Chapter 8: Energy Balance

Energy Balance

the amount of energy taken in (from foods and beverages) versus the amount of energy expended

How much body fat is stored for each 3500kcal eaten in excess?

1 lb

How much energy must be expended to lose 1 lb of body fat?

3500 kcal

How much energy does the fat stores of a healthy weight adult contain?

50,000 to 200,000 kcal

What percentage of an adult's body weight is made from water?

60%

Positive Energy Balance

a state in which energy intake is higher than energy expenditure, excess energy is stored as fat, and the individual gains weight

Negative Energy Balance

a state in which energy intake is lower than energy expenditure, energy is derived from tissue stores of fat and lean tissue, and the individual loses weight

What is the composition of rapidly-lost weight?

some fat, large amounts of fluid, and some lean tissues

What is the composition of long-term weight loss?

75% fat and 25% lean muscle

What is the composition of weight loss during starvation?

50% fat and 50% lean muscle

Energy Intake

the kcal taken into the body from foods and drinks

What are some of the methods of calculating energy intake?

bomb calorimeter, indirect calorimetry, or calculations based on the proportion of carbs, fat, protein, and alcohol in food

Bomb Calorimeter

an instrument that estimates the energy contained in the chemical bonds of food by measuring the amount of heat energy released as it is burned

Physiological Fuel Value

The amount of energy the human body is able to derive from foods

What is the problem with using direct calorimetry?

it overestimates the physiological fuel value

How do researchers make up for the discrepancy between direct calorimetry and physiological fuel value?

using calculations and creating tables of energy values of foods which provide reasonable estimates of energy intake

Indirect Calorimetry

an estimation of energy based on the amount of oxygen consumed (used for both food energy and body energy expenditure)

How are the energy values of foods computed?

using the amounts of carbohydrate, fat, protein, and alcohol present in the foods

What are some internal cues that influence energy intake?

hunger, satiation, and satiety

hunger

an inbon irritating feeling that arises from lack of food and initiates food seeking behaviour; the sensation of a lack of food

What is hunger caused by?

the hypothalamus, which integrates messages about energy intake, expenditure, and storage from other parts of the brain, mouth, GI tract, and liver

Which factors influence hunger?

the presence or absence of nutrients in the bloodstream; the size and composition of the previous meal; customary eating patterns; climate; exercise; and hormones

Appetite

the integrated response to the sight, smell or taste of food, and other perceptions that initiates or delays eating

Satiation

a feeling of fullness that occurs during a meal and causes cessation of eating

What does hunger determine?

when, how much, and what we eat

What does satiation determine?

how much food is eaten

When does satiation occur?

as receptors in the stomach stretch and hormones (e.g. cholecystokinin) become active

Satiety

a feeling of fullness that occurs after a meal and inhibits eating until the next meal

What does satiety determine?

when we restart eating

Which nutrient type is considered the most satiating?

protein

Which nutrient seems to stimulate appetite and increase food intake?

fructose in a sugary fruit drink

Why is it wise to consume foods with lower energy density?

they can promote satiation for fewer calories

Which nutrient type has a weak effect on satiation (until it reaches the intestine where it produces strong signals)?

fat

What are some external cues that influence energy intake?

time of day; availability of food; portion sizes; preferred foods; abundance/variety of food; cognitive influences; and mental or physical illness

What are some cognitive cues that influence energy intake?

special occassions, stress, perceptions, memories, and social interactions

Which energy-intake cues tend to be overriden?

internal

Thermogenesis

the generation of heat; used in physiology and nutrition studies as an index of how much energy the body is expending

Which categories of thermogenesis does the body's total energy expenditure reflect?

basal metabolism, physical activity, food consumption (the Thermic Effect of Food), and sometimes adaptative thermogenesis

Adaptive Thermogenesis

adjustments in energy expenditure related to changes in the environment (e.g. extreme cold or stress) and to physiological events (e.g. overfeeding, trauma, or changes in hormone status)

Why is adaptive thermogenesis not always considered when looking at total body energy expenditure?

it only makes a considerable difference in some cases, and even then, it is very variable and specific to individuals

Basal Metabolism

all the activities that sustain life (e.g. breathing, maintaining body temperture, and metabolism, heartbeat, etc.)

What is basal metabolism influenced by?

genetics and lifestyle factors

Which factors increase basal metabolism?

growth, increased lean muscle tissue, fever, stressors, and increased thyroid hormones

Which factor makes up about 50 to 65% of our energy expenditure?

basal metabolism

Basal Metabolic Rate (BMR)

the energy used for basal metabolism

In which conditions is BMR measured?

the subject is in a fasted state (following an overnight 12 hour fast), awake, clothed ,and lying still in a thermoneutral setting

When may BMR vary?

between people and within the same individual with a change in circumstance or physical condition

How does increased weight usually affect BMR?

more total energy is expended, but the amount of energy per kilogram of body weight may be lower in someone with a smaller weight

What is one way people can increase their BMR?

participating in endurance and strength-training activities regularly to maximize lean body mass

