Nutrition And Metabolism Level 3 PDF

Dairy Department Dietetic program Level 3 Course:Nutrition and metabolism By Dr/ Esraa Mohamed Al-Amir Lesson 2  Energy requirements The amount of food energy needed to...

Dairy Department Dietetic program Level 3 Course:Nutrition and metabolism By Dr/ Esraa Mohamed Al-Amir Lesson 2  Energy requirements The amount of food energy needed to balance energy expenditure in order to maintain body size, body composition and a level of necessary and desirable physical activity consistent with long- term good health. This includes the energy needed for the optimal growth and development of children, for the deposition of tissues during pregnancy, and for the secretion of milk during lactation consistent with the good health of mother and child.  Daily energy requirements and daily energy intakes that the recommended energy intake is the amount of energy that should be ingested as a daily average over a certain period of time.  Average requirement and inter-individual variation Estimates of energy requirements are derived from measurements of individuals. Measurements of a collection of individuals of the same gender and similar age, body size and physical activity are grouped together to give the average energy requirement – or recommended level of dietary intake – for a class of people or a population group.  Sources Of Dietary Energy Energy for the metabolic and physiological functions of humans is derived from the chemical energy bound in food and its macronutrient constituents, i.e. carbohydrates, fats, proteins and ethanol, which act as substrates or fuels. After food is ingested, its chemical energy is released and converted into thermic, mechanical and other forms of energy.  Components Of Energy Requirements Human beings need energy for the following: 1- Basal metabolism. This comprises a series of functions that are essential for life, such as cell function and replacement; the synthesis, secretion and metabolism of enzymes and hormones to transport proteins and other substances and molecules; the maintenance of body temperature; uninterrupted work of cardiac and respiratory muscles; and brain function. The amount of energy used for basal metabolism in a period of time is called the basal metabolic rate (BMR). is measured under standard conditions that include: 1-being awake in the supine position after ten to 12 hours of fasting and eight hours of physical rest 2-being in a state of mental relaxation in an ambient environmental temperature that does not elicit heat-generating or heat-dissipating processes. Depending on age and lifestyle. 3-BMR represents 45 to 70 percent of daily total energy expenditure, and it is determined mainly by the individual’s age, gender, body size and body composition.  2- Metabolic response to food. Eating requires energy for the ingestion and digestion of food, and for the absorption, transport, interconversion, oxidation and deposition of nutrients. These metabolic processes increase heat production and oxygen consumption, and are known by terms such as dietary-induced thermogenesis, specific dynamic action of foodand thermic effect of feeding. The metabolic response to food increases total energy expenditure by about 10 percent of the BMR over a 24-hour period in individuals eating a mixed diet. 3- Physical activity. This is the most variable and, after BMR, the second largest component of daily energy expenditure. Humans perform obligatory and discretionary physical activities. Obligatory activities can seldom be avoided within a given setting, and they are imposed on the individual by economic, cultural or societal demands.  4- Growth. The energy cost of growth has two components: 1) the energy needed to synthesize growing tissues; 2) the energy deposited in those tissues. The energy cost of growth is about 35 percent of total energy requirement during the first three months of age, falls rapidly to about 5 percent at 12 months and about 3 percent in the second year, remains at 1 to 2 percent until mid- adolescence, and is negligible in the late teens.  5- Pregnancy. During pregnancy, extra energy is needed for the growth of the fetus, placenta and various maternal tissues, such as in the uterus, breasts and fat stores, as well as for changes in maternal metabolism and the increase in maternal effort at rest and during physical activity.  6- Lactation. The energy cost of lactation has two components: 1) the energy content of the milk secreted 2) the energy required to produce that milk. Well-nourished lactating women can derive part of this additional requirement from body fat stores accumulated during pregnancy.