Body Composition PDF

BODY COMPOSITION CHAPTER 7 Objectives Understand that body composition includes muscle mass and bone mass in addition to fat. Learn the common ways to measure body composition in the research lab and for your personal assessment purposes. Recognize how fat, muscle, and bone mass relate to the p...

BODY COMPOSITION CHAPTER 7 Objectives Understand that body composition includes muscle mass and bone mass in addition to fat. Learn the common ways to measure body composition in the research lab and for your personal assessment purposes. Recognize how fat, muscle, and bone mass relate to the primary diseases of obesity, sarcopenia, and osteoporosis. Use the “three-legged stool” of exercise and physical activity, nutrition, and hormones to manage your body composition to help you feel good and age well. Introduction Body composition is an important component of health-related physical fitness. Healthy body composition contributes to feeling well and being free of disease. If you successfully manage your body composition, you will enhance how you look, feel, and move. Body Composition Basics Your weight can be divided into three major components: fat mass, lean or muscle mass, and bone mass. All three are related to important health outcomes. Successfully managing your body composition can contribute to a long, healthy life! Measuring Body Composition: Three Models The most common model is the two-component model, which divides the body into fat and fat-free components. The gold standard in research is a four-component model that divides the body into water, protein, fat, and water. A three-component model—which divides the body into fat mass, lean soft tissue (including muscle), and bone mass—relates to health, especially for young adults. Fat Facts Fat stores energy, cushions organs, and helps regulate body temperature. It is contained in all cell membranes. We all need a certain amount of fat (essential fat) for healthy body function. The percentage of essential fat needed for health is about 3 to 5 percent for men and 8 to 12 percent for women. (continued) Fat Facts (continued) Most fat available for use as stored energy is located in adipocytes (i.e., fat cells). Most fat storage is located either right beneath the skin (subcutaneous fat) or deep within the abdomen surrounding the organs (visceral fat). Fat can also be stored in less typical locations, such as within the liver, around the heart, and near bundles of muscle fibers (ectopic fat). Figure 7.1 Interactions Between Fat, Muscle, and Bone Lean mass has a strong relationship to bone mass and bone density in adolescents and young adults. Weight changes (whether gains or losses) result not only from changes in fat mass but also changes in lean mass and bone mass. The exact composition of a weight change is influenced by many factors, including age, overall health, exercise level, and diet quality, especially protein and bone nutrients (e.g., calcium, vitamin D). Effects of Sex and Age on Body Composition After puberty, the average man has greater muscle and bone mass and less fat mass than the average woman due to differences in testosterone and estrogen. As a person moves beyond middle age, fat mass increases and muscle mass and bone mass decrease. The degree to which body composition changes with age is influenced by lifestyle choices, especially about physical activity and dietary habits. Genetics Influence Your Body Type Fat distribution is influenced by genetics. Women vary more in fat patterning than men do and may be more genetically inclined to a particular fat pattern. Android (i.e., male) fat pattern, often called an “apple shape,” is characterized by extra weight in the midsection. Gynoid (i.e., female) fat pattern, or “pear shape,” is characterized by extra weight in the hips and thighs. Fat depots carry varying risks for health. Figure 7.2 Somatotype or Body Type Most people have a blend of two body types. Some bodies do not match any particular type. Both men and women can align with any of the three body types. Regardless of body type, everyone can benefit from meeting the guidelines for physical activity and exercise. Endomorph This is the roundest body type, with relatively wide shoulders and hips. People with this body type tend to be pear shaped, gain and regain weight easily, excel in strength activities (e.g., weightlifting) and face a challenge in weight-bearing exercise (e.g., distance running). Mesomorph The m in mesomorph stands for muscle! People with this body type tend to have broad shoulders, be lean and muscular, and respond readily to exercise training. With their athletic build, they tend to excel at exercise and sport activities and to manage their body composition easily. Ectomorph People with this body type are thin and generally linear with narrow shoulders and hips. Regardless of their height, they have relatively little fat or muscle. These light-framed individuals excel at sports that require them to carry their weight, such as distance running. Assessing Body Composition Body composition can be measured in many ways—the greater the resources, the more accurate the results. Methods commonly used in clinics and fitness facilities are based on two-component and three-component models. They measure either the whole body or regions of the body. Body Density: Water Submersion Hydrodensitometry (underwater weighing) is based on a two-component model that divides the body into fat and fat-free components. Body density indicates degree of body fatness and ranges from a theoretical.9 gm/dL for a purely fat body to 1.1 gm/dL for a purely fat-free (i.e., lean) body Underwater weighing requires complete submersion in a tank of water while body weight is obtained on a scale. (continued) Density equals mass divided by volume. Body density can be calculated based on the difference between weight on land and weight underwater. Once body density is determined, a prediction equation can be used to estimate relative adiposity, or percent body fat (%Fat). Body Density: Water Submersion (continued) Body Density: Air Displacement Air displacement plethysmography is similar to underwater weighing but replaces water with air in order to