Physiological aspects of human milk lipids.

Human milk from healthy and well-nourished mothers is the preferred form of feeding for all healthy newborn infants. The nutrient supply with human milk supports normal growth and development of the infant. Here the general characteristics of human milk lipids and recent knowledge on lactational physiology, composition and functional aspects of human milk lipids are discussed. Lipids in human milk represent the main source of energy for the breastfed baby and supply essential nutrients such as fat-soluble vitamins and polyunsaturated fatty acids (PUFA). The essential fatty acids linoleic and alpha-linolenic acids (LA and ALA) are precursors of long-chain polyunsaturated fatty acids (LC-PUFA), including arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acids (AA and DHA). LC-PUFA serve as indispensable structural components of cellular membranes and are deposited to a considerable extent in the growing brain and the retina during perinatal development. The supply of preformed LC-PUFA with human milk lipids has been related to functional outcomes of the recipient infants such as visual acuity and development of cognitive functions during the first year of life. Recent stable isotope studies indicate that the major portion of milk PUFA is not derived directly from the maternal diet, but stems from endogenous body stores. Thus, not only the woman's current but also her long-term dietary intake is of marked relevance for milk fat composition.

Fat content and fatty acid composition of fresh, pasteurized, or sterilized human milk.

In hospitals, human milk is subjected to heat treatment to reduce risk of transmission of infectious agents such as human immunodeficiency virus (HIV), hepatitis B, cytomegalovirus, and bacterial contamination, especially during feeding of banked milk to preterm infants. Fat losses due to heat treatment have been extensively studied in cow milk but have received little attention in human milk. We studied the effect of human milk pasteurization and sterilization on total fat content available to the infant as well as on fatty acid composition. Milk samples from 12 mothers (days 5-35 of lactation) were divided into three equal parts: one remained fresh, one was pasteurized (62.5 degrees C for 30min), and one was sterilized (120 degrees C for 30min). Fat content was determined gravimetrically, and the contribution of 30 fatty acids was determined by gas chromatography. For investigation of loss of available fat in sterilized milk, milk was collected from two additional mothers and analyzed with a modified extraction method. Total fat content was the same in fresh, pasteurized, and sterilized milk. The available fat content was 3.1+/-0.4g/dL (mean +/- SE) in fresh human milk, 3.1+/-0.4g/dL in pasteurized human milk, and 2.7+/-0.3g/dL (P < 0.001 vs. fresh) in sterilized human milk because of formation of a surface skin and fat adherence to the vial wall after sterilization. The fatty acid composition of 10 saturated, 10 monounsaturated, and 10 polyunsaturated fatty acids of both the n6 and n3 series was not affected by pasteurization. In sterilized milk there was a slight decrease of linoleic acid (C18:2n6; -0.7% vs. fresh; P = 0.006) and arachidonic acid (C20:4n6; -2.5%; P = 0.045). Pasteurization and sterilization do not affect total fat content of human milk, but sterilization may reduce available fat content by >10%. Fatty acid composition of human milk is not changed by pasteurization, but is slightly changed by sterilization.

Polyunsaturated fatty acid supply with human milk. Physiological aspects and in vivo studies of metabolism.

The origin of polyunsaturated fatty acids (PUFA) in human milk has not been studied in detail. Diet, liberation from maternal stores and endogenous synthesis from precursors may contribute to PUFA present in human milk. Other factors influencing lipid content and fatty acid composition such as gestational age, stage of lactation, nutritional status and genetical background are known. In a series of in vivo studies using stable isotope methodologies we investigated the metabolism of PUFA during lactation. With this techniques the transfer of single dietary fatty acids into human milk, the oxidation and the deposition in tissues were estimated. Our studies demonstrate that the major part of PUFA in human milk seems not to be derived directly from the maternal diet but from body stores. Nevertheless diet is important, because long term intakes affect composition of body stores.

The fatty acid composition of human colostrum.

We reviewed 15 studies reporting on the fatty acid composition of colostrum lipids from 16 geographic regions: 11 European studies and one study each from Central America, the Caribbean, Australia and Asia. The contents of essential fatty acids, saturates and polyunsaturates were similar in the southern European countries Spain, Slovenia and France. Colostrum of St. Lucian women was high in saturates and low in oleic acid, reflecting a high-carbohydrate, low-fat diet. Abundant fish intake was reflected in high contents of docosahexaenoic acid and total n-3 long-chain polyunsaturated fatty acids in St. Lucia. Two French studies published with an interval of two years showed a very similar colostrum fatty acid composition, whereas two German studies obtained with an interval of 14 years showed higher docosahexaenoic acid and arachidonic acid contents in the later study, with an unchanged n-6/n-3 long-chain polyunsaturated fatty acid ratio. Studies from Spain reported a decline of alpha-linolenic acid in colostrum over a time period of 13 years. Colostrum of Australian women contained the lowest polyunsaturated/saturated and n-6/n-3 long-chain polyunsaturated fatty acids ratios (0.28 and 1.58) and the lowest contents of linoleic and alpha-linolenic acids (7.8 and 0.4 wt.%). In contrast, the contents of docosahexaenoic acid, eicosapentaenoic acid and total n-3 long-chain polyunsaturated fatty acids (0.6, 0.4 and 1.4 wt.%) were higher in Australian than in European samples. Fatty acid composition of human colostrum appears to be markedly influenced by geographic differences in maternal dietary composition.

