13 Nutritional Requirements and Growth
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).
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.
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