Nutrition Research, Vol. 19, No. 9, pp. 1339-1348, 1999 Copyright 0 1999 Elsevier Science Inc. Printed in the USA. All tights reserved 0271.5317/99/&see front matter
ELSEVIER
PII SO271-5317(!W)OOO91-3
FATTY ACID COMPOSITION
OF THE MILK LIPIDS OF WOMEN IN NEPAL
Barbara L. Schmeits, BA’, Julia A. Cook, BS’, Dorothy J. VanderJagt, PhD’, Margaret A. Magnussen, BA, RN’, Shree Krishna Bhatt, BA3, Emil G. Bobik, Jr., BS4, Yung-Sheng Huang, PhD4 and Robert H. Glew, P~xD’.~ ‘Department of Biochemistry and Molecular Biology, University of New Mexico School of Medicine, Albuquerque, New Mexico, U.S.A 2 United States Peace Corps, Dhangali, Nepal 3Public Health Clinic, Kailali District, Dhangali, Nepal 4Abbott Laboratories, Ross Products Division, Columbus, Ohio, U.S.A.
ABSTRACT We analyzed the fatty acid composition of the triacylglycerol and phospholipid fractions of human milk samples obtained 2-4 weeks postpartum from 48 women living in rural Nepal. The most noteworthy aspects of the fatty acid composition of the triacylglycerol fraction were the proportions of the two essential fatty acids, linoleic acid (C18:2n-6) and a-linolenic acid (C18:3n-3). The proportion of linoleic acid was very low (7.91%), while that of a-linolenic acid was relatively high (1.93%). Together, the n-3 and n-6 polyunsaturated fatty acids accounted for 12.4% of the total fatty acids in the triacylglycerol fraction, and de nova fatty acids (ClO:O-C14:O) accounted for 25.0% of the total, arachidonic acid 0.35%, and docosahexaenoic acid (DHA) 0.21% of the total. In the phospholipid fraction, the two essential fatty acids accounted for 6.38% of the fatty acid total. In the phospholipid fraction, 23.0% of the fatty acids were contributed by de novo fatty acids, 0.57% by arachidonic acid and 0.78% by DHA. The mean body mass index (BMI, kg/m*) of the women in the Nepal study was in the middle range of other groups we have studied in Nigeria, yet the value of linoleic acid in the triacylglycerol fraction of their milk was lower than the value we found in the milk lipids of the Nigerian women. This leads us to speculate the low proportion of linoleic acid in the milk fat of the Nepalese women is due more to the diet of the population rather than the overall nutritional status of the mothers, as reflected in their BMI values. Q,999F.lar”,cr sc1rnce Inc Key Words: Human milk, Nepal, Essential fatty acids, Lactation, Fulani
5Towhom all correspondence should be addressed: Robert H. Glew, Ph.D., Department of Biochemistry and Molecular Biology, University of New Mexico School of Medicine, Room 249 BMSB, Albuquerque, NM 87131. Telephone: (505) 272-2362; FAX: (505) 272-6587; e-mail: rglew @ salud.unm.edu.
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B.L. SCHMEITS et al.
