Agriculture Reference
In-Depth Information
at least, some long-chain polyunsaturated fatty acids, polyamines, and nucleotides
present in their mother's milk are essential.
Besides micronutrients, specific fatty acids, amino acids, and minerals are also
essential nutrients (see Chapters 6-8). The role of individual essential amino acids
tends to be overlooked as they are supplied in protein. Protein deficiency is recog-
nized as important, but protein quality, its content, and balance of amino acids tend
to be ignored. For growth, sufficient of each of the essential amino acids is neces-
sary. The protein of many plant cereals, for example, maize meal, is lysine deficient;
by itself, it is inadequate to support optimum growth. Consuming vast quantities
may get over the lysine problem, but the excess other amino acids, which cannot be
incorporated into body protein, have to be catabolized and excreted, a major task for
young or malnourished infants' kidneys.
The various roles and requirements of minerals also tend to be overlooked. Thus,
it is essential, especially during growth, that there is adequate dietary calcium and
phosphate for the skeleton. Not surprisingly, calcium deficiency can present like
vitamin D deficiency. Potassium is of fundamental importance and is concentrated
intracellularly. Experimental deficiency of potassium results in edema, among other
features. Correct management of potassium depletion in severe malnutrition is cru-
cial to recovery (Golden 1988). Potassium metabolism is interrelated with that of
magnesium, whose metabolism is also related to that of calcium. Sulfates are needed
for connective tissue structure, its growth, and metabolism. Sodium and chloride are
also essential for homeostasis. Without a single essential nutrient involved in syn-
thesis of new tissue, growth is limited to the extent necessary to allow the available
supply to meet the demand. Thus, growth achievement is a useful index of nutritional
status, not only of energy and protein supply but also of supply of each and every
essential nutrient.
nutRIent InteRActIons
It is clear that for much of the developing world living in poverty, nutrient deficien-
cies are common and rarely occur singly or in isolation. For example, poor growth
is not simply due to energy, protein, lysine, iodine, or zinc deficiency; anemia is not
simply due to iron, folate, or vitamin A deficiency. Duque et al. (2007) concluded
from studies in Mexico that although iron and zinc were the most prevalent deficien-
cies in young children, anemia associated with low iron stores accounted for less
than 50% of cases. Similarly, the effects of deficiencies are not independent of one
another, although this is seen more clearly with the effects of supplementation. Not
only do nutrients interact with other nutrients, but also other dietary components
(including antinutrients and toxins) affect their bioavailability. Furthermore, dis-
eases, particularly infections, cause nutrient losses and alter demand for particular
nutrients as part of the host immune responses.
There have been numerous studies of the effects of iron and zinc fortification on
the absorption and nutrient status of each. The results have not been clear-cut. In gen-
eral, if given in meals there appears to have been little effect, while if given in water,
there were significant inhibitory effects, each on the other (Whittaker 1998). Which
