Nutrient requirements also depend on body composition. In the adult, the brain, which accounts for only 2% of body weight, contributes 19% to the total basal energy expenditure. In contrast, in a full-term neonate, the brain accounts for 10% of body weight and for 44% of total energy needs under basal conditions. Thus, in the young infant, total basal energy expenditure and the energy requirement of the brain are relatively high.

Composition of new tissue is a third factor influencing nutrient requirements. For example, fat should account for about 40% of weight gain between birth and 4 months but for only 3% between 24 and 36 months. The corresponding figures for protein are 11% and 21%; for water, 45% and 68%. The high rate of fat deposition in early infancy has implications not only for energy requirements but also for the optimal composition of infant feedings.

Because of the high nutrient requirements for growth and the body composition, the young infant is especially vulnerable to undernutrition. Slowed physical growth rate is an early and prominent sign of undernutrition in the young infant. The limited fat stores of the very young infant mean that energy reserves are modest. The relatively large size and continued growth of the brain render the central nervous system (CNS) especially vulnerable to the effects of malnutrition in early postnatal life.

ENERGY

The major determinants of energy expenditure are (1) basal metabolism, (2) metabolic response to food, (3) physical activity, and (4) growth. The efficiency of energy use may be a significant factor, and thermoregulation may contribute in extremes of ambient temperature if the body is inadequately clothed. Because adequate data on requirements for physical activity in infants and children are unavailable and because individual growth requirements vary, recommendations have been based on calculations of actual intakes by healthy subjects. Suggested guidelines for energy intake of infants and young children are given in Table 11–2. Also included in this table are calculated energy intakes of infants who are exclusively breast-fed, which have been verified in a number of centers. Growth velocity of breast-fed infants during the first 3 months equals and may exceed that of formula-fed infants, but from 6 to 12 months breast-fed infants typically weigh less than formula-fed babies and may show a decrease in growth velocity. The World Health Organization has developed growth standards derived from an international sample of healthy breast-fed infants and young children raised in environments that do not constrain growth. These are considered to represent physiologic growth for infants and young children. (See also section Pediatric Undernutrition.)

After the first 4 years, energy requirements expressed on a body weight basis decline progressively. The estimated daily energy requirement is about 40 kcal/kg/d at the end of adolescence. Approximate daily energy requirements can be calculated by adding 100 kcal/y to the base of 1000 kcal/d at age 1 year. Appetite and growth are reliable indices of caloric needs in most healthy children, but intake also depends to some extent on the energy density of the food offered. Individual energy requirements of healthy infants and children vary considerably, and malnutrition and disease increase the variability. Premature infant energy requirements can exceed 120 kcal/kg/d, especially during illness or when catch-up growth is desired.

One method of calculating requirements for malnourished patients is to base the calculations on the ideal body weight (ie, 50th percentile weight for the patient’s length-age, 50th percentile weight-for-length, or weight determined from current height and the 50th percentile body mass index [BMI] for age), rather than actual weight.

PROTEIN

Only amino acids and ammonium compounds are usable as sources of nitrogen in humans. Amino acids are provided through the digestion of dietary protein. Nitrogen is absorbed from the intestine as amino acids and short peptides. Absorption of nitrogen is more efficient from synthetic diets that contain peptides in addition to amino acids. Some intact proteins are absorbed in early postnatal life, a process that may be important in the development of protein tolerance or allergy.

Because there are no major stores of body protein, a regular dietary supply of protein is essential. In infants and children, optimal growth depends on an adequate dietary protein supply. Relatively subtle effects of protein deficiency are now recognized, especially those affecting tissues with rapid protein turnover rates, such as the immune system and the gastrointestinal (GI) mucosa.

