among the diets and nutrients were tested with linear contrasts (F test). Gastric delivery of nutrients to the jejunum and intestinal absorption were evaluated from mean values over the 90-min period. The length of gut required for complete absorption was tested for fixed effects of meals and nutrients and for random effects of animals (ANOVA; n = 4 pigs). Differences in the length of gut required for complete absorption were estimated with linear contrasts (F test). None of the tests revealed an animal effect.

Kinetics were analyzed by using the curve fitting software TABLECURVE (version 1.0; Jandel Scientific, Erkrath, Germany). Statistical analyses were performed with SAS (version 7.0; SAS Institute Inc, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Absorption of nutrients and optimal composition of enteral diets (enteral diet experiments)
As the energy load on the jejunal segment increased, the absorption of carbohydrate, fat, and protein displayed saturation kinetics with all diets (Figure 1Go). The kinetic parameters and the significance of the curve fits are summarized in Table 3Go. Diets with different nutrient compositions produced different nutrient absorption kinetics. When equal amounts of nutrients were perfused—either 60% carbohydrate with diet C, 60% protein with diet P, and 60% fat with diet F or 33.3% of each nutrient with diet E—the absorption rates of carbohydrate were significantly larger than those of protein and fat (Figure 1Go and Table 3Go). As a result of the saturation kinetics, the amounts of carbohydrate, protein, and fat remaining unabsorbed at the distal end of the jejunal segment increased markedly with increasing intestinal load of nutrients (Figure 2Go). Additionally, a smaller absorption rate of the nutrients resulted in even larger amounts of nutrients remaining unabsorbed. Therefore, nutrients characterized by large absorption rates required a shorter length of the small intestine for complete absorption. Consequently, there must be a nutrient composition of a diet at which the absorption of all 3 nutrients is completed within the same intestinal length. Such a composition was defined as being optimal.



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  		FIGURE 1. With an increasing nutrient load in the jejunal segment, the absorption of carbohydrate ({blacktriangleup}), protein ({square}), and fat ({circ}) display saturation kinetics (diet contained 33.3% of energy from each nutrient; significance of curve fit: P < 0.01, t statistic; n = 6 perfusion rates). The absorption rates were significantly different among all nutrients (P < 0.001, ANOVA, F test; n = 4 pigs). Values are grand means ± SDs (n = 4 pigs).

 

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  		TABLE 3. Kinetics of absorption1
 


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  		FIGURE 2. With an increasing intestinal load, the unabsorbed nutrients recovered at the distal end of the jejunal segment increase. Because of the saturation of absorption (the dotted line represents the maximal absorption rate, Vmax), nutrient recovery markedly exceeded the absorption rates (diet contained 33.3% of energy from each nutrient).

 
Optimal composition can be derived by determining the difference between the amounts of nutrients absorbed and the amounts remaining unabsorbed at the end of the jejunal test segment. For this purpose, kinetics of absorption were subtracted from those of recovery for each nutrient (Figure 3Go). With an increasing nutrient load, the differences between absorption and recovery showed parabolic curves. The load of nutrients at the maximal difference represented the optimal relation between absorption and recovery of nutrients, ie, percentage absorption was maximal. Therefore, this load was defined as the optimal nutrient load.



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  		FIGURE 3. The optimal load of carbohydrate, protein, and fat was defined as the load providing the maximal difference between absorption and recovery of each nutrient at the end of the jejunal test segment, ie, percentage absorption was maximal. Therefore, the optimal load of nutrients represented the optimal relation between absorption and recovery of each nutrient. The differences between absorption and recovery ({Delta}) were calculated by subtracting the kinetics of absorption from those of recovery. As the nutrient load increased, the differences showed parabolic curves (inset). The load providing the maximum of a curve was determined with peak analysis ({Delta}max). The optimal loads for carbohydrate, protein, and fat corresponded to the nutrient composition of the optimally composed diet.

