Physiologic Factors Growth, strenuous physical activity, pregnancy, and lactation increase needs for energy and several essential nutrients, including water. 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 in older persons, especially those over 70, tend to be less than those of younger persons. Dietary Composition Dietary composition affects the biologic availability and utilization of nutrients. . | Chapter 070. Nutritional Requirements and Dietary Assessment Part 5 Physiologic Factors Growth strenuous physical activity pregnancy and lactation increase needs for energy and several essential nutrients including water. 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 in older persons especially those over 70 tend to be less than those of younger persons. Dietary Composition Dietary composition affects the biologic availability and utilization of nutrients. For example the absorption of iron may be impaired by high amounts of calcium or lead non-heme iron uptake may be impaired by the lack of ascorbic acid and amino acids in the meal. Protein utilization 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 utilization 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 since 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
