Metabolic Balance Studies Research Articles

Calcium, copper, iron, magnesium and zinc utilization of humans as affected by consumption of black, decaffeinated black and green teas

The objective of the study was to compare effects of black, decaffeinated black and green teas on the utilization of calcium, copper, iron, magnesium and zinc in young adults. Minerals were quantitated using atomic absorption techniques. A 56-d metabolic balance study was divided into four experimental treatments arranged in a randomized crossover design during which no black, decaffeinated black or green tea was consumed. Subjects (five females and four males) consumed a laboratory controlled diet low in the above minerals. The subjects received the same diet, except for the teas, during all treatments. Initial hematologic measurements indicated that subjects had normal iron status. For calcium, copper, magnesium and zinc, no significant differences were found in intake, fecal, urinary and balance values by gender, treatment or gender-by-treatment. Some small, but significant differences were observed by gender for urinary iron values. Iron balance values of both genders were significantly more negative (P < .05) in the green tea treatment than other treatments; no differences were observed by gender. No differences occurred in intake and fecal iron values by gender, treatment or gender-by-treatment. Overall, with few exceptions, these teas did not affect the calcium, copper, iron, magnesium and zinc balances of young adults fed diets low in these minerals.

Conjugated bile acid replacement therapy for short-bowel syndrome

Background & Aims: Although fat malabsorption in the short-bowel syndrome is caused in part by decreased bile acid secretion, bile acid replacement therapy is not used because of the belief that ingested bile acids would worsen diarrhea, outweighing the benefits of improved fat absorption. This study compared the effect of a natural conjugated bile acid mixture from ox bile with that of cholylsarcosine, a synthetic conjugated bile acid, on fat absorption and diarrhea in a patient with the short-bowel syndrome. Cholylsarcosine is resistant to bacterial metabolism and has no cathartic activity. Methods: Metabolic balance studies and a clinical trial were performed in an emaciated patient with the short-bowel syndrome and ileostomy in whom parenteral nutrition could not be used. Results: In balance studies, conjugated bile acid replacement therapy with either preparation caused fat absorption to increase by approximately 40 g/day. Calcium absorption also increased. Neither bile acid product caused a clinically significant increase in ileostomy water output. During a 4-month outpatient trial, while the patient ingested 2 g/meal natural bile acids, her weight increased from 80 to 98 lb, without side effects. Conclusions: Conjugated bile acid replacement therapy should be part of the armamentarium for the treatment of selected patients with the short-bowel syndrome. GASTROENTEROLOGY 1999;116:15-21

Zinc Metabolism in Patients with Exocrine Pancreatic Insufficiency

Objective: Metabolism of zinc was studied by administering radioactive zinc (Zn65), and by performing metabolic balance studies in eight patients with exocrine pancreatic insufficiency and eighteen control subjects.Methods: Retention of radioactive zinc was measured by total body counter, and its urinary and fecal excretion by gamma scintillation counter. Metabolic balance studies were carried out by measuring dietary zinc intake as well as fecal and urinary excretion of zinc by atomic absorption spectrophotometry in this group of patients.Results: These studies revealed a 50% reduction in intestinal absorption of Zn65 in patients with exocrine pancreatic insufficiency as compared to alcoholic and non-alcoholic control subjects. In addition, there was a 2 to 4 fold increase (p<0.05) in urinary excretion of zinc in subjects with pancreatic disease. In pancreatic insufficiency, reduced zinc absorption and increased urinary zinc excretion were balanced by lower (p<0.05) endogenous excretion of zinc as evidenced by reduced excretion of Zn65 in feces during the second 4-day period. The mean biological half-life of Zn65 tended to be lower in patients with pancreatic insufficiency as compared to alcoholic control subjects, however the difference did not reach statistical significance.Conclusion: These observations indicate marked alterations in zinc metabolism in patients with advanced chronic pancreatic disease and provide greater insight into development of zinc deficiency in this group of patients.

