Protein

Most recommendations for the protein intake of children are based on the 1985 FAO/WHO report, although much of the data were collected from studies on formula-fed infants. Because of differences in growth rates, efficiency of protein utilization, and the amino acid pattern of breast and cow's milk, these recommendations are likely to be an overesti-mation of true requirements. More recent data compiled on breast-fed infants give lower estimates of requirements. The Dewey estimates of minimum and safe protein intakes plus recommendations from other authorities are shown in Tables 4 and 5. The minimum and safe intakes refer to a diet based on high biological value proteins such as breast milk or eggs. Adjustments need to be made for infants receiving an alternative source of protein (e.g., soya or a protein hydrolysate) and for older children consuming a mixed diet.

Protein requirements are highest during the first month of life and decrease thereafter. The proportion of protein intake that is required for growth decreases from 64% of requirement during the first month of life to 35% at age 3-6 months, 16% at age 1-2 years, and 11% at age 2-5 years.

Essential amino acid requirements are dependent on the growth rate of the infant and the rate of protein deposition, which changes throughout infancy. Some nonessential amino acids, including creatine, taurine, glycine, cysteine histidine, and arginine, cannot be synthesized in adequate quantities to meet the demands of the very rapid protein deposition that occurs during the first month of life, and these are considered to be semiessential during early infancy. It is likely that part of the nonprotein nitrogen portion of breast milk, such as choline, carnitine, and nucleotides, is used in metabolism and for amino acid synthesis and may also be conditionally essential.

Some countries express protein as a percentage of the estimated energy requirements, with a range of 8-15% energy from protein (i.e., 2-3.75 g protein per 100 total kilocalories). The protein: energy ratio is approximately 7.5% in human milk and 8-8.5% in infant formulas. These ratios are adequate for a normal rate of growth, although it may be argued that the more rapid growth rate seen in young formula-fed infants indicates that the ratio has been set too high in infant formulas.

Table 4 Recommended protein intakes for infants (g/kg body weight/day)

Age (months) UK RNI Europe PRI USA Recommended FAO/WHOa

Dietary Allowance -

Minimum Safe minimum intakec requirements'

Age (months) UK RNI Europe PRI USA Recommended FAO/WHOa

Dietary Allowance -

Minimum Safe minimum intakec requirements'

0-1

2.11

2.16

1.99

2.69

1-2

2.11

2.16

1.54

2.04

2-3

2.11

2.16

1.19

1.53

3-4

1.65

2.16

1.06

1.37

4-5

1.65

1.81

2.16

0.98

1.25

5-6

1.65

1.81

2.16

0.92

1.19

7-9

1.55

1.64

1.55

0.85

1.09

10-12

1.54

1.50

1.55

0.78

1.02

Statistically will only meet requirements of 50% of the population. cShould meet the requirements of 97.5% of the population.

Statistically will only meet requirements of 50% of the population. cShould meet the requirements of 97.5% of the population.

Table 5 Recommendations for protein intake for children

Age

Sex

UK RNI

Europe PRI

USA RDA

WHCf

(years)

(g/day)

(g/day)

(g/day)

Minimum requirements (g/kg/day)b

Safe minimum intake (g/kg/day)c

2

M + F

14.5

15.5

16.0

0.74

0.92

3

M + F

14.5

17.0

16.0

0.72

0.90

4

M + F

19.7

18.5

24

0.71

0.88

5

M + F

19.7

20.0

24

0.69

0.86

6

M + F

19.7

22.0

24

0.69

0.86

7

M + F

28.3

24.5

28

0.69

0.86

8

M + F

28.3

27.5

28

0.69

0.86

9

M + F

28.3

29.5

28

0.69

0.86

10

M

28.3

32.5

28

0.69

0.86

F

28.3

34.0

28

0.69

0.86

11

42.1

36.0

45

0.69

0.88

F

41.2

37.0

46

0.69

0.86

12

42.1

41.0

45

0.71

0.88

F

41.2

41.5

46

0.69

0.86

13

42.1

45.5

45

0.71

0.88

F

41.2

45.0

46

0.69

0.86

14

42.1

51.0

45

0.69

0.86

F

41.2

45.5

46

0.68

0.84

15

55.2

53.5

59

0.69

0.86

F

45.4

45.5

44

0.66

0.82

16

55.2

46.5

59

0.68

0.84

F

45.4

45.0

44

0.66

0.81

17

55.2

55.5

59

0.67

0.83

F

45.4

43.5

44

0.63

0.78

18

55.2

56.0

59

0.65

0.81

F

45.4

47.0

44

0.63

0.78

Statistically will only meet the requirements of 50% of the population. cShould meet the requirements of 97.5% of the population. F, female; M, male.

Statistically will only meet the requirements of 50% of the population. cShould meet the requirements of 97.5% of the population. F, female; M, male.

An increase in the protein:energy ratio is necessary for infants and children who are wasted or stunted and who need to grow at an increased velocity in order to catch up. Malnutrition during the first year of life, whether a result of a poor environment or because of conditions such as malabsorption or cystic fibrosis, is more serious than wasting and stunting later in childhood. Although the potential for catch-up growth remains until the end of puberty, deficits during early life can lead to permanent impairment of cognitive function. Estimates of requirements for malnourished infants and children should be based on the height age (i.e., the age at which the child's measured height falls on the 50th centile) because estimations based on normal requirements for chronological age are likely to be difficult to achieve and may lead to obesity. The increase in protein requirement for catch-up growth is proportionally greater than the increase in energy requirement and is dependent on age and growth velocity. For example, a child aged 1 year who is growing at twice the normal rate has a 5% increase in energy requirements and a 32% increase in protein requirements. When designing regimens for infants and children who need to catch up, a protein:energy ratio of at least 10% and possibly up to 15% is necessary. Ratios less than this will result in changes in body composition, with greater amounts of fat and water and lower amounts of lean tissue being deposited.

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