Nutrition during Pregnancy and Early Chidhood.

The following pargraphs are part of a chapter that I've reviewed with Dr Katz  for the last edition of the Enciclopedya of Primary Prevention.  It was super interesting because I 've learnt many evidence based information about nutrition during Pregnancy and Early Childhood. The Chapater is meant for health professionals particularly, so I admit that it can be a little bit boring and relatively long.  In the next few weeks I will try to generate some more easy-to -read posts   based on this for all my friends who are facing motherhood. 

"In general, pregnancy requires a calorie increase over baseline of approximately 300 kcal/day, and lactation requires 500 kcal/day.  Nutrients for which the recommended daily allowance (RDA) is specifically raised in pregnancy include: total protein, total energy, magnesium, iodine, zinc, selenium, vitamin E, vitamin C, thiamin, niacin, iron, calcium, and folate.  Lactation requires further increases in protein, zinc, vitamin A, vitamin E, vitamin, C, and niacin.  Requirements for iron and folate actually decline   These adaptations in the maternal diet are necessary to assure optimal nutrition for the fetus/newborn.

Immediately postpartum for a period of approximately 3-5 days, human mammary glands produce colostrum, a fluid rich in sodium, chloride, and immune globulins that confer passive immunity to the newborn.  Colostrum is replaced by milk, which is rich in lactose and protein, and comparatively low in sodium and chloride.  Milk volume consumed by the neonate is 50 cc per day at birth, 500 cc by day 5, and 750 cc at 3 months.  Milk production is maintained by infant suckling.  The first four months of lactation consume, and convey to the infant, a comparable amount of energy as the entire gestational period.  Human milk is appropriate as the sole source of infant nutrition for up to 6 months provided it is free of dangerous contaminants or pathogens (e.g., the HIV virus).  There is uncertainty whether milk meets all of the infant's nutritional needs beyond this point.  Breastfeeding, under most circumstances, is the preferred nutritional source for neonates.  A generous intake of dietary calcium, and continued use of prenatal vitamins, is indicated throughout the period of lactation. 

Breast milk and infant formulas differ substantially in a variety of nutrients.  The significance of all of the differences has yet to be established.  The prevailing view is that breast milk favors optimal brain development, and breast-feeding is associated with greater intelligence, at least during childhood, although such observations are subject to confounding.  There is interest in the role breast-feeding may play in preventing the development of atopy (allergy). Evidence is convincing that breast-feeding confers protection against infections, although the mechanisms by which breast milk influences infant immunity remain under study.  Provided that a sanitary water supply is available, the safety of formula is generally not of concern.  Soy-based formulas are available for infants intolerant of bovine milk protein.  Properly nourished, the healthy infant should double in weight by 4-5 months, and triple in weight by 12 months.  Demand feeding is the preferred method of assuring adequate energy intake......"

Strategies That Work

Optimal development in utero is associated with several nutrients in particular.  Supplementation with approximately 400 mg of folic acid per day beginning prior to conception markedly reduces the risk of neural tube defects, including anencephaly and spina bifida.  Evidence for this association has been extensively reviewed and is considered definitive.  Ingestion of more than 1 mg per day of folate is generally not recommended.  However, in women with prior pregnancies leading to neural tube defects, the ingestion of up to 4 mg per day of folate may confer additional benefit.

Pregnancy consumes approximately 1040 mg of iron in total, of which 200 mg are recaptured after pregnancy from the expanded red cell mass, and 840 mg are permanently lost.  The iron is lost to the fetus (300 mg), the placenta (50-75 mg), expanded red cell mass (450 mg), and blood loss at parturition (200 mg).  Only about 10% of ingested iron is absorbed in the non-pregnant state, but pregnancy may enhance absorption up to 30%.  There was initial concern that supplementing iron in areas with malaria might increase the risk of malaria during pregnancy, although recent studies have not shown this to be the case.  Therefore, an intake of between 13 and 40 mg per day is recommended during the third trimester for all women.  