Relative to body weight, rates of protein synthesis and turnover and accretion of body protein are exceptionally high in the infant, especially the premature infant. Eighty percent of the dietary protein requirement of a premature infant is used for growth, compared with only 20% in a 1-year-old child. Protein requirements per unit of body weight decline rapidly during infancy as growth velocity decreases. The recommendations in Table 11–2 are derived chiefly from the Joint FAO/WHO/UNO Expert Committee and are similar to the Recommended Dietary Allowances (RDAs). They deliver a protein intake above the quantity provided in breast milk. The protein intake required to achieve protein deposition equivalent to the in utero rate in very low-birth-weight infants is 3.7–4.0 g/kg/d simultaneously with adequate energy intake. Protein requirements increase in the presence of skin or gut losses, burns, trauma, and infection. Requirements also increase during times of catch-up growth accompanying recovery from malnutrition (approximately 0.2 g of protein per gram of new tissue deposited). Young infants experiencing rapid recovery may need as much as 1–2 g/kg/d of extra protein. By age 1 year, the extra protein requirement is unlikely to be more than 0.5 g/kg/d.

The quality of protein depends on its amino acid composition. Infants require 43% of protein as essential amino acids, and children require 36%. Adults cannot synthesize nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Cysteine and tyrosine are considered partially essential because their rates of synthesis from methionine and phenylalanine, respectively, are limited and may be inadequate in infants, the elderly, and those with malabsorption. In young infants, synthetic rates for cysteine, tyrosine, and, perhaps, taurine are insufficient for needs. Taurine, an amino acid used to conjugate bile acids, may also be conditionally essential in infancy. Lack of an essential amino acid leads to weight loss within 1–2 weeks. Wheat and rice are deficient in lysine, and legumes are deficient in methionine. Appropriate mixtures of vegetable protein are therefore necessary to achieve high protein quality.

Because the mechanisms for removal of excess nitrogen are efficient, moderate excesses of protein are not harmful and may help to ensure an adequate supply of certain micronutrients. Adverse effects of excessive protein intake may include increased calcium losses in urine and, over a life span, increased loss of renal mass. Excessive protein intake of more than 4 g/kg/day in older children and adolescents may also cause elevated blood urea nitrogen, acidosis, hyperammonemia, and, in the premature infant more than 6g/kg/day has caused failure to thrive, lethargy, and fever. Impaired capacity to deaminate proteins from liver insufficiency or to excrete excess nitrogen as urea from renal insufficiency can further limit tolerable protein intake.

LIPIDS

Fats are the main dietary energy source for infants and account for up to 50% of the energy in human milk. Over 98% of breast milk fat is triglyceride (TG), which has an energy density of 9 kcal/g. Fats can be stored efficiently in adipose tissue with a minimal energy cost of storage. This is especially important in the young infant. Fats are required for the absorption of fat-soluble vitamins and for myelination of the central nervous system. Fat also provides essential fatty acids (EFAs) necessary for brain development, for phospholipids in cell membranes, and for the synthesis of prostaglandins and leukotrienes. The EFAs are polyunsaturated fatty acids, linoleic acid (18:2ω6) and linolenic acid (18:3ω3). Arachidonic acid (20:4ω6) is derived from dietary linoleic acid and is present primarily in membrane phospholipids. Important derivatives of linolenic acid are eicosapentaenoic acid (20:6ω3) and docosahexaenoic acid (DHA, 22:6ω3) found in human milk and brain lipids. Visual acuity and possibly psychomotor development of formula-fed premature infants is improved in formulas supplemented with DHA (22:6ω3) and ARA (20:4ω6). The benefits of long-chain polyunsaturated fatty acid supplementation in formulas for healthy term infants are unclear (though safety has been established).

Clinical features of EFA omega-6 deficiency include growth failure, erythematous and scaly dermatitis, capillary fragility, increased fragility of erythrocytes, thrombocytopenia, poor wound healing, and susceptibility to infection. The clinical features of deficiency of omega-3 fatty acids are less well defined, but dermatitis and neurologic abnormalities including blurred vision, peripheral neuropathy, and weakness have been reported. Fatty fish are the best dietary source of omega-3 fatty acids. A high intake of fatty fish is associated with decreased platelet adhesiveness and decreased inflammatory response.