Absorption of Fat and Calcium by Infants Fed a Milk-Based Formula Containing Palm Olein

Objective: The study tested the hypothesis that inclusion of palm olein (45% of fat) in the fat blend of a milk-based infant formula decreases the absorption of fat and calcium.Methods: Formula PO contained palm olein (45%) in addition to soy, coconut and high-oleic sunflower oils (20%, 20%, and 15%, respectively); Formula HOS contained high-oleic safflower oil (42%) in addition to coconut and soy oils (30% and 28%, respectively) and no palm olein. Fat and calcium levels in the two formulas were similar. In a balanced crossover design, fat and calcium absorption were determined in 10 normal infants ranging in age from 22 to 192 days. In three infants metabolic balance studies with complete separation of urine and feces were performed, whereas in seven infants excreta were in part collected at home, resulting in incomplete separation of urine and feces.Results: Mean (±SD) fecal excretion of fat was higher when Formula PO was fed than when Formula HOS was fed (0.55±0.29 vs. 0.09±0.04 g/kg/day; p<0.001). Hence % fat absorption was lower with PO than with HOS (90.0±6.4 vs. 98.5±0.6% of intake; p<0.01). The difference in percent fat absorption was explained by significantly (p<0.05) lower % absorption of palmitic (16:0) and stearic (18:0) acids when Formula PO was fed than when Formula HOS was fed. Fecal excretion of calcium was higher with Formula PO than with Formula HOS (53.4±12.0 vs. 37.4±14.9 mg/kg/day; p<0.01), and hence % calcium absorption was lower with Formula PO than with Formula HOS (37.5±11.5 vs. 57.4±14.9%; p<0.001).Conclusion: Absorption of fat and calcium by normal infants is lower when palm olein provides a substantial proportion of formula fat than when formula does not contain palm olein.

Urinary acidification and net acid excretion in adult rats treated neonatally with enalapril.

Neonatal blockade of the renin-angiotensin system in rats induces irreversible renal histological abnormalities, including papillary atrophy and an impaired urinary concentrating ability. The aim was to investigate urinary acidification and net acid excretion in adult Wistar rats treated neonatally with enalapril (10 mg . kg-1 . day-1) or vehicle from 5 to 24 days of age. Analyses were performed in both metabolic balance studies and renal clearance experiments performed under pentobarbital sodium anesthesia. There were no differences between groups in urine pH or urinary excretion rates of bicarbonate, titratable acid, or ammonium, neither during control conditions nor after chronic NH4Cl loading (assessed before and after Na2SO4 infusion). Glomerular filtration rate, maximal tubular bicarbonate reabsorption, and the urine-to-blood PCO2 gradient in alkaline urine during NaHCO3 infusion did not differ between groups. Neonatally enalapril-treated rats showed a urine concentration defect and papillary damage. In conclusion, neonatal enalapril treatment produces a differentiated abnormality in tubular function in which urine concentration is impaired but urinary acidification and net acid excretion are intact.

Trace mineral balance in acute diarrhea of infants. Association to etiological agents and lactose content of formula

We studied zinc and copper losses during dehydrating acute diarrhea requiring hospitalization, in relation to etiological agents and lactose content of formula, in previously healthy infants. We analyzed 39 male infants, 2–10 mo of age, infected with rotavirus(Rt, n=21) or enteropathogenic E. coli (EPEC, n=18). Metabolic balance studies were carried out during the initial 48 h. (Period 1) and on days 6 and 7 after admission (Period 2). All patients were offered oral rehydration solution (Na 90 mEq/L); refeeding began within 4 h of admission. The infants were randomly assigned to a cow's milk based formula (F I) or to the same formula with previous lactose digestion (F II). Fecal Zn losses were greater than intake and Zn balance was not significantly different in Rt and EPEC infected infants fed any formula, during P1; apparent mean zinc absorption was over 76% in all the groups during P 2. Zn retentions were, during P1: Rt, F I −53± 39.2, Rt, F II −43± 42.1; EPEC, F I −27± 21.6, and EPEC, F II −39± 56.5 μg/kg/d. Fecal Cu losses decreased from P1 to P2 (p<0.01). Cu retentions remained negative during P 1 and P2. No differences attributable to the diarrheal agents were observed in plasma Zn and Cu levels, but plasma Zn increased from P 1 to P 2 among infants infected with rotavirus and fed lactose formula. We conclude that the considerable Zn and Cu losses for infants with acute diarrhea due to rotavirus and treated with ORS solution and early refeeding, are not different from those of infants infected with enteropathogenic E. coli and treated similarly. Copper balances remain negative during recovery from diarrhea. The lactose content of the formula influences plasma zinc and plasma copper levels of infants with acute diarrhea due to rotavirus.

