High protein enteral feedings: a means of achieving positive nitrogen balance in head injured patients

In an attempt to improve early enteral nitrogen replacement, nitrogen status was compared in two groups of head injured patients receiving enteral regimens of 38 to 51 kcal/kg/day with different protein concentrations. Eleven control patients received 1.5 g protein/kg/day and 10 study patients received 2.2 g protein/kg/day. Daily nitrogen excretion, corrected nitrogen balance, blood urea nitrogen changes, and enteral formula tolerance were compared between groups over a 10-day period. Those receiving 2.2 g protein/kg/day had significantly higher daily and cumulative nitrogen balances despite their higher nitrogen excretion levels. Over 10 days, the study group retained 9.2 g nitrogen. By comparison, the control group sustained a cumulative loss of 31.2 g nitrogen over 10 days, despite a mean intake of 109 g protein/day. In both groups, full strength, full rate feedings were not possible until day 10 postinjury. These data indicate that once enteral formulas are tolerated high nitrogen regimens are required to achieve positive nitrogen balance in acute severe head injury patients.     

Maintenance of visceral protein levels in serum during postoperative parenteral nutrition

Nitrogen metabolism and plasma insulin level were studied postoperatively in 14 patients (six males and eight females) with a disease of the upper gastrointestinal tract and therefore operated on electively. The patients received one of the two isocaloric parenteral nutrition regimens postoperatively: one, on the average, with 1.2 g of amino acids/kg/day and the other with 3.1 g of amino acids/kg/day. During postoperative intravenous alimentation rich in amino acids the cumulative nitrogen balance over 3 days was +13.1 (interval from -1.3 to +21.4) gN but -10.1 (interval from -12.1 to -2.4) gN during parenteral nutrition with a smaller amount of amino acids. The difference was significant (p less than 0.001). During parenteral nutrition rich in amino acids the changes of the serum albumin level, ie, -0.4 (SEM 1.1) g/liter, and of the serum transferrin level, ie; -0.16 (SEM 0.22) g/liter, were statistically insignificant (p greater than 0.05). During intravenous alimentation poor in amino acids serum albumin decreased by 3.8 (SEM 1.2) g/liter (p less than 0.01) and serum transferrin by 0.44 (SEM 0.05) g/liter (p less than 0.001). The differences of the changes between the groups were significant (p less than 0.01 and p less than 0.01, respectively). These various effects of the two parenteral nutrition regimens were not dependent on the different fluid balances during intravenous alimentation or on the different plasma insulin levels. It is concluded that a rich supply of amino acids--more than 1.2 g/kg/day--in postoperative parenteral nutrition better maintains the visceral protein levels in the serum, which possibly depends on the greater protein production in the liver.     

Minimum protein requirements in liver cirrhosis determined by nitrogen balance measurements at three levels of protein intake

Nitrogen balance at three levels of protein intake was measured in eight patients with cirrhosis of the liver; moreover, at each level of protein intake, the effects on nitrogen balance of branched-chain amino-acid enriched protein and natural protein were compared. From these nitrogen balance data, minimum protein requirements were calculated by linear regression analysis. The patients were in a negative nitrogen balance on a 40 g protein diet (-0.75 +/- 0.15 gN.), and in positive nitrogen balance on 60 g (+1.23 +/- 0.22 gN.) or 80 g of protein per day (+2.77 +/- 0.20 g N.). Their mean minimum protein requirement (48 +/- 5 g of protein/day or 0.75 g/kg/day) is higher than expected in healthy people; the safe level of protein intake (mean + 2 sd) is 58 g per day or 1.2 g/kg/day. Nitrogen balances and protein requirements were not different on branched-chain amino-acid enriched diets. The physical condition of the patients improved when they came into positive nitrogen balance; the higher rates of protein intake were well tolerated without onset of encephalopathy. We conclude that protein requirements are elevated in cirrhosis of the liver; diets supplying less than 60 g of protein per day should not be prescribed in long term treatment of cirrhotic patients.     