determine body density. This methodology uses a closed chamber called a BOD POD to acquire body density. The person being measured wears minimal clothing, removes air from the hair by wearing a swim cap, and sits very still. (continued) The BOD POD chamber uses computerized sensors to measure changes in air volume. Once body density has been determined, that value is entered into an equation to estimate %Fat. This approach is safer and more comfortable than underwater weighing, especially for children, older adults, people with movement disabilities, and those afraid of water. The BOD POD is expensive. Body Density: Air Displacement (continued) Dual-Energy X-Ray Absorptiometry (DEXA) This approach is one of the best technological advances for estimating body composition. Using a three-component model, it measures fat mass, lean soft tissue (muscle), and bone mass. It is available in nearly all hospitals and in many university departments of exercise science and nutrition. It works by exposing the body to low- and high-energy X-rays. (continued) DEXA provides both whole-body and regional (arm and leg) estimates of body composition. It is a valid and reliable method for estimating body composition. It is easy to perform (merely requires lying still on a scanning table for a few minutes). Its downsides include high cost, necessity of expertise, and radiation exposure (a small amount). Dual-Energy X-Ray Absorptiometry (DEXA) (continued) Magnetic Resonance Imaging (MRI) This approach shows ectopic adipose depots (where only small amounts of fat should be stored), including visceral fat (deep in the abdomen)—a major health risk. It can be used to assess fat infiltration into muscles (intermuscular adipose tissue), which has been linked to higher risk for metabolic diseases and poor muscle quality. It is available in most hospitals and many research centers. Bioelectrical Impedance Analysis (BIA) This approach is suitable for laboratory, field, and personal use. It is based on the fact that nearly all body water is contained in fat-free mass; thus measuring body water enables us to estimate fat-free mass. A bioelectrical instrument sends a small electrical current through the body and measures the resistance to the current. (continued) Resistance to the current is determined by the balance between water (a great conductor) and fat (a good insulator). Because this approach measures water, the person being tested must be properly hydrated; being dehydrated or overhydrated can greatly affect accuracy. Lower-cost BIA instruments offer a less accurate measure of total body water and %Fat. Bioelectrical Impedance Analysis (BIA) (continued) Skinfolds This method is often used in the field to assess body composition based on the fact that most stored fat is located just beneath the skin. Skinfold thicknesses are obtained from several sites and summed; the total reflects overall skinfold thickness, which represents %Fat. Standardized measures can be taken on the legs, arms, back, and abdomen. (continued) Skinfolds (continued) Skinfolds should be measured by high-quality calipers. Obtaining valid and reliable measurements requires much practice on various body types. Skinfold assessment requires the measurer to touch the person being measured on multiple parts of the body, which some may find uncomfortable. (continued) Research-grade calipers can cost several hundred dollars; well-calibrated spring-loaded ones are also expensive. When converting a skinfold sum into a %Fat estimate, the tester must choose from numerous prediction equations, which can influence accuracy. This method cannot measure visceral adipose tissue, which is located beneath the muscle wall of the abdomen. Skinfolds (continued) Personal Measurement of Weight Status and Body Composition Your choice of method will depend on your purpose, the availability of equipment, testing expertise, and the amount of money you can or want to spend. At a minimum, you should monitor your weight and waistline. Weight Status It is evaluated primarily based on body mass index (BMI), which hinges on the ratio of weight to height. Despite some limitations, BMI is a well-established index for health risk. Waist circumference is highly related to visceral fat. Weight status is influenced by diet (especially salty and starchy foods), weather, stress, and hormonal changes. Four S’s of Monitoring Weight Status Same time of day Same day each week Same clothing (or none!) Same scale Body Composition Assessments Are Estimates! They all have a degree of error. More expensive equipment and sophisticated expertise provide more accurate estimates. DEXA estimates have an error margin of only 1 to 2 percent. Many BIA instruments have an error rate of 4 to 5 percent. Weight Status, Body Composition, and Your Risk of Chronic Disease Body composition is linked directly to primary diseases. Having too much fat mass (high %Fat) is defined as overweight or obesity. Overweight is linked to many chronic diseases and conditions that occur in middle age and beyond. Having too little muscle mass and low bone mass can cause serious conditions and diseases that often arrive later in life. Weight Status Classified BMI is based on the ratio of weight to height (weight in kilograms divided by the square of height in meters). BMI classifications include underweight, normal weight, overweight, and obese. Because of the key link between waist size and visceral fat and the related risk for metabolic diseases, risk is estimated based on BMI and waist circumference. A person with a normal BMI can be at an increased risk for disease due to an elevated waist size. BMI and Adiposity Relationships BMI is related relatively strongly to %Fat across all age groups, doctors use it to assess health status. For a typical adult, BMI levels in the overweight and obese categories are linked to increased risk of chronic disease and death. Risk is also influenced by many other factors, such as physical activity and exercise, diet quality, smoking, alcohol and drug habits, and stress. BMI Values: Interpret With Caution Heavily muscled athletes. Increased muscle mass increases weight, thereby increasing BMI as well. Altered height. We lose several inches as