Up to 5%–10% of fatty acids in human milk are polyunsaturated, with the specific fatty acid profile reflective of maternal dietary intake. Most of these are omega-6 series with smaller amounts of long-chain omega-3 fatty acids. About 40% of breast milk fatty acids are monounsaturates, primarily oleic acid (18:1), and up to 10% of total fatty acids are medium-chain triglycerides (MCTs) (C₈ and C₁₀) with a calorie density of 7.6 kcal/g. In general, the percentage of calories derived from fat is a little lower in infant formulas than in human milk.

The American Academy of Pediatrics recommends that infants receive at least 30% of calories from fat, with at least 2.7% of total fat as linoleic acid, and 1.75% of total fatty acids as linolenic. It is appropriate that 40%–50% of energy requirements be provided as fat during at least the first year of life. Children older than 2 years should be switched gradually to a diet containing approximately 30% of total calories from fat, with no more than 10% of calories either from saturated fats or polyunsaturated fats.

β-Oxidation of fatty acids occurs in the mitochondria of muscle and liver. Carnitine is necessary for oxidation of the fatty acids, which must cross the mitochondrial membranes as acylcarnitine. Carnitine is synthesized in the human liver and kidneys from lysine and methionine. Carnitine needs of infants are met by breast milk or infant formulas. In the liver, substantial quantities of fatty acids are converted to ketone bodies, which are then released into the circulation as an important fuel for the brain of the young infant.

MCTs are sufficiently soluble that micelle formation is not required for transport across the intestinal mucosa. They are transported directly to the liver via the portal circulation. MCTs are rapidly metabolized in the liver, undergoing β-oxidation or ketogenesis. They do not require carnitine to enter the mitochondria. MCTs are useful for patients with luminal phase defects, absorptive defects, and chronic inflammatory bowel disease. The potential side effects of MCT administration include diarrhea when given in large quantities; high octanoic acid levels in patients with cirrhosis; and, if they are the only source of lipids, deficiency of EFA.

CARBOHYDRATES

The energy density of carbohydrate is 4 kcal/g. Approximately 40% of caloric intake in human milk is in the form of lactose, or milk sugar. Lactose supplies 20% of the total energy in cow’s milk. The percent of total energy in infant formulas from carbohydrate is similar to that of human milk.

The rate at which lactase hydrolyzes lactose to glucose and galactose in the intestinal brush border determines how quickly milk carbohydrates are absorbed. Lactase levels are highest in young infants, and decline with age depending on genetic factors. About 20% of nonwhite Hispanic and black children younger than 5 years of age have lactase deficiency. White children typically do not develop symptoms of lactose intolerance until they are at least 4 or 5 years of age, while nonwhite Hispanic, Asian American, and black children may develop these symptoms by 2 or 3 years of age. Lactose-intolerant children have varying symptoms depending on the specific activity of their intestinal lactase and the amount of lactose consumed. Galactose is preferentially converted to glycogen in the liver prior to conversion to glucose for subsequent oxidation. Infants with galactosemia, an inborn metabolic disease caused by deficient galactose-1-phosphate uridyltransferase, require a lactose-free diet starting in the neonatal period.

After the first 2 years of life, 50%–60% of energy requirements should be derived from carbohydrates, with no more than 10% from simple sugars. These dietary guidelines are, unfortunately, not reflected in the diets of North American children, who typically derive 25% of their energy intake from sucrose and less than 20% from complex carbohydrates.

