The effects of surgery on the nitrogen metabolism of parenterally fed human neonates

Nitrogen retention and rates of whole body amino nitrogen flux, protein synthesis, and breakdown were measured in 18 neonates during the 72 h immediately postsurgery. The infants were all intravenously fed with a crystalline amino acid source (Vamin), glucose, and Intralipid The infants were divided into two groups based on amino acid intake: either 2.3 SD 0.4 g or 3.9 SD 0.5 g/kg/day. Nonprotein energy intakes were similar and averaged 81 kcal/kg/day. Group A (n = 11) retained 145 SD 110 mg N/kg/day, whilst group B (n = 7) retained 315 SD 93 mg N/kg/day (p less than 0.001). There were no differences seen in flux, synthesis or breakdown. However, group B had significantly higher net protein synthesis rates (synthesis-breakdown) (p less than 0.01). The improved nitrogen utilization in group B was achieved principally by a reduction in endogenous protein breakdown. There were no differences between the two groups in urinary creatinine or 3-methylhistidine excretion. Since these two parameters reflect skeletal muscle turnover the differences between groups in nitrogen retention and turnover appear to be mediated through visceral protein.     

Whole body protein turnover measured with 13C-leucine and energy expenditure in preterm infants

Our study was undertaken in preterm infants to examine the relationship of whole body protein kinetics with protein intake and energy expenditure. Leucine kinetics were determined in seven low birth wt preterm infants fed human milk or human milk enriched with protein (2.5 to 4.3 g protein/kg.d). The infants received a short (4-h) constant infusion of L-[1-13C]leucine and leucine turnover and oxidation were calculated from 13C-plasma leucine and expired 13CO2 enrichments measured by mass spectrometry. Energy expenditure was measured by indirect calorimetry. Nonoxidative leucine disposal (an estimate of protein synthesis) and leucine derived from protein (an estimate of protein breakdown) were, respectively, 2.98 +/- 0.82 and 2.06 +/- 0.74 mumol/kg.min. Whole body protein turnover and deposition, derived from leucine kinetics, were 8.22 +/- 2.31 and 2.17 +/- 0.50 g/kg.d, whereas energy expenditure was 56.3 kcal/kg.day. Protein turnover was correlated with protein intake but not with protein deposition. Energy expenditure was correlated with protein turnover, synthesis, and breakdown but not with protein deposition. These data are in agreement with the fact that protein deposition depends upon protein intake, but they also suggest that an elevated protein deposition is not necessarily the result of a rapid protein turnover or associated with an elevated energy expenditure.     

Supplementation of pooled human milk with casein hydrolysate: energy and nitrogen balance and weight gain composition in very low birth weight infants

Growth and nitrogen and energy balances were studied with a combined technique of nutrient balance and indirect calorimetry measurement in two groups of eight very low birth weight infants fed pooled pasteurized human milk (HM) or cow's milk casein hydrolysate supplemented HM (HM-Pr). There was no difference in the amount of energy absorbed (91 +/- 17 kcal/kg/day with HM-Pr versus 95 +/- 8 with HM-P) or in the growth rate. The infants fed HM-Pr had a higher nitrogen intake (602 +/- 80 versus 395 +/- 64 mg/kg/day; p less than 0.001), urinary nitrogen excretion (160 +/- 64 versus 78 +/- 16 mg/kg/day; p less than 0.005) and nitrogen retention (326 +/- 32 versus 252 +/- 48 mg/kg/day; p less than 0.01). They also had increased plasma concentrations of essential amino acids, urea nitrogen, and total protein without metabolic imbalance. Energy expenditure was higher (58 versus 49 kcal/kg/day; p less than 0.005) and energy storage lower (33 versus 47 kcal/kg/day; p less than 0.05) with HM-Pr. In percent of weight gain, protein and fat accretion represented 12 and 14% in HM-Pr group versus 10 and 27% in HM group. Very low birth weight infants fed casein hydrolysate supplemented pooled HM achieved a growth rate and a weight gain composition similar to the fetus.     