INTRODUCMON
Milk fat is the major source of energy, essential fatty acids and fat-soluble vitamins for breast-fed infants. Furthermore, dietary intake of nutritionally critical fatty acids in infancy may have effects upon the future development of diseases such as atopic dermatitis and atherosclerosis (1). Long-chain polyunsaturated fatty acids (LCPUPA) are of particular interest due to their established role in promoting the development of the nervous system (2,3). Premature infants who are exclusively breast-fed have a vital need for a constant supply of LCPUFA from milk because these fatty acids are stored in the fetus only during the third trimester of pregnancy and their reserves are usually marginal (4). Linoleic (C18:2n-6) and a-linolenic acid (C18:3n-3) are two essential fatty acids that serve as precursors for all of the n-6 and n-3 fatty acids, respectively. The balance between these two fatty acids is significant because increased levels of one series can depress the synthesis of the other (1). The ratio of n-6:n-3 fatty acids increases with days postpartum (5). Arachidonic acid (AA) (C20:4n-6) and docosahexaenoic acid (DHA) (C22:6n-3) arc two important LCPUFA that are synthesized from linoleic and a-linolenic acid, respectively. Arachidonic acid plays a major role in growth during the first few months of life, serves a structural function as a component of membrane phospholipids and it is a precursor to the prostaglandins. DHA is important in the development of the central nervous system and retina (6). Triacylglycerols account for 98 percent of the lipids in human milk and function in fatty acid transport and storage. Phospholipids comprise a much smaller fraction of the total lipids of human milk and arise by ejection of membrane-surrounded fat globules into the duct. Differences in the content of lipid between term and pre-term human milk have been reported (7,8) and the lipid composition of breast milk varies widely across populations and geographic regions (9-12). Several factors affect the lipid composition of milk, including time postpartum, time of day, the mother’s diet, parity, metabolic disorders, infections and socioeconomic status (13,14). Dietary factors also influence the AA and DHA content of human milk. Differences in the composition of milk lipids across populations can usually be accounted for by differences in the proportions of fat and carbohydrate in the diet ( 13). Many studies have been performed to determine the content of fatty acids in the milk of women of industrialized countries, but information on the composition of milk from women in less industrialized countries remains incomplete. Herein we report the fatty acid composition of the triacylglycerol and phospholipid fractions of milk from women living in rural Nepal.
METHODS AND MATERIALS
Subiects The study populations were recruited from the village of Dhangali, in rural Nepal. Fortyeight milk samples were collected from women living in or around the village. Samples were collected from 40 women native to Nepal, and 8 women of unmixed That-u ethnicity, the original settlers of the Terai, the main rice-growing region in the southern section of Nepal. Milk was obtained during the months of July through November 1997, and the lactation stage of the women was 2-4 weeks postpartum. Approximately 10 ml of milk were collected from each
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HUMAN MILK AND FATTY ACIDS
mother by manual expression midway through nursing. The samples were aliquoted into 1.5 ml cryovials and stored at -2O’C for 3-6 weeks until the samples were transported on dry ice to the United States for analysis. The mean body mass index (BMI, kg/m*) of the mothers was 19.7 f 1.8 and their average parity was 2.3 + 1.2 (Table 1). The relatively low mean BMI value for the combined study population, along with the fact that the BMI values of the subjects were as low as 15.8, indicates that the overall nutrition of the women was suboptimal. The Ethics Review Board of the Ministry of Health in Nepal approved this study.
Summary of the Anthropometric
Tharu (n=8) Native Nepalese (n=40) Combined Nepalese (n=48) -8 Due to only one significant
TABLE 1 Characteristics of the Lactating Nepalese Women*.
Weight (kg) Mean (&SD) 43.9Q.O) 45.3(4.8) 45.1(4.8)
Height (m) Mean (&SD) 1.52(0.06) 1.51(0.05) 1.51(0.05)
BMI(kg/m*) Mean (*SD) 18.9(1.3) 19.9(1.8) 19.7(1.8)
parity Mean @SD) 2.6(1.2) 2.2(1.2) 2.3( 1.2)
difference between the two groups, the data were pooled.
The subjects were interviewed about their dietary habits. Meals are typically eaten twice a day (9am and 7pm) with the mothers eating last and taking in only what is left by the other family members. The low BMI of the mothers could be a result of reduced caloric intake based on the low availability of food. Local public health informants have estimated a daily caloric intake of 1600 calories. The typical daily diet of the Nepalese women we studied consisted of mainly carbohydrates and low amounts of protein and fat. Rice, the staple of the diet, accounts for the high proportion of carbohydrate in their diet and dahl (lentils) provides most of the protein in their diets. Less frequently, the women eat peanuts. Chai tea is the primary source of sugar in the diet. Vegetables, including okra, cauliflower, cabbage and sag (spinach or any green leafy plant) are consumed at every meal, the quantities of which vary depending on the season and availability. Pickled cucumbers, tomatoes and papaya are eaten with lemon juice. Additionally, bananas and tangerine-like fruits are eaten when available. Mustard oil and ghee (buffalo milk fat) were the sole fat sources in the diets of the lactating women in this study. Fattv Acid Analvsis Milk samples were thawed, warmed to 37’C and vortexed before analysis. Lipids were extracted by the method described by Folch et aE. (15). The triacylglycerol and phospholipid fractions were separated by thin layer chromatography using a hexane-diethyl ether-acetic acid solvent system (80:20:1 by volume). Boron trifluoride-methanol (14%, w/v) was used for transesterification of the fractions and the fatty acid methyl esters were extracted using hexane (16). Fatty acids were quantified using a Hewlett Packard Gas Chromatograph (5890 Series II; Mississauga, Ontario) equipped with a flame-ionization detector and a 50 m fused silica capillary column coated with 0.25 urn Supelcowax 10 (Supelco Inc., Bellefonte, PA) (17). The injector and detector temperatures were 230-C. Commercial standards (Nu-Chek-Prep, Inc., Elysian, MN, USA and Supelco, Inc., Bellefonte, PA) were used for identification and quantification of fatty acid methyl esters. Results are expressed in g/100 g total fatty acid.
