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Retinol concentration in human milk is considered a better indicator of changes in maternal vitamin A status than serum levels (Rice et al. 2000). Carotenoid distribution pattern and concentrations in human milk vary widely worldwide and may be related to the characteristics of the local diet (Canfield et al. 2002). Although carotenoid concentrations in plasma may be used as biomarkers of dietary intake, correlations for individual carotenoids vary substantially (El-Sohemy et al. 2002). Supplementation of lactating women with single doses of vitamin A and β-carotene, in amounts several times higher than those obtained through daily dietary intake, increases plasma and milk levels of the respective nutrient (Stoltzfus et al. 1993; Canfield et al. 1997). However, the responses of retinol concentration in human milk and of carotenoid concentrations in both maternal plasma and milk to short-term changes in dietary intake have not been evaluated.

The endocrine changes that occur in human lactation lead to increased mobilization of fatty acids from adipose tissue and may result in altered plasma levels of non-esterified fatty acids (NEFA) (Neville et al. 1994). Fasting total NEFA concentration in plasma is elevated in lactating compared with nonlactating women three to six months postpartum (Butte et al. 1999), but the composition of individual NEFA in plasma from lactating women has not been determined. Fatty acid mobilization from adipose tissue is a selective process, influenced by the fatty acid structure (Raclot et al. 1997). During lactation, mobilization of individual fatty acids might be selectively affected and result in altered plasma NEFA composition. Since adipose tissue seems to be the most important source of polyunsaturated fatty acids (PUFA) in human milk (Demmelmair et al. 1998), these alterations could affect PUFA transfer to milk.

Fatty acid composition of phospholipids in mature erythrocyte membranes are directly affected by alterations in the intermediate metabolism, transit of substrates between organs and tissues, and by changes in the dietary fat intake. During lactation, maternal fatty acid metabolism is altered to fulfill the demand for milk synthesis and, as lactation progresses, further endocrine and metabolic alterations occur in the maternal organism. All these changes might affect cell membrane composition, which could be of concern to maternal health, depending on the quality and extent of such alterations. Besides, data on fatty acid composition of erythrocyte membrane in lactating women with different patterns of fat and energy intakes, nutritional status and lactational periods are scarce. The aims of the present work were to determine erythrocyte fatty acid composition of Brazilian low-income nursing women and to evaluate the relationship between the lactational period and erythrocyte fatty acid composition.

Conjugated linoleic acids (CLA) are found in food products from ruminants, and the c-9,t-11 and t-10,c-12 isomers show many biological effects (Pariza et al., 2000). Data on CLA contents in human milk are scarce. The determination of human milk CLA content and its interaction with other fatty acids, in populations with different dietary habits could be of concern to the mother-infant dyad. The aims of the present work were to determine the fatty acid contents of milk from underprivileged Brazilian nursing women, with special reference to CLA, and to investigate the association of human milk CLA contents with other milk fatty acids, and also with the intake of dairy fat.