15N-tracer investigations into the nitrogen metabolism of preterm infants fed mother's milk and a formula diet

Protein synthesis, protein breakdown, protein-N turnover, and other parameters describing the nitrogen metabolism were measured in five male preterm infants. The weight of the subjects at birth was 2,064 +/- 107 g and the measurements were performed at age 16.0 +/- 4.5 days in the case of the mother's milk diet and 27.4 +/- 6.8 days in the case of the formula diet containing 1.8% protein. The parameters were measured by means of the 15N-tracer technique using [15N]glycine (95 atom %) applied in a single oral dose of 20 mg/kg as a tracer. The three-pool model proposed by Winkler and Faust was used to calculate the whole body protein parameters. No difference in net protein gain, protein synthesis, protein breakdown, or the other protein metabolism parameters were recorded despite the different protein inputs. Renal nitrogen excretion and the rate of endogenous urea N excretion were significantly higher for the formula diet than for the mother's milk diet. The protein synthesis rate of 7.9 g X kg-1 X day-1 was, as has previously been observed, higher than in other age groups. The protein metabolism of the preterm infant older than 33 weeks of gestational age does not benefit from a formula diet based on cow's milk that is richer in protein than mother's milk.     

Protein and energy intake during weaning: I. Effects on growth

The growth and food consumption of 30 healthy infants from 4 to 6 months of age have been measured. Two groups were assigned randomly to either a formula with 1.9 g of protein and 72 kcal per 100 ml (F1) or 2.7 g of protein and 69 kcal per 100 ml (F2). A third group of infants were fed breast milk (0.96 g of protein and 65 kcal per 100 ml (HM)). All infants received supplementary food according to the same regimen and were fed ad libitum. The mean protein intake was 1.3, 2.6 and 3.6 g/kg/day in the HM-, F1- and F2-groups respectively. The corresponding mean energy intake was 80, 101 and 94 kcal/kg/day. The formula-fed infants had significantly higher protein and energy intakes when compared to the breast-fed group. No significant differences were found in the rate of growth of crown-heel length, head circumference or in weight gain. The differences in protein intake between the breast- and formula-fed infants without differences in growth indicate that the formulas may provide a protein intake in excess to the needs.     

Metabolic consequences of intrauterine growth retardation in very low birthweight infants

By the combination of energy and macronutrient balances, continuous open circuit computerized indirect calorimetry, and anthropometry, we have compared small for gestational age (SGA) and appropriate for gestational age (AGA) very low birthweight infants with respect to metabolizable energy intake (mean +/- SE: 125.9 +/- 2.5 versus 130.4 +/- 3.5 kcal/kg X day), energy expenditure (67.4 +/- 1.3 versus 62.6 +/- 0.9 kcal/kg X day), storage of energy and macronutrients and growth. Fourteen studies in six SGA infants (gestational age, 33.1 +/- 0.3 weeks; birthweight, 1120 +/- 30 g) and 22 studies in 13 AGA infants (gestational age, 29.3 +/- 0.4 weeks; birthweight, 1155 +/- 40 g) were performed. The SGA infants had a lower absorption of fat (68.7 +/- 3.2 versus 79.7 +/- 1.7%) and protein (69.1 +/- 3.2 versus 83.4 +/- 1.5%) and hence increased (P less than 0.001) energy loss in excreta (29.9 +/- 2.8 versus 18.2 +/- 1.5 kcal/kg X day). The significant hypermetabolism of SGA infants by 4.8 kcal/kg X day was associated with an increased fat oxidation. Despite lower energy storage, SGA infants were gaining weight (19.4 +/- 0.9 g/kg X day), length (1.25 +/- 0.14 cm/week), and head circumference (1.16 +/- 0.9 cm/week) at higher rates than the AGA group. The energy storage per g weight gain was lower (P less than 0.001) in the SGA group (3.0 +/- 0.14 versus 4.26 +/- 0.26 kcal) reflecting higher water, lower fat (22.2 +/- 1.8 versus 33.8 +/- 2.5%; P less than 0.001) and lower protein (7.7 +/- 0.5 versus 12.5 +/- 0.8%; P less than 0.001) contents of weight gain in the SGA group.     

Metabolic and energy balance in small- and appropriate-for-gestational-age, very low-birth-weight infants

This study compared nutrient utilization and postnatal weight gain composition in eight appropriate for gestational age (AGA: birth weight 1293 ± 107 g; gestational age 28.8 ± 1.4 weeks) and eight symmetrically growth-retarded (SGA: birth weight 1110 ± 230 g; gestational age 32.7 ± 1.9 weeks), very low-birth-weight (VLBW) infants. There was no significant difference in protein, mineral and energy intake between AGA and SGA infants. Nitrogen absorption (84 ± 3 and 83 ± 4%) and nitrogen retention (356 ± 48 and 352 ± 43 mg/kg/day) were similar in both groups. Fat absorption tended to be lower in AGA (78 ± 15%) than in SGA (87 ± 4%) infants. Calcium, phosphorus and magnesium absorptions were similar in AGA and SGA infants. Metabolizable energy utilization was similar in both groups; about 55% was expended and 45% stored in new tissues. Energy expenditure was 58 ± 4 kcal/kg/day in SGA infants and 61 ± 9 kcal/kg/day in AGA infants. Weight gain and its composition were similar in both groups. We conclude that nutrient and energy utilization are similar in AGA and symmetrically growth-retarded, VLBW infants.     

