Preliminary evaluation of a new pediatric air displacement plethysmograph for body composition assessment in infants.

A preliminary evaluation of a new air displacement plethysmography (ADP) system for body composition assessment in infants was performed on 17 subjects on 2 consecutive days. Mean (+/-SD) percent body fat (%BF) obtained from test 1 on day 1, and tests 1 and 2 on day 2 was 23.21+/-7.63, 22.94+/-7.50, and 22.55+/-7.61, respectively. Mean differences in %BF of within- (-0.39+/-0.81) and between-day tests (-0.27+/-0.97) did not significantly differ from zero. %BF 95% limits of agreements were very close (-2.0-1.2, and -2.2-1.7 for within- and between-day tests, respectively). %BF SDs (0.52 and 0.60 %BF for within- and between-day reliability, respectively) were not a function of the subject's behavioral state, body weight, or %BF. Mean %BF obtained from the 3 tests (22.90+/-7.56) was comparable with expected %BF values calculated using data from multi-compartment studies (25.84+/-8.39 and 21.93+/-4.46).

Randomized trial of the short-term effects of dieting compared with dieting plus aerobic exercise on lactation performance.

BACKGROUND: Limiting postpartum weight retention is important for preventing adult obesity, but the effect of weight loss on lactation has not been studied adequately. OBJECTIVE: We evaluated whether weight loss by dieting, with or without aerobic exercise, adversely affects lactation performance. DESIGN: At 12+/-4 wk postpartum, exclusively breast-feeding women were randomly assigned for 11 d to a diet group (35% energy deficit; n = 22), a diet plus exercise group (35% net energy deficit; n = 22), or a control group (n = 23). Milk volume, composition, and energy output; maternal weight, body composition, and plasma prolactin concentration; and infant weight were measured before and after the intervention. RESULTS: Weight loss averaged 1.9, 1.6, and 0.2 kg in the diet, diet + exercise, and control groups, respectively (P < 0.0001) and was composed of 67% fat in the diet group and nearly 100% fat in the diet + exercise group. Change in milk volume, composition, and energy output and infant weight did not differ significantly among groups. However, there was a significant interaction between group and baseline percentage body fat: in the diet group only, milk energy output increased in fatter women and decreased in leaner women. The plasma prolactin concentration was higher in the diet and diet + exercise groups than in the control group. CONCLUSIONS: Short-term weight loss (approximately 1 kg/wk) through a combination of dieting and aerobic exercise appears safe for breast-feeding mothers and is preferable to weight loss achieved primarily by dieting because the latter reduces maternal lean body mass. Longer-term studies are needed to confirm these findings.

Weight change during lactation does not alter the concentrations of chlorinated organic contaminants in breast milk of women with low exposure.

The purpose of this longitudinal study was to evaluate whether a loss of body fat during lactation between 4 and 20 wk postpartum increases the concentration of environmental contaminants in breast milk. We examined this relationship in two different cohorts of exclusively breastfeeding women: (1) California women with low exposure to contaminants (n = 10 whose weight was stable [mean change, 0.0 +/- 0.2 kg] and n = 11 who lost weight [mean loss, -4.1 +/- 0.4 kg]) and (2) Hispanic women (n = 30) who had recently immigrated to North Carolina, primarily from Mexico, and were presumed to have a higher prior exposure to contaminants. Breast milk samples were analyzed for hexachlorobenzene (HCB) and DDT and its related products. There was no significant relationship between change in body composition and change in milk contaminant concentrations in either California or North Carolina women. Concentrations of HCB were similar between the California and North Carolina women, but those of DDT and related products were higher in the North Carolina subjects. Results suggest that moderate weight loss in lactating women with low exposure to environmental contaminants does not increase contaminant concentration in breast milk.

Stress during labor and delivery and early lactation performance.

