Gastrointestinal response to nutrient variation of defined formula diets

An Anthology of Advances in Enteral Tube Feeding Formulations

This article summarizes several major advances in tube feeding formulas marketed in the United States. It traces the progress in tube feeding formulas, starting with blenderized formulas to commercially available intact-nutrient formulas and culminating in the introduction of the concept of immunonutrition. The impact of packaging is also described.

[Surgical access routes in enteral nutrition]

There are many known routes of access to the digestive tract for enteral nutrition (EN) and significant advances have been made in recent years. Administration techniques and nutritional products have also improved. Placement of these systems may be temporary or permanent. Indications often overlap. If feasible, the enteral route is preferred over the parenteral route. When enteral nutrition will last < or = 6 weeks, nasoenteral tubes are the best option. In NE > or = 6 weeks, enterostomy tubes are indicated and the procedure of choice is percutaneous endoscopic gastrostomy. Postpyloric access should be considered in patients with a high risk of aspiration. Finally, needle catheter jejunostomy during interventions in the upper gastrointestinal tract is the ideal technique for initiating early EN. All these techniques continue to be valid and the choice of procedure will be determined by the patient's clinical status and the experience of the team. The present article is divided into two parts. In the first part, surgical access techniques for EN, their indications and contraindications and the most frequent complications related to the technique, the care of the stoma and the intubation material are analyzed. In the second part, we report data from our personal experience of the various techniques we have performed and describe the patients, results and complications. A total of 287 procedures were performed: 48 surgical gastrostomies, 40 using the technique of Fontan or Stamm, and 8 Janeway gastrostomies; 27 of these procedures were permanent. There were 169 jejunostomy catheters, with a mean dwelling time of 29.05 +/- 21.9 days, and 72 double lumen nasojejunal tubes.

Inhibition of lipid absorption as an approach to the treatment of obesity

A reduction in fat intake may be achieved by making educated choices to reduce total calorie intake, to consume a lower quantity of total fats, or to modify the ratio of saturated-to-polyunsaturated lipids. Leptin agonists or NPY or CCK antagonists may prove to be useful to diminish appetite and thereby reduce the total intake of food. But eating has such cultural, social, and hedonistic attributes that such a single-pronged approach is unlikely to be successful. The use of fat substitutes may prove to be popular to provide a wide range of snack food options, but these are likely to be of minimal use in weight reduction programs because of their distribution of additives in only a limited number of foods. The inhibitors of lipid digestion will be modestly successful in the short term; their long-term success will be influenced by gastrointestinal adverse effects and the need to consume fat-soluble vitamin supplements to prevent the development of fat-soluble vitamin deficiencies. The inhibition of lipid absorption is an attractive targeted approach for the treatment of obesity, since this would reduce the uptake of visible as well as invisible fats, which would potentially offer convenient dosing, and could also be a means to inhibit secondarily the uptake of carbohydrate calories.

Role of bombesin on gut mucosal growth

OBJECTIVE

The authors examined the effects of exogenous bombesin (BBS) on gut mucosal growth in chow-fed rats and the mucosal regeneration after gut atrophy brought about by feeding an elemental diet and after intestinal injury produced by methotrexate (MTX).

SUMMARY BACKGROUND DATA

Bombesin is one of many gastrointestinal peptides implicated in the regulation of gut mucosal growth. Although BBS is known to stimulate growth of normal pancreatic tissue, the trophic effect of BBS on gut mucosa is less clear and its exact role in gut mucosal regeneration and repair is not known.

METHODS

Rats were fed a regular chow diet (control) or an elemental diet plus either saline or BBS (10 micrograms/kg). In another experiment, rats fed a chow diet and treated with saline or BBS were given MTX (20 micrograms/kg) or a single intraperitoneal injection. In all experiments, small and large bowel mucosa and pancreas were removed and analyzed for BBS-mediated proliferation.

