Lactation
Lactation Background
The benefits of breastfeeding for both mothers and infants are well established
and rates of breastfeeding have been increasing across all socioeconomic
and ethnic groups in the US during the last decade. In 2001, the prevalence
of the initiation of breastfeeding and breastfeeding until 6 months of
age increased to 69.5% and 32.5%, respectively, and breastfeeding rates
are projected to increase at least 2 percent per year through 2010 (29).
Yet very few studies have applied specific measures of nutritional status
to the lactating mother.
Lactation is an anabolic state with an even greater maternal nutritive
burden than pregnancy (12). Infants double their birth weight in just
4 to 6 months postpartum. The energy value of the milk excreted in just
4 months is equivalent to the total energy cost of pregnancy (12). Complex
hormonal interactions orchestrate mammary gland development, milk production
and secretion, and redirection of nutrients to the mammary gland for transfer
to the infant (12). As in pregnancy, the lack of validated biological
markers of nutrient intake during lactation is a significant methodological
barrier to dietary assessment research. The growth of the breastfed infant
and the quantity and nutrient content of the breast milk are often used
as proxies to assess maternal nutritional adequacy during lactation (12).
Another issue has been a lack of a consistent definition of breastfeeding
behaviors (e.g., exclusive, partial) in the lactation literature (30).
Presenting additional challenges is the variation in breast milk output
and composition between women and within the same woman from day to day,
from feed to feed, and during a single lactation (31;32). Among the multitude
of factors with the potential to affect self report of dietary intake
are maternal concerns about her breast milk adequacy and ability to successfully
support infant growth and development, the challenge of parenting a newborn
infant, maternal fatigue and time constraints, desire to quickly return
to pre-pregnant maternal weight, concerns about infant colic and food
sensitivities, and cultural beliefs about diet and botanical supplement
use during lactation (33).
Validation Studies in Breastfeeding Women
Only four studies examining the validity of dietary assessment methods
in breastfeeding women were found (Table
2.3). Two small European studies examining the energy costs of lactation
provided an opportunity to evaluate the validity of self-reported weighed
FRs (Food
Records). Basal Metabolic Rate (BMR), TEE (Total
Energy Expenditure) by the DLW (Doubly
Labeled Water) method, physical activity plus thermogenesis (TEE-BMR),
changes in body fat stores, milk energy transfer, and energy intake reported
in a 7-day weighed FR were studied in 10 Cambridge women at 4, 8, and
12 weeks of lactation and when not pregnant and not lactating (34).
Reported energy intake for the group was within 10-20% of measured energy
output. However, data examined for individuals found the largest degree
of under-reporting of energy intake only in the overweight subject (BMI
29.9). In 22 exclusively breastfeeding Swedish women, 4-day weighed FRs
at 2 months postpartum reported only two-thirds of the measured energy
costs of lactation (TEE by DLW method + BM Energy Output from 24-hour
infant test weighing) (15).
In 1983, Stuff and colleagues (35)
measured dietary intake in 40 lactating women with a 7-day estimated FR
and a 105-item FFQ (Food
Frequency Questionnaire). Interclass correlations for measuring agreement
between methods for calories and five nutrients showed poor agreement
between the FFQ and 7-day FR (r = 0.00 to 0.24). FFQ estimates were higher
than FR estimates for energy and all nutrients examined. Analysis of randomly
selected 1- and 3-day FRs from the 7-day FR, showed that the 3-day FR
did not provide good individual estimates of nutrient intake, but did
provide reasonable estimates of group intake. When individuals were classified
into high, medium, and low intake groups by each method, none of the intakes
was found to agree with the 7-day FR classification. Intra-individual
variation was found to be greater than inter-individual variation in this
study.
In 150 breastfeeding WIC participants, the NCI-Block HHHQ (NCI
Health Habits and History Questionnaire) was found to be more valid
than the Harvard FFQ, based on correlations between each FFQ and three 24HR
interviews for energy and five nutrients (25).
Neither FFQ was valid in Hispanic women.
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