The amount of stress experienced by both the mother and fetus during labor and delivery varies considerably and is likely to be different in primiparous and multiparous women. In this study we explored relations between the birth experience and lactation performance of 40 women. Stress hormones were measured in serum or plasma during pregnancy, parturition (cord and maternal blood), and lactation. Milk samples were obtained and breast-feeding frequency was recorded each day during the first 2 wk postpartum. Four outcomes were used as markers of lactogenesis: the time when the subject first felt fullness in the breasts, 24-h milk volume on day 5 postpartum, milk lactose concentration on day 5, and the day of appearance of casein in the milk as determined by gel electrophoresis. There were significant intercorrelations among the outcome variables, except for milk lactose. Compared with multiparous women, primiparous mothers experienced a delay in breast fullness and lower milk volume on day 5. In multiple regression analyses excluding subjects who had cesarean deliveries (n = 5), markers of both fetal and maternal stress during labor and delivery (cord glucose concentration and maternal exhaustion score) were associated with delayed breast fullness and casein appearance; delayed casein appearance was also associated independently with a longer duration of labor. Milk volume on day 5 was lower in women with higher exhaustion scores, and, in multiparous women, those who breast-fed less frequently on day 2. The milk lactose concentration was inversely related to pregnancy weight gain. These results indicate that primiparity, long labor, stress to the mother and fetus during labor and delivery, and elevated cord glucose concentrations are risk factors for delayed lactogenesis.

Between-day and within-day variability in the relation between heart rate and oxygen consumption: effect on the estimation of energy expenditure by heart-rate monitoring.

Estimation of energy expenditure (EE) by heart-rate (HR) monitoring (HRM) assumes that the relation between HR and oxygen consumption (VO2) is stable between days and within a day. To evaluate this assumption, 12 healthy subjects underwent an HR-VO2 calibration session on two mornings and two afternoons, with one morning and one afternoon session on the same day. Measurements were made while subjects were supine, sitting, standing while shifting body weight side-to-side, and walking at four intensities. Subjects wore an HR monitor during waking hours on another day (15.1 +/- 1.5 h). Regression analysis was used to determine the relation between HR and VO2 in the sedentary and active HR ranges, and four EE values (HRM-EE) based on the four calibration sessions were calculated for each subject. The four group mean HRM-EE values were nearly identical (CV: 1.1%). The regression equations generated from the four calibration sessions did not differ significantly for the group as a whole, but for some subjects there were significant differences among sessions in the slope of the active regression equation (P = 0.005). Intraindividual CVs for HRM-EE were generally < 10%, but ranged from 0.1% to 24.7%. In general, within an individual, HR was more variable than was VO2, and intraindividual variability in EE was associated with intraindividual variability in the flex HR and sedentary HR range. HRM is appropriate for assessment of EE for a group; however, caution is recommended when HRM is used for individual determinations of EE.

Differences in morbidity between breast-fed and formula-fed infants.

To determine whether breast-feeding is protective against infection in relatively affluent populations, morbidity data were collected by weekly monitoring during the first 2 years of life from matched cohorts of infants who were either breast fed (BF) (N = 46) or formula fed (FF) (N = 41) until at least 12 months of age. Cohorts were matched for characteristics such as birth weight and parental socioeconomic status, and we controlled for use of day care in data analysis. Mean maternal educational level was high (16 years) in both groups. In the first year of life the incidence of diarrheal illness among BF infants was half that of FF infants; the percentage with any otitis media was 19% lower and with prolonged episodes (> 10 days) was 80% lower in BF compared with FF infants. There were no significant differences in rates of respiratory illness; nearly all cases were mild upper respiratory infections. Morbidity rates did not differ significantly between groups in the second year of life, but the mean duration of episodes of otitis media was longer in FF than BF infants (8.8 +/- 5.3 vs 5.9 +/- 3.5 days, respectively; p = 0.01). These results indicate that the reduction in morbidity associated with breast-feeding is of sufficient magnitude to be of public health significance.

Effects of exercise on plasma lipids and metabolism of lactating women.

To examine the effects of exercise on plasma lipids and metabolism during lactation, sedentary, exclusively breast-feeding women were randomly assigned to an exercise (E) or control (C) group at 6-8 wk postpartum. E subjects performed aerobic exercise 45 min.d-1, 5 d.wk-1, for 12 wk. Resting metabolic rate (RMR), energy expenditure, body composition, and dietary intake were measured at 6-8, 12-14, and 18-20 wk postpartum. Maximum oxygen uptake (VO2max), postprandial insulin, glucose, and thermic response, and plasma lipid levels were measured at 6-8 and 18-20 wk. VO2max increased by 25% vs 5% in the E vs the C group, respectively (P < 0.0001). RMR was similar between groups and did not change over time. Weight and percent body fat declined (P < 0.01) during the study, but there was no difference between E and C groups. Exercise marginally increased high-density lipoprotein cholesterol levels (P < 0.08), but did not affect other lipid concentrations. Insulin response decreased as VO2max increased (P = 0.05). There was no effect of time or group on glucose or thermic response. Exercise improves cardiovascular fitness during lactation, but does not increase the rate of postpartum weight loss.