Calcium, Copper, Iron, Magnesium and Zinc Utilization of Humans as Affected by Consumption of Black, Decaffeinated Black and Green Teas

LEARNING OUTCOME: The black, decaffeinated black and green teas had little, if any, influence on the subjects’ utilization of calcium, copper, iron, magnesium and zinc. Controversy exists as to the nutritional effects of tea. Both beneficial and detrimental nutritional effects have been demonstrated in animal and human studies. The objectives of the study were to compare effects of black, decaffeinated black and green teas on the utilization of calcium, copper, iron, magnesium and zinc in young adults. All minerals were quantitated using atomic absorption techniques. A 56-day metabolic balance study was divided into four experimental treatments arranged in a randomized crossover order during which no, black, decaffeinated black or green teas were consumed. International students (five females and four males) consumed a laboratory controlled diet low in the above minerals. The subjects received the same diet, except for the teas, during all treatments. Initial hematologic measurements indicated that subjects had normal iron status. For calcium, copper, magnesium and zinc, no significant differences were found in intake, fecal, urinary and balance values by gender, treatment or gender-by-treatment interactions. For urinary iron values, significant (P<0.05) or near significant (P=0.07) differences by gender were observed in all treatments. Iron balance values of both genders were significantly higher (P<0.05) in the green tea than in other treatments. No significant differences were observed in intake and fecal iron values by gender, treatment or gender-by-treatment interactions or in urinary and balance iron values by sex. Overall, with few exceptions, these teas did not affect the calcium, copper, iron, magnesium and zinc balances of young adults fed diets low in these minerals.

Mineral balance of rats fed on diets containing sweet lupin (Lupinus angustifolius L.) or its fractions

Metabolic balance studies were conducted in growing rats to investigate the effect of Lupinus angustifolius (sweet lupin) seed meal and its fractions on the balance of calcium, phosphorus, magnesium, potassium, sodium and apparent absorption of zinc. Diets contained: unsupplemented lupin seed meal (LMU); lupin seed meal, fully supplemented with essential amino acids to fulfil the target requirements for growing rats, at 360 g kg−1 diet (LMFS); aqueous non-dialysed and soluble protein fraction (LPAND); aqueous lupin seed meal extract, dialysed and soluble at pH 7.0, at 148 g kg−1 (LPAD); aqueous extract, dialysed and insoluble at pH 7.0, at 124 g kg−1 (LPADI); buffer dialysed and soluble at pH 7.0, at 136 g kg−1 (BUSOL); buffer dialysed and insoluble at pH 7.0 at 119 g kg−1 (BUDI); lupin meal residue after aqueous and buffer extraction, at 170 g kg−1 diet (LMR). Rats were pair-fed for 10 days with the above diets which had been supplemented with essential amino acids up to the target requirements for growing rats. As the diets differed in mineral composition, an increase in intake resulted in higher apparent absorption and faecal excretion. The inclusion of LMU and its protein and fibre (LMR) fractions in the diet had significant effects on the mineral content of the faeces and on mineral balance. The relatively low concentration of phytates in seed meal and the LPAND fraction (5.3 and 3.5 g kg−1, respectively) and its absence in LPAD, LPADI, BUSOL, BUDI and LMR fractions could not adequately explain the increased mineral excretion. The results suggest that lupin protein is involved in the elevated loss of minerals associated with long-term effects of this seed as a protein source in non-ruminants. The fibre fraction (LMR) was regarded as a modest metal binder compared with the proteins and may be used as a new source of dietary fibre; however, further work is warranted.