 
The optimal loads for carbohydrate, protein, and fat represented measures of the corresponding amounts of nutrients in an optimally composed diet. The optimal loads for each nutrient were evaluated from the kinetics of absorption and recovery of all diets (Table 4Go). With diet E, the optimal loads for carbohydrate, protein, and fat were 0.83, 0.42, and 0.52 kJ/min, respectively. Because the amounts of carbohydrate, protein, and fat differed in diets C, P, and F, the resulting loads were only apparent optimal loads and apparent optimal compositions. Definite optimal loads and definite optimal compositions can only be obtained during perfusion of diets containing equal amounts of the 3 nutrients. Therefore, it was necessary to calculate the mean values for each nutrient from diets C, P, and F. These mean values corresponded to a diet providing 33.3% of energy from each nutrient; the values were 0.62, 0.31, and 0.35 kJ/min for carbohydrate, protein, and fat, respectively. The calculated mean values were almost identical to values obtained with diet E. Therefore, the grand means of the optimal loads of nutrients for diets C, P, and F combined plus diet E (0.68, 0.33, and 0.40 kJ/min) were used to determine optimal diet composition. The sum of these nutrient loads was set at 100% and optimal diet composition was determined by the optimal load of each nutrient. The optimal diet provided 48% of energy as carbohydrate, 23% of energy as protein, and 29% of energy as fat (Table 4Go).


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  		TABLE 4. Apparent and definite optimal jejunal load of nutrients and optimal composition of enteral diets1
 
Gastric delivery of nutrients and absorption after test meals
In the second set of experiments we studied whether the length of small intestine required for complete absorption of carbohydrate, protein, and fat depended on the nutrient composition of the test meals. For this purpose, amounts of nutrients entering the proximal jejunum and the nutrient composition of the jejunal chyme were determined after the 4 test meals (Table 5Go). The composition of the jejunal nutrients was similar to that of the test meals. By considering the flow rate and the composition of nutrients, we calculated the absorption per unit length according to the absorption kinetics established in the first set of experiments. The length of small intestine required for complete absorption of each nutrient is shown in Figure 4Go. The intestinal length depended on the composition of the meals. A meal with an optimal nutrient composition required the shortest intestinal length for complete absorption of protein. Furthermore, nutrients from an optimally composed meal were completely absorbed within the same intestinal length. As composition deviated from what was optimal, the intestinal length required for complete absorption increased. The greater the deviation from the optimal composition, the greater the length of intestine required. The length of small intestine required for complete absorption of protein and fat was significantly longer with meal P (60% protein) and meal F (60% fat) than with the optimally composed meal (23% protein, 29% fat).


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  		TABLE 5. Flow of nutrients, composition of chyme, and absorption of nutrients in the proximal jejunum after different test meals1
 


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  		FIGURE 4. The length of small intestine required for complete absorption depended on the nutrient composition of the meal: E, meal containing equal amounts of energy (33.3%) as carbohydrate, protein, and fat; C, meal rich (60%) in carbohydrate; P, meal rich (60%) in protein; F, meal rich (60%) in fat. After an optimally composed meal, the length of small intestine required for complete absorption was the same for carbohydrate, protein, and fat. In addition, with an optimally composed meal, the length of small intestine required for complete absorption of protein and fat was shorter than that with other meals. Values are grand means ± SDs (n = 4 pigs). *Significantly different from the optimally composed meal, P < 0.05 (ANOVA, F test; n = 4 pigs).

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The present study revealed different absorption rates for carbohydrate, protein, and fat. After meals with different nutrient compositions, these differences in absorptive capacity of the small intestine were compensated for by the different lengths of small intestine required for absorption. There was an optimal nutrient composition that resulted in the shortest length of intestine being required for complete absorption of the 3 nutrients. The optimal diet provided 48% of energy as carbohydrate, 23% of energy as protein, and 29% of energy as fat. In the present study, only the proximal half of the small intestine was required for absorption despite large differences in the composition of the test meals. This complete absorption of easily digestible meals in the proximal gut agrees with previous studies in humans (12–14).

In healthy individuals, variations in the composition of meals will not result in malabsorption because the small intestine has sufficient reserve capacities. In patients with disturbances of digestion and absorption, however, the composition of meals or of enteral diets may be more important. Enteral nutrition in intensive care patients is often associated with bloating, vomiting, or diarrhea (2, 5, 15). Multiple etiologies of these sequelae have been postulated but have not yet been clarified in detail. A major factor might be a discrepancy between the load of nutrients and digestive and absorptive capacity (16). According to the present findings, the nutrient composition of enteral diets may also play a role. The commercial diets offered for enteral nutrition differ widely in composition; concentrations of carbohydrate, protein, and fat vary from 45% to 75%, from 9% to 25%, and from 10% to 39%, respectively (n = 57; not including specific enteral diets used for patients with trauma, liver disease, or renal failure) (1). The present study showed that for protein and fat in particular, the more the nutrient composition differed from that of the optimal diet, the greater the length of intestine required for absorption. This aspect of enteral diets had not been considered previously but may contribute to reducing problems during enteral nutrition.