Children and adolescents in North America consume large quantities of sucrose and high-fructose corn syrup in soft drinks and other sweetened beverages, candy, syrups, and sweetened breakfast cereals. A maximum intake of 10% of daily energy from sucrose has been recommended by the World Health Organization, but typical intakes have been reported to far exceed this recommended level. A high intake of these sugars, especially in the form of sweetened beverages, may predispose to obesity and insulin resistance, is a major risk factor for dental caries, and may be associated with an overall poorer quality diet, including high intake of saturated fat. Sucrase hydrolyzes sucrose to glucose and fructose in the brush border of the small intestine. Fructose absorption through facilitated diffusion occurs more slowly than glucose absorption through active transport. Fructose does not stimulate insulin secretion or enhance leptin production. Since both insulin and leptin play a role in regulation of food intake, consumption of fructose (eg, as high-fructose corn syrup) may contribute to increased energy intake and weight gain. Fructose is also easily converted to hepatic triglycerides, which may be undesirable in patients with insulin resistance/metabolic syndrome and cardiovascular disease risk.

Dietary fiber can be classified in two major types: nondigested carbohydrate (β1–4 linkages) and noncarbohydrate (lignin). Insoluble fibers (cellulose, hemicellulose, and lignin) increase stool bulk and water content and decrease gut transit time. Soluble fibers (pectins, mucilages, oat bran) bind bile acids and reduce lipid and cholesterol absorption. Pectins also slow gastric emptying and the rate of nutrient absorption. Few data regarding the fiber needs of children are available. The Dietary Reference Intakes recommend 14 g of fiber per 1000 kcal consumed. The American Academy of Pediatrics recommends that children older than 2 years consume in grams per day an amount of fiber equal to 5 plus the age in years. Fiber intakes are often low in North America. Children who have higher dietary fiber intakes have been found to consume more nutrient-dense diets than children with low-fiber intakes. In general, higher fiber diets are associated with lower risk of chronic diseases such as obesity, cardiovascular disease, and diabetes.

MAJOR MINERALS

Dietary sources, absorption, metabolism, and deficiency of the major minerals are summarized in Table 11–3. Recommended intakes are provided in Table 11–4.

TRACE ELEMENTS

Trace elements with a recognized role in human nutrition are iron, iodine, zinc, copper, selenium, manganese, molybdenum, chromium, cobalt (as a component of vitamin B₁₂), and fluoride. Information on food sources, functions, and deficiencies of the trace elements is summarized in Table 11–5. Supplemental fluoride recommendations are listed in Table 11–6. Dietary Reference Intakes of trace elements are summarized in Table 11–4. Iron deficiency is discussed in Chapter 30.

VITAMINS

Fat-Soluble Vitamins

Because they are insoluble in water, the fat-soluble vitamins require digestion and absorption of dietary fat and a carrier system for transport in the blood. Deficiencies in these vitamins develop more slowly than deficiencies in water-soluble vitamins because the body accumulates stores of fat-soluble vitamins; but prematurity and some childhood conditions can place infants and children at risk (Table 11–7). Excessive intakes carry a considerable potential for toxicity (Table 11–8). A summary of reference intakes for select vitamins is found in Table 11–9. Dietary sources of the fat-soluble vitamins, absorption/metabolism, and causes and clinical features of deficiency are summarized in Table 11–10, and vitamin deficiency and related diagnostic laboratory findings and treatment are detailed in Table 11–11.

Recent recognition of low levels of 25-OH-vitamin D in a relatively large percentage of the population and the broad range of functions beyond calcium absorption have led many experts including the American Academy of Pediatrics to recommend a daily intake of at least 400 IU (10 mcg)/d for all infants, including those who are breast-fed, beginning shortly after birth.

Water-Soluble Vitamins

Deficiencies of water-soluble vitamins are generally uncommon in the United States because of the abundant food supply and fortification of prepared foods. Cases of deficiencies (eg, scurvy) in children with special needs have been reported in the context of sharply restricted diets. Most bread and wheat products are fortified with B vitamins, including the mandatory addition of folic acid to enriched grain products since January 1998. There is conclusive evidence that folic acid supplements (400 mcg/d) during the periconceptional period protect against neural tube defects. Dietary intakes of folic acid from natural foods and enriched products also are protective. Biological roles of water-soluble vitamins are listed in Table 11–12.

The risk of toxicity from water-soluble vitamins is not as great as that associated with fat-soluble vitamins because excesses are excreted in the urine. However, deficiencies of these vitamins develop more quickly than deficiencies in fat-soluble vitamins because of limited stores, with the exception of Vitamin B₁₂.