CONTRIBUTION OF DIET; HUMAN MILK FORTIFIER OR PRETERM FORMULA IN THE OCCURENCE OF OSTEOPENIA IN VLBW INFANTS

Background: For bone formation, an adequate intake of protein and energy is first required for collagen matrix synthesis whereas an ample supply of calcium and phosphorus is necessary to adequate mineralisation. Metabolic and energy balance studies suggest that feeding human milk fortifier (HMF) induces a slower growth rate but a higher Ca retention compared to preterm formula (PTF). Presently, dual energy X-ray absorptiometry (DXA) measurements of bone mineral content (BMC) and of bone projected area (BA) allow to estimate bone growth as well as mineral accretion. Population and method: From two DXA measurements, using an Hologic QDR 2000 Infants Whole body Software V 5.65, gain in weight, BMC and BA, and change in volumetric bone mineral density (VBMD=BMC/BA1.5) were determined in VLBW infants. Two DXA measurements were performed during hospital stay in 34 VLBW infants fed HMF (n=10) or PTF (n=24) and after discharge in 16, either osteopenic (VBMD=9.1±0.6;n=8), either non osteopenic (VBMD=10.2±0.3;n=8), VLBW infants fed term formula. Table Results: During the early study, weight gain and bone growth were significantly higher in VLBW infants fed PTF. By contrast, bone mineralisation were significantly higher in VLBW infants fed HMF. After discharge, weight gain and bone growth were similar in the osteopenic and non-osteopenic groups. However, bone mineralisation was significantly higher in osteopenic than in non-osteopenic group. In conclusion: In VLBW infants, the use of PTF seems to be a contributive factor of osteopenia, inducing a larger bone growth but a lower mineral deposition. Nevertheless, after discharge a catch-up mineral accretion is observed in osteopenic preterm infants. Thus, in preterm infants, growth and mineralisation appear as two distinguishable phenomena which can be evaluated with DXA.

Role of Etiology on the Clinical and Nutritional Outcomes of Acute Diarrhea

244 male infants were admitted for studies on dietary therapy of acute diarrhea. All patients had complete history and physical exams, anthropometrics, and extensive laboratory tests, including stool studies for virus, bacteria and parasites and metabolic balance studies. Rehydration and replacement of ongoing losses were carried out following WHO guidelines. Feeding was started after 4-8 hours rehydration. Antibiotics were given for proven Shigella or Campylobacter. Giardia was treated on day 7. Treatment failures defined as recurrence of dehydration, and severe or prolonged diarrhea, were treated individually. Patients were grouped by etiological agent to compare initial presentation and clinical and nutritional outcomes. Covariance analysis was used to correct the effect of confounding variables not associated to etiology; then discrete and continuous variables were compared by chi square and ANOVA, respectively. Patients were divided in 6 groups: ETEC: 31(13%), EPEC: 29(12%), RV: 23(9%), other bacteria: 24(10%), mixed infections: 70(29%) and no pathogens: 67 (27%). Diarrhea duration before admission was longer in the EPEC group and shorter in RV patients, who also had more vomiting, dehydration and acidosis. There were no differences in frequency of failures according to etiology. Diarrhea duration was shorter for the RV group and longer with the ETEC group. Stool output was higher for the RV and mixed groups and lower for the “none” group on the first 2 days. Likewise, nitrogen, fat, carbohydrate and energy absorption and nitrogen retention were lower for the RV, other, and mixed groups during the first 2 days. Begining on day 3 there were no differences among the etiological groups regarding stool volume and nutrient absorption. Neither there were differences regarding changes in weight, skin fold thickness or serum albumin, from day 1 to day 7. Conversely, weight and skin folds increments correlated strongly with total energy intake.