Vitamin/mineral supplements generally contain 30 mg of iron, and diet (in the U.S.) provides an additional 15 mg, easily meeting the needs of most women without anemia.  Women with iron deficiency anemia during pregnancy require increased intake to replete bone marrow stores and still provide for the metabolic needs of the fetus.  In this situation, daily intake of between 120 and 150 mg of iron is typically required.  Iron supplementation prior to conception will facilitate meeting the iron needs of pregnancy and lactation, which together result in a net loss of between 420 and 1030 mg of elemental iron.  Iron supplementation should continue post-partum, both to provide iron for breast milk and to replenish losses due to bleeding at delivery.  Strategies useful in the prevention of iron deficiency among children include promoting breastfeeding, using iron-fortified formulas if formulas are used, and introducing age appropriate, iron rich solid foods.

The fatty acid composition of human milk varies with maternal dietary intake.  With the exception of iodine and selenium, there is little evidence that the levels of minerals and trace elements in milk vary with maternal diet.  In contrast, vitamin levels in milk are responsive to dietary intake, with the strength of the relationship varying by nutrient.  Both fat and water soluble vitamin levels in milk vary in proportion to maternal intake.  Calcium and folate, and possibly other nutrients, are preserved in milk at the expense of maternal stores when maternal intake is less than daily requirements.  Energy requirements to sustain lactation are based on the caloric density of human milk (approximately 70 kcal/100 cc), the metabolic cost of milk production, and total milk volume.  The consensus view that lactation requires 500 kcal per day above the energy required to maintain maternal weight assumes that approximately 200 kcal per day of milk production energy will derive from pregnancy-related fat stores.  Weight loss of 0.5 to 1 kg per month is common during lactation, while loss in excess of 2 kg per month generally implies inadequate nutrition unless such weight loss is intentional.  Maintenance of weight and weight gain during lactation are not uncommon.

Maternal diet strongly influences the fatty acid and vitamin composition of breast milk but generally exerts a modest influence on minerals. Iodine and selenium are exceptions, varying substantially in response to maternal intake .  Vitamins D and K are generally at low levels in breast milk, and supplementation is recommended . However, a recent study suggests that low vitamin D intake in breast-fed neonates may not adversely affect bone metabolism.

Recommended dietary allowances (RDAs) have been established for essential nutrients for both the first and second 6-month intervals of life (see Table 2).  Iron deficiency is the most common nutrient deficiency in early childhood.  Iron absorption from breast milk is apparently particularly efficient, as iron deficiency rarely occurs in breast-fed infants despite the lower levels of iron in breast milk than in formula.  Increased use of iron-fortified infant formula among non-breast fed babies has substantially reduced the incidence of iron deficiency in this age group.  Iron requirements may relate to vitamin E and polyunsaturated fat content of the diet.  Supplementation is recommended in non-breast fed infants until age 2.  Vitamin deficiencies are rare in adequately nourished infants.  Vitamin K is provided by injection at or near the time of birth to prevent neonatal hemorrhage; subsequently, deficiency is uncommon.

By 6 months of age, gastrointestinal physiology is substantially mature, and infants metabolize most nutrients comparably to adults.  Nutrient needs can be met with breast milk or formula (see Table 3), but most authorities advocate the gradual introduction of solid foods beginning at or around 6 months.  As infant foods begin to replace breast milk or formula, the nutrient density of the diet is apt to decline, and the introduction of a multivitamin supplement is indicated .  Completion of weaning to solid food by 1 year of age is common practice and appropriate.

The nutrient recommendations for infants 6-12 months of age are based largely on extrapolation from the first 6-month period; less is known about the nutrient needs of infants 6-12 months old.  There is currently debate regarding the optimal level of energy intake, with some recommending a reduction from 95 to 85 kcal/kg per day (Heird, 1996). Adequate growth is apparently maintained at the lower energy intake level.

Means of assuring optimal nutritional exposure for all children up to age 5 are elusive.  Practices of clear value in the prevention of nutritional deficiencies include: food-supply fortification (e.g., folate); widespread use of prenatal vitamin supplementation; nutrient supplements for lactating women; nutrient supplements for children at weaning; use of commercial infant formulas rather than bovine milk as breast-milk alternatives; and the continued efforts of food assistance programs in the U.S. (e.g., WIC) and abroad to protect access to an adequate supply of food energy and nutrients.

