Maternal Nutrition and Supplements for Mother
and Infant
Lactation is the physiologic completion of the repro- ductive cycle. The maternal body prepares during pregnancy for lactation, not only by developing the breast to produce milk but also by storing addi- tional nutrients and energy for milk production. The transition to fully sustaining an infant should not be complex or require major adjustments for a woman.
After delivery, mothers usually note an increase in appetite and thirst and a change in some dietary preferences. In some cultures, anthropologists have noted that, traditionally, the birth of a baby means that members of the community take gifts of special foods—usually high in protein, nutrients, and calo- ries—for the mother to ensure she will make good milk for the infant. This tradition may have affected some early studies in which relatively malnourished women were noted to produce milk comparable with that produced by well-nourished women in industrialized countries.
After an exhaustive study of the world’s literature and current scientific evidence, the Subcommittee on Nutrition During Lactation of the Committee on Nutritional Status During Pregnancy and Lactation of the Food and Nutrition Board of the Institute of Medicine at the National Academy of Sciences112 published its first report. The subcommittee stated that breastfeeding is recommended for all infants in the United States under ordinary circumstances. Women living in a wide variety of circumstances in the United
States and elsewhere are capable of fully nourishing their infants by breastfeeding them. Furthermore, exclusive breastfeeding is preferred for the first 4 to 6 months. The report further stated that mothers with less than perfect diets could make good milk.
The overwhelming evidence indicates that women are able to “produce milk of sufficient quan- tity and quality to support growth and promote the health of infants—even when the mother’s supply of nutrients is limited.” Nonetheless, the depletion of the mother’s nutrient stores is a risk if efforts to achieve adequate food intake are not made to replace maternal stores.
Most material for nursing mothers regarding maternal diet during lactation set up complicated
“rules” about dietary intake that fail to consider the mother’s dietary stores, normal dietary prefer- ences, and cultural patterns. Thus, one barrier to breastfeeding for some women is the “diet rules”
they see as being too hard to follow or too restric- tive.40 All over the world, women produce ade- quate and even abundant milk on inadequate diets. Women in cultures with modest but ade- quate diets produce milk without any obvious detriment to themselves and with none of the fatigue and loss of well-being that some well-fed Western mothers experience. Insufficient milk is a problem in Western cultures and rarely in devel- oping countries.
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Impact of Maternal Diet on Milk Production
Although much has been learned about dietary requirements for lactation by studying women from many cultures and various levels of poor nutrition, some of the information is conflicting, principally because of varying sampling techniques and the improvement over time in laboratory analysis.
Extensive reviews of the current literature on vari- ous nutrients in human milk and the influence of maternal dietary intake have been referenced.* Those readers needing access to the original studies are referred to the bibliographies from these reviews, which include hundreds of items, a listing beyond the scope of this text.
MILK VOLUME
The volume of milk produced varies over the dura- tion of lactation from the first few weeks to 6 months and beyond but is remarkably predictable except during extreme malnutrition or severe dehydration.
In periods of acute water deprivation, manifested in a healthy mother by an acute bout of vomiting and diarrhea, the volume of milk will diminish only after the maternal urine output has been significantly compromised (10% dehydration).
Malnutrition, however, is complex, and single- nutrient deficiencies are rare. Malnutrition does seem to have an effect on the total volume of milk produced. In the extreme, when famine occurs, the milk supply dwindles and ceases, with ultimate star- vation of the infant. The classic study is the report of Smith105on the effects of maternal undernutri- tion on the newborn infant in the Hunger Winter in Holland in 1944 to 1945. It was reported that the volume of milk was slightly diminished, but the duration of lactation was not affected. The lat- ter is a testimony to courage rather than diet. Anal- ysis of milk produced showed no significant deviations from normal chemical structure. Milk was produced at the expense of maternal tissue.
These data from the Dutch famine in the 1940s during World War II were reexamined by Stein et al.,109who pointed out that women who con- ceived during the famine did develop some mater- nal stores in anticipation of lactation that were not accounted for by the fetus, placenta, or amniotic fluid, even though the fetus was a pound lighter at birth. They reported fetal weight down by 10% but maternal weight down by only 4%. This demonstrates the maternal body’s strong biologic commitment to preparing for lactation during pregnancy.
