Lysine requirement of adult males is not affected by decreasing dietary protein

Recently, we reported the lysine requirement to be 41.2 mg.kg-1.d-1 using indicator amino acid oxidation (IAAO) in healthy adult males fed a protein intake of 1.0 g.kg-1.d-1. A lower protein intake has been hypothesized to significantly lower the requirement estimate. We tested this hypothesis using IAAO by estimating the lysine requirement at a protein intake of 0.8 g.kg-1.d-1 in five healthy adult males. Lysine requirement was determined from the rate of appearance of 13CO2 in breath (F13CO2) by using a primed 4-h continuous infusion of L-[1-(13)C]phenylalanine. Phenylalanine flux was not affected by graded increases in dietary lysine. Phenylalanine oxidation and F13CO2 decreased linearly (P < 0.05) as lysine intake increased to a breakpoint, after which the rates were not significantly different. Two-phase linear regression determined this breakpoint (mean lysine requirement) to occur at a dietary lysine intake of 45.0 mg.kg-1.d-1. We conclude that no reduction appears in the lysine requirement with a lower protein intake. Thus, lysine requirement appears not to be altered by protein intakes within the lower end of the protein requirement range.

Effect of low- and high-fat, peptide-based diets on body composition and disease activity in adolescents with active Crohn's disease

BACKGROUND

The effect of nasogastric feeding with high- and low-fat, peptide-based diets on body composition and disease activity was studied in adolescents with active Crohn's disease.

METHODS

Fourteen patients with active Crohn's disease (12 to 17 years) were fed exclusively through nasogastric feedings with two isocaloric, isonitrogenous, peptide-based diets, either with low- or high-fat content, for 3 weeks each in a randomized manner then were "crossed over" to the other diet for another 3 weeks of feeding. At the end of each 3-week period, urine and stools were collected for 72 hours for measuring energy absorption and nitrogen utilization (n = 6). Weight, height, triceps skin folds, fat free body mass, and disease activity were also monitored (n = 14).

RESULTS

There was no difference in any parameter of energy absorption or nitrogen utilization between the two formulas irrespective of the order in which they were administered. The changes in nutritional parameters were also comparable with both formulas. There was a significant increase in weight, fat free body mass and triceps skinfold thickness during both the 3-week periods of feeding (p < .05). This was accompanied by a significant reduction in the pediatric Crohn's disease activity index (p < .05).

CONCLUSIONS

Peptide-based diets may be useful in restoring the fat free body mass and improving the disease activity in patients with Crohn's disease. A high fat (high medium-chain triglycerides) diet did not offer any nutritional advantage over a similar but low-fat diet. The improvement in disease activity during feeding with a low-fat diet was comparable to that with a high-fat diet. The improvement in disease activity seems to be associated with improvement in lean body mass irrespective of the type of diet used to achieve it.

Use of bioelectrical impedance analysis measurements in the clinical management of malnutrition

It is valuable to be able to measure the body composition of malnourished (undernourished) patients and to monitor their response to refeeding. The use of direct measurements, such as total body water, extracellular water, and total body potassium for clinical monitoring is expensive and cumbersome. We therefore have developed predictive equations for these variables by using fixed-frequency bioelectrical impedance analysis (BIA). Our equations deliberately do not include weight because they are used to predict changes in body composition in patients who are gaining weight during refeeding. BIA could predict changes in body composition with significantly greater precision than anthropometry alone. We conclude that BIA can be used to monitor changes in body composition in patients during refeeding.

Use of amino acid profiles of preterm and term human milks in evaluating scoring patterns for routine protein quality assessment of infant formulas

Reports on the amino acid composition of human milk vary considerably with respect to concentrations of sulfur amino acids. Often, analyses forego tryptophan determination. A complete analysis of protein and amino acid concentrations was performed on human milk samples (5-10 days postpartum) collected from mothers of preterm (gestations of 25-32 weeks) and term (gestations of > 36 weeks) infants. Careful attention was given to quantitate amino acids such as cysteine and tryptophan, which are vulnerable to acidic hydrolysis conditions. Differences in concentrations of total amino acids (expressed on protein basis) between preterm and term milks were small, despite the higher true protein content of preterm milk versus term milk (19.20 versus 12.60 g/L). The methionine + cyst(e)ine contents of term and preterm milks (3.72-3.84 g/100 g protein) were comparable with those reported in 1991 by the Food and Agricultural Organization/World Health Organization (FAO/WHO) for mature human milk (4.20 g/100 g protein) but higher than those reported in 1991 by the European Commission (2.9 g/100 g protein). The amino acid pattern of human milk obtained in this study confirms that the 1991 FAO/WHO amino acid scoring pattern for predicting protein quality of infant formulas is representative of the amino acid quality of both preterm and term human milks.

Recent advances in methods of assessing dietary amino acid requirements for adult humans

The requirements for the indispensable amino acids have been determined by a number of different methods. Historically, descriptive or gross measures like growth and nitrogen balance have been used. However, technological advancements in recent years have resulted in the use of more precise and mechanistic metabolic approaches (i.e., plasma amino acid concentrations, amino acid oxidation, indicator amino acid oxidation) to examine requirement. Nevertheless, the current recommendations are still based on nitrogen balance studies. Requirement estimates based on other methodologies, such as plasma amino acid concentrations and direct amino acid oxidation, suggest that the requirement estimates derived from nitrogen balance experiments are too low. However, these higher estimates have also been criticized on conceptual and methodological grounds, resulting in considerable controversy in the area of indispensable amino acid requirements. A new technique, indicator amino acid oxidation, addresses many of the criticisms directed toward the alternative methods and the proposed higher requirement estimates. This paper reviews the current knowledge of amino acid requirements and makes recommendations in light of new information that has been provided from recent indicator amino acid oxidation research. It is concluded that the nitrogen balance-based estimates of amino acid requirement are too low.

Whole-body protein turnover in obese subjects during two very low energy diets of differing amino acid composition

OBJECTIVE

To determine whether the kinetics of protein metabolism would differ with the prolonged use of a casein-soy 96 g protein, 1.7MJ/d very low energy diet (VLED) from those of a tryptophan- and methionine-supplemented hydrolyzed collagen VLED, in obesity.