B.L. SCHMEITS et al. Statistical Analvsis
Multiple variable regression analyses and t-tests were performed using NCSS 6.0 (Kaysville, Utah). A p-value of 0.05 was considered significant.
RESULTS
Fattv acid comnosition of the triacvlglvcerol fraction The milk samples were divided based on ethnicity, and two groups of women were identified: the Tharu and the native Nepalese. In our preliminary analysis of the data, because there were only eight Tharu women, the same number of Nepalese subjects were selected for comparison based on a match of the BMI and the number of pregnancies. When the critical fatty acids of the triacylglycerol fraction of the milk samples of these two groups were compared, only one statistically significant difference (p = 0.03) was observed: the concentration of DHA in the milk of the Tharu women (0.24%) was higher than that in the matched native Nepalese group (0.16%). Since this was the only difference we observed between the two groups, and because the difference was not large, the data for the two populations were pooled (Table 2). TABLE 2 The.Fatty Acid Composition (wt%) of the TriacylglycerolFraction of Milk from Women of Nepal and Nigeria. Triacylglycerols Fatty Acids Saturated ClO:O c12:o c14:o De mvo Total c15:o c16:o C18:O c2o:o c22:o c24:o Total Monounsaturates C14:l Cl&l C18:l C2o:l C22:l C24:ln-9 Total
Nepal Mean (SD)
Nigeria’ (Fulani) Mean (*SD)
2.53 12.0 lo.5 25.0 0.59 21.7 4.88 0.19 0.11 0.07 52.6
(0.63) (3.89) i3.42j (7.95) (0.371 (4.Olj (1.78) io.o6j (0.05) (0.03) (14.3)
3.92 18.4 13.9 36.3 0.41 21.5 3.80 0.16 0.06 0.07 62.3
(1.62) (7.82) i4.77j (0.00) (0.31) (3.75j (1.90) (0.07j (0.03) (0.05) (20.3)
0.20 2.76 25.5 2.22 2.98 0.71 34.4
(0.07) il.OOj (4.26) (1.14) (2.08) (0.47) (9.02)
0.21 1.97 21.5 0.38 0.10 0.05 24.2
(0.13) (1.39) (5.25) (0.14) (0.04) (0.05) (7.00)
Nepal
Fatty Acids
Mean (&SD)
Nigeria (Fulani) Mean (*SD)
Polyunsaturatesn6 c18:2 C18:3 c20:2 C20:3 C20:4 C22:4 C22:5 Total
7.91 0.10 0.35 0.31 0.35 0.10 0.91 10.0
(2.34) io.o4j (0.11) (0.08) io.llj (0.05) (0.44) (3.16)
9.95 0.10 0.33 0.40 0.42 0.14 0.07 11.41
(2.13) io.o4j (0.13) (0.12) (0.22j (0.12) (o.o4j (2.81)
Polyunsaturatesn3 C18:3 C20:5 C22:5 C22:6 Total
1.93 0.13 0.17 0.21 2.44
(1.30) (0.08) (0.07) (0.09) (1.54)
0.50 0.04 0.07 0.15 0.76
(0.16) (0.02) (0.04) (0.08) (0.31)
‘Adapted from Schmeitset al. (18)
As shown in Table 2, the most noteworthy aspect of the fatty acid composition of the triacylglycerol fraction of the milk of women of Nepal were the proportions of the two essential fatty acids, linoleic acid (Cl8:2n-6) and a-linolenic acid (C18:3n-3). The proportion of linoleic acid was very low, accounting for only 7.91% of the total fatty acids; in contrast, the proportion of the other essential fatty acid, a-linolenic acid, was relatively high (1.93%). Collectively, the proportions of n-3 and n-6 polyunsaturated fatty acids accounted for 12.4% of the total. The combined proportions of n-6 polyunsaturated fatty acids averaged were relatively low (lO.O%), while the proportion of total n-3 polyunsaturated fatty acids was very high (2.44%).