Comparison of ground-based and space flight energy expenditure and water turnover in middle-aged healthy male US astronauts

Energy requirements during space flight are poorly defined because they depend on metabolic-balance studies, food disappearance, and dietary records. Water turnover has been estimated by balance methods only. The purpose of this study was to determine energy requirements and water turnover for short-term space flights (8-14 d). Subjects were 13 male astronauts aged 36-51 y with normal body mass indexes (BMIs). Total energy expenditure (TEE) was determined during both a ground-based period and space flight and compared with the World Health Organization (WHO) calculations of energy requirements and dietary intake. TEE was not different for the ground-based and the space-flight periods (12.40 +/- 2.83 and 11.70 +/- 1.89 MJ/d, respectively), and the WHO calculation using the moderate activity correction was a good predictor of TEE during space flight. During the ground-based period, energy intake and TEE did not differ, but during space flight energy intake was significantly lower than TEE; body weight was also less at landing than before flight. Water turnover was lower during space flight than during the ground-based period (2.7 +/- 0.6 compared with 3.8 +/- 0.5 L/d), probably because of lower fluid intakes and perspiration loss during flight. This study confirmed that the WHO calculation can be used for male crew members' energy requirements during short space flights.

Palm olein in infant formula: absorption of fat and minerals by normal infants

Palm olein, a low-melting fraction of palm oil, and soy oil can be combined to obtain fat blends with proportions of palmitic and oleic acids similar to those of human milk. We compared the absorption of fat and calcium by infants fed a formula containing a blend of palm olein (53%) and soy oil (47%) (Formula PO/S) with that by infants fed a formula containing a blend of soy oil (60%) and coconut oil (40%) (Formula S/C). In a randomized crossover design, one study was performed with each formula in each of 11 normal infants ranging in age from 27 to 161 d. Six of the infants were admitted for 72-h metabolic balance studies. In the other five infants, feces (with some admixture of urine) were collected at home for 96 h by using acid-washed cloth diapers. Mean (+/- SD) absorption of fat was 90.6 +/- 1.6% of intake when Formula PO/S was fed and 95.2 +/- 1.1% of intake when Formula S/C was fed; the difference was significant (P < 0.001). The difference in excretion of fat by infants fed the two formulas was explained by the difference in excretion of palmitic acid. Absorption of calcium averaged 39.0 +/- 8.3% of intake with Formula PO/S and 48.4 +/- 10.3% with Formula S/C; the difference was significant (P < 0.01). We conclude that fat is less well absorbed from a mixture of 53% palm olein and 47% soy oil than from a mixture of 60% soy oil and 40% coconut oil, and that absorption of calcium is less from a formula containing palm olein, presumably because of the formation of insoluble calcium soaps of unabsorbed palmitic acid.

Dose-dependent metabolism of carbamazepine in humans.

48-h steady-state metabolic balance studies were carried out in 17 adults receiving long-term anticonvulsant monotherapy. With increasing carbamazepine dosage (1) carbamazepine overall plasma apparent clearance (CL/F), (2) plasma clearance of carbamazepine to urinary carbamazepine-10,11-epoxide, (3) plasma clearance of carbamazepine-10,11-epoxide to urinary unconjugated carbamazepine-10,11-trans-diol and (4) plasma clearances of carbamazepine to urinary 2- and 3-hydroxy carbamazepine all increased. However, with increasing carbamazepine dose there was no increase in the clearance of carbamazepine to (5) its acridan derivative in urine or of (6) the diol, phenolic or acridan metabolites to their metabolically subsequent conjugates excreted in urine. These findings are consistent with ongoing dose-dependent autoinduction of carbamazepine metabolism along the first two stages, but not the final stage, of the epoxide-diol pathway and, to a lesser extent, along pathways yielding phenolic metabolites. However, conjugations of the various plasma phase I metabolites of carbamazepine are not dose-dependent. Plasma concentration ratios of substances involved in consecutive stages of the epoxide-diol pathway, as in previous published studies, suggested apparent dose dependence of the epoxide-->unconjugated diol stage only. Presumably, increased flux along the first two stages of the full epoxide-diol pathway reduces plasma carbamazepine and carbamazepine-10,11-epoxide concentrations largely in parallel, concealing the dose dependence of the conversion of carbamazepine to its epoxide.