DESIGN

Clinical intervention study of 1 week isoenergetic diet followed by 6 weeks VLED.

SUBJECTS

6 (1M,5F) healthy obese subjects (age: 38 +/- 4 y, BMI: 33 +/- 1 kg/m2, weight: 97 +/- 7 kg).

MEASUREMENTS

Whole-body nitrogen (N) flux rate (Q) from 15N abundance in urinary urea using the oral 15N-glycine method and rates of protein synthesis (S) and breakdown (B) calculated from Q; N balance; resting metabolic rate; metabolic and hormonal responses.

RESULTS

Q (per kg LBM) was maintained with both collagen and casein-soy VLED. S and B decreased (P < 0.05) at week 4 of both VLEDs with resulting decreases in net protein synthesis. At week 6, S decreased with both VLEDs, but B decreased only with casein-soy, at which time N balance was at equilibrium with casein-soy but returned to negative with collagen. Initial resting metabolic rate correlated with baseline Q and S. It decreased by 16% with the VLEDs; 25% of the decrease may derive from the decline in S.

CONCLUSION

A 6 week casein-soy VLED with 46% of amino acids as essential does not provide a substantial advantage compared to hydrolyzed collagen with 16% of amino acids as essential. With prolonged use, it may better maintain N equilibrium by preventing further increments in protein breakdown.

Propionate inhibits incorporation of colonic [1,2-13C]acetate into plasma lipids in humans

Acetate and propionate, produced during colonic fermentation of unabsorbed carbohydrate, may influence systemic lipid metabolism. As a preliminary study to see whether colonic acetate is incorporated into plasma lipids and whether propionate inhibits this process, 5 healthy males were studied after fasting overnight. They were given, in random order, 12.5 mmol (1.05 g) [1,2-13C]sodium acetate by intravenous or rectal infusion, and the rectal infusion was given with or without 6 mmol (0.58 g) sodium propionate. Two hours after rectal acetate, 13C recoveries in plasma cholesterol (0.59 +/- 0.22%) and triglycerides (1.24 +/- 0.69%) were significantly greater than after intravenous acetate (0.09 +/- 0.12% and 0.29 +/- 0.18%, respectively). Addition of propionate reduced 13C recovery in triglycerides (0.19 +/- 0.06%, P = 0.024) compared with rectal acetate alone, but the effect on cholesterol (0.26 +/- 0.05%) was not significant. These data suggest that incorporation of colonic acetate into plasma triglycerides is inhibited by propionate. Further studies are required to quantify the effects of colonic acetate and propionate on lipid synthesis.

Nutritional management of dumping syndrome associated with antireflux surgery

Eight children were identified as having dumping syndrome by a glucose tolerance test and evidence of rapid gastric emptying. All had undergone a fundoplication with concomitant feeding gastrostomy placement at 18.4 +/- 17.4 months of age (range, 3 to 54 months). Symptoms suggestive of dumping syndrome occurred 1 to 4 months after surgery. There was considerable delay in diagnosis (3 to 8 months). These children were successfully managed with nutritional manipulation alone, using a combination of a complex carbohydrate and a fat emulsion. Complete resolution of symptoms and normoglycemia was achieved in all the children, without any complications.

Aromatic amino acid metabolism of neonatal piglets receiving TPN: effect of tyrosine precursors

Low tyrosine solubility in total parenteral nutrition (TPN) solutions complicates meeting the aromatic amino acid needs of infants. This study compared the effectiveness of two tyrosine precursors to supply the aromatic amino acid needs of TPN-fed neonatal piglets with a control group in which total aromatic acid needs were met by the addition of phenylalanine (Phe). Eighteen 3-day-old male Yorkshire piglets (6/group) received TPN for 8 days by central line. The solution was supplemented with Phe or one of the following two tyrosine precursors: N-acetyltyrosine (N-AcTyr) or glycyltyrosine (GlyTyr). Aromatic amino acid metabolism, growth, and nitrogen utilization were measured. Average amino acid and energy intakes were 14.6 g.kg-1.day-1 and 1,050 kJ.kg-1.day-1. Nitrogen balance and utilization were significantly higher (P < 0.05) in piglets in the control Phe group and on the GlyTyr regimen. The high urinary excretion of N-AcTyr (65%) confirms its low bioavailability. Flux and oxidation were significantly higher (P < 0.05) in the Phe group. High plasma Phe levels and excretion of Phe catabolites, as well as the high plasma tyrosine in the GlyTyr group, indicate that current strategies employed to meet the aromatic amino acid needs of neonates on TPN need further refinement.

Amino acid profile and aromatic amino acid concentration in total parenteral nutrition: effect on growth, protein metabolism and aromatic amino acid metabolism in the neonatal piglet

1. The protein and amino acid utilization of two commercially available amino acid solutions, one egg-patterned (Vamin), the other human-milk-patterned (Vaminolact), were studied in piglets receiving total parenteral nutrition. It was hypothesized that Vaminolact was deficient in total aromatic amino acids, so a third group received a human-milk-patterned amino acid solution with added phenylalanine. 2. The piglets were on total parenteral nutrition for 8 days from day 2 or 3 of life. They all received a total energy intake of 1040 kJ day-1 kg-1 with macronutrient intakes of 14.6 g of amino acid, 27.4 g of glucose and 9.4 g of fat day-1 kg-1. 3. Nitrogen balances were performed on days 3-8 of total parenteral nutrition. On day 8 a primed constant infusion of (1-14C]-phenylalanine was given to measure phenylalanine flux and fractional conversion to tyrosine. Transamination catabolites of phenylalanine and tyrosine were measured in urine on day 7. 4. The piglets receiving Vaminolact gained significantly less weight (0.86 kg compared with 1.18 kg for Vamin and 1.20 kg for phenylalanine-supplemented Vaminolact; P < 0.02) and nitrogen (1435 mg day-1 kg-1 compared with 1601 mg and 1836 mg day-1 kg-1 for the other groups; P < 0.0001). 5. The piglets receiving Vamin had high plasma phenylalanine levels (2234 mumol/l compared with 156 mumol/l for Vaminolact and 399 mumol for phenylalanine-supplemented vaminolact; P < 0.0001). Those receiving Vamin also had an elevated excretion of phenylalanine transamination metabolites and low plasma lysine levels. Phenylalanine flux was highest in the Vamin group, intermediate in the phenylalanine-supplemented Vaminolact group and lowest in the Vaminolact group. 6. We conclude that Vaminolact is limiting in aromatic amino acids and that the addition of phenylalanine to the level in Vamin significantly improves growth and nitrogen retention; however, increasing the phenylalanine content of total parenteral nutrition is not the most metabolically suitable way to provide aromatic amino acids in neonatal total parenteral nutrition.