HUMAN MILK AND FAll-Y ACIDS
De nova fatty acids (ClO:O-C14:O) accounted for half of the triacylglycerol fatty acids were saturated Cl0 fatty acids accounted for 34.4% of the total fatty acids. relatively high percentages were found in the proportions C24: In-9 (0.7 1%).
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25.0% of the total, and approximately to C24 fatty acids. Monounsaturated Of these monounsaturated fatty acids, of C20: 1 (2.22%), C22: 1 (2.98%), and
Finally, at 0.35% the contribution of arachidonic acid to the total triacylglycerol fatty acid fraction was found to be substantial, while the proportion of docosahexaenoic acid (DHA) was found to be adequate at 0.2 1%. Fattv acid comnosition of the nhosnholiuid fraction Table 3 is a summary of the fatty acid composition of the phospholipid fraction of the milk specimens of the 48 subjects in Nepal. De novafatty acids accounted for 23.0% of the fatty acids in the phospholipid fraction. Together, the two essential fatty acids, linoleic and alinolenic acids, accounted for 6.38% of the fatty acid total. Arachidonic acid, which can be synthesized from linoleic acid in humans, contributed 0.57% to the phospholipid fraction. DHA, which is derived from ol-linolenic acid, accounted for 0.78% of the fatty acids in the phospholipid fraction of the Nepalese milk specimens.
TABLE 3 The Fatty Acid Composition (wt%) of the Phospholipid Fraction of Milk from Women of Nepal and Nigeria. Phospholipids Fatty Acids Saturated c1o:o c12:o c14:o Denovo Total Cl50 Cl6:O C18:O c2o:o c22:o C24:O Total Monounsaturates C14:l C16:l C18:l c20: 1 c22: 1 C24:ln-9 Total
Nepal Mean (*SD)
Nigeria’ (Fulani) Mean (*SD)
1.48 (0.38) 11.4 (2.65) 10.1 i4.35j 23.0 (7.39) 1.28 (0.63j 30.2 (10.3) 9.76 (5.84) 0.72 (0.56j 0.56 (0.52) 0.37 (0.34) 65.8 (25.6)
0.54 4.81 14.1 19.4 0.96 42.0 3.65 0.26 0.14 0.22 66.7
(0.23) (1.78) (5.43) (7.44) (0.79) (16.9) (1.46) (0.18) (0.12) (0.19) (27.0)
0.22 0.88 14.6 1.43 2.02 1.43 20.6
0.13 0.83 11.3 0.82 0.30 0.06 13.4
(0.00) (0.55) (6.09) (0.76) (0.30) (0.04) (7.73)
(0.19) (0.52) (10.1) (0.82j (1.32) (1.77) (14.7)
Nepal Fatty Acids Polvunsaturates n6 C18:2 C18:3 c20:2 C20:3 C20:4 C22:4 C22:5 Total
Polyunsaturates n3 C18:3 C20:5 C22:5 C22:6 Total
Mean (*SD)
Nigeria (Fulani) Mean (&SD)
5.23 0.37 0.26 0.32 0.57 0.24 0.68 7.68
(3.97) (0.74) (0.57) (0.16) (0.26) (0.25) (0.58) (6.53)
2.63 1.71 0.41 0.22 0.86 0.60 0.13 6.55
(1.08) (1.68) (0.33) (0.23) (2.16) (1.23) (0.09) (6.79)
1.15 0.57 0.15 0.78 2.65
(1.20) (1.82) (0.09) (1.00) (4.11)
0.20 0.29 0.08 0.12 0.69
(0.14) (0.27) (0.04) (0.07) (0.52)
*Adapted from Schmeits et al. (18)
DISCUSSION
One of the noteworthy findings of this study and one of potential nutritional significance was the relatively small contribution the essential fatty acid linoleic acid (C18:2n-6) made to the fatty acids in the triacylglycerols in the milk of the Nepalese women. When compared to human milk data reported for many countries representing a wide range of geographical locals and
B.L. SCHMEITS et al.
