Nutritional Requirements and Growth

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13 Nutritional Requirements and Growth

Carrie Daymont, Beth Rezet

Adequate nutrition is essential for good health at all ages. However, because of rapid growth and development, nutritional requirements vary throughout infancy and childhood. Assessment of a child’s growth is a crucial part of any evaluation of a child, whether the child is well or ill. Assessment of growth depends on an understanding of the wide variation in the normal range of growth. This chapter provides an introduction to nutritional requirements and growth throughout childhood.

Nutritional Requirements

Fluids and Electrolytes

Weight-based recommendations for adequate fluids in children have been made based on metabolic rates. The Holliday-Segar method recommends 100 mL/kg/d for the first 10 kg of weight, 50 mL/kg/d for the next 10 kg of weight, and then 25 mL/kg/d for each kilogram above 20 kg. This estimate does not take excess losses into account; children with diarrhea, vomiting, severe burns, and other sources of fluid loss could require even more fluids. This may provide an overestimate of fluid requirements because these estimates have not been tested in children.

In general, infants who are voiding six times in 24 hours are getting adequate fluids. Infants’ immature kidneys are not capable of producing either very concentrated or very dilute urine; therefore, it is essential that the fluid and electrolytes consumed be balanced. Breast milk and properly prepared commercial infant formula contain appropriate amounts of electrolytes for infants. Free water should not be given to infants younger than 6 months of age, and intake should be limited until 1 year of age. The electrolyte composition of cow’s milk is not appropriate for infants.

Healthy children are generally able to regulate their own fluid intake when it is provided, and many children get a substantial amount of fluid through the high water content of most foods. Urine output and signs and symptoms of dehydration can be used to assess fluid status in older children.

Calories

Neonates need approximately 110 to 120 kcal/kg/d for appropriate growth. Calorie requirements steadily decrease to approximately 90 kcal/kg/d in toddlers. After 3 years of age, calorie requirements vary by gender, age, weight, and activity. Children with very low levels of activity, such as children with profound mental or motor disability who receive tube feedings, usually have significantly lower energy requirements than healthy children. When offered but not forced to take food, most infants and children are able to self-regulate their calorie, or energy, intake to optimal levels over time. Children are generally able to increase their calorie intake when needed, such as during brief periods of rapid weight gain in infancy and pubertal growth spurt and then decrease their intake back to appropriate levels for typical growth. If a toddler is gaining weight well, parents of picky eaters should provide healthy food options and can be reassured that the child is appropriately regulating his or her calorie intake (Figure 13-1).

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Figure 13-1 Diet.

Macronutrients

Protein

Protein should make up approximately 10% to 35% of a child’s diet. In infancy, protein requirements are based on the protein consumed by “on-demand” feeding of breastfed infants (≈1.5 g/kg/d for infants up to 6 months of age). Commercial infant formulas provide somewhat higher values of protein; there is no evidence that this increase in protein is either beneficial or harmful. Protein requirements decrease to a recommended daily allowance of 0.85 g/kg/d in adolescents.

Human milk and animal protein generally provide adequate levels of all essential amino acids. However, plant sources of protein, such as beans, nuts, and grains, do not provide adequate levels of all essential amino acids. Children who consume their protein from plant sources primarily need to receive a balance of legumes and grains to ensure adequate essential amino acid intake. Parents may need to consult with a nutritionist regarding alternative diets to ensure the provision of adequate sources of all essential amino acids and vitamins.

Fat

Fat is an important nutrient, particularly for children younger than 2 years of age who have high energy needs and require fatty acids for nervous system myelination. Children younger than 2 years of age should get approximately 25% to 40% of their calories from fat. From age 1 to 2 years of age, children of normal weight should drink whole milk to ensure adequate fat intake. Children who are overweight can drink 2% milk to reduce fat and caloric intake, but they should not be placed on a low-fat diet at this age. Older children should get 10% to 35% of their calories from fat. Children who are overweight or obese in particular should aim for a fat intake that does not exceed this range.

