Chapter 6: Energy1

Energy Balance - Introduction2

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 Balance3

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

Objectives4

Identify the human energy system

Identify the human energy balance

Identify the human energy requirements

Human Energy System5

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 processesElectrical energy: in brain and nerve activitiesMechanical energy: in muscle contractionThermal energy: to keep the body warm

Sources of fuel- fuel is provided in the form of nutrients3 energy nutrients: Carbohydrates

(primary), fat (secondary) and protein (last resort)

Types of energy7

Measurement of energy8

Unit of measure: calorie or kilocalorieIn 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 fat10

Measurement of Energy11

Nutrient Density: concentration of all nutrients in a given amount of food

Relative fuel densities:CHO: 4kcal/gFat: 9 kcal/gProtein: 4 kcal/gAlcohol: 7 kcal/g

12

Energy Balance13

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 Balance14

Overall energy balance within the human body depends on the energy intake in relation to energy output.

3 energy-yielding nutrients in food:CarbohydratesFatsProteins

Energy Intake15

Sources of Stored EnergyGlycogen – 12- 48 hour reserve of glycogen

exist in liver and musclesAdipose Tissue – Fat storage is larger than

glycogenMuscle 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 Output16

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 regulation17

Energy Output18

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 expenditure19

Energy Output20

Also known as “Basal Metabolic Rate” –BMRMeasures 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 Output21

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 BMR22

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 Activity23

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 Food24

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 Requirement25

Resting energy expenditure (REE) + physical activity + thermic effect of food

To maintain daily energy balance:Food-energy intake =

body-energy outputIntake > output = weight

gain (extreme: obesity)Intake < output = weight

loss (extreme: anorexia)

Total Energy Requirement26

Graph of total energy expenditure

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 offAging – energy needs decline

30-40 decrease by 3 %40-50 decrease by 3 %50-60 decrease by 7.5 %60-70 decrease by 7.5 %70-80 decrease by 10%

Energy needs in the life cycle28

Recommendations29

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 weightTo prevent gradual weight gain over time, make

small decreases in food and beverage calories and increase physical activity

Adopt a balanced eating pattern

Recommendations30

MyPlate2011 graphic guideline

MyPyramid: Can outline an individualized calorie

level and corresponding serving sizesCan provide helpful information re:

Maintaining balance between food intake and energy output through physical activity

Recommendations31