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Chapter 8

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Biomedical Physio & Kines
BPK 140
Michael Walsh

1 KIN 140 Section 8 Dr Mike Walsh WEIGHT MANAGEMENT A. What is Overweight? From an anthropometric perspective, it is common to divide the body into 2 compartments: fat and nonfat. The nonfat compartment includes you muscle, bones, liver, eyeballs, etc. Although being overweight can be due to an extra large fat or nonfat compartment on your body, it is commonly applied to just the fat compartment. This makes the term obesity synomonous with being overweight. Obesity has a few different definitions. One definition is having more than 25 % more fat than average. Another definition is being 30 lb overweight (which in the adult population has increased 60 % in the last decade). In many epidemiological studies it is common to measure the body mass index (BMI) of each subject. It is a quick and inexpensive measure. BMI = weight / height^2. The units must be kg and m respectively. BMI indicates how much weight you have for a given amount of height. It is a reasonable measure for a population but not necessarily for an individual. Of course a person with large bones or extra muscles may be inaccurately considered a health risk. There are also some individuals who are overfat, but very fit. Many competitors in the Vancouver Marathon have a substantial amount of fat and perform well, passing a lot of ‘healthier BMI’ competitors. There are also people who have a normal (healthy) BMI yet are quite overfat. Their shape is determined more by fat than by muscle. Replacing muscle weight with fat weight has little effect on the BMI but increases health risk all the same. In North America, about 60 % of the population, above the age of 50 yr, are considered overweight as assessed by BMI. BMI is not perfect. The relation of BMI to health, morbidity, and percent fat does differ between ethnicities and sex. However, the measures of height and weight are very reliable and simple to gather. The increase in obesity and subsequent BMI values are dramatically increasing medical costs. The costs are greater than that of smokers. Furthermore, smokers die much earlier than obese people, hence secondary medical costs such as nursing homes expenses, are much less for smokers than obese people. In terms of obesity and health, the waist measurement and the waist-to-hip ratio are also extremely predictive of poor health outcomes. B. Types of Fat Fat can be classified into essential and storage fat. 1. Essential Fat 2 Essential fat is fat that is required to normal physiological functioning. Essential fat is about 3 % of male body weight and 12 % of female body weight. For both genders essential fat includes fat in nervous tissue and other organs providing functionality or protection, fats in blood for the transport of some essential nutrients etc. For females, essential fat also includes sex-specific fat deposits in the thigh and butt region and breast. This fat is considered essential for proper reproductive capacity and is not associated with a health risk. This fat is determined in large part by circulating estrogens and is resistant to attempts by dieting and exercise to reduce it. 2. Storage Fat Storage fat is the fat found under the skin as well as internally surrounding organs. Storage fat is not considered essential. It is the fat most readily recruited when energy demand increases. The amount of storage fat is directly related to health risk, especially if located in the abdominal region. Androgens are partly responsible for this type of fat deposition. This is why it is more common in men and post- menopausal women. Storage fat is located both externally and internally. We can only easily measure external fat with skinfold calipers. Internal fat may account for 10-60 % of the total fat mass in a normal adult. The correlation of internal to external fat varies between 0.2 and 0.6. This relatively weak correlation indicates that skinfold measures cannot be used to estimate total fat mass in all individuals. Because of the higher health risk of abdominally located fat, waist girth and the waist-to-hip ratio are often used to evaluate a person’s health. An increased risk of disease is indicated for males with a waist greater than 40 inches and 35 inches for females. A waist -to-hip ratio greater than 0.90 for men and 0.85 for women is a health risk. In obese individuals, surgical removal of visceral fat increases insulin sensitivity. C. Energy Balance Energy Balance is Energy In – Energy Out The metabolic costs of living (Energy Out) is referred to as total energy expenditure (TEE) TEE = BMR + DIT + EEA Where BMR is basal metabolic rate, DIT is digestion-induced thermogenesis, and EEA is energy expenditure of activity. 1. Basal Metabolic Rate This is the energy required to maintain minimal function of staying alive. It is usually determined after a 12 hour fast and in the resting reclined state for 30 min at a room temperature of 20-25 C. This includes the energy to pump blood, inflate lungs, do cognitive functions, maintain membrane potentials, replace used tissues, etc. One’s BMR is about 20-25 kcal/kg of body weight and accounts for 55-75 % of TEE. 3 BMR has a strong genetic component. This means some people are more predisposed to gaining weight if they have a lower BMR. BMR is also dependent on the amount of lean tissue one has: brain (40 %) and muscle (30 %) account for about 70 % of BMR. Fever, thyroxin, stress hormones, increase in muscle mass, and a significant change in environmental temperature will increase BMR. Malnutrition can reduce BMR. 2. Digestion Induced-Thermogenesis This is the energy cost required to digest food. It takes energy to breakdown proteins, carbohydrates, and fats. On average it is about 15 % of protein calories, 10 % of carbohydrate calories, and 5 % of fat calories consumed. DIT accounts for about 10 % of TEE. 3. Energy Expenditure of Activity This is the energy cost of all physical activity, be it running or doing dishes. The exact EEA will depend on body weight, efficiency, intensity, duration, etc. In most people it accounts for about 10-40 % of TEE. Recently a subcomponent of EEA has been investigated. This component is nonexercise activity thermogenesis (NEAT). This is colloquially referred to as fidgeting energy. In a study in which subjects were fed an extra 1,000 kcal/day for 8 weeks, the change in body weights observed were inversely related to NEAT. 4. Energy Balance Equations Your weight is stable when energy consumed equals TEE. You gain weight when energy consumption is greater than TEE (positive energy balance). You lose weight when energy consumption is less than TEE (negative energy balance). When you gain weight energy is stored as glycogen and fat. The reverse is true when you lose weight. Women and older adults require about 1,600 kcal/day. Children, teenage females, active women, and sedentary males required about 2,200 kcal/day. Active males, teenage males, and very active females required about 2,800 kcal/day. One pound of fat is equivalent to 3,500 kcal. Thus if you consume 500 kcal more than you expend each day, then you will gain one pound of fat in one week. (500 Kcal/day * 7 day/week = 3,500 kcal/week). These energy balance equations imply a linear system. This is not true as will be exemplified when we talk about set point and motivation. D. Hunger and Satiety 4 The drive to eat is certainly one of our most robust homeostatic drives. Despite decades of intense research, all we have learned is that the signals to eat and stop eating are very complex. What is the signal to tell a person they are satiated? Is it the amount of distension in the GI tract? Is it the level of glucose and/or fat and or/ amino acids in the plasma? Is it the amount of one of numerous circulating hormones than change in response to eating? Is it some hormone not yet discovered? Such was the case with leptin a few years ago. There are at least 17 different hormones that influence feeding behaviour. E. Set Point Theory of Fat Regulation In some individuals at least, the body seems to protect a certain level of fatness. There is a linear relation between body weight and energy expenditure (Kleiber’s Law). If a lean person gains weight, they have a higher metabolic rate than predicted. Similarly, if an obese person loses weight, the metabolism lowers to a level below that predicted form body weight. This will mean fewer cal
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