cultures (Table 4), the proportion of linoleic acid (7.91%) in the milk lipids of the Nepalese women was comparable to the lowest value reported (range, 8.20-17.2%). The total proportion of n-6 polyunsaturated fatty acids, too, was also considerably lower than the lowest value reported for populations worldwide, this being due primarily to the low content of linoleic acid in the milk of the Nepalese women. In light of the fact that linoleic acid is the precursor of arachidonic acid in humans, and despite the fact the proportion of linoleic acid was very low in the milk fat of the Nepalese women, the proportion of arachidonic acid (C20:4 n-6) (0.35%) in their milk was in the middle of the range of values reported for other populations worldwide (0.09-O&t%, Table 4). It seems that either the Nepalese women were consuming foodstuffs rich in arachidonic acid at the time we conducted our study, or that the arachidonic acid-forming pathway was able to convert the low amounts of linoleic acid that were available into arachidonic acid. The finding that the arachidonic acid content of the milk was adequate is important, because arachidonic acid is a precursor to the prostaglandins.
Table 4 Cornparisooof the Fatty Acid Composition(wt%) of HumanMilk Triacylglycxrolsfor Various PopulationsWorkiwii’. Nepal Nigeria Nigaia DominicaTanzaniaSwinatn Coracao Beliz USA ChiieseMalaysia India GambiaS.Africa (Fulaoi) (Yomba) (Rat=0
Saturated Cl&O 2.53 3.92 cno 11.99 18.43 Cl40 10.47 13.91 Denmo Total 25.0 36.3 c15:o 0.59 0.41 Cl&O 21.74 21.52 Cl&O 4.88 3.80 C2O:O 0.19 0.16 c22:o 0.11 0.06 cm0 0.07 0.07 Total 52.57 62.28
2.10 31.40 9.00 42.5 NR 20.10 3.40 NR 0.10 NR 66.10
3.42 16.34 14.95 34.7 NR 21.59 5.18 0.24 0.08 0.08 61.88
2.75 16.51 14.72 34.0 NR 19.98 3.65 0.12 0.06 0.06 57.85
3.08 13.12 10.80 27.0 NR 20.85 4.5 1 0.18 0.11 0.01 52.66
2.40 2.07 1.00 0.84 10.71 9.47 6.50 5.28 10.47 9.57 6.20 6.53 23.6 21.1 13.7 12.7 NR NR NR 0.17 19.77 22.85 20.90 22.00 6.23 7.64 7.30 5.16 0.27 0.19 NR 0.28 0.14 0.08 NR 0.09 0.14 0.07 NR 0.16 50.13 51.94 41.90 40.51
0.90 1.22 0.92 8.86 8.44 6.99 10.05 8.90 8.80 19.8 18.6 16.7 0.16 0.22 NR 28.86 25.77 14.10 4.09 4.98 3.94 0.19 0.26 0.47 0.09 0.06 0.03 0.16 0.19 NR 53.36 50.04 35.25
1.30 7.40 15.90 24.6 NR 21.80 6.80 0.10 0.10 0.10 53.50
Moaoonsatarates C14:I 0.20 Cl&l 2.76 C18:l 25.55 C2o:l 2.22 C22:l 2.98 c24h9 0.71 Total 34.42
0.21 1.97 21.46 0.38 0.10 0.05 24.17
NR 3.10 20.80 0.90 NR NR 24.80
0.22 2.65 17.93 0.47 NR 0.04 21.31
0.19 0.27 19.42 0.20 NR 0.02 20.10
0.22 3.23 25.16 0.40 NR 0.08 29.09
0.20 1.97 23.40 0.47 NR 0.12 26.16
0.25 NR 0.18 2.70 2.90 3.03 28.09 36.70 33.82 0.47 NR 0.66 NR NR 0.18 0.06 NR 0.13 31.57 39.60 38.00
0.33 0.26 4.17 3.39 30.82 30.66 0.51 0.63 0.20 0.18 0.09 0.07 36.12 35.19
0.23 0.66 47.00 0.83 0.22 0.05 48.99
0.60 3.10 23.90 0.10 TR N-R 27.70
Polyoosatoratesa6 C18:2 7.91 C18:3 0.10 c20:2 0.35 C20:3 0.31 C20:4 0.35 C22:4 0.10 C22:5 0.91 10.04 Total
9.95 0.10 0.33 0.40 0.42 0.14 0.07 11.41
8.20 ND NR NR 0.60 NR NR 8.80
10.14 0.07 0.30 0.39 0.45 0.11 0.03 11.49
13.88 0.11 0.29 0.40 0.60 0.13 0.07 15.48
12.02 0.10 0.32 0.41 0.09 0.14 0.08 13.16
16.06 0.08 0.58 0.50 0.09 0.22 0.43 17.96
10.27 0.10 0.34 0.38 0.51 0.16 0.05 11.81
17.20 11.96 TR NR 0.71 NR NR 0.51 0.10 0.64 NR NR NR NR 17.30 13.82
8.84 TR 0.29 0.27 0.47 NR NR 9.87
10.71 nz 0.39 0.40 0.57 NR NR 12.07
13.00 NR 0.83 0.21 0.31 0.08 0.30 14.73