RESULTS

Bombesin produced significant mucosal proliferation of the small bowel at day 14, but not at day 7, in rats fed regular chow. In contrast, BBS treatment for 7 days produced significant proliferation in both the atrophic and injured gut mucosa of rats given elemental diet or MTX.

CONCLUSIONS

Bombesin may be an important enterotrophic factor for normal mucosal proliferation and may be clinically beneficial as an agent to restore or maintain gut mucosa during periods of atrophy or injury.

Neurotensin prevents intestinal mucosal hypoplasia in rats fed an elemental diet

Liquid elemental diets are associated with mucosal hypoplasia of both the small intestine and colon. Neurotensin, a tridecapeptide widely distributed in the gut, is trophic for the small intestine of rats fed a normal chow diet. The purpose of this study was to determine whether neurotensin could reverse the hypoplasia of intestinal mucosa that is associated with feeding a liquid elemental diet. Forty male Sprague-Dawley rats were randomized into five groups. Four groups were fed (for seven days) a glutamine-free liquid elemental diet. Subcutaneous injection of saline (control) or neurotensin (33, 100 or 300 micrograms/kg) were given to the groups of rats every 8 hr for seven days. Group five (Chow) received rat chow ad libitum for seven days. Rats were killed on day 8, and the proximal jejunum, distal ileum, and proximal colon removed. Mucosal weight, DNA, RNA, and protein contents were determined. Neurotensin (300 micrograms/kg) increased the cellularity of the small intestinal mucosa and reversed mucosal hypoplasia due to an elemental diet; a more pronounced effect was noted in the jejunum compared to the ileum. Neurotensin (33 and 100 micrograms/kg) increased mucosal DNA content in the jejunum but was not effective in reversing the hypoplasia. Neurotensin had no effect on growth of colonic mucosa. These results suggest that neurotensin may be an important trophic hormone for the small intestine. Administration of neurotensin may alleviate hypoplasia of the small bowel mucosa and maintain functional integrity of the gut during prolonged feeding of an elemental diet.

Alteration of methotrexate toxicity in rats by manipulation of dietary components

Administration of a chemically defined, elemental diet to rats given 20 mg/kg of methotrexate intraperitoneally has consistently resulted in a 100% mortality from severe enteritis within 156 h. This study examined the importance of specific dietary components in the etiology of this enhanced toxicity. Rats were given their respective diets for 7 days, whereupon methotrexate (20 mg/kg) was given intraperitoneally, and percent of survivors was recorded. Varying the concentration of carbohydrate as polysaccharide (0%, 50%, 100%) (n = 30) had no effect on survival. An increase in the percent of protein as polypeptide (0%, 25%, 50%, 75%, 100%) (n = 50) in the elemental diet resulted in a progressively significant increase in percent survival. Addition of either fat or bulk to this elemental diet had no effect on survivorship. Serum and bile methotrexate levels of rats fed an elemental liquid diet (whether or not all of the protein was provided as polypeptide) were significantly increased from 12 to 72 h (p less than 0.03) compared with rats fed a regular Chow diet. When the protein content of the elemental liquid diet was provided as 100% polypeptide, serum and bile methotrexate levels were significantly lower at 48 h compared with the elemental diet group given 100% of protein as amino acid. Administration of methotrexate to rats fed an elemental liquid diet in which all of the protein is provided as amino acids is extremely toxic to the gastrointestinal tract, probably as a result of delayed clearance of the drug from the systemic circulation and from bile. This toxicity is alleviated by the provision of protein as polypeptide in the elemental diet. No toxicity to the drug is seen at this dose in rats fed a regular Chow diet. If these results are applicable to humans, the use of elemental liquid diets as the only source of enteral nutrition would appear contraindicated in patients receiving methotrexate.