Plasma and urine enrichments following infusion of L-[1-13C]phenylalanine and L-[ring-2H5]phenylalanine in humans: evidence for an isotope effect in renal tubular reabsorption

Amino acids labeled with 13C or deuterium are commonly used in studies of amino acid metabolism. Traditionally, amino acid flux has been estimated by measurement of isotopic enrichment in the plasma pool; however, urine sampling as a noninvasive means of determining isotope enrichment has been increasing. The isotope enrichments and fluxes estimated from plasma and urine sampling were compared when two phenylalanine tracers (L-[1-13C]phenylalanine and L-[ring-2H5]phenylalanine) were intravenously infused for 4 hours in seven healthy men. This is the first evaluation of these isotopes as urinary tracers for assessing amino acid metabolism in adult humans. Before infusion, the mean ratio of plasma to urine (P:U) isotope enrichment was 0.99 +/- 0.03 (SD) and 0.99 +/- 0.02 for [13C]phenylalanine and [13C]tyrosine, respectively (isotope enrichment of [2H5]phenylalanine is zero at baseline). At isotopic steady state, the ratio was 1.06 +/- 0.05, 0.98 +/- 0.03, and 0.60 +/- 0.10 for [13C]phenylalanine, [13C]tyrosine, and [2H5]phenylalanine, respectively. The [13C]phenylalanine isotope showed a high correlation (R2 = .96) between enrichment in plasma and urine. However, use of [2H5]phenylalanine resulted in a significantly higher enrichment in urine than in plasma. Since amino acid flux is inversely related to enrichment, urine sampling would result in an underestimation of flux. The plasma to urine difference is probably due to discrimination of the [2H5]phenylalanine isotope in renal transport; therefore, this isotope may not be suitable for in vivo use where cellular transport mechanisms are involved.

Glutamine supplementation to total parenteral nutrition promotes extracellular fluid expansion in piglets

The effect of glutamine-supplemented total parenteral nutrition was studied in 18 neonatal piglets (1.97 kg, 3 d old) for 8 d. They were grouped as follows: total parenteral nutrition with 0 (controls), 5 or 10 g glutamine/100 g total amino acids. Live weight gain (g/d) tended (P < 0.07) to increase with supplementation (129, 143, and 166 [SD = 20] for control, 5% and 10% glutamine), but there was no effect on total gain (g) in body protein (180, 171, 197; SD = 25), fat (135, 126, 143; SD = 33) or ash (13, 13, 16; SD = 5) for control, 5% and 10% glutamine groups, respectively. Total body water gains were significantly higher in the 10% group than in controls, with the 5% group showing intermediate gains (control = 696 g; 5% glutamine = 822 g, 10% glutamine = 970 g, SD = 119). Increased glutamine supplementation was accompanied by a trend (P < 0.08) toward increasing total body chloride space, an indicator of extracellular volume, explaining, in part, the observed differences in water gains. These results indicate that glutamine may not be a conditionally indispensable amino acid for the neonate on total parenteral nutrition. Furthermore, glutamine supplementation to total parenteral nutrition leads to disturbances in water balance that could cause increased accumulation, particularly in the extracellular space.

Metabolic consequences of increasing energy intake by adding lipid to parenteral nutrition in full-term infants

The effect on energy metabolism and fuel utilization of increasing energy intake by adding intravenous lipid to a glucose and amino acid regimen was examined. Twenty fullterm, appropriate-for-gestational-age, intravenously fed neonates were entered into one of two groups: total energy intake was 261 kJ.kg-1 x d-1 (62 kcal.kg-1 x d-1) in group 1 and 355 kJ.kg-1 x d-1 (85 kcal.kg-1 x d-1) in group 2. Both groups received 2.8 g protein.kg-1 x d-1 and 14 g glucose.kg-1 x d-1. Group 2 received an additional 2 g lipid.kg-1 x d-1. Metabolic rate, respiratory gas exchange, and nonprotein substrate oxidation were similar in both groups. The addition of energy as lipid enhanced nitrogen retention (230 vs 306 mg.kg-1 x d-1; P < 0.02) and utilization (52.8% vs 66.5%; P < 0.03). Our data suggest that nitrogen utilization is improved in parenterally fed neonates by adding fat and increasing energy intake without change in metabolic rate, carbon dioxide production, oxygen consumption, and nonprotein substrate utilization. Energy expenditure does not necessarily increase with increasing energy intake independently of diet composition.