Absorption of Macronutrients from a Calorie‐Dense Diet in Malnourished Children during Acute Shigellosis

SummaryA metabolic balance study was performed to determine the absorption of macronutrients and energy from different food items in 23 malnourished children aged 12 to 48 months with clinically severe acute dysentery due to shigellosis. In a 72‐h balance period, the absorption of carbohydrate, protein, fat, and total energy was determined. All the children received a standard hospital diet; 12 children in the test group were offered an additional calorie‐dense milk (5.0 kJ/ml with a protein‐energy ratio of 11.0), and 11 children in the control group, on the other hand, received a milk formula with an energy of 2.5 kJ/ml with a protein‐energy ratio of 11.0. The intakes (g/kg/day) of protein, fat, carbohydrate, and energy between test and control groups were 4.25 versus 2.32 (p = 0.01), 7.63 versus 3.00 (p = 0.01), 21.09 versus 11.14 (p = 0.01), and 711 kJ/kg/day versus 338 kJ/kg/day (p = 0.01), respectively. The coefficients of absorption of protein, fat, carbohydrate, and energy between test and control groups were 61 versus 67% (p = 0.45), 69 versus 82% (p = 0.11), 77 versus 86% (p = 0.13), and 72 versus 82% (p = 0.13), respectively. The losses (g/kg/day) of protein, fat, carbohydrate, and energy between the two groups were 1.61 versus 0.76 (p = 0.00), 2.44 versus 0.55 (p = 0.00), 5.0 versus 1.6 (p = 0.00), and 204 kJ/kg/day versus 60 kJ/kg/day, respectively. The results of this study indicate that during the acute stage of shigellosis (with a substantially enhanced total intake of protein, fat, carbohydrate, and energy), by adding calorie‐dense meals in malnourished children younger than 5 years, the absorption of macronutrients is not significantly different from that with the usual diet but suboptimal dietary energy intake, as is the case under ordinary treatment conditions.

Small bowel necrosis associated with postoperative jejunal tube feeding CD SCHUNN, JM DALY University of Pennsylvania School of Medicine, Philadelphia

Small bowel necrosis associated with postoperative jejunal tube feeding CD SCHUNN, JM DALY University of Pennsylvania School of Medicine, Philadelphia

Influence of age on energy requirements

The effects of aging on energy requirements and energy expenditure were investigated in 35 healthy young men (mean +/- SE age, 22.7 +/- 0.6 y) and elderly men (68.0 +/- 1.5 y). Over a 10-d metabolic balance study, measurements were made of metabolizable energy intake for weight maintenance, total energy expenditure, resting energy expenditure, and thermic effect of feeding. Values for both metabolizable energy intake and total energy expenditure were significantly higher than the current recommended dietary allowance for energy in both age groups (P < 0.01). Total energy expenditures were 14.48 +/- 0.65 and 11.26 +/- 5.40 MJ/d in young and elderly men, respectively. The difference in total energy expenditure between the groups was accounted for by a significant decrease in all the major components of expenditure. These results suggest that the current recommended dietary allowances for energy may underestimate the usual energy needs of healthy adult men.

Measurement of fecal carbohydrate in human metabolic balance studies: Calculated versus determined

Fecal carbohydrate in human metabolic balance studies is normally determined using a calculation method where fecal energy (kcal) from protein and fat is subtracted from total fecal energy, and divided by 4.1 kcal/g, the heat of combustion of carbohydrate. This method, however, has not been validated. In this study fecal carbohydrate in 17 preschool children, consuming diets containing cassava, amaranth, maize, or a casein control diet, was determined analytically as fiber and starch. A correlation coefficient of r=0.856 (P<0.001) was found when comparing the two methods, thus, supporting the use of the calculation method. Mean calculated fecal carbohydrate slightly underestimated actual values in the cassava group (17.6 vs. 20.3 g/day) and slightly overestimated values in the amaranth group (12.3 vs. 8.3 g/day), though this was not considered a significant problem.