Lactational capacity of marginally nourished mothers: infants' milk nutrient consumption and patterns of growth

The consumption of human milk by 58 Bangladeshi infants of marginally nourished mothers was measured during longitudinal studies. Daily milk consumption, as estimated by test weighing, and intakes of energy and protein, as calculated from the measured concentrations of macronutrients in the milk, were related to infant body weight, to internationally recommended intakes of these nutrients, and to the infants' patterns of physical growth. Each of the milk variables, when related to infant body weight, declined significantly with increasing (log) infant age (P less than .001). The average consumption of energy and protein was less than current recommendations at all ages. Nevertheless, the average growth of the Bangladeshi infants approximated the fifth centile of the US National Center for Health Statistics during the first 4 months of life. By the fourth month, however, the weight increments of more than half the infants (79%) were less than the reference data. The intakes of energy and protein by individual infants less than 90 days of age were related to their patterns of growth. There were significant positive relationships between the change in Z score weight-for-age and weight-for-length and the consumption of breast milk energy (kilocalories per kilogram of body weight per day) and protein (grams per kilogram per day). Consumptions of 86.5 kcal/kg/d and protein 1.48 g/kg/d were associated with a nonchanging Z score weight-for-age. Thus, intake of these amounts of nutrients permitted weight gain comparable to the reference population but did not permit recovery from the existing relative weight deficits.     

Protein and Energy Intake during Weaning: I. Effects on Growth

ABSTRACT. The growth and food consumption of 30 healthy infants from 4 to 6 months of age have been measured. Two groups were assigned randomly to either a formula with 1.9 g of protein and 72 kcal per 100 ml (F₁) or 2.7 g of protein and 69 kcal per 100 ml (F₂). A third group of infants were fed breast milk (0.96 g of protein and 65 kcal per 100 ml (HM). All infants received supplementary food according to the same regimen and were fed ad libitum. The mean protein intake was 1.3, 2.6 and 3.6 g/kg/day in the HM-, F₁- and F₂-groups respectively. The corresponding mean energy intake was 80, 101 and 94 kcal/kg/day. The formula-fed infants had significantly higher protein and energy intakes when compared to the breast-fed group. No significant differences were found in the rate of growth of crown-heel length, head circumference or in weight gain. The differences in protein intake between the breast- and formula-fed infants without differences in growth indicate that the formulas may provide a protein intake in excess to the needs.     

Energy intake, metabolic balance and growth in preterm infants fed formulas with different nonprotein energy supplements

OBJECTIVE: To study metabolic and energy balances, growth and composition of increased body mass in healthy preterm infants fed control formula or control formula with three different nonprotein energy supplements. PATIENTS AND METHODS: Growing preterm infants (birth weight < 1,500 g and gestational age < 31 weeks) were fed standard preterm formula (control group) or the same formula enriched with three different nonprotein energy supplements. An energy supplement of 23 kcal/kg/day was achieved by adding medium-chain triglyceride and dextrinomaltose in three different caloric ratios: 33:66 in group A, 66:33 in group B, and 85:15 in group C. Energy balance was determined by open-circuit continuous (5-6 hours) measurements of energy expenditure, with simultaneous measurement of 24-hour urinary nitrogen excretion. Metabolic balance was determined by measurements of energy intake, energy oxidation, and energy output in urine and stool. The composition of body mass accretion was determined as the accretion of fat and protein in the total weight gain. RESULTS: The fat accretion (4.9, 5.9, 6.2, and 3.8 g/kg/day in groups A, B, C and D, respectively) correlated directly with fat intake. Infants receiving standard energy intake had a fat percentage of weight gain significantly lower (28%) than that of the high-energy intake groups (31%, 40%, and 38% in groups A, B, and C, respectively). This difference corresponded to the results obtained from skinfold thickness measurements. CONCLUSIONS: Excess nonprotein energy is stored as fat regardless of its source (fat or carbohydrate). High caloric and medium-chain triglyceride intake in otherwise healthy growing preterm infants does not promote nitrogen retention.     