Major dietary sources of the water-soluble vitamins are listed in Table 11–13. Additional salient details are summarized in Tables 11–7, 11–14, and 11–15.

Carnitine is synthesized in the liver and kidneys from lysine and methionine. In certain circumstances (see Table 11–14), synthesis is inadequate, and carnitine can then be considered a vitamin. A dietary supply of other organic compounds, such as inositol, may also be required in certain circumstances.

INFANT FEEDING

BREAST-FEEDING

Breast-feeding provides optimal nutrition for the normal infant during the early months of life. The World Health Organization recommends exclusive breast-feeding for approximately the first 6 months of life, with continued breast-feeding along with appropriate complementary foods through the first 2 years of life. Numerous immunologic factors in breast milk (including secretory immunoglobulin A [IgA], lysozyme, lactoferrin, bifidus factor, and macrophages) provide protection against GI and upper respiratory infections.

In developing countries, lack of refrigeration and contaminated water supplies make formula feeding hazardous. Although formulas have improved progressively and are made to resemble breast milk as closely as possible, it is impossible to replicate the nutritional or immune composition of human milk. Additional differences of physiologic importance continue to be identified. Furthermore, the relationship developed through breast-feeding can be an important part of early maternal interactions with the infant and provides a source of security and comfort to the infant.

Breast-feeding has been reestablished as the predominant initial mode of feeding young infants in the United States. Unfortunately, breast-feeding rates remain low among several subpopulations, including low-income, minority, and young mothers. Many mothers face obstacles in maintaining lactation once they return to work, and rates of breast-feeding at 6 months are considerably less than the goal of 50%. Skilled use of a breast pump, particularly an electric one, can help to maintain lactation in these circumstances.

Absolute contraindications to breast-feeding are rare. They include tuberculosis (in the mother) and galactosemia (in the infant). Breast-feeding is associated with maternal-to-child transmission of human immunodeficiency virus (HIV), but the risk is influenced by duration and pattern of breast-feeding and maternal factors, including immunologic status and presence of mastitis. Complete avoidance of breast-feeding by HIV-infected women is presently the only mechanism to ensure prevention of maternal–infant transmission. Current recommendations are that HIV-infected mothers in developed countries refrain from breast-feeding if safe alternatives are available. In developing countries, the benefits of breast-feeding, especially the protection of the child against diarrheal illness and malnutrition, outweigh the risk of HIV infection via breast milk. In such circumstances, mixed feeding should be avoided because of the increased risk of HIV transmission with mixed feeds.

In newborns less than 1750 g, human milk should be fortified to increase protein, calcium, phosphorus, and micronutrient content, as well as caloric density. Breast-fed infants with cystic fibrosis can be breast-fed successfully if exogenous pancreatic enzymes are provided. If normal growth rates are not achieved in breast-fed infants with cystic fibrosis, energy or specific macronutrient supplements may be necessary. All infants with cystic fibrosis should receive supplemental vitamins A, D, E, K, and sodium chloride.

Support of Breast-Feeding

In developed countries, health professionals are now playing roles of greater importance in supporting and promoting breast-feeding. Organizations such as the American Academy of Pediatrics and La Leche League have initiated programs to promote breast-feeding and provide education for health professionals and mothers.

Perinatal hospital routines and early pediatric care have a great influence on the successful initiation of breast-feeding by promoting prenatal and postpartum education, frequent mother-baby contact after delivery, one-on-one advice about breast-feeding technique, demand feeding, rooming-in, avoidance of bottle supplements, early follow-up after delivery, maternal confidence, family support, adequate maternity leave, and advice about common problems such as sore nipples. A 2011 CDC Morbidity and Mortality Report found that most US hospitals do not have policies that optimally support breast-feeding. Medical providers can modify their own practice patterns and advocate for hospital policies that support breast-feeding.