Optimal diet composition may also play a major role in patients with short-bowel syndrome. In several clinical studies the effects of nutrient composition on intestinal absorption and secretion were evaluated. Early observations suggested that low-fat, high-carbohydrate intakes may be of benefit because long-chain fatty acids induce colonic water secretion (6, 17–19). On the other hand, high-carbohydrate diets also induce water secretion through osmotic effects (10, 20). High-fat diets have been shown to be well tolerated (21) and to be equivalent to high-carbohydrate diets in terms of volume output (10). Several studies suggested that high-fat diets may be beneficial to patients with a short bowel (9, 22, 23). Regarding the absorption of total energy, however, no differences were found between high-fat and high-carbohydrate diets (9). In clinical studies, the relation between nutrient composition and absorption is influenced by other factors such as the extent and site of resection and the presence or absence of the colon and consequently colonic fermentation. Therefore, clear-cut relations between the nutrient composition of diets and absorption could not be established. Messing et al (24) investigated the dietary habits of patients with short-bowel syndrome who had unrestricted nutrient intakes. These patients consumed a diet composed of 46% carbohydrate, 23% protein, and 31% fat, which matches closely the optimal composition found in the present study. However, Messing et al did not investigate effects of different meal compositions and therefore could not elucidate an advantage of these dietary habits. It is likely that systematic investigations with graduated nutrient compositions might clarify the importance of an optimal nutrient composition in patients with short-bowel syndrome.

The present data on the optimal nutrient composition for absorption reveal a striking convergence to recommendations for nutritional requirements. The World Health Organization recommends an uptake of 50–55% of energy as carbohydrate, 15–20% as protein, and 25–30% as fat (25). The present data suggest for the first time that the diet composition recommended for meeting the nutritional requirements of healthy subjects is the same as the diet composition resulting in optimal intestinal absorption. Therefore, it is likely that the capacity for intestinal absorption and nutritional requirements are related to each other.

Different rates of absorption of glucose and several amino acids were described in humans (26) and pigs (27) during single-nutrient perfusion of the jejunum. In these studies, absorption rates of glucose were {approx}2 times larger than those of amino acids. The data of the present study, determined after feeding pigs complex diets containing carbohydrate, protein, and fat, agree with these previous results and confirm the hypothesis that in the jejunum the number or capacity of glucose transporters is larger than that of amino acid and peptide transporters. It is well established that intestinal absorption can adapt to the dietary intake of nutrients (28–30). However, this adaptation might be limited. Although in the present study the animals were adapted to a diet composed of 33.3% carbohydrate, protein, and fat, clear-cut differences in the absorption rates of these 3 nutrients existed. This indicated that intestinal transport mechanisms are genetically determined and that adaptation cannot override the differences in the absorption rates of the macronutrients. The genetic limitation of intestinal adaptation was also shown in strict carnivores. In these animals, neither the number of glucose transporters nor their transport capacity was enhanced after adaptation to a diet rich in carbohydrate (28). In omnivores, such as pigs and humans, systematic investigations on intestinal nutrient absorption after graduated dietary adaptation are still lacking.


   ACKNOWLEDGMENTS
 
We thank Margrit Hartmann and Ingeborg Ehrlein for technical assistance.


   FOOTNOTES
 
1 From the Institute of Physiology, University of Hohenheim, Stuttgart, Germany.

2 Supported by the Deutsche Forschungsgemeinschaft (grant EH 64/6-4).

3 Reprints not available. Address correspondence to HJ Ehrlein, Universität Hohenheim, Institut für Physiologie, Garbenstrasse 30, D-70593 Stuttgart, Germany. E-mail: ehrlein{at}uni-hohenheim.de.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
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Received for publication January 7, 1998. Accepted for publication August 14, 1998.




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H. Fouillet, C. Gaudichon, C. Bos, F. Mariotti, and D. Tome
Contribution of plasma proteins to splanchnic and total anabolic utilization of dietary nitrogen in humans
Am J Physiol Endocrinol Metab, July 1, 2003; 285(1): E88 - E97.
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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
J. B. Schwimmer, L. Ee, S. Zheng, and P. Tso
Glutamine promotes triglyceride absorption in a dose-dependent manner
Am J Physiol Gastrointest Liver Physiol, February 1, 2002; 282(2): G317 - G323.
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