Strategies That Might Work

Preliminary evidence suggests that high consumption of marine oils is associated with longer gestation, and that dietary supplementation with n-3 polyunsaturated oils may increase the proportion of term births in diverse populations. There is evidence that n-3 fatty acids are important in the normal development of eye and brain function. A recent case-control study in Greece supports the hypothesis that n-3 fatty acids may be especially important in fetal brain development, and that low maternal fish consumption may elevate risk of cerebral palsy.  Increased consumption of n-3 fatty acids may therefore confer health benefits to both mother and baby.  Relative to the prehistoric dietary pattern, the modern diet is deficient in n-3's  lending the support of an evolutionary context to the hypothesis that increased intake may be beneficial.

Essential fatty acids are of particular interest with regard to early childhood development.  The n-3 content of breast milk is mediated by maternal intake.  Long-chain polyunsaturated fatty acids (PUFAs) are particularly concentrated in the brain and retina.  Eicosapentneoic acid (EPA) and docosahexanoic acid (DHA) are relatively abundant in human breast milk and prominently incorporated into the developing brain.  DHA in particular is considered essential to healthy brain development. Impaired cognitive development in premature babies may relate in part to insufficient availability of DHA during a critical period of brain development .  Breast-feeding is associated with enhancement of both IQ and visual acuity in infants.  The apparent health benefits of breast-feeding relative to formula feeding may relate in part to the DHA content of breast milk.  Increasingly, long-chain PUFAs including DHA are being added to commercial formulas.  Although the essential fatty acid, a-linolenic acid, is a precursor to DHA as well as EPA, conversion to DHA in particular appears to be limited and variable.  The putative benefits of DHA apparently require that it be administered directly in the diet.  While health benefits of DHA supplementation are likely on the basis of confluent lines of evidence, they are as yet not conclusively proved .

The amino acid pattern of breast milk is species-specific.  For this and other reasons, human milk might make unique contributions to early development.  Breast milk contains more than 100 different oligosaccharides.  There is current interest in the influence these carbohydrates have on intestinal flora of the infant, and their capacity to play a role in the prevention of infection.

Maternal diet influences the flavor of breast milk and thereby serves as a means of introducing the neonate to a variety of taste experiences. Strong flavors, and the familiarity or novelty of such flavors, may influence the feeding behaviors of infants.  Thus, variation in the maternal diet during lactation may play some role in determining childhood food preferences.  There is some evidence to suggest that breast-feeding, especially if protracted, may confer protection against the later development of obesity, although this remains controversial.

While the principal goal of nutrition management in early childhood is the preservation of optimal growth and development, children in the U.S. and other developed countries are increasingly susceptible to the adverse effects of dietary excess, particularly obesity.  As a result, there is intense interest regarding the age at which dietary restrictions might first be safely imposed.  In general, restriction of macronutrients (dietary fat being of particular concern) is discouraged prior to age 2, with increasing evidence that restrictions comparable to those recommended for adults may be safe and appropriate after age 2.  The establishment of health-promoting diet and activity patterns in childhood may be of particular importance, as preferences established early in life tend to persist.  Proponents of dietary fat restriction beginning at age 2 cite evidence that atherosclerosis begins in childhood, and that a diet with not more than 30% of calories from fat beginning at age 2 is compatible with optimal growth. Others in the U.S. argue for the Canadian approach, with a gradual transition to lower fat intake and attention to the type and distribution of dietary fat.  Controversy on the optimal dietary recommendations for young children has persisted for more than a decade. 

There is increasing evidence that efforts to modify the diets of children to reduce long-term cardiovascular risk are likely to be safe.  Whether or not such diets do reduce long-term risk is less clear.  Obviously, evidence of long-term outcome effects is difficult to obtain.  To be considered in the debate is the importance of providing a single, consistent dietary pattern for a family, as well as the issue of dietary patterns tracking over time.  Data from the Bogalusa Heart Study demonstrate that there is tracking, between the ages of 6 months and 4 years, of both dietary pattern and cardiovascular risk factors . In light of these considerations, it appears that the recommendation in the U.S. to advocate a similar diet for everyone over the age of 2 years is reasonable and safe  and may offer long-term benefits.  While there is some evidence that a comparable diet may be safe even prior to age 2, consensus opinion in the U.S., and prudence, argue against the imposition of macronutrient restrictions in this age group.  Conclusive evidence of benefit from early dietary modification efforts will accrue very slowly.