15.30 0.30 0.30 0.80 1.00 TR NR 17.70
Polyunsaturateso3 C18:3 1.93 cm5 0.13 C22:5 0.17 C22:6 0.21 Total 2.44
0.50 0.04 0.07 0.15 0.76
NR TR TR 0.30 0.30
0.73 0.05 0.11 1.15 2.04
1.00 0.19 0.15 0.27 1.61
0.70 0.06 0.17 0.41 1.34
NR 0.05 0.21 0.43 0.69
0.62 0.00 0.13 0.25 1.00
0.10 NR NR NR 0.10
0.30 NR 0.21 0.09 0.60
0.33 NR 0.19 0.09 1.42
0.84 NR 0.20 0.39 1.43
0.10 0.10 0.10 0.10 0.40
~~NotDetectai,NR=NotRetmted.TR=Trace *~daptadficm ~easenet 01. (24);except Nigeria@hoi)
0.38 NR 0.21 0.71 1.30
thn Schmits et aL (18) and Nigeria(Yoruba) from Glew et 01. (19).
HUMAN MILK AND FATTY ACIDS
In two of our previous studies on the lipids in the milk of two different groups in southwestern Nigeria, the Fulani (18) and the Yoruba (19), we found relatively low proportions of linoleic acid in the triacylglycerol fraction despite significant differences in mean body mass indexes of the groups (18.3 kg/m*, Yoruba; 26.2 kg/m*, Fulani). This leads us to speculate that the relatively low proportion of linoleic acid we observed previously (18) in the milk of these Nigerian women was most likely the result of consumption of plant foods that were deficient in this essential n-6 fatty acid. The mean BMI of the Nepalese women was relatively low (19.7 kg/m’) (Table 1) and the proportion of linoleic acid in the triacylglycerol fraction of their milk was lower than the values we found for the milk lipids of both Yoruba and Fulani women. This indicates that the low proportion of linoleic acid in the milk fat of the Nigerians and Nepalese women was probably due more to the foodstuffs eaten by these populations rather than the overall nutritional status of the mothers, as reflected in their BMI values. It has been reported that when the proportion of linoleic acid (C18:2n-6) in the body is low, the A9 desaturase operates to produce increased amounts of n-9 fatty acids (17). This phenomenon may explain the high proportions of n-9 fatty acids (C20: 1, C22: 1, C24: 1) we found in the milk of the Nepalese women. The milk samples contained relatively high proportions of C20: 1 (2.22%), 22: 1 (2.98%) and 24: ln-9 (0.71%) monounsaturated fatty acids. At 1.93%, the mean proportion of the other essential fatty acid, a-linolenic acid (C18:3n3), in the milk of the Nepalese women was nearly twice the highest proportion reported for populations worldwide (range, O.lO-l.OO%, Table 4). Due mainly to the high proportion of CXlinolenic acid in the milk of the Nepalese women, the total contribution of n-3 polyunsaturated fatty acids to the total was also high (2.44%). Although the proportion of a-linolenic acid in the milk lipids of the Nepalese women was very high, the percentage of DHA, which is synthesized from a-linolenic acid, was unremarkable. For the developing newborn, DHA is critical for the development of the nervous system and retina. If the DHA content of the milk becomes too low, the needs of the exclusively breast-fed infant may not be met, particularly during the first six months of life. However, the milk of the Nepalese women we studied appears to provide sufficient DHA to satisfy the needs of their breast-feeding infants (20). This observation is significant because of the critical need infants and newborns have for DHA. (21,22). When the percentage of each of the fatty acids in the triacylglycerol fraction of the milk of the Nepalese women were plotted versus the body mass