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chapter

8

Fluid and Electrolyte Balance

5

Energy and Nutrient Balance

chapter

Prof Jennifer Broxterman, RD, MScFN3373: Nutrition for Physical ActivityLecture 7

Introduction

• Most individuals maintain a stable weight over time– How is it possible to maintain a stable body weight

within such a narrow range, especially when we pay little attention to the amount of energy we eat or expend each day?

Energy & Macronutrient Balance Equations

Energy Balance

• Energy balance equation:– Energy intake (total kcals consumed) equals energy

expenditure (total kcals expended)– Intakes of protein, CHO, fat, and EtOH must also

equal their oxidation rates to achieve energy balance

• Factors affecting energy balance:– Genetic makeup– Dietary intake and habits– Physical activity and activities of daily living– Environmental conditions– Lifestyle

Energy and Nutrient Balance Equations Required for Long-Term Weight

Maintenance

Chocolate Chip Cookie Mystery

• What would happen if you consumed an extra chocolate chip cookie (~100 kcal) every day for 40 years?

Macronutrient Balance

Macronutrient Balance

• Energy intake / energy expenditure is only one component of the energy balance equation

• Changes in the type & amount of macronutrients consumed (CHO, protein, fat, EtOH) and the oxidation of these nutrients within the body must be considered

• Under normal conditions:– CHO, protein, and EtOH are not easily converted into

body fat

Carbohydrate Balance

• CHO balance is tightly regulated by the body– Ingestion of CHO stimulates both glycogen storage and

glucose oxidation and inhibits fat oxidation– Glucose not stored as glycogen is oxidized directly in

almost equal balance to that consumed– What happens when large amounts of CHO are

consumed?

Figure 5.1

Carbohydrate Intake & Glycogen Storage

• Glycogen storage:– The body’s storage sites for glycogen are limited to

the liver and skeletal muscle – Glycogen storage fluctuates greatly in response to:

• Feeding – increases glycogen stores• Exercise – depletes glycogen stores

– Becoming physically fit increases one’s ability to store glycogen, making this carbohydrate unavailable for conversion to body fat

Protein Balance

• Protein (nitrogen) balance:– The body adjusts to a wide range of protein intakes

by altering the oxidation rate of dietary protein– After anabolic needs are met, carbon skeletons of

any excess aa’s are diverted into the energy substrate pool

– Inadequate intakes of either energy or CHO result in negative protein balance and may adversely affect the balance of individual aa’s

– Excess protein consumed may contribute indirectly to fat storage by sparing dietary fat

Fat Balance

• Fat oxidation:– As fat intake increases, fat oxidation does not

increase proportionally– Body adipose stores are large

• Excess energy eaten as dietary fat is stored as triglycerides in adipose tissue

• Little energy is consumed in the storage process

– What happens in long-term positive fat balance?

Figure 5.3a

Figure 5.3b

Figure 5.3c

Figure 5.3d

Figure 5.3e

Figure 5.3f

Alcohol Balance

• Alcohol (EtOH) oxidation:– EtOH is a “priority fuel”– Suppresses the oxidation of fat and to a lesser extent

that of protein and CHO– EtOH is not converted to TG and stored as fat– 7 kcal/g

Energy Expenditure

Components of Energy Expenditure

1. Resting Metabolic Rate (RMR)

Basal Metabolic Rate (BMR)

Resting Energy Expenditure (REE)

2. Thermic Effect of Food (TEF)

3. Energy Expended in Physical Activity and Activities of Daily Living

(Thermic Effect of Activity – TEA)

Figure 5.5

Biological Factors that Influence RMR

• Age:– RMR declines ~1-2% per

decade from the 2nd through the 7th decade of life

• Gender:– Men generally have larger RMRs

than women because on averagethey usually weigh more and havemore fat-free mass

Biological Factors that Influence RMR

• Genetics:– RMR has a genetic component– Parent-child and twin studies

• Body temperature:– RMR increases as body temp.

increases above normal (fever)– What about the relationship

between RMR and body temp.within normal temp. ranges?

Biological Factors that Influence RMR

• Reproductive hormones:– Menstrual cycle

fluctuations in RMR– Difference of 100-300

kcal/day

Physical Activity Factors that Influence RMR

• Exercise can affect energy expenditure both directly and indirectly:– Metabolism increases during exercise, increasing

the amount of energy expended– Exercise can also increase the

amount of FFM, elevating RMR

Physical Activity Factors that Influence RMR

• Research questions:– Does aerobic training increase RMR?– For a given individual, does becoming more

physically fit increase RMR?– Does metabolic rate stay elevated after exercise is

over?

Figure 5.12

Table 5.2

Factors that Influence the Thermic Effect of Food

• Effect of food composition (macronutrients):– Thermic effect of fat = 3-5%– Thermic effect of glucose = 5-10%– Thermic effect of protein = 20-30%

• Energy cost of storing macronutrients:– Converting dietary CHO & protein to stored fat

requires more energy than converting dietary fat to stored fat

• Meal size:– A meal higher in calories will have a higher TEF

compared to a low-calorie meal

Predicting Energy Expenditure

Equations for Estimating Resting Metabolic Rate (RMR) in Healthy

Individuals

World Health Organization’s Equations for Estimating RMR in Healthy Individuals

Equations for Estimating Resting Metabolic Rate (RMR) in Healthy

Individuals

Figure 5.15