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 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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

Energy Balance Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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) Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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) Copyright 2005 Wadsworth Group, a division of Thomson Learning

Sustaining satiation and satiety –lower-fat foods can be eaten in larger portions for the same number of kcalories Copyright 2005 Wadsworth Group, a division of Thomson Learning Food Intake

Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 ℃ Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 food 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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

Components of Energy Expenditure Copyright 2005 Wadsworth Group, a division of Thomson Learning

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

Components of Energy Expenditure Basal metabolic rate (BMR) –Rate at which the body expends energy for basic metabolism Resting metabolic rate (RMR) Copyright 2005 Wadsworth Group, a division of Thomson Learning

Kcalories expended Studying = 1 or 2 kcalories/minute

Components of Energy Expenditure 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) Copyright 2005 Wadsworth Group, a division of Thomson Learning

Defining Healthy Body Weight Copyright 2005 Wadsworth Group, a division of Thomson Learning The fashion industry is not made up of health professionals The criterion of fashion: BMI of Miss America

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Defining Healthy Body Weight The criterion of health Body mass index (BMI) =weight (kg)/height (m) 2] Copyright 2005 Wadsworth Group, a division of Thomson Learning

BMI Values Used to Assess Weight

Distribution of Body Weights in U.S. Adults Copyright 2005 Wadsworth Group, a division of Thomson Learning

Body Weight, Body Composition, and Health Body composition Body weight = fat + lean tissue (including water) Copyright 2005 Wadsworth Group, a division of Thomson Learning

Body Fat and Its Distribution Copyright 2005 Wadsworth Group, a division of Thomson Learning

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. Copyright 2005 Wadsworth Group, a division of Thomson Learning

Body Fat and Its Distribution 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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

Body Fat and Its Distribution Waist circumference Women – >35 inches Men – >40 inches Higher risk of central obesity Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning

The Latest and Greatest Weight-Loss Diet - Again The claims and truths of diet fads Copyright 2005 Wadsworth Group, a division of Thomson Learning

The Latest and Greatest Weight-Loss Diet - Again High-protein, low carbohydrate diets –The diet’s appeal Copyright 2005 Wadsworth Group, a division of Thomson Learning

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 Copyright 2005 Wadsworth Group, a division of Thomson Learning