Effect of NIDDM on the kinetics of whole-body protein metabolism

We postulated that dietary protein utilization and body protein metabolism are altered in hyperglycemic individuals with non-insulin-dependent diabetes mellitus (NIDDM). This was tested by estimating the kinetics of protein metabolism in obese NIDDM patients in the hyperglycemic state of isoenergetic feeding and in the normoglycemic state induced by the prolonged use of a very-low-energy diet (VLED) and comparing them with results in obese nondiabetic subjects studied previously. Seven obese subjects with NIDDM (one male, six females, body mass index = 35.8 +/- 2.0 kg/m2) were given a 1.7 MJ (410 kcal) all protein (93 g/day) diet derived from hydrolyzed collagen and supplemented with tryptophan and methionine, which provides 16% of its amino acids as essential, a multivitamin and mineral supplement, and 16 mmol KCl for 42 days. During the seven-day isoenergetic diet and at weeks 4 and 6 of the VLED, amino nitrogen (N) flux rate was calculated from the urine [15N]urea enrichment by using the 60-h oral [15N]glycine method to obtain the integrated feeding-fasting metabolism. Rates of synthesis (S) and breakdown (B) were calculated from N flux. At day 7 of the isoenergetic diet, whole-body N flux, S, B, and resting metabolic rate (RMR) were 12-24% greater (P < 0.05) in the NIDDM subjects than observed in nondiabetic obese subjects. Mean plasma glucose decreased (P < 0.05) from the isoenergetic period (14.9 +/- 2.4 mM) to 7.2 +/- 1.2 mM at week 4 and 6.5 +/- 1.1 mM at week 6 of the VLED. RMR declined progressively by 25% at week 5 of the VLED. Corresponding significant (P < 0.05) decreases from isoenergetic feeding to weeks 4 and 6 of the VLED occurred in whole-body N flux (from 51 +/- 2 to 42 +/- 1 g N/day), in S (from 38 +/- 3 to 24 +/- 1 g N/day), and in B (from 39 +/- 3 to 26 +/- 1 g N/day) resulting in net losses (S-B). S-B was significantly more negative (P < 0.05) in NIDDM than in the nondiabetic obese subjects at week 4 (-1.5 +/- 0.5 vs. 0.9 +/- 0.3 g N/day) but not at week 6 (-1.3 +/- 0.4 vs. -0.9 +/- 4 g N/day). During the VLED, N balance became less negative with time but never reached equilibrium in NIDDM. Thus, abnormal protein metabolism is present in NIDDM in the isoenergetic fed state with moderate hyperglycemia and persists during a VLED that restores glycemia to near normal.

Impact of nutritional rehabilitation on gastroesophageal reflux in neurologically impaired children

The impact of nutritional rehabilitation on gastroesophageal reflux (GER) in 10 malnourished neurologically impaired children (NIC) was studied (mean age, 9.1 +/- 3.1 years). None of the children had an antireflux procedure (ARP), and all were fed exclusively through a percutaneous endoscopic gastrostomy (PEG). Malnutrition was defined as triceps skin fold thickness (TSF) below the fifth percentile for age and sex. GER was established using standard criteria for a 24-hour pH probe study. All children were treated with an H2 antagonist and a prokinetic agent, along with aggressive nutritional rehabilitation. When TSF was > or = 50th percentile, medications were stopped, and the 24-hour pH probe study was repeated. The mean weight gain was 8.8 +/- 3.7 kg over 8.4 +/- 2.3 months. The 24-hour pH probe study showed marked improvement after nutritional rehabilitation in six of 10 children. These children remained asymptomatic throughout long-term follow-up, without the use of medications. Two children had abnormal pH probe results and worsening clinical symptoms when taken off medications after nutritional rehabilitation. They were reexamined after reinstituting the prokinetic drug; results of the pH probe study were normal, and there was no clinical symptomatology. The patients were then given long-term medication. Two children (one with erosive esophagitis and one with persistent symptoms) underwent ARP. We conclude that despite accompanying GER, successful nutritional rehabilitation can be achieved in malnourished NIC, using PEG feeding and antireflux medication. Although some NIC with GER may need an ARP or long-term medication, in most malnourished NIC nutritional rehabilitation is associated with resolution of GER.

Development and validation of a total parenteral nutrition model in the neonatal piglet

A model was developed for total parenteral nutrition (TPN) in neonatal piglets, with ingredients typical of those in clinical use. Our goal was to characterize the model and to compare growth and body composition of TPN-fed piglets with a reference sow-fed group. Forty piglets (1 to 3 d of age) received TPN (1040 kJ.-1.d-1, 14.6 g.kg-1.d-1 of amino acids, with nonprotein energy supplied equally by glucose and fat) for 8 d. Weight gain, linear growth, serum biochemistry, hematology and body composition were compared with the reference group of 20 sow-raised piglets. Piglets receiving TPN gained 63 +/- 12 g.kg-1.d-1, less than the mean (79 +/- 21 g.kg-1.d-1, P < 0.01), but within the range (49-118 g.kg-1.d-1), of sow-raised piglets. The TPN-fed piglets used the amino acids in TPN effectively, retaining 80% of infused nitrogen. At postmortem, dry-matter analysis of the bodies yielded similar findings in both groups. Wet-tissue protein concentration was lower in TPN-fed animals (12.5 +/- 0.8 vs 13.8 +/- 1.8 g.100 g body wt) because TPN-fed piglets were more hydrated. Ash concentration was lower in TPN-fed piglets, reflecting limitations in calcium and phosphorous supply.

Utilization of non-protein nitrogen in whey-dominant formulae by low-birthweight infants

1. The effects of increasing non-protein nitrogen intake on nitrogen balance and alpha-amino nitrogen flux rate using [15N]glycine were examined in 30 low-birthweight appropriate-for-gestational-age infants (birthweight 1.5-2.0 kg). The compositions of the three whey-dominant formulae were similar except for the ratios of non-protein nitrogen/protein nitrogen, which were 6.5:93.5, 11.4:88.6 and 17.5:82.5. 2. Infants in the three diet groups each received similar total nitrogen intakes (395 mg of N day-1 kg-1, SD 2.6; n = 3). Protein nitrogen and non-protein nitrogen intakes were different as expected. Energy absorption (449 kJ day-1 kg-1, SD 13; n = 3) did not differ significantly between groups. A similar weight gain was observed in all groups. 3. Nitrogen absorption (76%, SD 4; n = 3) was not significantly different between groups. Apparent urea balance was significantly increased and became positive in the group receiving the formula with the higher proportion of non-protein nitrogen and urea nitrogen. Nitrogen retention, however, was significantly depressed in this group, indicating decreased efficiency of nitrogen utilization at this level of non-protein nitrogen despite an enhanced urea salvage. 4. The enrichment of the 15N label in urinary urea at isotopic steady state was significantly reduced in infants receiving the highest urea-containing formula, presumably due to the dilution of 15N-labelled urea by dietary urea. No difference, however, was found in the enrichment of the 15N label in urinary ammonia. Rates of alpha-amino nitrogen flux, protein synthesis and protein breakdown calculated from the ammonia labelling did not differ significantly between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chemotherapy on the energy and protein metabolism of children near the end of treatment for acute lymphoblastic leukemia

Eight children in the final 3 mo of chemotherapy for acute lymphoblastic leukemia were studied while on oral 6-mercaptopurine (6MP) maintenance therapy and then again 4-9 mo after chemotherapy had been completed. Six of the eight were also studied a second time while on 6MP in the 24-h period after receiving intravenous methotrexate (MTX). 6MP reduced protein oxidation after a test meal and reduced fasting urinary urea excretion by enhancing the reutilization of endogenous amino acids for protein synthesis. MTX had no detectable effects on protein metabolism but reduced overnight carbohydrate utilization by enhancing fat utilization. A similar enhancement of fat utilization was evident after a test meal. The two drugs in combination resulted in effects on protein and energy metabolism that were the sum of the individual effects plus an increase in the rate of whole-body protein turnover and synthesis.

