nificance to lysine requirements. These may be important nutritional considerations in individuals consuming marginal amounts of proteins of plant origin and undoubtedly have an impact on overall amino acid utilization when protein intake is very low.

As outlined above, protein is the fundamental component necessary for cellular and organ function. Not only must sufficient protein be provided, but also sufficient nonprotein energy (i.e., carbohydrates, fats) must be available so that the carbon skeletons of amino acids are not used to meet energy needs (Duffy et al., 1981). Similarly, unless amino acids are present in the diet in the right balance (see later section, “Protein Quality”), protein utilization will be affected (Duffy et al., 1981). In the world as a whole, protein-energy malnutrition (PEM) is fairly common in both children and adults (Stephenson et al., 2000), and is associated with the deaths of about 6 million children each year (FAO, 2000). In the industrialized world, PEM is seen predominantly in hospitals (Bistrian, 1990; Willard et al., 1980), is associated with disease (Wilson and Pencharz, 1997), and often found in the elderly (Allison, 1995). Hypoalbuminemic malnutrition has been described in hospitalized adults (Bistrian, 1990) and has also been called adult kwashiorkor (Hill, 1992).

Clearly, protein deficiency has adverse effects on all organs (Corish and Kennedy, 2000). In infants and young children, it has been shown to have harmful effects on the brain and may have longer-term effects on