There is a wide range of volume of milk intake among healthy breastfed infants, averaging 750 to 800 g/day and ranging from 450 to 1200 g/day.13 Any factor that influences the frequency, intensity, or duration of suckling by an infant influences the volume.85 In a study of wet nurses in the 1920s, Macy et al.75 reported human capacity at 3500 mL/day. Compared with the 800 mL from mothers with singletons, studies of mothers pro- ducing for multiples, done by Saint et al., confirmed production of 2 to 3 L/day for twins and triplets. At 3 months of age for all populations, the volume aver- ages 770 g/day (range 500 to 1200 g/day).61,88The self-regulation of milk supply by the infant has been confirmed by a study by Dewey et al.29 in which additional milk was pumped after each feeding for 2 weeks, thus increasing the milk supply. The infants, however, remained at baseline consumption during the pumping. The residual milk supply of healthy women (i.e., that which can be extracted after a full feeding) is about 100 g/day, even when an infant consumes comparatively low volumes of milk.29,84,86
Topographic computer imaging has been used to study breast production and storage capacities in the laboratory of Hartmann. Using moire´ pat- terns projected onto the breast, it has been possible to calculate the volume of milk produced. As the breast expands with increasing milk, the moire´ pat- terns change. By correlating the maternal weights before and after a feeding and the imagery patterns, data were converted to accurate milk volumes. This technique has remarkable potential for clinical use.
Hartmann reports the normal range of milk produc- tion from 1 to 6 months postpartum to be between 440 and 1220 g/day for mothers who gave birth at full term.
Prentice and Prentice99described “energy spar- ing adaptations” that were associated with normal lactation when energy intake is limited. These were decreases in basal metabolic rate, thermogenesis, and physical activity.
When well-nourished mothers reduced their intake by 32% for 1 week, consuming no less than 1500 kcal/day, no reduction in milk volume occurred, although plasma prolactin levels increased. Mothers who consumed less than 1500 kcal/day for a week did experience decreased milk volumes compared with those of the control group and the group con- suming more than 1500 kcal.
Exercise, manual labor, and losing weight do not usually alter an established milk volume. Milk pro- duction will increase with infant demand, but infant demand will only increase with growth, which depends on sufficient nourishment.61 Having the mother take supplements could improve produc- tion and stimulate the infant’s appetite.
*References40,80,83,87.
ENERGY SUPPLEMENTATION AND LACTATION PERFORMANCE
When women received supplements during the last trimester of pregnancy, no effect was noted in their milk production. This suggests that short-term sup- plementation may be ineffective. Other studies that provided supplementation of a maximum of 900 kcal/day for 2 weeks resulted in an increase in milk production (662 to 787 g/day).114 No increase in infant weight compared with the con- trol group’s infants was seen in this period of 2 weeks.
The problem of insufficient milk supply for a baby is reported in well-nourished as well as poorly nourished populations, but in cross-cultural studies it appears to be unrelated to maternal nutrition sta- tus.116The effect of supplementation may be more psychologic than physiologic.
In countries where food supplies vary with the season, milk supplies drop 1 dL/day during periods of progressively greater food shortages. Studies continue on lactation performance of poorly nour- ished women around the world, including Burma, The Gambia, Papua New Guinea, and Ethiopia as well as among Navajo people. Results continue to reflect an impact on quantity, not quality, of milk.13,23,65,105
The interrelationship of milk volume, nutrient concentration, and total nutrient intake by the infant must be considered.29 The reason for low protein content in a given sample may be lack of protein stores, lack of total energy content, or lack of vitamin B6, a requirement of normal protein metabolism.
Of concern, however, is the report of dietary supplementation of Gambian nursing mothers in whom lactational performance was not affected by increased calories (700 kcal/day).100 The sup- plement produced a slight initial improvement in maternal body weight and subcutaneous fat but not in milk output. Whether the mothers utilized the increased energy to work harder farming or whether the infants did not stimulate increased milk production is unresolved. Food supplementation of lactating women in areas where malnutrition is prevalent has generally had little, if any, impact on milk volume.112Such supplementation improves maternal health and is more likely to benefit the mother than the infant except where milk compo- sition had been affected by specific deficiencies.