we age; therefore, if our weight is stable, our BMI increases. Reduced physical activity. The relationship between BMI and %Fat can be greatly altered by reduced muscle mass in individuals who are bedridden or unable to walk due to illness, spinal cord injury, or other challenges. %Fat: Health and Fitness Categories Unlike BMI, %Fat has no universally accepted norms. Generally, a range of 10 to 22 %Fat for men and 20 to 32 %Fat for women is considered satisfactory for health. A slight increase (of 3 to 5 %Fat) is a normal part of the aging process. A %Fat level below 3 to 5 for young men or 8 to 12 for young women can be harmful to health. Fat Depots: Not All Equal The location of fat storage influences a person’s risk for many chronic conditions and diseases. Where you store fat as a healthy young adult depends on genetics and sex hormones, as well as (to a lesser extent) level of physical activity, diet quality, and stress hormones. Changes in whole-body composition during the aging process shift the preferred fat storage depot more centrally and less in the lower body. Preventing Sarcopenia: Keep Your Muscle Mass! With advancing age (45 to 65), many adults are at risk for sarcopenia—age-related loss of muscle mass and strength. Sarcopenia is a major cause of functional decline and loss of independence in older adults. The good news: Our muscles retain the ability to get stronger in response to resistance training well into our 90s. Osteoporosis: Build the Bone Bank Early in Life Osteoporosis is a bone disease in which the body loses too much bone, makes too little bone, or both. As bones become weak, they are at higher risk of breaking from nontraumatic injury (e.g., fall in the bathroom or on an icy sidewalk). Osteoporosis is “silent,” which means that you can be completely unaware of having it until you suffer a fracture. Osteoporosis: Diagnosis and Who Gets It Screening typically occurs based on age and health history. The DEXA instrument measures bone mass and bone density. The bone density T-score value is primary tool for diagnosing osteoporosis. A T-score of −2.5 or below indicates being 2.5 standard deviations below the peak bone density of a young healthy person of the same sex. Risk Factors for Osteoporosis Age. This is the primary risk factor for osteoporosis because loss of bone is a normal part of the aging process. Sex. Women have a greater risk of osteoporosis than men do because of bone size and differing sex hormone profiles. Race or ethnic group. White and Asian people have greater risk of osteoporosis than do African-American people. (continued) Risk Factors for Osteoporosis (continued) Diseases, conditions, and medical procedures. Risk can be increased by cancer, endocrine or hormonal disorders, autoimmune disorders, and digestive disorders. Medications. Bones can be compromised by many medications (e.g., steroids). Nutrition. Bone health is directly affected by poor intake of calcium and vitamin D. Physical activity and exercise. Bone health is greatly affected by being sedentary (especially if bedridden). Figure 7.4 Benefits of Healthy Body Composition Energetic physical function Enhanced work, recreation, or sport performance Healthier self-esteem and self-image Prevention of the big metabolic three and physical-function diseases and conditions Body Composition Management: The Three-Legged Stool Exercise and physical activity Adequate nutrition Appropriate hormones Figure 7.5 Physical Activity and Exercise: Movement Mode Matters Fat mass. Choose high-energy activities. Endurance activities expend many calories, and energy balance is crucial for maintaining a healthy level of fat mass. Lean soft tissue (mainly muscle). Relatively high-intensity strength training is the most effective mode for gaining and keeping muscle mass. Bone mass and density. Bones must be loaded in order to adapt. Nutrition Adequate protein intake is important for muscle maintenance and bone health, especially later in life. Calcium and vitamin D are critical for bone health. Poor dietary habits (along with physical inactivity) are major reasons for rising rates of obesity, sarcopenia, and osteoporosis. Hormones Differences in fat, muscle, and bone mass seen in men and women during and after puberty are greatly affected by sex hormones, testosterone and estrogen, and other growth hormones. Age-related declines in these hormones constitute a key reason for changes in body composition (increase in fat mass and decreases in muscle and bone mass). Female Athlete Triad Disordered eating (with a range of poor nutritional behaviors) Amenorrhea (irregular or absent menstrual cycle) Osteoporosis (low bone mass and poor bone quality, thus leading to weak bones and risk of fracture) Though most common in women, it also occurs in men who aim to compete in weight-class sports. Summary Body composition is the fifth and final component of health-related physical fitness. Primary components are body fat, muscle mass, and bone mass. Body composition can be measured in the research lab or the privacy of your home. Optimal nutrition and regular physical activity and resistance training can go a long way toward successful management of body composition. Review Questions Using a three-component model as a frame, list and describe the primary body composition components that can affect your health. Describe the primary ways that body composition can be measured in the laboratory, in the field, and in the privacy of your home. Which method is the most accurate? Body mass index (BMI) is a useful health index, but it does have limitations. When does caution need to be used when interpreting BMI to classify weight status? (continued) Review Questions (continued) Although chronic diseases often don’t present until middle age, they often begin in young adulthood. Describe how the three body composition components relate to primary diseases that occur later in life. List and describe the primary ways that a healthy body composition will make you both function better and feel better during your campus life. What are the three legs of the body composition stool? What specific behaviors or factors do you need to address to apply these to your life as a young adult?