Use of bioelectrical impedance analysis to measure total body water in patients with cystic fibrosis

The purpose of this study was to measure whole-body bioelectrical variables and to validate the technique of bioelectrical impedance analysis (BIA) as a measure of total body water (TBW) in patients with cystic fibrosis (CF). In 20 normally nourished males with CF, aged 7 to 39 years, bioelectrical impedance measurements were compared with TBW measured by isotopic distribution of H2(18)O. The relationship between the two measurements was found to be highly significant (r = 0.96; p < 0.0001). The major genotype mutation delta F508 was found to have no effect on BIA. Comparison of the CF patients with 21 normal controls matched for age and TBW volumes as measured by H2(18)O volume of distribution showed no difference in electrical parameters. However, the slope of the regression lines (H2(18)O, H2/R) was significantly steeper for the CF subjects (p < 0.03) than for controls. These data show that BIA can be used to measure TBW in patients with CF. However, the predictive equations developed in healthy control subjects should not be used; rather, separate predictive equations for patients with CF will need to be developed.

Dietary lysine requirement of young adult males determined by oxidation of L-[1-13C]phenylalanine

Lysine requirement was determined in seven adult males by examining the effect of varying dietary lysine intake on phenylalanine flux and oxidation under dietary conditions of adequate energy and phenylalanine (14 mg.kg-1 x day-1) and excess tyrosine (40 mg.kg-1 x day-1). Phenylalanine flux was determined from primed, constant intravenous infusions of L-[1-13C]phenylalanine (1.2 mg.kg-1 x day-1) and L-[ring-2H5]phenylalanine (0.5 mg.kg-1 x day-1) and measurement of isotopic enrichments of phenylalanine in plasma. Phenylalanine flux was not affected by graded increases in dietary lysine intake or by the isotope infused. Mean phenylalanine conversion to tyrosine was low (3.4%) and not significantly affected by lysine intake. Phenylalanine oxidation, estimated from the rate of 13CO2 released in expired air during the infusion of L-[1-13C]phenylalanine, decreased linearly as lysine intake increased to a break point that was interpreted as the mean dietary lysine requirement (37 mg.kg-1 x day-1). At lysine intakes of > 37 mg.kg-1 x day-1 phenylalanine oxidation was low and constant. Plasma lysine concentrations supported this estimate of requirement. These data show that: 1) indicator amino acid oxidation can be used as a new method to determine amino acid requirements of humans and 2) the lysine requirement of adult males is three times greater than the World Health Organization recommendation of 12 mg.kg-1 x day-1.

Energy expenditure in cystic fibrosis during activities of daily living

Energy expenditure during various activities of daily living in normally nourished female adolescents with cystic fibrosis was compared with that in matched healthy control subjects. Energy expenditure at rest, during sitting and standing, and during two levels of exercise was increased significantly in patients with cystic fibrosis (122% +/- 14%) compared with control subjects (104% +/- 10%) (p < 0.05), but incremental increases from one level of activity to another did not differ. We conclude that the various activities of daily living are not responsible for increased energy needs in female adolescents with cystic fibrosis.

The effect of a high protein-low calorie diet on the energy expenditure of obese adolescents

Resting energy expenditure (REE), and body composition, as fat-free mass (FFM) and fat mass, were determined in seven obese adolescents before and after weight loss of a mean 13.5 kg on an approximately 800 kcal/d (3349 kJ), high protein reducing diet regimen. Ideal body weight decreased from 166% to 142% in 8 weeks. There were no significant changes in total body potassium (TBK), extracellular water (ECW), intracellular water (ICW) or total body water (TBW) with weight loss. The REE (kcal/d) fell from 2034 +/- 392 (8514 +/- 1641 kJ) to 1762 +/- 453 (7376 +/- 1896 kJ) with weight loss (P < 0.05). However, when the REE was expressed as kcal/body weight there was no difference between before and after weight loss, 21.4 +/- 2.8 (90 +/- 21 kJ) and 21.6 +/- 4.5 (90 +/- 19 kJ). Similarly, when REE was examined in relation to FFM (kcal/kg) before and after weight loss, there were also no significant differences: 34.6 +/- 5.1 (145 +/- 21 kJ) and 32.1 +/- 7.9 (134 +/- 33 kJ).

Cystic fibrosis: nutrition

There has been renewed interest in examining the multiple causes of undernutrition and growth failure in cystic fibrosis. It is now recognized that undernutrition is caused by unfavourable energy balance rather than an inherent component of the disease. Furthermore, there appears to be a direct association between the degree of undernutrition and the severity of pulmonary disease, which in turn affects overall prognosis. Energy imbalance may be caused by three main factors: increased energy loss because of nutrient maldigestion; reduced energy intake due to an improper diet and/or anorexia from respiratory disease, abdominal symptoms or clinical depression and increased energy expenditure with advanced lung disease. Most patients are capable of compensating for these factors; provided energy intake is sufficient, normal growth velocity and nutritional status is maintained. However, in a minority of older patients, when advanced lung disease supervenes, energy expenditure rises resulting in an energy deficit. Undernutrition, with loss of energy stores and lean tissue may in turn contribute to progressive deterioration of lung function. When this occurs, long-term invasive methods of nutritional support can restore energy balance.