Protein metabolism and lipid balance in dietary treatment of acute enteritis in infants with a defined standardized oligopeptide diet

The advantage of a standardized oligopeptide formula (Peptisorb p?d) for dietary management of diarrhea was proved in 10 infants aged 1 to 10 months with body weights between 4000 and 8860 g. The nitrogen balance turned to normal already at day 3 to 4 of the treatment due to the rapid increase of food supply. Whole body protein parameters estimated by 15N yeast protein thermitase hydrolyzate as a tracer substance were already normalized at that time. Protein synthesis amounted to 5.0 +/- 1.5 g/kg/day, protein breakdown to 3.7 +/- 1.5 g/kg/day and net protein gain to 1.3 +/- 0.6 g/kg/day, resp. Reutilisation rate of endogenous nitrogen was found to be 83%. This correlates with the relatively high nitrogen supply of the oligopeptide diet in comparison to mother's milk feeding. Approximately 15% of the administered amount of total nitrogen were excreted in the feces in contrast to only 5.8% of the 15N tracer dose, indicating the higher losses of endogenous nitrogen due to enteritis. The absorption of the medium chain triglycerides from the diet was 97.5% at an average and thus extremely high.     

Nutrient balance, energy utilization, and composition of weight gain in very-low-birth-weight infants fed pooled human milk or a preterm formula

Growth, protein, and energy balances were studied in two groups of very-low-birth-weight premature infants fed pooled pasteurized human milk (HM) or a preterm formula (PF). Each infant was studied at 33 and 36 weeks gestational age with a combined technique of nutrient balance and indirect calorimetry measurement. Weight and length gains were higher with PF than with HM, but head circumference growth was similar with both milks. Although the volume of milk given was lower, energy intake was higher with PF than with HM in both studies (126 to 130 vs 103 to 109 kcal/kg/day). Percentage of energy absorbed was better with PF than with HM (94% vs 84%) at 33 weeks, and similar (95%) with both milks at 36 weeks. Energy expenditure, which had increased from 33 weeks to 36 weeks, was higher with PF than with HM (57 to 63 vs 46 to 52 kcal/kg/day) during both studies. Energy retention accounted for about 50% of energy absorbed with both milks, but was higher with PF than with HM (60 vs 40 to 50 kcal/kg/day) in both studies, and resulted in fat accretion well above that seen during intrauterine growth for both milks in both studies. Protein intake was higher with PF than with HM (3.1 vs 2.4 gm/kg/day) in both studies, giving a protein accretion similar to the intrauterine accretion with PF (2.2 gm/kg/day), but lower with HM. Our results suggest that the nutritional value of pooled pasteurized human milk for VLBW infants should be reconsidered, especially because of its low protein content, and that energy density of preterm formulas must be questioned in view of elevated fat deposition.     

4～12个月中国婴儿能量摄入研究

目的以体重增长值（△WAZ）在±0．67之间为依据研究4～12个月婴儿能量摄入、乳类摄入产能与其他食物产能比,分析其相关因素。方法以2004年11月-2005年3月重庆医科大学儿童医院儿童保健门诊就诊的4个月龄132名婴儿为研究对象,定期随访至12月龄。分A组（4～5月龄组）、B组（6～8月龄组）、C组（9～12月龄组）。两名专业人员负责体格测量。若△WAZ〈-0．67则终止随访。食物称重与食物记录法计算每日食物摄入情况。结果各组婴儿体格发育良好,△WAZ在-0．67～0．67时婴儿平均食物摄入量为119～128g／（kg·d）;A、B、C组平均蛋白质摄入量分别为1．82、2．76、3．52g／（kg·d）;乳类摄入分别是总能量的93％、64％、56％;平均乳类摄入量为750～900g/d;平均能量摄入分别为83．9、81．6、85．8kcal／（kg·d）,接近世界卫生组织2003标准,低于中国营养学会推荐值;能量密度为0．6～0．8kcal／g。多元线性回归分析结果显示食物摄入量、能量密度是影响能量摄入的主要因素。结论（1）本组4～12月龄婴儿能量摄入为82～86kcal／（kg·d）时婴儿体格发育正常;（2）4～12月龄婴儿期乳类摄入量达750～900g／d可满足婴儿大部分能量、蛋白质需要;（3）食物摄入量和能量密度是影响婴儿能量摄入的两个最重要因素;婴儿食物能量密度以0.6～0．8kcal／g为宜。     

