Energy Balance and Body Composition Many of us are aware of body weight and its effects on image. In...

Energy Balance and Body Composition

• Many of us are aware of body weight and its effects on image.

• In this chapter we will learn about:– how body composition and energy balance are

linked– approaches to appropriate weight management for

health, and – reaching and maintain fitness levels for optimal

health.

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

Energy Balance and Body Composition

• Fitness or ideal body composition does not mean having a certain physical appearance

• It definitely does not match with what is fashionable

• Moderate, short-term weight fluctuations are normal especially for women

• A big part of such short-term weight changes are related to water content


Energy Balance


Food Intake • Hunger

– The stimulus that drives us to eat– Necessary for the survival of the species– Main reason is empty stomach– It is a physiological response to the chemical

messengers sent by the hypothalamus to other parts of the brain that create the feeling of hunger

– It is influenced by:• Presence or absence of certain nutrients• Time since last meal• Temperature (heat reduces hunger and cold increases it)• Exercise• Hormones• Illnesses• Stress


Food Intake • Appetite

– Also initiates eating– You may not be hungry and have an appetite (e.g.

tempted by a piece of chocolate cake even when full)– You may be hungry and not have an appetite (e.g.

stress)

• Satiation– Feeling full– Receptors in the stomach are stretched– Satiation lags behind the hunger signals so you may

continue to eat even when you are actually full– There fore it is a good idea to stop eating before you

feel completely full (wait a few minutes and you may feel full)


Food Intake • Satiety

– Staying full– Signalling not to eat till the next meal

• Overriding signals– Overriding satiety signals (see section on

appetite)• Habit• Bored or anxious• Depressed or happy

– Overriding hunger signals• Fasting• Anorexia nervosa


Food Intake • Sustaining satiation and satiety and

satiating– Certain foods help to keep you feeling full– Proteins are the major players in triggering

satiety– Carbohydrates also work well– High fiber foods slow down digestion and can

create satiety– Fats are least successful in creating satiety

• Why? Shouldn’t they be better since they slow down the digestion too?

• The reason may be that fats are not seen by the body as immediate fuel (more as long term storage material) plus they do not increase blood glucose levels)


• Sustaining satiation and satiety– lower-fat foods can be eaten in

larger portions for the same number of kcalories


Food Intake

Food Intake


Food Intake • Hypothalamus

– Monitors a large array of body signals – Coordinates signals that will control

size and frequency of meals– Dozens of brain chemicals are involved

•E.g. Neuropeptide Y causes carbohydrate cravings, initiates eating, decreases energy usage and increases fat storage

•Obviously too much Neuropeptide Y would cause obesity


Food Composition • Finding out how

many kcalories there are in food

• Bomb calorimeter– Burns food (literally)

and uses that heat to raise the temperature of water

– Remember 1kcalorie is the amount of energy needed to raise the temperature of 1kg of water by 1℃


Food Composition • Direct calorimetry vs. indirect

calorimetry– Detecting the amount of heat generated– Detecting the amount of oxygen consumed

(since oxygen is needed for the breakdown of nutrients to release energy)

• Physiological fuel value– Calorimeters detect almost 100% of the

energy in a food– Your body cannot extract all this energy

from the food– The amount of energy your body can

derive from the foodCopyright 2005 Wadsworth Group, a division of Thomson Learning

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Thermogenesis • Basal thermogenesis

• Exercise-induced thermogenesis

• Diet-induced thermogenesis– Not really a major contributor to

calorie use• Adaptive thermogenesis


Components of Energy Expenditure



• Basal metabolism– Included in basal metabolism are

• Heart beat• Breathing• Nerve transmission

– Kidney filtration and reabsorption• Active transport (movement of materials

across cell membranes)• Protein synthesis • Cell growth, maintenance, tissue repair,

replacement, etc.Copyright 2005 Wadsworth Group, a division of Thomson Learning

Copyright 2005 Wadsworth Group, a division of Thomson Learning


• Basal metabolic rate (BMR)– Rate at which the body expends energy

for basic metabolism

• Resting metabolic rate (RMR)



Kcalories expended

Studying = 1 or 2 kcalories/minute


• Physical activity– The total time using muscles.– The amount of weight being moved by the muscles

• i.e. someone who is heavier will burn more calories doing the same activity thansomeone who is lighter.

– How many muscles being used affects the calories used.

– Which muscles are used (larger muscles burn mor calories)

– How intensely one uses the muscles (puts demand on the muscles)

– The level of fitness and skill of person (As your body gets used to certain activities, the calories burned goes down. Hence the need to change your exercise regimen occasionally)




Defining Healthy Body Weight


• The fashion industry is not made up of health professionals

• The criterion of fashion: BMI of Miss America



Defining Healthy Body Weight

• The criterion of health• Body mass index (BMI)

=weight (kg)/height (m)2]


BMI Values Used to Assess Weight

Distribution of Body Weights in U.S. Adults


Body Weight, Body Composition,

and Health

• Body composition

• Body weight = fat + lean tissue (including water)


Body Fat and Its Distribution


Body Fat and Its Distribution• Body fat evolutionarily was meant to help

survive famines, support pregnancy, to insulate against cold etc.

• But now, most humans do not have to worry about these contingencies. Instread some people need less body fat e.g. athletes. But they have to be careful not to reduce their body fat too much

• The only people who need more body fat in today’s world are people living in extremely cold environments like Alaska fishermen and pregnant women.



• Fat distribution– Intra-abdominal fat– Central obesity

• Fat around the organs• Associated with a number of chronic

problems such as heart disease, stroke, diabetes hypertension




• Waist circumferenceWomen – >35 inchesMen – >40 inchesHigher risk of central obesity


Methods Used to Assess Body Fat

There are scales and hand-held devices available based on the impedance method

Health Risks Associated With Body Weight and Body Fat

• Health risks of underweight– Causes of being underweight is important

• E.g. smoking, other disease?

– Loss of lean tissue– Menstrual irregularities and infertility in

women– If pregnancy occurs - unhealthy infant– Osteoporosis and bone fractures


BMI and Mortality

Health Risks Associated With Body Weight and Body Fat

• Health risks of overweight i.e. obesity– Cardiovascular disease– Hypertension– Diabetes– Sleep apnea (breathing stops while sleeping,

associated with some types of snoring– Some cancers– Risks are greater for whites than blacks– Yo-Yo dieting increases risk of cardiovascular

disease not to mention it gets harder and harder to lose weight with each new attempt


• Fat and fit versus sedentary and slim– There are three factors

that are important• Body weight• Body fat• Cardiorespiratory fitness

(your heart)

• Fitness has values beyond weight control


The Latest and Greatest Weight-Loss

Diet - Again

• The claims and truths of diet fads



The Latest and Greatest Weight-Loss

Diet - Again• High-protein, low carbohydrate

diets– The diet’s appeal


The Latest and Greatest Weight-Loss Diet - Again

• High-protein, low carbohydrate diets– Don’t count kcalories– Satisfy hunger– Follow a plan– Limit choices– Too much fat– Too much protein– Too little everything else– The body’s perspective



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Energy Balance and Body Composition Many of us are aware of body weight and its effects on image. In...

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