Carbohydrates

Carbohydrates make up approximately 45% to 65% of total caloric intake. Most carbohydrate intake should come from complex carbohydrates rather than simple sugars, which contribute to dental caries as well as obesity. Fruits have significant amounts of sugar but also supply vitamins and fiber and are part of a healthy diet for children. Most other sources of sugar, such as soda, candy, and many juices, do not contain other significant sources of nutrients and should be limited. One hundred percent fruit juice contains vitamins but lacks fiber and provides more concentrated sugar than whole fruit. Therefore, the American Academy of Pediatrics (AAP) recommends no more than 4 to 6 oz per day of 100% fruit juice between 6 months and 6 years of age and no more than 8 to 12 oz per day of 100% fruit juice after 6 years of age. Excess juice intake contributes to obesity by increasing caloric intake and can contribute to failure to thrive in children who drink juice in place of eating more nutritious food. Low-carbohydrate diets are not generally recommended for children and should never be followed without supervision by a nutritionist or physician.

Micronutrients

This section briefly discusses three of the most important micronutrients and the problems that can arise when they are deficient. Chapter 16 addresses these and other deficiencies in more detail.

Calcium

Adequate calcium intake during childhood is important for long-term bone health. Recommendations for calcium intake have been published by the Food and Nutrition Board of the National Academy of Sciences and affirmed by the AAP. Breast milk and infant formula provide adequate calcium intake for infants (210-270 mg/d). Preterm infants who are formula fed should receive preterm formula with increased calcium. Children who are 1 to 3 years of age should receive 500 mg/d of calcium, which can be supplied in two or three servings of dairy products per day. Children between 4 and 8 years of age need 800 mg/d of calcium, and children older than 9 years of age need 1300 mg/d of calcium achieved by consuming, respectively, three and four servings of dairy a day.

Children who do not consume adequate dairy products can get calcium through calcium-fortified orange juice, other naturally occurring sources such as tofu or leafy green vegetables, or oral supplements. Soy milk does not naturally contain calcium and vitamin D, so it should be fortified with calcium and vitamin D.

Vitamin D

Adequate vitamin D intake is also important for long-term bone health, and recent research has shown its importance in a wide variety of other functions (Figure 13-2). Vitamin D can be ingested or synthesized when the skin is exposed to ultraviolet light. Vitamin D deficiency in infants causes rickets and when very severe can lead to hypocalcemic seizures. Vitamin D deficiency is relatively common in the United States. Risk factors include breastfeeding, darker skin, little sun exposure, and fat malabsorption. Infant formula is supplemented with vitamin D, but breastfed infants are at risk for rickets without vitamin D supplementation. Infants who are breastfed should receive a vitamin D supplement with 400 IU of vitamin D per day to prevent rickets. Children who do not receive at least 400 IU of vitamin D in their diets should also receive a supplement. Future research may show that the current recommendations for vitamin D are too low and should be revised.

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Figure 13-2 Bone health.

Iron

Prevention of iron deficiency in infants and young children is crucial because it can lead to neurologic deficits in developing children that may not be reversible. The iron in breast milk is highly bioavailable and provides adequate levels of iron for infants of mothers who maintain an adequate source of their own dietary or supplemental iron. After 6 months of age breastfed infants should also be given iron-rich foods, such as proteins or iron-fortified rice cereal, to provide adequate iron intake. Commercial infant formulas that are fortified with iron also provide adequate iron. Studies have shown that iron-fortified formulas do not lead to gastrointestinal symptoms, and formulas with low iron should not be used. Preterm infants require additional iron, which can be given as a multivitamin with iron. The iron in cow’s milk is not very bioavailable and should not be given to infants. Meat and egg yolk are good sources of iron that is readily bioavailable. Many cereals are fortified with significant amounts of iron, although their shelf life may make the iron less bioavailable. Iron is also found in many fruits and vegetables, but consideration should be given to giving a daily iron supplement of 10 mg of elemental iron to children who do not eat meat.

Other Micronutrients

Deficiencies of other micronutrients are rare in the United States, but children with metabolic diseases or very restricted diets can have deficiencies in other micronutrients, such as zinc or vitamin C.