PROTEIN CONTENT
Since the work of Hambraeus reestablished the norms for protein in human milk to be 0.8 to 0.9 g/dL in well-nourished mothers, figures from previous studies have been recalculated to consider
that all nitrogen in human milk is not protein; 25%
of the nitrogen is nonprotein nitrogen (NPN) in human milk, and only 5% of the nitrogen is NPN in bovine milk. The protein content of milk from poorly nourished mothers is surprisingly high, and malnutrition has little effect on protein concen- tration. An increase in dietary protein increases volume but not overall protein content, given the normal variations seen in healthy, well-nourished women.
Observations made over a 20-month period of continued lactation showed that milk quality did not change, although the quantity decreased slightly, which has been attributed to the decreas- ing demand of a child who is receiving other nour- ishment. Therefore, the total protein available with the decreased volume of milk and increased weight of the child decreased from 2.2 g/kg of body weight to 0.45 g/kg. The need for additional protein sources from other foods for the child after 1 year of age becomes obvious.
The composition of human milk is maintained even with less-than-recommended dietary intake of macronutrients. The concentrations of major minerals, including calcium, phosphorus, magne- sium, sodium, and potassium, are not affected by diet. Maternal dietary intakes of selenium and iodine, however, are positively affected: an increase in the diet increases the level in the milk. The pro- portion of different fatty acids in human milk varies with the maternal dietary intake.
In Zaire,83lactating mothers with protein mal- nutrition were given 500 kcal (2093 kilojoules [kJ]) and 18 g of protein as a cow milk supplement for 2 months, after which their nutritional status improved significantly.31The volume of milk did not change (607 versus 604 mL). Their breastfed infants, however, did show significant improve- ment in their mean serum albumin levels, and their growth matched that of healthy infants of the same age.
The effect of very-low-protein (8% of energy) and very-high-protein (20% of energy) diets on the protein and nitrogen composition of breast milk in three healthy Swedish women “in full lactation”
was significant.50 High-protein diets produced higher production and greater concentrations of total nitrogen, true protein, and NPN. The increased NPN was caused by increased urea levels and free amino acids. The 24-hour outputs of lacto- ferrin, lactalbumin, and serum albumin were not significantly higher.
When marginally nourished women were pro- vided a mixed-protein diet predominantly from plant sources up to 1.2 g/kg/day, equilibrium was achieved at a protein intake of 1.1 g/kg. In a study of healthy women given marginal protein intakes, Motil et al.82 reported that maternal milk production and the
protein nitrogen, but not the NPN, fraction of human milk were relatively well preserved in the short term.
The practical significance, except as related to fad diets, of these results is limited because the diets were extreme and were maintained for only 4 days.
The impact on human nutritional physiology, how- ever, was significant.50
Taurine, an amino acid found only in animal products, is the second most abundant free amino acid in human milk. Even milk of women who have no animal foods in their diet contains some taurine at levels (35 mg/dL) that are lower than those in women who consume animal products (54 mg/
dL).102Taurine is singularly important as the prin- cipal protein in the human brain. Cow milk does not contain taurine.
Of practical significance for counseling healthy women in the industrialized world is the work of Butte et al.13 investigating the effect of maternal diet and body composition on lactational perfor- mance; 45 healthy lactating women were followed for 4 months from delivery with detailed measure- ments of milk production, dietary intake, and maternal body composition. The overall mean energy intake was 2186463 kcal/day. Milk pro- duction averaged 751, 725, 723, and 740 g/day for months 1, 2, 3, and 4. Average maternal weight reduction was from 64.6 to 59.3 kg. Energy was cal- culated to be sufficient for maintenance and activ- ity, yet the mothers achieved gradual weight reduction. The authors conclude that energy intakes of approximately 15% less than those cur- rently recommended are compatible with full lacta- tion, full activity, and gradual weight reduction to prepregnant weight (Tables 9-1 and 9-2). Diets otherwise contained recommended daily allow- ances for lactation. Other investigators studying the impact of weight loss noted that the rate of postpregnancy weight loss affected the level of ela- idic acid in milk and of trans fatty acid level.15This
is explained by the mobilization of fatty acids from maternal adipose tissue.
