Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients)

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Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids

brain function (Pollitt, 2000). Furthermore, protein deficiency has been shown to have adverse effects on the immune system, resulting in a higher risk of infections (Bistrian, 1990). It also affects gut mucosal function and permeability, which, in turn, affects absorption and makes possible bacterial invasion from the gut, which can result in septicemia (Reynolds et al., 1996). Protein deficiency has also been shown to adversely affect kidney function, where it has adverse effects on both glomerular and tubular function (Benabe and Martinez-Moldonado, 1998).

Total starvation will result in death in initially normal-weight adults in 60 to 70 days (Allison, 1992). For comparison, protein and energy reserves are much smaller in premature infants, and survival of 1,000-g neonates is only about 5 days (Heird et al., 1972).

Clinical Assessment of Protein Nutritional Status

No single parameter is completely reliable to assess protein nutritional status. Borderline inadequate protein intakes in infants and children are reflected in failure to grow as estimated by length or height (Jelliffe, 1966; Pencharz, 1985). However, weight-height relationships can be distorted by edema and ascites (Corish and Kennedy, 2000). Mid-upper arm parameters such as arm muscle circumference have been used to measure protein status (Young et al., 1990). The triceps skinfold is reflective of energy nutritional status while the arm muscle circumference (or diameter) is reflective of protein nutritional status (unless a myopathy or neuropathy is present) (Patrick et al., 1994).

In addition, urinary creatinine excretion has been used as a reflection of muscle mass (Corish and Kennedy, 2000; Forbes, 1987; Young et al., 1990), but it is not very sensitive. The most commonly used methods to clinically evaluate protein status measure serum proteins; the strengths and weaknesses of these indicators are summarized in Table 10-6. In practical terms, acute protein depletion is not clinically important as it is rare, while chronic deficiency is important. Serum proteins as shown in Table 10-6 are useful, especially albumin and transferrin (an iron-binding protein). In a study from Nigeria, low transferrin levels were more predictive of risk of death in children with PEM than were albumin levels (Ramsey et al., 1992). Due to their very short half-lives, prealbumin and retinol binding protein (apart from their dependence on vitamin A status) may reflect more acute protein intake than risk of protein malnutrition (which is a process with an onset of period of 7 to 10 days (Ramsey et al., 1992). Hence, albumin and transferrin remain the best measures of protein malnutrition, but with all of the caveats listed in Table 10-6.

Physical examination related to protein malnutrition focuses attention on the skin and hair as they are rapidly growing protein-containing

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