Counseling

Infants

The AAP recommends breastfeeding for at least the first year of life, with exclusive breastfeeding for the first 6 months (Figure 13-3). Solid foods should be introduced at age 6 months, including iron-rich high protein foods and iron-fortified cereals and pureed fruits, vegetables, and meats. Infants diets can be slowly expanded to more complex textures as tolerated, always avoiding foods that could cause choking. When breastfeeding is not an option, infants should be given properly prepared commercial iron-fortified infant formula with introduction of solid foods between 4 and 6 months of age. Juice, with its high sugar content, should be avoided or limited to no more than 4 oz/d.

image

Figure 13-3 Breastfeeding.

Parents of infants should also be counseled on distinguishing the signs of hunger and satiety in infants to allow children to self-regulate their energy intake. Moving lips, sucking on hands, and rooting are some signs of hunger that precede fussing or crying. Releasing the nipple, biting the nipple, pulling head away, and shaking the head are some signs of satiety. Healthier eating habits will result if parents are encouraged to respond to their baby’s cues rather than adhering to a feeding schedule or to measured amounts of foods. Parents may find the normal erratic eating patterns of babies and toddlers to be confusing and frustrating. Confirming that the baby is satisfied and is adequately gaining weight can be very assuring.

Children

Parents should provide children with a variety of healthy foods. Telling children to “clean their plates” or overly restricting the type or amount of food inhibits their ability to respond to their own feelings of satiety.

Beverages

Fluids can be a good source of nutrients or a large source of empty calories. Recommended beverages change with age (Table 13-1). Parents should choose nutrient-rich liquids or water and avoid empty-calorie options such as soda.

Table 13-1 Recommended Fluids by Age for Healthy, Typically Growing Children

Age Fluid Recommendations
0-6 months
• Breast milk
• Properly prepared commercial infant formula

6-12 months
• Breast milk
• Properly prepared commercial infant formula
• Water: no more than 8 oz/d
• 0-4 oz/d of 100% fruit juice

12-24 months
• Breast milk
• Whole milk: 16-24 oz/d (2% milk if child is overweight or obese)
• Water
• 0-4 oz/d of 100% fruit juice

2-6 years
• Water
• Low-fat milk (skim or 1% milk)
• 0-4 oz/d of 100% fruit juice
6-18 years
• Water
• Low-fat milk (skim or 1% milk)
• 0-8 oz/d of 100% fruit juice

Growth

During well-child visits, assessment of growth serves as a screening tool for a wide variety of medical problems that may need further evaluation. In children presenting with an illness, assessment of growth can provide clues about the nature and time course of the illness. Because there is such wide variation in the distribution of normal growth, the challenge for clinicians is to determine whether children with unusual growth patterns are unhealthy or if they are healthy patients with a less common growth pattern. This segment focuses on how to assess growth and growth patterns seen in healthy patients. Further information on disorders of growth can be found in this section, as well as the chapter on disorders of growth in the endocrinology section (Chapter 73), and disease-specific chapters.

Types of Measurements

Weight is the most important and most commonly used measure of growth in children. Length (in children younger than 2 years), height (in children older 2 years), and head circumference are also useful. From these measures, weight-for-length percentiles or body mass index (BMI) can be calculated. Methods that can indicate body fat percentage, such as subscapular skin-fold thickness and arm circumference, are used less often but can be helpful when assessing children with suspected malnutrition.

Measurement Methods

It is crucial that all measurements are accurately assessed. Infants should be weighed without clothing or a diaper, and older children should be weighed with very light clothing because apparent weight loss or weight gain may be an artifact of differences in clothing. All staff taking measurements should be properly trained, and equipment should be calibrated to ensure proper measurements. A stadiometer should be used for measuring length and height.

Use of Growth Curves

Growth in children is typically assessed by plotting a child’s measurement and age on a gender-specific growth curve (Figure 13-4). Growth curves allow clinicians to compare a child’s measurements with those of other children of the same age and to evaluate patterns in an individual child’s growth if measurements from multiple points in time are plotted on the same curve. On weight and BMI charts, the upper lines are not true percentiles; they have been adjusted so that the increasing prevalence of obesity does not lead to the classification of overweight children as having a healthy weight.

image

Figure 13-4 Weight and height growth curves for boys ages 0 to 36 months.

There are two standard forms commonly used in the United States: the Centers for Disease Control and Prevention (CDC) charts published in 2000 based on data from multiple national cross-sectional studies including both healthy children and those with medical problems and the World Health Organization (WHO) charts published in 2006 based on a prospective longitudinal study of healthy, breastfed children on six continents. The CDC and WHO’s length curves are similar. The WHO curves classify more children as being overweight and fewer children as underweight than the CDC curves. The WHO curves also classify more children as being macrocephalic than the CDC curves.