index, no significant correlations were observed. The proportion of de mvo fatty acids we found in the triacylglycerol fraction of the milk of the Nepalese women (25.0%) was within the range of values reported for populations worldwide (range, 12.7-42.5%, Table 4). These intermediate chain-length fatty acids are important in the nutrition of the nursing infant. First, triacylglycerols comprised of ClO-Cl4 fatty acids are preferentially digested by gastric and lingual lipases to produce fatty acids that are rapidly absorbed in the stomach of the infant, thereby providing a ready source of fuel. Second, in the small intestine, pancreatic lipase degrades triacylglycerols into intermediate chain-length fatty acids that are absorbed directly into the blood circulation without first having to be incorporated into chylomicrons. Third, fatty acids containing less than 16-carbon atoms can be taken up directly by mitochondria without having to go through the acyl-camitine/carnitine transport system (23). Because the milk fat of the Nepalese women contained a reasonably high percentage of de now fatty acids, it seems their milk provides sufficient quantities of intermediate chain-length fatty acids to satisfy the energy needs of the infants they nurse. When the fatty acid composition of the phospholipid fraction of milk from women of Nepal was compared to that of the Fulani women of northern Nigeria, several significant
1346
B.L. SCHMEITS
et al.
differences were observed (Tables 2, 3). The triacylglycerol fraction of the milk of the Fulani women contained a higher proportion of de nova fatty acids than that of the milk of the Nepalese women (Table 2) (36.3 % vs. 25.0%, respectively) (p&01), and the proportion of linoleic acid in the triacylglycerol fraction of milk of the Fulani women was greater than that found in the milk of the Nepalese women (9.95% vs. 7.91%, respectively) (pcO.01). However, when the proportions of linoleic acid in the phospholipid fractions of the Fulani and Nepalese women were compared, the milk from the Fulani women was found to contain a higher proportion relative to the proportion in the milk of the Nepalese women (5.23% vs. 2.63%, respectively) (p=O.Ol). In summary, this study has drawn attention to the low proportion of linoleic acid (C18:2n6) in the milk of Nepalese women. Whether or not the low amounts of this essential fatty acid compromise the growth and development of the children they nurse remains to be seen. Despite the low proportion of this essential n-6 fatty acid in the milk lipids of the Nepalese women, their milk seems to provide adequate amounts of arachidonic acid. However, we do not know whether this arachidonic acid arises from the conversion of the essential fatty acid, linoleic acid, or from the consumption of foodstuffs rich in this fatty acid. Our study raises other questions as well: as the parity of the Nepalese mothers increases beyond five or six, does the decreasing DHA content of her milk put the exclusively breast-fed infant at risk for developmental abnormalities? Can foods rich in linoleic acid and n-6 fatty acids be identified and provided to breast-feeding Nepalese mothers to combat the relatively low levels of this essential fatty acid in the milk of Nepalese women we studied? These and other questions will be the subject of future studies.
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