A COMPARATIVE STUDY OF VARYING PROTEIN INTAKE IN LOW BIRTHWEIGHT INFANT FEEDING

Svenningsen, N.W., Lindroth, M. and Lindquist, B. (Department of Paediatrics, University of Lund, Sweden). A comparative study of varying protein intake in low birthweight infant feeding. Acta Paediatr Scand. Suppl. 296: 28, 1982. — In a prospective longitudinal study of 48 very low birthweight and preterm infants with mean birthweight 1 385±343 and gestational age 30.8±2.9 w an assessment was made of the impact of varying the protein intake in the postnatal period from the 3rd to 7th week of life. The infants were randomly allocated to one of three dietary groups with isocaloric energy supply but different protein content—i.e. human milk (1.6 g/100 kcal), formula 1 (2.3 g/100 kcal) and formula 2 (3.0 g/100 kcal). In the human milk group 12 of 18 infants were fed their own mother's breastmilk. During the study period the mean weight gain was slightly higher in the infants fed formula 1 and 2. There were no group differences in S-albumin whereas B-urea-N and B-base deficit were significantly increased in the formula fed infants in comparison to infants fed human milk. After the study period until around 15 weeks of age the slope in weight gain remained slightly higher for formula fed infants. However, the gain in body length and head circumference was equal in all three groups. After around 8 months of age there was no difference in any growth parameter. Neurodevelopmental examinations showed no group differences during the follow-up period to 2 years of age.     

Nutritionally regulated hormonal factors in prolonged postnatal growth retardation and its associated adverse neurodevelopmental outcome in extreme prematurity

Recent published data show that at hospital discharge, most infants born at <30 weeks of gestation would not achieve the median birth weight of the reference fetus at the same postconceptional age, and many would be less than the 10th centile. Estimating from the current recommendations of calorie and protein intakes, these infants accrue large deficits in intakes of protein and calorie during the first weeks of life. Postnatal growth retardation over a prolonged period of time is related to neurodevelopmental delays. While a total energy intake of 120 kcal/kg/day has generally been considered adequate, protein requirement in low gestation infants remains a matter for debate. Increasing the dietary protein:calorie ratio has previously been proposed as a strategy to enhance growth and to achieve a body composition similar to that of the reference fetus. Previous study data reveal that serum insulin-like growth factor I (IGF-I) concentration is positively correlated with protein intake, and nitrogen retention, in turn, is positively correlated with serum IGF-I concentration. Remarkably, elevated serum growth hormone but low serum IGF-I concentrations have been reported in low gestation infants and in infants with intrauterine growth retardation, suggesting IGF-I being a nutritionally regulated hormonal factor in the postnatal growth retardation. As neurodevelopment in extreme prematurity is likely affected by multiple factors, we hypothesize that a combined strategy of the previously proposed hormonal supplement with hydrocortisone and tri-iodothyronine together with increased dietary protein intake (progressively increasing from 1.5 g/kg/day intravenously administered amino acids immediately after birth, then 3.6 g/100 kcal at approximately 125 kcal/kg/day when enterally fed till the infant reaches a body weight of >or=1.8 kg and at >or=50th centile weight of the reference fetus at the same postconceptional age) would likely be synergistic and more effective in improving neurodevelopmental outcome.     

Energy balance in low birth weight infants fed formula of high or low medium-chain triglyceride content

We tested the effect on energy balance of the partial substitution of medium-chain for long-chain triglycerides in the diet of growing low birth weight infants. Fifteen infants were studied in a randomized double-blind crossover clinical trial in which each infant was fed each of two formulas, which were of equal gross energy and protein content but differed in fat composition. The high medium-chain triglyceride (MCT) formula contained medium- and long-chain triglycerides in a weight/weight ratio of 46:54; in the low MCT formula the ratio was 4:96. The hypothesis tested was that under conditions of equal gross energy intake the two diets would differ in their digestible and metabolizable energy contents and would produce differences in the infants' rates of energy expenditure and energy storage. Gross energy intakes averaged 562 and 555 kJ/kg/day (134 and 133 kcal/kg/day) with the high and low MCT formulas, respectively. With each diet, coefficients of energy digestibility (0.93) and metabolizability (0.91) were identical; the rates of energy expenditure were 262 (high MCT) and 265 (low MCT) kJ/kg/day (63 kcal/kg/day for both diets), and of energy storage were 246 (high MCT) and 239 (low MCT) kJ/kg/day (59 and 57 kcal/day). These differences were not significant. There were also no significant differences between the two diets in coefficients of nitrogen retention (mean 0.70) or in rate of weight gain (mean 21.5 gm/kg/day). The use of high MCT content in infant formula neither provided a nutritional advantage in energy digestibility or metabolizability nor resulted in an increased rate of energy expenditure or of energy storage.     