FAT, CHOLESTEROL, AND OMEGA-3 FATTY ACIDS
Mature human milk contains about 50% of its energy as fat. This fat is necessary for the tremen- dous growth of the newborn and is essential to the structural development of the brain, retina, and other tissues. Both n-6 and n-3 fatty acids are essential components of the phospholipids of cell membranes. They are critical to the fluidity, permeability, and activity of membrane-bound enzymes and receptors. During the first 4 to 6 months of life, an infant accumulates 1300 to 1600 g of lipids.
Considerable attention has been focused on the impact of dietary fat and cholesterol on the compo- sition of human milk. Fat is the main source of kilo- calories in human milk for the infant. The fatty acid composition of the triglycerides, which make up more than 98% of the lipid component of human milk, can be affected by maternal diet. Diets with different lipid composition, caloric content, pro- portion of calories from fat, and fatty acid compo- sition have been studied.
In a classic work that was carefully controlled, Insull et al.58 fed lactating women in a metabolic ward diets that differed in caloric content, propor- tion of calories from fat, and fatty acid composition.
Neither milk volume nor total milk fat was affected by diet. When the high-calorie, no-fat diet was fed, milk triglycerides were higher in fatty acids 12:0 and 14:0 and lower in 18:0 and 18:1, which indi- cated that when fatty acids were synthesized from carbohydrate, more intermediate-chain fatty acids were produced. With the low-calorie, no-fat diet, the fatty acid composition of the milk resembled the maintenance diet and the depot fat. When corn oil was the fat source, milk levels of 18:2 and 18:3
TABLE 9-1 Milk Production over First 4 Months of Lactation
Month 1 (n537) Month 2 (n540) Month 3 (n537) Month 4 (n541)
Human milk*(g/day) 751 (130)† 725 (131) 723 (114) 740 (128)
Feedings (no./day) 8.3 (1.9) 7.2 (1.9) 6.8 (1.9) 6.7 (1.8)
Total nitrogen (mg/g) 2.17 (0.30) 1.94 (0.24) 1.84 (0.19) 1.80 (0.21)
Protein nitrogen (mg/g) 1.61 (0.24) 1.42 (0.17) 1.34 (0.15) 1.31 (0.17)
Nonprotein nitrogen (mg/g) 0.56 (0.28) 0.52 (0.20) 0.50 (0.13) 0.48 (0.14)
Fat (mg/g) 36.2 (7.5) 34.4 (6.8) 32.2 (7.8) 34.8 (10.8)
Energy (kcal/g) 0.68 (0.08) 0.64 (0.08) 0.62 (0.09) 0.64 (0.10)
*At the onset of the study, milk was estimated by deuterium dilution, a technique that was later determined to be inaccurate. For this reason, data are missing at 17 time points during the first 3 months.
†Mean (SD).
From Butte NF, Garza C, Stuff JE, et al: Effect of maternal diet and body composition on lactational performance,Am J Clin Nutr39:296, 1984.
were higher, with a major increase in linoleic acid, than when lard or butter was used. Multiple studies have shown that medium-chain fatty acids, lauric and myristic acid (12:0 and 14:0), are not affected by diet, indicating synthesis by the mammary gland.34
Trans fatty acids are produced in hydrogenation reactions and appear in human milk as a reflection of dietary intake, so that women who eat margarine rather than butter have high levels in their milk.65 Elaidic acid (18:1 trans) is found in margarine, for instance. Because of the high level of trans fatty acids in hydrogenated vegetable oils such as marga- rine, the milk of women in the United States is high in trans fatty acids, whereas the milk of women in West Germany who do not use margarines is low in trans fatty acids.34 Considerable controversy sur- rounds the biologic effects. The recommendations for substituting margarines were reversed in 1997.
In mammals, trans isomers have been noted to alter permeability and fluidity of membranes, inhibit a number of enzyme reactions of lipid metabolism, and impair synthesis of arachidonic acid (AA) and prostaglandins.
