Lactation - Background & Validation Studies - NCS Dietary Assessment Literature Review

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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.