Effects of an elemental diet, inert bulk and different types of dietary fibre on the response of the intestinal epithelium to refeeding in the rat and relationship to plasma gastrin, enteroglucagon, and PYY concentrations

Refeeding starved rats with an elemental diet resulted in a marked increase in crypt cell production rate (CCPR) in the proximal small intestine but not in the distal regions of the gut. Little effect on CCPR was noted when inert bulk (kaolin) was added to the elemental diet. Addition of a poorly fermentable dietary fibre (purified wood cellulose) had little effect on intestinal epithelial cell proliferation except in the distal colon where it significantly increased CCPR. A more readily fermentable fibre (purified wheat bran) caused a large proliferative response in the proximal, mid, and distal colon and in the distal small intestine. A gel forming fibre only significantly stimulated proliferation in the distal colon; the rats in this group, however, did not eat all the food given. There was no significant correlation between CCPR and plasma gastrin concentrations, but plasma enteroglucagon concentrations were significantly correlated with CCPR in almost all the sites studied. Plasma PYY concentrations also showed some correlation with CCPR, especially in the colon. Thus while inert bulk cannot stimulate colonic epithelial cell proliferation fermentable fibre is capable of stimulating proliferation in the colon, and especially in the distal colon: it can also stimulate proliferation in the distal small intestine and it is likely that plasma enteroglucagon may have a role to play in this process.

Gastrointestinal toxicity of chemotherapy and the influence of hyperalimentation

The effect of combination chemotherapy on human small intestinal morphology and disaccharidase activities and their relation with clinical and chemical (fecal wet weight and K-excretion) parameters for gastrointestinal toxicity were evaluated in patients with disseminated malignant melanoma receiving enteral normoalimentation (NA). Also evaluated were the supposed protective effects on gastrointestinal toxicity of enteral hyperalimentation (HA) with an elemental diet. After chemotherapy, a comparable decrease in villus height, total mucosal height, and mitotic index was found in jejunal biopsy specimens of both groups. However, in the NA group, the crypt depth decreased (in contrast to the HA group), whereas the disaccharidase activities in the HA group deteriorated to lower values than in the NA group. The authors found no correlation between disaccharidase levels and mucosal morphology, nor was there a correlation between these variables, fecal parameters and clinical diarrhea, suggesting that diarrhea occurring after chemotherapy was not due to loss of mucosal tissue or decrease in enzyme activities. A protective effect of HA with an elemental diet on gastrointestinal toxicity could not be established.

Defined formula diets alter jejunal and colonic uptake of lipids in rabbits with intact intestinal tract and following ileal resection

An in vitro technique was used to measure the jejunal and colonic uptake of fatty acids, decanol and cholesterol in sham-operated control (CONT) rabbits and in animals with a surgical resection of the distal half of the small intestine (RES). CONT and RES were fed standard Purina chow, Ensure, or Flexical HN for 2 weeks. The animals fed Ensure or Flexical HN consumed half the number of calories as the chow-fed rabbits and failed to gain weight. The mean of the jejunal dry weights were unchanged by diet or by ileal resection, although the height of the villi was lower in the animals fed the defined formula diets. Restricting chow intake to match the body weight gain of the animals fed Ensure or Flexical HN was associated with alterations in the uptake of lipids, but the pattern of changes was dissimilar to the pattern of changes observed in the resected animals or in the rabbits fed Ensure or Flexical HN. Ileal resection was associated with changes in the jejunal uptake of lipids and the influence of the defined formula diets on the uptake of short-, medium- and long-chain length fatty acids, decanol and cholesterol varied depending upon whether the animal had an intact intestinal tract or whether the animal had an ileal resection. It is concluded that the passive uptake of a homologous series of saturated fatty acids, cholesterol, and decanol into the jejunum and colon is modified by ad libitum feeding of Ensure or Flexical HN; the functional adaptation of the intestine and colon to dietary modification is influenced by the previous resection of the distal half of the small intestine; and these changes in the uptake of lipids are not explained solely by alterations in food intake, body weight gain, or intestinal morphology.

