Human Energy System & Energy Measurement

• The body extracts energy from the chemical bonds in food

Human Energy System

• The majority of the body's energy is used for basal metabolic needs
• Energy needs include involuntary body work, which uses the greatest amount of energy, and voluntary work and exercise

Measurement of Energy

• A kilocalorie (kcal) is the amount of heat needed to raise 1 kg of water 1° C.
• A joule (J) is the international unit of measure for energy.
• To convert kilocalories (kcal) into kilojoules (kJ), multiply the number of kilocalories by 4.184.
• Adenosine triphosphate (ATP) is the metabolic end product of the energy-yielding foods consumed
• Carbohydrates provide 4 kcal/g, fat provides 9 kcal/g, protein provides 4 kcal/g, and alcohol provides 7 kcal/g.
• Energy density refers to foods with a high concentration of energy.
• Nutrient density refers to foods with a high concentration of vitamins and minerals.
• Empty calorie foods are the opposite of nutrient-dense foods.
• A balance between food energy intake and body work output helps maintain life and health
• Energy imbalances can result in body weight being underweight or overweight

Energy Systems

• Life is supported by two energy systems
• The external energy cycle transforms the sun's radiation into stored energy via plants
• The internal energy cycle involves people eating plant and animal foods where the food's stored energy is broken down into simple fuels and returned to the external environment
• Food and caloric drinks are the main source of energy, supplemented by energy stored in body tissues.
• Dietary energy intake can be estimated by tracking intake and calculating energy value.
• Glycogen provides a 12 to 48-hour energy reserve.
• Adipose tissue energy reserves vary by individual
• Muscle mass is used only during longer periods of fasting or starvation

Energy output

• Basal energy expenditure (BEE) is the sum of all internal activities of the body while at total rest
• Basal energy expenditure (BEE) is measured via direct and indirect calorimetry
• Basal energy expenditure (BEE) can be predicted by multiplying 0.9 kcal/kg body weight for women and 1 kcal/kg body weight for men by the number of hours in a day
• Basal energy expenditure is affected by high metabolic activity organs, body composition, growth periods, body temperature, hormonal status, and disease state

Physical Activity

• Physical activity includes work, recreation, and activities of daily living
• The thermic effect of food is the energy required for the physical processes of digestion, absorption, and transportation of nutrients to the cells
• Total energy expenditure (TEE) is comprised of the energy needs for BEE, the physical activities of the person, and the thermic effects of food
• Basal energy expenditure accounts for 60-75% of energy expenditure
• Physical Activity accounts for 15-30% of energy expenditure
• Thermic effect of food accounts for 10% of energy expenditure

Dietary Energy Intake

• During periods of rapid growth, extra energy per unit of body weight is necessary to build new tissue
• Energy needs decline with age but the specific amount of decline is highly individual during adulthood
• Dietary Reference Intakes (DRIs) for vitamins and minerals are set at two standard deviations above the mean to meet the needs of 97.5% of the population
• Dietary Guidelines for Americans include choosing a healthy eating pattern at an appropriate calorie level and meeting Physical Activity Guidelines for Americans
• MyPlate offers Individualized plans