Protein metabolism in obese subjects during a very-low-energy diet

We postulated that the return to nitrogen equilibrium after 3 wk of a negative balance during a very-low-calorie diet (VLCD) providing low-quality protein in obese subjects was due to availability of endogenously originating amino acids from a "pool" that, when depleted, would result in worsening balance. This should be reflected in altered kinetics of protein metabolism with the requirement for increased breakdown to maintain synthesis constant. Seven female obese subjects [body mass index (BMI) = 34.4 +/- 1.8 kg/m2] were given a 1.7-MJ/d all-protein diet (16.8 g N) derived from hydrolyzed gelatin (supplemented with tryptophan and methionine) that provides 18% of its amino acids as essential, a multivitamin-mineral supplement, and 16 mmol KCl for 42 d. At baseline (7-d isocaloric diet), and weeks 4 and 6 of VLCD, amino nitrogen flux rate was calculated from the 15N abundance in urinary urea using the oral 15N-glycine method and rates of synthesis (S) and breakdown (B) inferred from N flux. Whole-body N flux did not change from baseline to weeks 4 and 6 (39.5 +/- 2.0 vs 37.4 +/- 2.0 vs 39.2 +/- 1.9 g N/d). By contrast, S and B decreased at weeks 4 and 6 with S decreasing more so that net protein synthesis (S-B) was less positive at week 4 than at baseline (2.2 +/- 0.2 and 0.9 +/- 0.3 g N/d; P less than 0.05) and became negative at week 6 (-0.9 +/- 0.2 g N/d; P less than 0.05). Concurrently, N equilibrium was achieved by week 4 but returned to negative balance by week 6.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycine, leucine, and phenylalanine flux in low-birth-weight infants during parenteral and enteral feeding

Kinetics of three amino acids with different sites and characteristics of metabolic regulation were studied in low-birth-weight infants during enteral and parenteral feeding regimens typical of clinical practice. Primed constant infusions of [15N]glycine, L-[1-13C]leucine, and L-[1-13C]phenylalanine were administered simultaneously by the same route as the feeding, with isotope enrichment measured in urine over 12 h. The effect of feeding regimen was specific to each amino acid (mean +/- SD): glycine flux was lower during parenteral feeding (470 +/- 15 vs 561 +/- 69 mumol.kg-1.h-1, P less than 0.05), leucine flux was unaffected (360 +/- 77 vs 388 +/- 78 mumol.kg-1.h-1), and phenylalanine flux was higher (106 +/- 29 vs 56 +/- 6 mumol.kg-1.h-1, P less than 0.01). Kinetics were influenced by the interaction of several factors, including amino acid intake and routes of feeding and tracer administration. Glycine was most affected by route of feeding and phenylalanine was most affected by intake whereas leucine was little affected. Estimates of whole-body protein turnover calculated from leucine and phenylalanine were different; thus calculations of protein turnover from kinetics of a single amino acid should be interpreted with caution.

Reexamination of protein requirements in adult male humans by end-product measurements of leucine and lysine metabolism

We examined leucine and lysine metabolism in adult humans (n = 8 and n = 5, respectively) to assess the current estimate of protein requirement. Each subject consumed a controlled isoenergetic liquid diet for three 10-d periods at three intakes of protein, 0.6, 0.8 and 1.0 g.kg-1.d-1, in random order. Measurements of flux and catabolism were determined in each subject in both the fed and postabsorptive states, with a primed, 4-h continuous infusion of L-[1-13C]leucine and L-[alpha-15N]lysine. Fluxes of leucine and lysine were not affected by feeding state or protein intake. Adaptation to different protein intakes did not affect the oxidation of leucine and lysine in the postabsorptive state, but leucine oxidation was significantly higher during the fed period compared with the postabsorptive period at a protein intake of 1.0 g.kg-1.d-1 (P less than 0.05) and tended to be greater (P = 0.06) at an intake of 0.8 g.kg-1.d-1. Nitrogen balance assessed over the last 72 h of each dietary period was positive for all subjects at protein intakes of 0.8 and 1.0 g.kg-1.d-1 of protein and, hence, was consistent with the leucine oxidation data. These data suggest that experiments conducted during the postabsorptive period are not appropriate for estimating protein requirements. Leucine oxidation data obtained during the fed state estimate a protein requirement for young men of between 0.6 and 0.8 g.kg-1.d-1.

Decrease in gastric emptying time and episodes of regurgitation in children with spastic quadriplegia fed a whey-based formula

The gastric emptying times associated with three whey-based formulas were significantly shorter than that associated with a casein-based formula in nine gastrostomy-fed patients with spastic quadriplegia (p less than 0.001). Patients fed whey-based formulas had significantly fewer episodes of emesis than when they were fed casein-based formula (p less than 0.001). We conclude that whey-based formulas reduce the frequency of emesis by improving the rate of gastric emptying.

Protein turnover and resting energy expenditure in patients with undernutrition and chronic lung disease

Whole-body protein metabolism was studied in 11 undernourished cystic fibrosis (CF) patient (7 female), 12 normally nourished CF patients (3 female), 7 anorexia nervosa (AN) patients (all female), and 15 normal control subjects (9 female). Protein turnover was studied by the single dose [15N]glycine method and the cumulative excretion of labeled urinary urea and ammonia. Energy metabolism was studied by open-circuit indirect calorimetry. Contrary to previous reports, no differences were found between the protein turnover of CF groups and the normal control group. However, patients with AN had a negative net protein deposition. Resting energy expenditure was significantly reduced in AN patients and increased in CF patients. The gender of CF patients did not affect protein and energy metabolism but fat mass was higher and fat-free mass was lower in CF females.

Nutritional manipulation in the management of dumping syndrome

Two children with Nissen's fundoplication and either gastrocystoplasty or pyloroplasty developed dumping syndrome. Correction of their blood glucose abnormalities, resolution of symptoms, and weight gain were effectively achieved by addition of fats and uncooked corn starch (50 g/l) to their feeds.

The cystic fibrosis gene and resting energy expenditure

To determine whether the increase in resting energy expenditure in cystic fibrosis is associated with the primary genetic defect (delta F508) or with declining pulmonary function, or both, we tested resting every energy expenditure prospectively in 32 male subjects (aged 7 to 39 years) who were normally nourished and had good pulmonary function. They were categorized into three genotype groups on the basis of the presence or absence of delta F508 and pancreatic function. Mean resting energy expenditure was 104% of the predicted value and was not associated with genotype. When 29 subjects with normal nutritional status but variable lung function were added to the group, there was a strong correlation between declining pulmonary function and increased resting energy expenditure. We conclude that increased resting energy expenditure in normally nourished boys and men with cystic fibrosis appears to be more closely associated with declining pulmonary function than with genotype.

