Essentials of Nutrition for Sports

Partially Complete Protein Example

Proteins of most cereal grains are low in lysine. If the lysine

content of a whole-wheat flour is 2.6% and the value for lysine in the scoring pattern based on the amino acid needs of the young child is 5.8%, the amino acid score for lysine in wheat proteins is 2.6/5.8 x 100 = 45.

The scores for all other amino acids are higher, so lysine is the

limiting amino acid. The amino acid score for wheat proteins is 45.

The score for whole egg proteins is 100. To meet the requirement for lysine, a young child would have to

consume more than twice as much protein from whole wheat as from whole egg. Scores Change With Age

Both protein and amino acids requirements are higher, in

milligrams per kilogram of body wei

ght, at birth than as we mature.

Amino acid requirements, in milligrams per kilogram of body

weight, decline relatively more rapidly with increasing age than protein requirements.

A protein that may not meet the indispensable amino acid

requirements of a child when consumed in an amount that meets the total nitrogen requirement may pr

ovide amounts of amino acids in

excess of the requirements of an adult.

For example, during the first two years of life, lysine

requirements decline from 5.8% of protein to 1.6%, more than one-thirds, while the protein requirement declines by half.

The partially complete whole-wheat flour, with a 2.6% value for

lysine, will have a 100 amino acid score for adults.

The Food and Agriculture Organization (FAO)/World Health

Organization (WHO) amino acid scores are most commonly used. Other groups’ values may be as much as 20% lower or higher.

Amino acid

Requirement

Composition

1

Milligrams per gram crude protein

Infant

2

2-5 yrs

10-12 yrs

Adult

Egg

Milk, cow

Beef

Histidine

26

19

19

16

22

27

34

Isoleucine

46

28

28

13

54

47

48

Leucine

93

66

44

19

86

95

81

Lysine

66

58

44

16

70

78

89

Methionine & cysteine

42

25

22

17

57

33

40

Phenylalanine & tyrosine

72

63

22

19

93

102

80

Threonine

43

34

28

9

47

44

46

Tryptophan

17

11

9

5

17

14

12

Valine

55

35

25

13

66

64

50

Total

460

339

241

127

512

504

479

Table 9. Amino acid requirements and composition of high-quality animal proteins, from FAO/WHO/UNU (1985). 1 Composition from Lunven

et al.,

1972.

2 Based on breast milk.

Adults Less Concerned About Quality

As can be seen in

Table 9

, a minimum of 460 milligrams out of

every 1,000 milligrams must contain essential amino acids for infants in order for protein to be of the highest quality.

The proportion of essential protein to the total protein

requirement falls from 46% for infants to about 13% for adults.

This is the basis for the conclusion of the FAO/WHO/UNO

committee that only digestibility, not protein quality, need be considered in estimating protein needs of adults.

This does not apply to young children, whose indispensable

amino acid requirements are several times those of adults.

Nutrition for Sports, Essentials of 60