Very few women are unable to nurse their babies. The newborn is generally fed ad libitum every 2–3 hours, with longer intervals (4–5 hours) at night. Thus, a newborn infant nurses at least 8–10 times a day, so that a generous milk supply is stimulated. This frequency is not an indication of inadequate lactation. In neonates, a loose stool is often passed with each feeding; later (at age 3–4 months), there may be an interval of several days between stools. Failure to pass several stools a day in the early weeks of breast-feeding suggests inadequate milk intake and supply.

Expressing milk may be indicated if the mother returns to work or if the infant is premature, cannot suck adequately, or is hospitalized. Electric breast pumps are very effective and can be borrowed or rented.

Technique of Breast-Feeding

Breast-feeding can be started after delivery as soon as both mother and baby are stable. Correct positioning and breast-feeding technique are necessary to ensure effective nipple stimulation and optimal breast emptying with minimal nipple discomfort.

If the mother wishes to nurse while sitting, the infant should be elevated to the height of the breast and turned completely to face the mother, so that their abdomens touch. The mother’s arms supporting the infant should be held tightly at her side, bringing the baby’s head in line with her breast. The breast should be supported by the lower fingers of her free hand, with the nipple compressed between the thumb and index fingers to make it more protractile. The infant’s initial licking and mouthing of the nipple helps make it more erect. When the infant opens its mouth, the mother should rapidly insert as much nipple and areola as possible.

The most common early cause of poor weight gain in breast-fed infants is poorly managed mammary engorgement, which rapidly decreases milk supply. Unrelieved engorgement can result from inappropriately long intervals between feeding, improper infant suckling, a nondemanding infant, sore nipples, maternal or infant illness, nursing from only one breast, and latching difficulties. Poor maternal feeding technique, inappropriate feeding routines, and inadequate amounts of fluid and rest all can be factors. Some infants are too sleepy to do well on an ad libitum regimen and may need waking to feed at night. Primary lactation failure occurs in less than 5% of women.

A sensible guideline for duration of feeding is 5 minutes per breast at each feeding the first day, 10 minutes on each side at each feeding the second day, and 10–15 minutes per side thereafter. A vigorous infant can obtain most of the available milk in 5–7 minutes, but additional sucking time ensures breast emptying, promotes milk production, and satisfies the infant’s sucking urge. The side on which feeding is commenced should be alternated. The mother may break suction gently after nursing by inserting her finger between the baby’s gums.

Follow-Up

Individualized assessment before discharge should identify mothers and infants needing additional support. All mother-infant pairs require early follow-up. The onset of copious milk secretion between the second and fourth postpartum days is a critical time in the establishment of lactation. Failure to empty the breasts during this time can cause engorgement, which quickly leads to diminished milk production.

Common Problems

Nipple tenderness requires attention to proper positioning of the infant and correct latch-on. Ancillary measures include nursing for shorter periods, beginning feedings on the less sore side, air drying the nipples well after nursing, and use of lanolin cream. Severe nipple pain and cracking usually indicate improper infant attachment. Temporary pumping may be needed.

Breast-feeding jaundice is exaggerated physiologic jaundice associated with inadequate intake of breast milk, infrequent stooling, and unsatisfactory weight gain. (See Chapter 2.) If possible, the jaundice should be managed by increasing the frequency of nursing and, if necessary, augmenting the infant’s sucking with regular breast pumping. Supplemental feedings may be necessary, but care should be taken not to decrease breast milk production further.

In a small percentage of breast-fed infants, breast milk jaundice is caused by an unidentified property of the milk that inhibits conjugation of bilirubin. In severe cases, interruption of breast-feeding for 24–36 hours may be necessary. The mother’s breast should be emptied with an electric breast pump during this period.

The symptoms of mastitis include flulike symptoms with breast tenderness, firmness, and erythema. Antibiotic therapy covering β-lactamase–producing organisms should be given for 10 days. Analgesics may be necessary, but breast-feeding should be continued. Breast pumping may be helpful adjunctive therapy.

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