Zinc and nitrogen balance in adolescent females fed varying levels of zinc and soy protein

Zinc and nitrogen balances were determined in 14 girls, 12.5 to 14.5 years of age, during a 30-day period. Diets were composed of ordinary foods and supplied 100% of the Recommended Daily Allowance for protein. The lunch menus were typical of those served in School Lunch Programs except that milk was omitted and calcium supplements were added. The dietary variables were the levels of zinc and the amount of defatted soy which replaced the meat in noon meals. The diets were: S0Z13.4 (13.4 mg zinc and no soy); S30Z13.4 (13.5 mg zinc and 30% of meat replaced by soy); and S30Z7.4 (7.4 mg zinc and 30% of meat replaced by soy). Subjects fed 7.4 mg zinc daily lost significantly (P less than 0.01) less zinc in their feces than the subjects fed the higher level of zinc during the 18-day collection period. Partial substitution of soy for meat in lunch menus did not affect fecal or urinary zinc or nitrogen losses. Mean retentions of zinc by subjects Diets S0Z13.4 nad S30Z7.4 were +0.53, +0.42 and -0.32 mg/day, respectively. Nitrogen retention was not significantly affected by zinc intake. However, nitrogen and zinc retentions were significantly correlated (r = 0.416, P less than 0.015).     

Influence of varying energy intake on nitrogen balance in men on two levels of protein intake.

Effect of changing energy levels of the diet at constant protein intakes on nitrogen balances in five young men were studied at two levels of protein--40 and 60 g. Nitrogen balance increased with increase in energy intake at both levels of protein. This was brought about primarily by a reduction in urinary nitrogen excretion. Energy levels at which nitrogen equilibrium was obtained were different for the two levels of protein intake. At 40 g protein intake the energy intake required for zero nitrogen balance was 2,249 kcal, while it was 2,066 kcal when the diet provided 60 g protein.     

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.     

Relationship between protein intake and nitrogen balance in obese patients on low energy diet

The effect of nitrogen intake on nitrogen balance was studied in six obese patients receiving low energy diets. They were given a control diet containing 2,000 kcal of energy and 80 g of protein for the first ten days. Then they were given Diet A with 1,100 kcal of energy and 70 g of protein for the next 2 weeks, followed by Diet B with 1,100 kcal of energy and 50 g of protein for 2 weeks. The relationship between nitrogen intake (X, mg/kg) and nitrogen balance (Y, mg/kg) during the low energy diet periods was statistically significant, with Y = 0.388X-60.32 (SD = 17.71, r = +0.67, n = 11, p less than 0.05). The nitrogen and protein requirements were estimated from this equation to be 201.1 mg/kg and 1.26 g/kg, respectively. In our experiment, the nitrogen balance in obese patients was well maintained although total energy was reduced to 1,100 kcal/day in Diet A. It is suggested that protein quantity in the diets should be taken into account when a low energy diet is used for the treatment of obesity.     

Minimum nitrogen requirement from glandless cottonseed protein for nitrogen balance in college women

Seven women, 18 to 23 years of age, were fed cooked cottonseed products for 42 days in order to determine the minimum nitrogen requirements for glandless cottonseen flour after baking. The women consumed from 81 to 213 mg N/kg body weight from cottonseed protein. Nitrogen intake from each experimental period was calculated from the average nitrogen content of the cottonseed products consumed each day of the experiment period. Nitrogen excretion was determined from the measurement of nitrogen in a total collection of urine and feces for each experimental period plus an obligatory loss of 5 mg/kg body weight. Fasting blood samples were taken prior to the study and at the end of each 7-day experimental period thereafter. The minimum requirement for cottonseed protein to maintain a positive nitrogen balance was 106 mg N/kg body weight. For the "reference woman," weighing 58 kg, at least 6.1 g of cottonseed flour nitrogen would be required to maintain nitrogen equilibrium. Plasma amino acid values of threonine, proline, valine, isoleucine, leucine, tyrosine, and lysine decreased significantly from day 0 to day 7 of the study. There were no significant differences in these plasma amino acids thereafter. Cottonseed flour incorporated into baked products maintained nitrogen balance in college women with no change in their nutritional status.     

Dietary protein and nitrogen balance in lactating and nonlactating women

Adaptive responses of body protein metabolism to dietary protein intakes of 1.0 g.kg body wt-1.d-1 were determined by nitrogen balance and urinary 3-methylhistidine excretion in lactating and nonlactating women. Despite higher energy intakes (p less than 0.04), lactating women had lower nitrogen balances compared with nonlactating postpartum and nulliparous women (p less than 0.001). Nitrogen losses in milk did not account entirely for these differences. Nitrogen balance showed linear (p less than 0.04) and quadratic (p less than 0.03) trends over time postpartum among the lactating women. Urinary 3-methylhistidine excretion also was reduced (p less than 0.05) in lactating compared with nonlactating women. These observations suggest that protein intakes of 1.0 g.kg body wt-1.d-1 in lactating women are associated with adaptive responses that promote the conservation of skeletal muscle protein stores and that currently recommended dietary protein allowances may be insufficient to meet the nutritional needs of well-nourished lactating women.     

