Chapter 6: Energy 1

Energy Balance - Introduction 2 Energy metabolism deals with change and balance. Our bodies constantly convert fuel energy from food into the energy used at work, play, and rest. Fuel is “burned” and stored as necessary to provide a continuous flow of energy for the body’s work

Energy Balance 3 Key concepts  Food energy is changed into body energy to do work  The body uses most of its energy intake for basal metabolic work needs  A balance between intake of food energy and output of body-work energy maintains life and health  States of being underweight and overweight reflect degrees of body energy imbalance

Objectives 4  Identify the human energy system  Identify the human energy balance  Identify the human energy requirements

Human Energy System 5 Basic energy needs – Body needs constant energy to do the work necessary to maintain life and health Voluntary work and exercise –includes all physical actions related to a person’s usual activities, as well as any additional activities Involuntary body work – all activities of the body that are not consciously performed - such as digestion, circulation, respiration, and absorption - Referred to as the “thermic effect of food”

Human Energy System/Basic Energy Needs 6 The body requires energy in various forms : Chemical energy: in many metabolic processes Electrical energy: in brain and nerve activities Mechanical energy: in muscle contraction Thermal energy: to keep the body warm Sources of fuel- fuel is provided in the form of nutrients 3 energy nutrients: Carbohydrates (primary), fat (secondary) and protein (last resort)

Types of energy 7

Measurement of energy 8  Unit of measure: calorie or kilocalorie  In common usage:  an amount of energy in food or expended in physical actions  In Nutritional Science:  Kilocalorie – the large caloric unit  1000 calories = Kcal or Kcalorie-  the amount of heat necessary to raise 1 kg of water 1 degree centigrade- “Joule” is the international measurement of energy

Measurement of Energy 9 Energy-yielding nutrients have “basic fuel factors” Basic fuel factors reflect the relative fuel densities: Density: refers to the degree of concentrated material in a given substance. More material in a smaller amount of substance gives that substance a greater density. Caloric Density: higher concentration of energy (kcals) in a smaller amount of food. Foods high in fat have the highest caloric density

Caloric density due to fat 10

Measurement of Energy 11 Nutrient Density: concentration of all nutrients in a given amount of food Relative fuel densities: CHO: 4kcal/g Fat: 9 kcal/g Protein: 4 kcal/g Alcohol: 7 kcal/g

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Energy Balance 13 Two energy systems: External energy cycle – In the environment, the ultimate source of energy is the sun. Using water and carbon dioxide as raw material, plants transform the sun’s radiation into stored chemical energy -> mainly CHO Internal energy cycle – When humans eat plants and animals, the stored energy is changed into body fuel, glucose and fatty acids and cycles them into various energy forms to serve the body’s needs

Energy Balance 14 Overall energy balance within the human body depends on the energy intake in relation to energy output. 3 energy-yielding nutrients in food: Carbohydrates Fats Proteins

Energy Intake 15 Sources of Stored Energy Glycogen – hour reserve of glycogen exist in liver and muscles Adipose Tissue – Fat storage is larger than glycogen Muscle Mass – Limited supply stored in muscle mass, lean muscle must be maintained for health. Only during longer periods of fasting or starvation does the body turn to this tissue for energy

Energy Output 16 The necessary activities to sustain life – i.e. normal body functions, regulation of temperature, tissue growth and repair - use energy from food and body reserves Three demands for energy determine the body’s total energy requirements:  Resting energy expenditure  Physical activity  Thermal effect of food

Temperature regulation 17

Energy Output 18 Resting Energy Expenditure (REE) = RMR (Resting Metabolic Rate) *The sum of all internal working activities of the body at rest *Expressed as kcal/day Amount of Kcal needed to consume over 24 hours to maintain current weight while at rest – often called Basal Energy Expenditure (BEE)

Resting energy expenditure 19

Energy Output 20 Also known as “Basal Metabolic Rate” – BMR Measures resting energy expenditure or basal metabolic rate Thyroid test often are used to indicated BMR – measures the thyroid gland and the blood levels of the hormone thyroxine

Energy Output 21 Calculating Basal Energy Needs  Men: 1 kcal x kg body wt. x 24 hrs  Women: 0.9 kcal x kg body wt. x 24 hrs

Factors influencing BMR 22 Lean body mass – There is increased metabolic activity in lean tissue (muscle and tissue) as compared to fat and bone Growth periods – Growth hormone stimulate cell metabolism and raises BMR 15 % - 20 % - also raises in pregnancy requiring 300 kcal/day extra Body temperature – Fever increases BMR 7 % per each degree F rise in temperature (.83 Degree C) Hormonal status – Depending of hormone secretion BMR will rise or fall Thyroid ---Hyper vs Hypo

Physical Activity 23 Energy expenditure for physical activity goes above and beyond energy used for resting energy needs Energy output during physical activity varies widely across individuals

Thermal Effect of Food 24 After eating, food stimulates metabolism Requires extra energy for digestion, absorption, and transport of the nutrients to the cells 5-10% of the body’s total energy needs for metabolism relates to the processing of food

Total Energy Requirement 25 Resting energy expenditure (REE) + physical activity + thermic effect of food To maintain daily energy balance: Food-energy intake = body- energy output Intake > output = weight gain (extreme: obesity) Intake < output = weight loss (extreme: anorexia)

Total Energy Requirement 26

Recommendations for Dietary Energy Intake 27 General life cycle: Growth periods – chart page 88 (Table 6 – 3) Extra energy per unity of body weight is necessary to build new tissue – e.g. infancy, adolescence, pregnancy Adulthood – energy needs level off Aging – energy needs decline 30-40decrease by 3 % 40-50decrease by 3 % 50-60decrease by 7.5 % 60-70decrease by 7.5 % 70-80decrease by 10%

Energy needs in the life cycle 28

Recommendations 29 Dietary Reference Intakes (DRIs) Food and Nutrition Board of the Institute of Medicine created recommendation for energy intake based on gender, age, and other considerations Refer to chart page 89 (Table 6 – 5) Dietary Guidelines for Americans indicate energy needs based on two recommendations: Maintain ideal weight To prevent gradual weight gain over time, make small decreases in food and beverage calories and increase physical activity Adopt a balanced eating pattern

Recommendations 30 MyPlate  2011 graphic guideline MyPyramid:  Can outline an individualized calorie level and corresponding serving sizes  Can provide helpful information re: Maintaining balance between food intake and energy output through physical activity

Recommendations 31