Energy balance, physical activity, and thermogenic effect of feeding in premature infants

In order to assess the contribution of the thermogenic effect of feeding and muscular activity to total energy expenditure, nine premature infants were studied for 2 consecutive days during which time repeated measurements of energy expenditure by indirect calorimetry were performed throughout the day, combined with a visual activity score based on body movement. The infants were growing at 16.6 +/- 4.0 g/kg/day (mean +/- SD) and received 110 +/- 8 kcal/kg/day metabolizable energy (milk formula) and 522 +/- 40 mgN/kg/day. Their total energy expenditure was 68 +/- 4 kcal/kg/day indicating that 41 +/- 7 kcal/kg/day was retained for growth. Based on the combination of energy + N balances it was estimated that 80% of the weight gain was fat-free tissue and 20% was fat tissue. The rate of energy expenditure measured minute-by-minute was significantly and linearly correlated with the activity score in both the premeal (r = 0.75;p less than 0.001) and the postmeal periods (r = 0.74; p less than 0.001) with no difference in the regression slope, but with a significant difference in intercept. In preset feeding schedules the latter allowed an estimation of the thermogenic effect without the confounding effect of activity. This was found to be 3.1 +/- 1.8% when expressed as a percentage of metabolizable energy intake. However when the "classical" approach was used as a comparison (integration of extra energy expenditure induced by the meal), the thermogenic effect was found to be greater, i.e. 9.5 +/- 3.8% of the meal's metabolizable energy, due to the superimposed effect of physical activity in the postprandial state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of varying protein and energy intakes on growth and metabolic response in low birth weight infants

Growth (weight, length, head circumference, and skinfold thickness), retention of major nutrients (nitrogen, sodium, potassium, chloride, calcium, and phosphorus), and chemical indices of protein adequacy (plasma albumin and transthyretin concentrations) and excess (blood urea nitrogen concentration and acid-base status; plasma amino acid concentrations) were determined serially from the time desired intake was tolerated until discharge weight (2200 gm) was reached in low birth weight infants (birth weight 900 to 1750 gm) fed one of three formulas, which provided protein and energy intakes, respectively, of 2.24 gm/kg/day and 115 kcal/kg/day (group 1), 3.6 gm/kg/day and 115 kcal/kg/day (group 2), and 3.5 gm/kg/day and 149 kcal/kg/day (group 3). Weight gain and rate of increase in length and head circumference were less in group 1 than in groups 2 and 3. Retention of most major nutrients also was less in group 1, as was blood urea nitrogen concentration, plasma albumin and transthyretin concentrations, and plasma concentrations of several amino acids. The rate of weight gain was not significantly greater in group 3 than in group 2, but the rate of increase in skinfold thickness was greater in this group. Neither nutrient retention nor metabolic indices differed between groups 2 and 3. These results suggest that a protein intake of 2.24 gm/kg/day is inadequate for the type of LBW infants studied, that the higher protein intakes are well tolerated, and that an energy intake of 149 vs 115 kcal/kg/day does not enhance utilization of the higher protein intakes studied.     

Breast milk volume and composition during late lactation (7-20 months)

Breast milk composition of 119 samples collected by 46 women during months 7-20 of lactation was compared with composition of 101 samples collected at 4-6 months. Breast milk intake of 10 infants was determined by test-weighing for 1 or more months during months 7-16 of lactation. Longitudinal decreases in milk concentrations of zinc, copper, and potassium, previously documented for the first 6 months, continued into the second 6 months, while protein, iron, and sodium concentrations showed no further decline. Lactose, fat, calcium, and magnesium concentrations were similar to those in earlier stages of lactation. Weaning was associated with significant changes in milk composition: When milk volume fell below 300 ml/day, there was an increase in protein and sodium and a decrease in lactose, calcium, and zinc. Breast milk intake of infants not supplemented with cow's milk or formula averaged 875 ml/day (93% of total energy intake) at 7 months and 550 ml/day (50% of total energy intake) at 11-16 months. Total energy intake increased from 610 to 735 kcal/day, but energy intake per kilogram remained constant at a relatively low 70-79 kcal/kg/day. Our results suggest the need for further studies of nutrient intake and requirements of breast-fed infants during late lactation.