Treatment of malnourished CAPD patients with an amino acid based dialysate

Nineteen malnourished chronic peritoneal dialysis patients who were ingesting a low protein intake underwent metabolic balance studies to test whether a dialysate that contained amino acids would improve their protein nutrition. Patients lived in the hospital for 35 days while they ate a constant diet and underwent their usual regimen of continuous ambulatory peritoneal dialysis (CAPD). The first 15 days served as a Baseline Phase. For the last 20 days, the usual dialysate was substituted with a dialysate of essentially the same composition except that it contained 1.1% essential and nonessential amino acids and no glucose. Patients received one or two dialysate exchanges with amino acids each day depending on the amount necessary to bring the individual's dietary protein plus dialysate amino acid intake to 1.1 to 1.3 g/kg body weight/day. During Baseline, patients were in neutral nitrogen balance; net protein anabolism was positive, as determined from 15N-glycine studies. After commencing intraperitoneal amino acid therapy, nitrogen balance became significantly positive, there was a significant increase in net protein anabolism, the fasting morning plasma amino acid pattern became more normal, and serum total protein and transferrin concentrations rose. Patients generally tolerated the treatment well, although some patients developed mild metabolic acidemia. These findings indicate that a dialysate containing amino acids may improve protein malnutrition in CAPD patients ingesting low protein intakes.

Metabolic Balance Studies in Premature Infants

Many investigators over the past three decades have successfully conducted traditional metabolic balance studies in efforts to determine the retention rates of key nutrients important to the optimal growth of preterm infants. Differences in methodologies discussed in this review may explain the inconsistent results of balance studies reported for some nutrients, particularly calcium. These methodologic differences include (1) variability in nutrient intake and nutritional course prior to the balance period, (2) differences in the method of stool collection (with and without markers), (3) use of single versus repeated balance periods, and (4) different durations of balance periods. The data presented here suggest that the variability of net fat absorptions among VLBW infants was decreased when an acclimation period of nutrient intake supportive of growth was provided prior to a metabolic balance study. In addition, the use of markers affected the estimates of net calcium absorption but not fat absorption. Additional factors that may influence net calcium absorption and methods for the estimation of calcium absorption in VLBW infants warrant further investigation. This review describes the methods of specimen collection for metabolic balance studies in VLBW preterm infants that demonstrated reproducible data. The recent application of stable isotope methodology to metabolic balance studies can be extremely advantageous in identifying the rates of nutrient absorption versus endogenous secretion in the GI tract.

Mineral balance and whole body bone mineral content in very low‐birth‐weight infants

Fat and mineral metabolic balance studies were performed in 25 normal very low-birth-weight infants (< or = 1500 g at birth) fed either pooled pasteurized human milk supplemented with calcium, phosphorus and magnesium, or a preterm formula. Calcium, phosphorus and magnesium intake were similar in both groups and averaged 100 mg/kg/day, 72 mg/kg/day and 8 mg/kg/day, respectively. Calcium and phosphorus retention was higher in the subjects fed fortified human milk than in those receiving a preterm formula (65 +/- 14 and 62 +/- 9 mg/kg/day versus 55 +/- 12 and 47 +/- 7 mg/kg/day respectively). The difference was only significant for phosphorus. Magnesium retention was similar in the two groups and averaged 3 mg/kg/day. Fat intake and absorption was significantly higher in the preterm formula fed group than in the one fed fortified human milk (5.5 +/- 0.4 g/kg/day and 88 +/- 4% versus 4.2 +/- 1 g/kg/day, 79 +/- 6% respectively). Assessment of the whole body bone mineral content by dual energy X-ray absorptiometry was performed at 3 and 6 months of age in another group of 25 low-birth-weight infants fed either fortified human milk or a preterm formula. Whole body bone mineral content (BMCt) was low (43.3 +/- 30.8 g of hydroxyapatite) at 3 months of age (theoretical term) compared to normal full-term newborns at birth. There was no significant influence of the diet. At 6 months of age, BMCt reached 168.6 +/- 36.6 g, a value similar to that of full-term newborns, with no significant difference between the two regimen groups.(ABSTRACT TRUNCATED AT 250 WORDS)