Which factors increase BMR?

increased height, growth, lean tissue (body composition), fever, stresses, smoking, caffeine, the cold and heat (environmental temperature), premenstrual hormones (slightly), and thyroxin (can speed it up or slow it down)

Which factors decrease BMR?

increased age, fasting/starvation, malnutrition, and sleep

Resting Metabolic Rate (RMR)

the energy used for basal metabolism when the subject is lying still in a comfortable setting

How does RMR differ from BMR?

it is slightly higher as there are less stringent criteria for recent food intake and physical activity

Which methods are used to measure RMR and BMR?

direct and indirect calorimetry

Direct Calorimetry (for BMR and RMR)

a measure of the amount of heat generated by a subject in an insulated room which is interpreted as the amount of energy burned

Why is direct calorimetry rarely used to measure BMR or RMR?

it requires specialized equipment

Indirect Calorimetry (for BMR and RMR)

an estimation of the amount of energy that the body is using based off of the respiratory quotient and a set of equations

Respiratory Quotient

the ratio of O2 and CO2 exhaled

Physical Activity

voluntary movements of skeletal muscles

Which component of energy expediture is most variable and most easily increased?

physical activity

Which factor makes up about 30 to 50% of our energy expenditure?

physical activity

What are the benefits of physical activity?

preventing weight gain; reduced risk for multiple chronic diseases; increased lean muscle mass; and improved mental health

How many minutes does the Canadian Physical Activity Guidelines recommend that adults accumulate per week?

150 minutes

What does the amount of energy needed for any activity depend on?

muscle mass, body weight, and the activity itself

Thermic Effect of Food

the energy expended to process (move, digest, absorb, transport, and store) ingested food and drink

Which factor makes up about 10% of our energy expenditure?

the thermic effect of food

Why can the thermic effect for food be ignored for most purposes when estimating energy expenditure?

its contribution to total energy output is smaller than the probable errors involved in estimating overall energy intake and output

How are the percentages of the thermic effect of foods calculated?

by dividing the energy expended during digestion and absorption by the energy content of the food

What is the % of the Thermic Effect of foods for Carbohydrate?

5-10%

What is the % of the Thermic Effect of foods for fat?

0-5%

What is the % of the Thermic Effect of foods for protein?

20-30%

What is the % of the Thermic Effect of foods for alcohol?

15-20%

How does one's sex affect EER?

women generally have a lower BMR than men, mostly because men typically have more lean body mass

How does growth affect EER?

pregnant and lactating women, infants, children and adolescents have higher BMRs

How does age affect EER?

BMR declines during adulthood as lean body mass and physical activities diminish

How does physical activity affect EER?

whether one engages in high, moderate, or little physical activity affects how much energy they need

How does body composition and size affect EER?

taller and heavier people have higher basal metabolism

Why may the energy needs of two individuals that are matched on all the factors for EER still differ?

genetic differences

How does one determine their EER?

by using the appropriate equation, inserting age in years, weight (wt) in kg, height (ht) in metres, and physical activity (PA) factor from the accompanying table

Estimated Energy Requirement (EER)

the average dietary energy intake that maintains energy balance and good health in a person of a given age, gender, weight, height, and level of physical activity

For most people, where does their actual energy requirement fall from their EER?

men: ± 200kcal
women: ± 160kcal

For almost all people, where does their actual energy requirement fall from their EER?

men: ± 400kcal
women: ± 320kcal

Healthy Body Weight

a body weight that has sufficient lean and fat tissue to support normal activities, serve as an energy reserve, and minimize the risk of morbidity (illness) and mortality

Lean Tissues

muscles, organs, and the bones

What is each individual's own healthiest body weight based on?

their genetics, age, physical development, and their usual activities

Body Composition

the proportions of muscle, bone, fat, and other tissue that make up a person's total body weight

Is it possible to directly tell the body composition of a living human being?

no

What assumption do researchers use when indirectly assessing body composition?

weight \= fat + lean tissue (including water)

What is the most important criterion for determining how much a person should weigh and how much body fat they need?

good health and longevity, not appearance

Body Mass Index (BMI)

a quick and convenient tool to screen for potentially unhealthy body weight, calculated by body weight (kg)/ height squared (m2)

What is the healthy BMI range?

18.5 to 24.9 kg/m2

What is the overweight BMI range?

25 to 29.9 kg/m2

What is the obese BMI range?

\>30 kg/m2

What is the underweight BMI range?

Which effects become apparent when BMI is below 17?

signs of illness, reduced work capacity, and poor reproductive function

Which effects become apparent when BMI is above 25?

obesity-related diseases

Why are standard BMI guidelines inappropriate for some populations?

there are differences in body composition among people of different ages and various ethnic and racial groups

Why are weight measures not always useful in assessing body composition?

they don't reveal how much of the weight is fat nor where the fat is located

What are the benefits of weight measures?

they are inexpensive, easy to take, and highly accurate

How do female body compositions change during adolescence?

fat assumes a large percentage as essential body fat is deposited in the mammary glands and pelvic region