Assessing a Child’s Growth

Growth is usually assessed in two ways: (1) current, attained growth relative to same-age peers and (2) growth velocity relative to peers. Using the 5th and 95th percentile parameters as cutoffs for normal growth is sensitive but not specific. It is important to remember that in using these cutoffs, approximately 10% of all children will be labeled as outside the normal range, including many healthy children. A child’s growth velocity can be estimated by determining if a child is following a certain percentile line or is crossing percentile lines. Crossing two or more major percentile lines can be indicative of a problem. However, a shift in percentiles in the first year of life may merely reflect a child’s transition to his or her genetic potential.

Weight

Neonates can lose up to 10% of their birth weight and should be at or above their birthweight by 10 to 14 days after birth. Expected weight gain early in infancy is approximately 26 to 31 g/d decreasing to 7 to 9 g/d at 12 months of age. Breastfed infants typically gain weight more quickly than formula-fed infants between 4 and 6 months but then gain weight more slowly and are ultimately slightly leaner, on average, than formula-fed infants. Children do not always gain weight steadily and may have periods of relatively little weight gain followed by periods of more rapid weight gain. If an infant or child loses weight or has not been gaining adequate weight, a careful history and physical examination should be used to determine possible causes, and the child should be reevaluated.

Height and Length

As with weight, periods of slower gain in height may be followed by more rapid gains in height. A significant change in height percentile is less common than for weight percentile, particularly after the first year of life. Children grow at a slightly decreasing velocity from infancy until puberty. The average gain in length is 4 cm/mo in the neonatal period, decreasing to 0.8 cm/mo at 2 years of age. At puberty, children have a growth spurt, gaining several inches in height, and have minimal gain in height after puberty. The pubertal growth spurt starts later and lasts longer in boys, which accounts for much of their increased average height.

Weight for Height and Body Mass Index

For infants and young children, weight relative to length can be evaluated with weight-for-length percentiles on the CDC 2000 or WHO growth curves or with the WHO curves for BMI. For older children, weight relative to height should be evaluated using BMI percentile. These charts are helpful when evaluating children who have familial short or tall stature. If these children are out of the normal range on the weight growth curve but have a normal weight for height, one can be reassured that their abnormal weight is likely proportional to their height. Overweight and obesity are discussed further in the Chapter 15.

Head Circumference

Head circumference should be measured by placing a tape measure around the head parallel to the floor with the tape just above the eyebrows in front and around the most prominent part of the occiput. In infants, a head circumference that is rapidly crossing increasing percentiles is concerning for hydrocephalus. A head circumference that is not increasing or is crossing decreasing percentile lines is concerning for a failure of brain growth.

Future Directions

In many parts of the world, children are hungry, and research continues to focus on high-energy, nutrient-rich, compact, portable foods to combat starvation. Obesity treatment and prevention is a focus of many current investigations. Research is also ongoing in the timing of introduction of solid foods, particularly in relation to food allergies. Research is continuing on recommendations for vitamin D requirements and prevention of deficiencies.

Suggested Readings

Barlow SE. Expert committee recommendations regarding the prevention, assessment, and treatment of child and adolescent overweight and obesity: summary report. Pediatrics. 2007;120(suppl 4):S164-S192.

Kleinman R, editor. Pediatric Nutrition Handbook, ed 6, Elk Grove, IL: American Academy of Pediatrics, 2009.

Kramer MS, Kakuma R. The optimal duration of exclusive breastfeeding: a systematic review. Adv Exp Med Biol. 2004;554:63-77.

Roche A. Human Growth. New York: Cambridge University Press; 2003.

Summerbell CD, Waters E, Edmunds L, et al: Interventions for preventing obesity in children. Cochrane Database Syst Rev (3):CD001871, 2005.

U.S. Preventive Services Task Force. Screening for Iron Deficiency Anemia—Including Iron Supplementation for Children and Pregnant Women: Recommendation Statement. Rockville, MD: Agency for Healthcare Research and Quality; 2006.

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