Phase tracking: an improved phase detection technique for cell membrane capacitance measurements.

We describe here a technique called phase tracking that greatly improves the accuracy of measurements of the membrane capacitance of single cells. We have modified the original phase detection technique to include a method for creating calibrated changes in the resistance in series with the cell. This provides a method to automate the adjustment of the phase detector to the appropriate phase angle for measuring membrane capacitance. The phase determination depends only on the cell's electrical parameters and does not require matching of the cell impedance with that of the slow capacitance cancellation circuitry of the patch-clamp amplifier. We show here that phase tracking can accurately locate the phase of the capacitance signal and can keep the detector aligned with this signal during measurements of exocytosis in mast cells, irrespective of the large drifts which occur in cell membrane resistance, membrane capacitance, or series resistance. The phase tracking technique is a valuable tool for quantifying exocytosis and endocytosis in single cells.

Fatty acid composition of human colostrum in Slovenian women living in urban and rural areas.

Colostrum samples were collected on the third day postpartum from 41 Slovenian women living in urban (n = 27) or rural (n = 14) areas. The fatty acid composition of total lipids, analysed by capillary gas-liquid chromatography, was very similar in women from both areas. The only difference was a higher content of oleic acid (18:1n-9) in rural vs. urban areas (36.85 vs. 34.94 wt%, p < 0.05). The fatty acid composition of colostrum lipids in Slovenia was as follows (mean wt%): saturated 37.68, monounsaturated 40.49, polyunsaturated 21.82, linoleic acid (18:2n-6) 15.25, alpha-linolenic acid (18:3n-3) 0.91, docosahexaenoic acid (22:6n-3) 0.43 and arachidonic acid (20:4n-6) 1.03. The ratio of polyunsaturated to saturated fatty acids was 0.58 and the ratio of n-6 to n-3 fatty acids was 8.0. Compared to published data on the colostrum fatty acid composition in other European, American and Asian countries, colostrum from Slovenian women is most similar to Spanish and French colostrum, probably due to a similar fatty acid composition of dietary lipids.

Fatty acid composition of human milk in different regions of Slovenia.

BACKGROUND: The fatty acid composition of human colostrum lipids is influenced by maternal diet. We measured the fatty acid composition of colostrum lipids in Slovenia. METHODS: Milk samples were collected on the 3rd day postpartum from 41 women recruited in three Slovenian regions (Celje, Ljubljana and Koper). Dietary habits were examined by a food-frequency questionnaire. In situ transesterification and capillary gas chromatography were performed to determine the fatty acid composition. RESULTS: The coefficients of variation of the determinations of individual fatty acids accounting for >0.09 wt% were 1.87-5.91%. Between regional areas there were differences in the contents of linoleic (12.62-17.35 wt%; p < 0.001) and alpha-linolenic acid (0.70-1.07 wt%; p < 0.01), whereas the linoleic/alpha-linolenic acid ratios were similar (15.8 in Celje, 16.3 in Ljubljana and 17.9 in Koper). The highest proportion of docosahexaenoic acid (C22:6n-3) was in Celje (0.49 wt%), the lowest in Ljubljana (0.35 wt%; p < 0.05). The long-chain polyunsaturated fatty acid (LCP) content did not correlate with linoleic and alpha-linolenic acid, but there was a correlation between the sum of n-3 and n-6 LCPs. The colostrum linoleic/alpha-linolenic acid ratio was positively correlated with the body mass index during pregnancy. CONCLUSIONS: The fatty acid composition of colostrum lipids in Slovenia shows some variation according to geographical regions.

Effects of human milk pasteurization and sterilization on available fat content and fatty acid composition.