Nutritional rehabilitation increases resting energy expenditure without affecting protein turnover in patients with cystic fibrosis

The effect of nutritional rehabilitation on several nutritional parameters was studied in eight malnourished patients with cystic fibrosis during the first year after gastrostomy tube insertion. Body composition was studied by fat skinfold measurements and by total body potassium count, resting energy expenditure (REE) by indirect calorimeter, and protein turnover by a single dose administration of [15N]glycine. Weight gain was accompanied by a significant increase in the various body compartments: weight 41.4 +/- 7.5 to 46.1 +/- 8.4 kg (p less than 0.0002), fat body mass 5.6 +/- 2.8 to 7.7 +/- 3.4 kg (p less than 0.005) and fat-free body mass (FFBM) 35.7 +/- 6.3 to 38.3 +/- 6.9 kg (p less than 0.0003). REE increased significantly per kg of body weight as well as per kg of FFBM. No significant differences were found in protein turnover during refeeding nor in pulmonary function. We conclude that nutritional support restores body composition, but is accompanied by an increase in energy expenditure. This increase could not be attributed to increased protein turnover.

Effect of refeeding on the energy metabolism of adolescent girls who have anorexia nervosa

The effect of refeeding on resting energy expenditure (REE) and substrate utilization was studied in 18 hospitalized adolescent girls (aged 12.9-19.1 years) suffering from anorexia nervosa. Changes in body composition were monitored weekly and included weight, fat body mass (FBM), lean body mass (LBM) and total body potassium (TBK). REE was studied weekly by open-circuit calorimetry. Weight gain was noted in all patients (38.2 +/- 5.6 to 44.5 +/- 5.3 kg), involving increased FBM and LBM. REE increased per kg of weight (91.6 +/- 15.1 to 101.7 +/- 18.0 kJ kg-1 d-1) and LBM over the first weeks of refeeding (P less than 0.025) and then stabilized. Substrate utilization showed an increase in carbohydrate and protein utilization (P less than 0.001) during the first few weeks of refeeding. We also studied the thermic effect of food (TEF) in 14 of the 18 subjects. Upon admission the subjects had a reduced TEF (36.4 +/- 24.3 kJ 2 h-1) (P less than 0.001). With refeeding TEF rose to a peak or plateau, then decreased to normal levels (61.9 +/- 36.0 kJ 2 h-1) before discharge from hospital. We conclude that the energy metabolism of adolescent girls adapts to semi-starvation by a reduction in both REE and TEF; with refeeding there is reversal of this adaptive function.

Phenylalanine flux, oxidation, and conversion to tyrosine in humans studied with L-[1-13C]phenylalanine

Phenylalanine metabolism was determined in 41 studies of adult males (n = 10) consuming an energy-sufficient diet and receiving graded levels of dietary phenylalanine and excess tyrosine (40 mg.kg-1.day-1). After a dietary adaptation period to either 4.2 or 14.0 mg.kg-1.day-1 of phenylalanine; flux, plasma concentration, oxidation, and conversion to tyrosine were measured at test phenylalanine intakes of 5, 7, 10, 14, 21, 28, or 60 mg.kg-1.day-1. Oxidation was low and constant (1.3 mumol.kg-1.h-1) at intakes at or below 10 mg.kg-1.day-1 and increased linearly above this level. Conversion to tyrosine was minimal (2.1%) at these intakes. Breakpoint analysis showed the phenylalanine requirement with excess tyrosine to be 9.1 mg.kg-1.day-1. Plasma phenylalanine concentrations confirmed this estimate of requirement. Prior adaptation did not significantly affect overall flux, plasma concentration, or oxidation nor did it affect the requirement estimate. With the assumption that tyrosine can supply two-thirds of the aromatic amino acid requirement, these data suggest that the aromatic amino acid requirement should be 30 mg.kg-1.day-1 and the World Health Organization recommendation of 14 mg.kg-1.day-1 is an underestimate.

Urine collection as an alternative to blood sampling: a noninvasive means of determining isotopic enrichment to study amino acid flux in neonates

The validity of measuring isotopic enrichment of amino acids in urine was tested in neonates during different feeding regimens and tracer administration protocols, and with different amino acid tracers. Twenty infants, fed enterally or parenterally, were given primed, constant infusions of 15N-glycine, L-[1-13C]leucine, and L-[1-13C]phenylalanine. Urine was collected every 2 h for 16 h. Blood was sampled only when required clinically. At baseline, enrichment in plasma and urine did not differ for any amino acid. At isotopic steady state, leucine enrichment was similar in plasma and urine, while the agreement was slightly weaker for glycine and phenylalanine, probably because of problems inherent in drawing blood samples from neonates. Study protocol did not affect the agreement. Since urine collection involves minimal invasive procedures, this approach could facilitate more indepth tracer studies in infants and children.

Development of a heating device for sampling arterialized venous blood from a hand vein

A practical and safe heating device for sampling arterialized venous blood from a hand vein was constructed and tested under experimental conditions. Blood chemistry values (pH, pCO2, pO2 and O2 saturation) were measured in nine individuals from blood sampled from an antecubital vein and a hand vein, as well as from a hand vein that had been heated in the handwarmer. Only blood sampled from the heated hand vein gave blood gas values that were consistently in the arterial range. Mean blood gas values were 38.0 +/- 2.5 mmHg, 79.8 +/- 6.8 mmHg and 95.7 +/- 0.9% for pCO2, pO2 and O2 saturation, respectively, for blood sampled from the heated hand vein. No significant difference (P greater than 0.05) was evident in blood gas values whether blood was sampled 15, 30, 45, 60, 75 or 90 min after placing the hand in the heated handwarmer. The handwarmer enables arterialized venous blood sampling after 15 min of warming and is safe to use in any experimental or clinical situation where sampling from an artery is impractical.