The concern about fat composition in terms of the polyunsaturated fatty acid (PUFA) to saturated fatty acid ratio (P/S ratio) and the high level of cho- lesterol normally found in breast milk have led to monitoring mothers on altered lipid intakes. Lactat- ing women were placed on one of two experimental diets after a period of a study of their normal Aus- tralian diet, which included 400 to 600 mg of cho- lesterol per day and fat that was rich in saturated fatty acids. After this baseline study, the mothers were given either diet A, with 580 mg cholesterol and a high level of saturated fats, or diet B, with 110 mg cholesterol and a higher level of polyunsat- urated fats from vegetable oils. A second study was
carried out with the two diets high in either satu- rated or unsaturated fats, but the cholesterol remained the same, 345 to 380 mg/day.95
The low-cholesterol diets lowered the maternal blood cholesterol but not the triglyceride levels.
The cholesterol level of the milk, however, was unaffected in any diet combination.69The increase in PUFA in the diet rapidly increased the levels of linoleate in the milk to twice the previous level at the expense of myristate and palmitate. Protein levels remained the same in the milk throughout the study. Infant plasma cholesterol levels decreased in response to an increase in the con- centration of linoleate in the milk. The significant dietary change seemed to depend on the con- sumption of high PUFA and low cholesterol to alter the levels in the milk and thus in the infant’s plasma (Table 9-3).95
Cholesterol levels remain relatively stable throughout at least 16 weeks of lactation. The pres- ence or absence of phytosterols influences both the accuracy of analysis (i.e., overestimated level of cholesterol) and the physiologic significance of cholesterol. Phytosterols are those sterols derived from plant sources. They are distinguishable from cholesterol, which is of animal origin. During a given feeding, the concentration of cholesterol in the milk may increase more than 60%, although the total for the feeding is constant. The effect of maternal diet on cholesterol and phytosterol levels in human milk was measured by Mellies et al.,77 who reported no change in cholesterol but a dra- matic increase in phytosterols on high-cholesterol and phytosterol diets. The level of phytosterol in infant plasma did not change, however. These observations further confirm that cholesterol is syn- thesized at least in part in the mammary gland, whereas phytosterol is not.
TABLE 9-2 Anthropometric Changes in Mothers During Lactation
Parameter Postpartum Month 1 Month 2 Month 3 Month 4
Wt (kg) 64.6 (9.1)* 61.3 (9.5) 60.7 (10.0) 60.2 (10.4) 59.3 (10.5)
Wt/ht (kg/cm)† 0.40 (0.04) 0.37 (0.05) 0.37 (0.05) 0.37 (0.05) 0.36 (0.06)
Wt/prepregnancy wt{ 1.16 (0.06) 1.08 (0.05) 1.07 (0.05) 1.06 (0.05) 1.05 (0.07)
Wt change (kg/mo) 3.83 (2.26) 0.59 (1.20) 0.62 (1.12) 0.80 (1.86)
Triceps (mm) 16.3 (5.1) 16.9 (4.6) 17.0 (4.7) 17.3 (5.3) 17.2 (5.2)
Subscapular (mm) 18.2 (7.1) 16.8 (6.4) 16.4 (7.4) 15.7 (7.2) 15.1 (7.3)
Biceps (mm) 7.8 (3.9) 6.9 (3.2) 6.9 (3.3) 7.3 (4.6) 6.8 (3.4)
Suprailiac (mm) 26.1 (8.5) 25.7 (6.9) 25.2 (7.6) 23.1 (8.1) 22.2 (8.0)
Sum skinfolds (mm) 68.4 (20.2) 66.3 (18.9) 65.5 (20.6) 63.4 (22.9) 61.7 (21.8) Midarm circumference (cm) 26.9 (3.5) 26.7 (2.6) 26.8 (3.2) 26.6 (2.9) 26.7 (3.6)
*Mean (SD).
†Maternal height (ht)ẳ163.0 cm (6.3 cm).
{Prepregnancy weight (wt) gainẳ14.4 kg (3.3 kg).
From Butte NF, Garza C, Stuff JE, et al: Effect of maternal diet and body composition on lactational performance,Am J Clin Nutr39:296, 1984.