Strategies That Do Not Work

Children over the age of 1 year will tend to eat an appropriate variety of foods/nutrients when provided access to such.  However, balance may not be achieved on any given day.  Provided the child continues to be provided reasonable food choices, balance will be achieved over several days.  Parents should be reassured that a balanced diet need not be measured on a per meal or even per day basis.  A reasonable approach is to avoid any major distinction between snacks and meals, so that healthy food can be eaten when the child is hungry, and meal size can be adjusted to account for snacking.

The prudence of advocating the same diet for adults and children has been challenged, largely based on the lack of evidence that dietary restrictions in childhood prevent chronic disease in adults. However, obtaining evidence that dietary interventions in early childhood prevent chronic disease in late adulthood is a daunting challenge.  Indirect, epidemiologic, and inferential evidence may be the best guidance available.  The safety of the American Heart Association Step 1 diet for children over the age of 2 has received fairly widespread support.

The provision of adequate, let alone optimal, nutrition to all of the world’s children requires that lines of supply be secure and reliable.  In myriad settings around the world, child nutrition is compromised by social upheavals that prevent access to an appropriate food supply.  Assistance programs do not adequately correct this problem, as food delivered to a site of great need may not reach those individuals for whom it is intended.  Thus, strategies that fail to contend with social and political barriers to food access are ill-fated.

In the industrialized world, children are early exposed to a vast array of nutrient-dilute, energy-dense foods.  Vast sums of money are spent by the food industry on advertisements aimed at children.  It is against this backdrop that an epidemic of childhood obesity is developing, and progressing.  Providing “guidelines” on healthy eating in a “toxic” nutritional environment is clearly ineffective.  A recent Cochrane review  failed to find quality evidence supporting any particular strategy for the prevention of childhood obesity.

The provision of optimal nutrition during infancy and early childhood is of vital importance to growth and development and is likely related to a wide array of health outcomes in later life.  The establishment of good nutriture for an infant begins in utero, during which maternal dietary practices may influence fetal metabolism.  The most reliable way to assure optimal nutrition for a newborn is breast-feeding.  Therefore, based on the confluence of multiple lines of evidence, breast-feeding for a period of 6 months is advisable unless the practice is contraindicated by communicable disease.  The maintenance of salutary maternal nutrition during lactation is of importance to the health of both mother and baby.  While commercial infant formulas provide generally balanced nutrition, there is concern that they are deficient in long-chain polyunsaturated fatty acids, DHA in particular.  As evidence of the importance of DHA and other essential fatty acids continues to accrue, the composition of commercial formulas will likely be revised.  In the interim, there is preliminary evidence that both cognition and vision are enhanced by breast as compared to formula feeding.

Weaning to solid food should generally begin at approximately 6 months; earlier weaning may increase the risk of food allergies.  Weaning from breast milk or formula is generally complete by around 12 months, although such practices are culturally determined; medically, weaning at 12 months is appropriate.  Children will generally self-select foods that meet micronutrient requirements when provided with an array of healthy food choices.  This practice is to be encouraged.  In the developing world, the transition from breast milk to solid food may represent a period of particular vulnerability to malnutrition.  This can be due to the poor nutrient quality of the food the children will be switched to, the lack of adequate amounts of food for a growing child (children are sometimes only fed twice a day in the developing world), and to the increased risk of infection.  Diarrheal illnesses are particularly common during the switch to solid food due largely to the lack of adequate hygiene.  Once a child becomes ill, he or she often has less appetite and because of cultural taboos is sometimes given less food.  This can lead to a spiraling effect where illness leads to inadequate nutrition, which then leads to increased susceptibility to disease.  Policies and programs aimed at providing balanced nutrition to children in this age group and improved hygiene are thus of vital importance. 

Children with access to an adequate diet reliably meet their energy needs, although energy intake may vary considerably by meal and even day.  Parents should be reassured in this regard and discouraged from placing too great an emphasis on “plate-cleaning”.  Whether or not such a practice contributes to later obesity is unknown, but an association is plausible.

For more Information

 Nutrition in Early Childhood. Encyclopedia of Primary Prevention, 2nd Edition