Influence of the intake and composition of elemental diets on bile acid metabolism and hepatic lipids in the rat

The effects of the elemental diets Vivonex (V) and Flexical (F) on bile acid metabolism and hepatic lipids in the rat has been investigated both with ad libitum feeding and when calorie intake was limited to that of control rats (C) fed a standard diet (Oxoid 41B). Ad libitum feeding of V and F for 9 weeks resulted in a weight gain in excess of that for the control diet. After 9 weeks of isocaloric feeding the V-fed rats were significantly lighter than those fed F and C. Fecal bile acid excretion (FBA) and the fractional turnover rates for cholic acid (CA) and chenodeoxycholic acid (CDC) were measured. The elemental diets significantly reduced FBA when fed both ad libitum and isocalorically compared with the control diet, the reduction with V being significantly greater than for F. In the isocaloric feeding study both elemental diets significantly increased the half life of CA and CDC. The increase for CA was significantly greater for V than F but for CDC the effect of the two diets was the same. Thus the percentage of CDC-derived 6 substituted bile acids was greater with V than F feeding. There was a strong negative correlation between bile acid half-life and fecal excretion of metabolites for the three dietary groups indicating that bile acid pool size was unchanged by the elemental diets. A gross increase in liver lipid both histologically and chemically was found for the ad libitum fed V rats with a marked but lesser increase for F.(ABSTRACT TRUNCATED AT 250 WORDS)

Intact protein versus free amino acids in the nutritional support of thermally injured animals

This study compared the nutritional effects of intact protein with that of constituent amino acids as the sole source of nitrogen in a burn guinea pig model. Forty-five guinea pigs bearing a gastrostomy feeding tube were given 30% total body surface area, full thickness flame burn and were randomized into four groups. Group I (n = 12) and group III (n = 15) received a diet containing whey protein, while group II (n = 9) and group IV (n = 9) received an otherwise identical diet containing free amino acids in a whey protein pattern. Full strength continuous intragastric feeding was initiated immediately postburn in groups I and II, but a 72-hr adaptive period was provided in groups III and IV. Resting metabolic expenditure was measured by indirect calorimetry on postburn days 2, 6,9, and 13. After 14 days of enteral feeding, the animals were killed. Immediate enteral feeding of intact protein or free amino acids reduced postburn hypermetabolic response (p less than 0.01). However, the intact protein was found to maintain body weight and provide nitrogen retention better than the amino acid mixture (p less than 0.05). The animals on the intact protein diet also showed statistically significant benefits in carcass, liver, and gastrocnemius muscle weights and in serum albumin, transferrin and C3 levels. It is concluded that intact protein is superior to free amino acids for nutritional support following burn injury.

Intestinal uptake of fatty acids, cholesterol and decanol in ileal resected rabbits: effect of Isocal and Portagen

Isocal, but not Portagen, is associated with increased villus surface area in control rabbits and in animals with an ileal resection. In control animals, Isocal feeding was associated with an increased in vitro jejunal uptake of short and medium-chain length fatty acids and cholesterol, whereas Portagen feeding was associated with a decline in the uptake of short-, medium- and long-chain fatty acids, but an increase in the uptake of cholesterol. In animals with an ileal resection both diets were associated with an increased uptake of long-chain fatty acids and cholesterol. These changes in lipid uptake are not explained by alterations in villus surface area or unstirred water layer resistance.

Guidelines for evaluating and categorizing enteral feeding formulas according to therapeutic equivalence

Because of the current rapid proliferation of commercially prepared formulas for use in supporting the nutritional status of patients, choosing among them is becoming progressively more difficult. There has been no unified discussion in the literature to date to help the clinician distinguish the important parameters of enteral feeding formula composition from the unimportant ones. Herein we stratify these parameters into three categories of relative importance, and classify the currently available formulas into categories of therapeutic equivalence. Together, the stratified parameters and the classification scheme may be used to evaluate new products in the future and establish a hospital enteral feeding formulary, which can simplify the clinician's choice of formulas and decrease patient costs.