BACKGROUND: Human milk is frequently heat treated in hospitals to reduce bacterial contamination, particularly in banked milk fed to preterm infants. Pasteurization and sterilization may induce oxidative losses of unsaturated lipids and vitamins and may inactivate enzymes and immunologic factors. This study was designed to examine the effects of pasteurization and sterilization on milk fat content available to the recipient infant and on fatty acid composition. METHODS: In fresh, pasteurized (62.5 degrees C for 30 minutes), and sterilized (120 degrees C for 30 minutes) milk samples (5 ml) of 12 mothers (days 5-35 of lactation), fat content was determined gravimetrically and the contribution of 30 fatty acids was determined by gas-liquid chromatography. RESULTS: The coefficients of variation for measurements of milk fat content were 0.7% and of fatty acids accounting for more than 0.09% of weight, 0.1-3.0%. Available fat content was 3.1+/-1.4 g/dl (mean +/- SD) in fresh human milk and 3.1+/-1.4 g/dl (not significant) in pasteurized human milk. Fat content declined to 2.7+/-1.1 g/dl (p < 0.001 vs. fresh) in sterilized human milk, because of increased fat adherence to the container surface after sterilization. The percentage composition of saturated, monounsaturated, and polyunsaturated fatty acids of the n-6 (C18:3, C20:2, C20:3, and C22:4) and the n-3 series (C18:3 C20:5, C22:5, and C22:6) was not affected by thermal treatment. Milk sterilization caused a slight decrease of linoleic (-0.7% vs. fresh milk; p = 0,006) and arachidonic (-2,6%; p = 0.045) acids. CONCLUSIONS: Pasteurization of human milk does not influence fat content and composition, but sterilization may reduce available fat content by more than 10%, whereas there are only slight changes in fatty acid composition.

Docosahexaenoic acid transfer into human milk after dietary supplementation: a randomized clinical trial.

Docosahexaenoic acid (DHA) is important for infant development. The DHA transfer from maternal diet into human milk has not been investigated in detail. We studied the effects of DHA supplementation on the fatty acid composition of human milk and the secretion of dietary (13)C-labeled fatty acids, including DHA, into human milk. Ten lactating women were randomized to consume, from 4 to 6 weeks postpartum, an oil rich in DHA (DHASCO, 200 mg of DHA/day) (n = 5) or a placebo oil (n = 5). Dietary intakes were followed by 7-day protocols. On study day 14 a single dose of [U-(13)C]DHASCO was given orally, milk samples were collected over 48 h, and milk production was recorded. Milk fatty acid composition was determined by gas-liquid chromatography and isotopic enrichment was determined by gas chromatography- combustion-isotope ratio mass spectrometry (GC-C-IRMS). Milk DHA content did not differ between the supplemented and placebo group at study entry (0.29 vs. 0.28 wt%, median). After 2 weeks of supplementation the milk DHA content was almost 2-fold higher in the supplemented versus placebo group (0.37 vs. 0.21 wt%, P = 0.003). Cumulative recovery of [(13)C]palmitic, [(13)C]oleic, and [(13)C]docosahexaenoic acids in human milk at 48 h was similar between supplemented and placebo groups (palmitic acid 7.40 vs. 8. 14%, oleic acid 9.14 vs. 9.97%, and docosahexaenoic acid 9.09 vs. 8. 03% of dose, respectively). Notable lower recovery was observed for [(13)C]myristic acid in both the supplemented and placebo groups, 0. 62 versus 0.77% of dose. Dietary DHA supplementation increases the DHA content in human milk. DHA transfer from the diet into human milk is comparable to palmitic and oleic acid transfer.

Oxidation of an oil rich in docosahexaenoic acid compared to linoleic acid in lactating women.

BACKGROUND: We studied the oxidation of an oil rich in docosahexaenoic acid (DHA; DHASCO((R))) in lactating mothers receiving a dietary DHA supplement or a placebo. The results were compared with the oxidation of linoleic acid. METHODS: Breast-feeding mothers received a dietary supplement (DHASCO; 200 mg DHA/day, n = 5) or a placebo (n = 5) for 14 days. Six weeks post partum all 10 mothers received a single dose of 2 mg/kg body weight uniformly (13)C-labeled DHASCO. In a previously reported study 6 mothers received 1 mg/kg body weight uniformly (13)C-labeled linoleic acid. Breath samples were collected over 48 h after tracer application. The total CO(2) production was measured by indirect calorimetry and the (13)C isotopic enrichment of labeled CO(2) by isotopic ratio mass spectrometry. RESULTS: The oxidation of (13)C-labeled DHASCO in the supplemented and placebo groups was similar. Maximal (13)C enrichment was reached earlier in the group receiving (13)C-DHASCO (median 1.0 vs. 3.0 h in the linoleic acid group). The cumulative (13)C recovery in breath was higher in the DHASCO versus the linoleic acid group until 10 h after tracer application and comparable thereafter. CONCLUSIONS: The difference in oxidation of DHASCO versus linoleic acid after tracer ingestion might be partly due to a faster absorption and oxidation of shorter chain saturated fatty acids contained in DHASCO. The cumulative oxidation of DHASCO and linoleic acid 24 and 48 h after tracer ingestion is similar.