Body compartment changes in sick children

Our studies showed that there are important changes in body composition in children in response to dieting and refeeding. Similarly, we showed changes in body composition in response to renal transplantation, which would be expected to restore more normal homeostasis, but in its early phases changes in body composition are complicated by the use of high doses of drugs, notably steroid. Some of the changes in body composition can be predicted from changes in weight but the majority cannot. Relatively simple measurements like the four skinfolds as a means of determining body fat are surprisingly accurate, except in extremely obese subjects. Similarly, the measurements of fat free body mass are useful. However, this measurement does not discriminate changes within fat free body mass in the proportions of body cell mass versus extracellular mass. Similarly, none of these measurements provide any information regarding the composition of body cell mass with regard to its potassium and protein content (as reflected by total body nitrogen). The main drawback with total body nitrogen measurements is the radiation exposure. Thus, we have had to limit the inclusion of total body nitrogen measurements. It has been estimated that two total body nitrogen measurements provide a gonadal dose of radiation roughly equivalent to that experienced by an individual living in a large North American city, that means 30 to 50 mREM per each total body nitrogen measurement. It becomes ethically possible then to carry out nitrogen measurements where it can be argued that their measurement is essential in monitoring the safety and well being of the subject; or alternatively if the subject's life expectancy is limited.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of the Higgins Nutrition Intervention Program on birth weight: a within-mother analysis

A study was conducted to evaluate the impact of the Higgins Nutrition Intervention Program of individual nutritional assessment and rehabilitation on pregnancy outcome in a group of urban low-income women. Developed as an adjunct to routine prenatal care, the Higgins program utilizes an individualized approach to dietary treatment that combines an assessment of the risk profile for the presenting pregnancy with the application of specific nutritional rehabilitation allowances to compensate for the negative impact of diagnosed risks. This report presents results of analyses evaluating differences in birth outcomes between 552 sibling pairs; each mother had participated in the Higgins program during the pregnancy of the second-born, but not of the first-born, member of her pair. After adjustment for parity and sex, the intervention infants weighed an average of 107 gm more than their matched siblings at birth (p less than .01). The rate of low birth weight was 50% lower among the intervention infants than among their siblings (p less than .01); rates of intra-uterine growth retardation and perinatal mortality were also lower in the intervention group. The high risk of poor pregnancy outcome in this group of urban low-income women was reduced by the Higgins program.

Energy metabolism in children with newly diagnosed acute lymphoblastic leukemia

The effect of tumor burden in acute lymphoblastic leukemia on resting energy expenditure, thermic effect of food, and substrate utilization was investigated with open-circuit indirect calorimetry after an overnight fast. Nine patients (six females, three males) ages 6.5 to 15.8 y were studied. Patients were divided into two groups according to their tumor burden at diagnosis (i.e. white cell count, presence or absence of mediastinal mass, or massive organomegaly). The patients with a greater tumor burden had increased energy expenditure. Their resting energy expenditure returned to normal in response to chemotherapy. These results must be interpreted with caution due to the small patients numbers (high tumor burden n = 3; low tumor burden n = 6). Substrate utilization was altered by chemotherapy with an increase in carbohydrate utilization and a decrease in fat oxidation (p less than 0.009). The magnitude of the thermic effect of food tended to increase on treatment (p less than 0.016). Inasmuch as most chemotherapy programs for children last up to 3 y, we believe it is important that the effects of chemotherapy on intermediary metabolism be studied, particularly in relationship to any possible permanent effects on growth and development.

Effect of replacing glucose with lipid on the energy metabolism of newborn infants

1. Indirect calorimetry and primed constant infusion of [U-13C]glucose were combined in 28 appropriate-for-gestational age newborn, parenterally fed infants, in order to measure glucose utilization and glucose oxidation and to estimate lipogenesis from glucose. 2. The infants were randomly allocated to either a group receiving glucose as the non-protein energy source or a group having one-quarter of the glucose energy replaced by intravenous fat. The energy intake (370 kJ day-1 kg-1) and protein intake (3.4 g day-1 kg-1) were similar in both groups. 3. Energy expenditure (P less than 0.005), non-protein carbon dioxide production (P less than 0.005) and non-protein oxygen consumption (P less than 0.05) were lower in the lipid-supplemented group. 4. The significant excess of glucose utilization over oxidation (P less than 0.001) can be accounted for by lipid synthesis from glucose. 5. Fat synthesis from glucose was higher in the glucose/amino acid group (P less than 0.02), but total fat storage was higher in the lipid-supplemented group (P less than 0.02). Nitrogen balance was similar in both groups. 6. As lipogenesis from glucose is an energy- and oxygen-consuming and a carbon dioxide-producing process, the data suggest that the differences between the glucose-only group and the lipid-supplemented group are due to different rates of lipogenesis from glucose.

A reappraisal of protein turnover values in neonates fed human milk or formula

We investigated the effect of human milk feeding on the nitrogen metabolism of appropriate-for-gestational age infants of birth weight 1.5-2.0 kg. Eight infants received pooled mature human milk. The remaining 20 were divided into two equal groups, who received one of two low-protein, milk-based formulae. The formulae were identical in composition except for the protein source, which was either casein- or whey-predominant. The three diet groups received similar total nitrogen (390 mg N.kg-1.d-1) and energy (500 kJ.kg-1.d-1) intakes. The human-milk-fed group, however, received a significantly higher intake of nonprotein and urea nitrogen and a significantly lower true protein nitrogen. Nitrogen metabolism was studied using a modified constant infusion of [15N]glycine, mixed with the feeding every 2-3 h. Urine was collected in approximately 3-h aliquots and analysed for total ammonia and urea nitrogen. Excretion of the 15N label was measured in urinary urea and ammonia. No differences were seen between the three diet groups in total [15N]urea or [15N]ammonia urinary excretion. However, the concentration of 15N in urinary urea in the human-milk-fed group was lower than in the two formula-fed groups. This reduction in concentration appeared due to a higher dietary intake of urea among the human-milk-fed group, and the consequent dilution of the label in the urine. As a result, protein turnover rates calculated from the [15N]urea end product were artificially raised in the milk-fed group, and were significantly higher than those in the formula groups.(ABSTRACT TRUNCATED AT 250 WORDS)