Factors related to duration of postpartum amenorrhoea among USA women with prolonged lactation.

Duration of postpartum amenorrhoea (PPA) was compared among women who breast-fed for > or = 6 months (breast-feeding group) or < or = 3 months (formula-feeding group) and was found to be significantly shorter among the latter. Associations between maternal factors and duration of PPA were examined. Within the formula-feeding group, the only variable associated with duration of PPA was duration of breast-feeding. Among breast-feeding mothers who resumed menstruation after 3 months postpartum, duration of PPA was positively associated with parity and negatively associated with maternal body mass index (BMI) at 3 months postpartum. Among breast-feeding mothers who resumed menstruation after 6 months, duration of PPA was positively associated with parity, pregnancy weight gain, number of night feeds and milk volume at 6 months, and negatively associated with maternal age and BMI at 6 months postpartum. These results indicate that maternal anthropometric status is related to duration of PPA, even in a relatively well-nourished population of lactating women.

PIP: This analysis of factors affecting duration of postpartum amenorrhea (PPA) indicates that maternal anthropometric status is related even for healthy women. The analysis of 61 breast-feeding mothers and 42 formula-feeding mothers, who were in the study for at least six months, showed that the formula-feeding mothers had shorter mean and average durations of PPA (an average of 11.8 weeks versus 38.9 weeks for breast-feeding mothers). At 22 weeks, all formula-feeding mothers had resumed menstruation, while only 17% of breast-feeding mothers were menstruating. 75% of breast-feeding mothers did not resume menstruation after 26 weeks, and about 20% did not resume menstruation after 52 weeks. Timing of supplementation and nursing frequency were related to delays in menstruation. Longer durations of PPA were associated with later supplementation and no reduction in nursing frequency. A reduction of even one feed per day within the first six months among breast-feeding mothers was sufficient to reduce PPA. Formula-feeding mothers who maintained at least one breast feeding per day for a week had longer PPA by eight weeks. Hazard analysis revealed that parity was positively associated with and maternal body mass index (BMI) was negatively associated with duration of PPA at three months postpartum. When resumption of menstruation occurred at six months and after, the important positively-related factors were parity, pregnancy weight gain, number of night feeds and milk volume at six months; maternal age and BMI at six months were negatively related. Time changes amounted to an increase in PPA duration of five weeks for multiparity mothers, 0.5 weeks for each kg of weight gain during pregnancy, five weeks for each night feed at six months, and three weeks for each 100 g of milk produced. PPA was reduced by two weeks for every unit increase of BMI at six months. Milk volume and feeding frequency were unrelated at three months. More research is needed on the influence of maternal body fat on hormonal levels in lactating women in order to understand the impact of maternal body mass on amenorrhea.

A randomized study of the effects of aerobic exercise by lactating women on breast-milk volume and composition.

BACKGROUND: The potential risks and benefits of regular exercise during lactation have not been adequately evaluated. We investigated whether regular aerobic exercise had any effects on the volume or composition of breast milk. METHODS: Six to eight weeks post partum, 33 sedentary women whose infants were being exclusively breast-fed were randomly assigned to an exercise group (18 women) or a control group (15 women). The exercise program consisted of supervised aerobic exercise (at a level of 60 to 70 percent of the heart-rate reserve) for 45 minutes per day, 5 days per week, for 12 weeks. Energy expenditure, dietary intake, body composition, and the volume and composition of breast milk were assessed at 6 to 8, 12 to 14, and 18 to 20 weeks post partum. Maximal oxygen uptake and the plasma prolactin response to nursing were assessed at 6 to 8 and 18 to 20 weeks. RESULTS: The women in the exercise group expended about 400 kcal per day during the exercise sessions but compensated for this energy expenditure with a higher energy intake than that recorded by the control women (mean [+/- SD], intake, 2497 +/- 436 vs. 2168 +/- 328 kcal per day at 18 to 20 weeks; P < 0.05). Maximal oxygen uptake increased by 25 percent in the exercising women but by only 5 percent in the control women (P < 0.001). There were no significant differences between the two groups in maternal body weight or fat loss, the volume or composition of the breast milk, the infant weight gain, or maternal prolactin levels during the 12-week study. CONCLUSIONS: In this study, aerobic exercise performed four or five times per week beginning six to eight weeks post partum had no adverse effect on lactation and significantly improved the cardiovascular fitness of the mothers.