Failure of BCAA supplementation to promote nitrogen retention in injured patients

The purpose of this study was to determine if supplementing total parenteral nutrition (TPN) with lipids or the branched chain amino acids (BCAA) leucine, isoleucine, and valine influences nitrogen balance in the injured patient. Four TPN study solutions were used, with each patient receiving two of the solutions for 4 days each. Group A received solutions consisting of 19% and 44% BCAA, with nonnitrogen calories supplied by 100% carbohydrate. Group B received a 7:3 carbohydrate-to-lipid ratio of nonnitrogen calories as a fuel source. Neither BCAA supplementation nor varying fuel substrates promoted a difference in nitrogen retention. The added cost of BCAA supplementation, along with the lack of an effect upon nitrogen accretion, indicates that greater benefits must be demonstrated before widespread use of BCAA supplementation can be recommended in the injured patient.     

The minimum cottonseed protein required for nitrogen balance in women

This study was designed to assess minimum amount of nitrogen from deglanded (LCP) and glandless (GSF) cottonseed protein required to maintain nitrogen balance in young adult women. Fourteen women aged 19 to 25 were divided into two groups, one group was fed LCP and the other GSF in a purified formula diet for the entire study. The protein level constituted approximately 15% of the total energy intake initially. After reaching and maintaining equilibrium, the protein level for each subject was decreased until that lowest level was found that would maintain the individual in nitrogen balance. Nitrogen status was calculated using the formula: Nitrogen Status = N Intake--N Output (Urinary + Fecal + other Obligatory Loss). Regression data for each subject was used to define nitrogen intake required to maintain equilibrium. The nitrogen intakes showed similar results for the two forms of cottonseed with a mean value of 0.106 g N per kg body weight to maintain equilibrium. The quality of cottonseed protein was between reported values in men for soybean and wheat protein.     

Effect of total parenteral nutrition with xylitol on protein and energy metabolism in thermally injured rats

The use of xylitol as an alternative carbohydrate calorie source in total parenteral nutrition may offer unique pharmacologic and nutritional properties in the therapy of the thermally injured. Male Sprague-Dawley rats (250 g) received a 15-second dorsal scald injury (25-30% BSA) and were parenterally fed isovolemic diets (60 ml/day) that provided 200 kcal/kg/d, 9.68 g of amino acids/kg/d, and 23.5% nonprotein calories (NPC) as fat for 3 days. The balance of NPC were provided as dextrose (Dex) or 50% xylitol:50% dextrose (Xyl/Dex). Rectus muscle and liver fractional protein synthetic rates (FSR, %/day), whole body leucine appearance (Flux), oxidation (OX), protein breakdown (PB), and synthesis (PS) were estimated using a 4-hour iv infusion of [1-14C]leucine on day 3. Mean values (+/- SE) for leucine kinetics (mumol leucine/hr/100 g), cumulative nitrogen balance (mg N) and plasma insulin concentration (Table I). (microU/mL). The partial replacement of dextrose calories with xylitol did not significantly alter whole body and tissue leucine kinetics, daily and cumulative nitrogen balance, insulin concentration, and energy expenditure (indirect calorimetry). These data indicate that xylitol may be useful as an alternative carbohydrate calorie source in parenteral nutrition to avoid possible deleterious side effects of glucose overfeeding in the critically ill but did not improve protein metabolism under the conditions of this study.     

Nutritional assessment in head injured patients through the study of rapid turnover visceral proteins

BACKGROUND & AIMS: Nutritional monitoring of rapid turnover visceral protein is important in the recognition of malnutrition in patients admitted to the Intensive Care Unit (ICU). We studied prealbumin and retinol-binding protein in patients who received three different kinds of artificial nutrition in order to evaluate the appropriateness of artificial nutrition. METHODS: 45 consecutive head injury patients received enteral (Group A), parenteral (Group B) or both enteral and parenteral nutrition (Group C) at random. We considered these parameters: prealbumin, retinol binding protein and nitrogen balance before (T1), after 3 (T2), 7 (T3) and 11 (T4) days after the beginning of study. Statistical analysis was performed with Kruskal-Wallis test and Bonferroni's t -test. RESULTS: Plasma prealbumin and Retinol binding protein (RBP) showed an increasing of basal values during the study period in all groups (< 0.0001) and more significantly in group A (Enteral nutrition P < 0. 001 vs Total parenteral nutrition (TPN) and Enteral P< 0.01 vs Enteral and parenteral nutrition). CONCLUSION: Data obtained in the present study indicate that a laboratory is essential for monitoring nutritional assessment and for checking the appropriateness of nutritional therapy. We found prealbumin to be the most sensitive measure and found it to be the test of choice for early assessment and intervention.