What are the factors that alter the need of eating

FACTORS ALTERING NUTRIENT NEEDS
The DRIs are affected by age, sex, rate of growth, pregnancy, lactation, physical activity, concomitant diseases, drugs, and dietary composition. If
requirements for nutrient sufficiency are close to levels indicating excess, dietary planning is difficult.
Physiologic Factors
Growth, strenuous physical activity, pregnancy, and lactation increase needs for energy and several essential nutrients. Energy needs rise during
pregnancy due to the demands of fetal growth and during lactation because of the increased energy required
for milk production. Energy needs
decrease with loss of lean body mass, the major determinant of REE. Because both health and physical activity tend to decline with age, energy needs
of older persons, especially those over 70, tend to be less than those of younger persons.
Dietary Composition
Dietary composition affects the biologic availability and use of nutrients. For example, the absorption of iron may be impaired by high amounts of
calcium or lead; also, non-heme iron uptake may be impaired by the lack of ascorbic acid and amino acids in the meal. Protein use by the body may
be decreased when essential amino acids are not present in sufficient amounts. Animal foods, such as milk, eggs, and meat, have high biologic values
with most of the needed amino acids present in adequate amounts. Plant proteins in corn (maize), soy, and wheat have lower biologic values and must
be combined with other plant or animal proteins to achieve optimal use by the body.
Route of Administration
The RDAs apply only to oral intakes. When nutrients are administered parenterally, similar values can sometimes be used for amino acids,
carbohydrates, fats, sodium, chloride, potassium, and most of the vitamins, because their intestinal absorption is nearly 100%. However, the oral
bioavailability of most mineral elements may be only half that obtained by parenteral administration. For some nutrients that are not readily stored in
the body or cannot be stored in large amounts, timing of administration may also be important. For example, amino acids cannot be used for protein
synthesis if they are not supplied together; instead, they will be used for energy production.
Disease
Specific dietary deficiency diseases include: protein-calorie malnutrition; iron, iodine, and vitamin A deficiency; megaloblastic anemia due to vitamin
B12 or folic acid deficiency; vitamin D–deficiency rickets and osteomalacia; and scurvy, beriberi, and pellagra (Chaps. 74 and 75). Each deficiency
disease is characterized by imbalances at the cellular level between the supply of nutrients or energy and the body's nutritional needs for growth,
maintenance, and other functions. Imbalances and excess in nutrient intakes are recognized as risk factors for certain chronic degenerative diseases,
such as saturated fat and cholesterol in coronary artery disease; sodium in hypertension; obesity in hormone-dependent endometrial and breast
cancers; and ethanol in alcoholism. Because the etiology and pathogenesis of these disorders are multifactorial, diet is only one of many risk factors.
Osteoporosis, for example, is associated with calcium deficiency, as well as risk factors related to environment (e.g., smoking, sedentary lifestyle),
physiology (e.g., estrogen deficiency), genetic determinants (e.g., defects in collagen metabolism), and drug use (chronic steroids) (Chap. 354).
DIETARY ASSESSMENT
In clinical situations, nutritional assessment is an iterative process that involves: (1) screening for malnutrition, (2) assessing the diet and other data to
establish either the absence or presence of malnutrition and its possible causes, (3) planning and implementing the most appropriate nutritional
therapy, and (4) reassessing intakes to make sure that they were consumed. Some disease states affect the bioavailability, requirements, use, or
excretion of specific nutrients. In these circumstances, specific measurements of various nutrients or th