PE 9A Information
Section 2: Fat Facts and Figures
Tracey Kobayashi
50 Phelan Ave, NGYM
San Francisco, CA 94112
(415)452-7311
tkobayas@ccsf.edu
PE 9A: Fit or Fat
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PE 50: Fitness Center
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Poor diets and sedentary lifestyles are two prime causes of the obesity and degenerative illness which plague many Americans. Obesity is being overweight or overfat which inhibits motor function and exacerbates conditions such as arthritis and diabetes. In spite of a health-conscious society, Americans are getting fatter:
- Between 1980 and 1994, the number of overweight children and adolescents increased by 6% and the number of overweight adults increased by 9%.
- 35% of U.S. adults weigh dangerously more than they should.
- 14% of children age 6 to 11 and 11% of adolescents age 12 to 17 are dangerously obese.
- Obesity and related conditions are regarded as the second leading preventable cause of death after smoking.
- Costs of obesity in the U.S. from excess medical expenses and loss of income are reported to exceed $68 billion every year (Nat'l Task Force on the Prevention and Treatment of Obesity).
Being overweight or overfat may be associated with other health problems. However, moderately high body fat with no other risk factors (diabetes, high blood pressure, etc) and a healthy lifestyle is typically not an immediate concern. In this case, it is best to focus on developing good habits that are sustainable over the long term.
The Diet Cycle
I'm sure you're aware of the yo-yo syndrome Ð the cycle of losing weight while dieting, and then ballooning past your old weight when resuming old eating habits. This happens because many diets work on caloric restriction alone, leaving the individual hungry. Hunger is one of the most basic and powerful instincts -- it prevents malnutrition and starvation by creating a strong urge to eat. Diets trigger survival mechanisms in response to hunger which work against caloric restrictions; metabolic rate decreases so the body requires less energy to function; incoming energy is absorbed more efficiently; and the weight lost on these diets tends to be lean mass, so even though body weight is lower, the individual is actually fatter.
After dieting, people tend to overeat to make up for lost calories and return to their old habits which caused the situation in the first place. Not only that, because lean mass was lost during the diet, the individual actually needs less calories. If the old diet was too much before, it is even more excessive now, and the weight comes back, often more than before.
Successful body composition control comes not through short-term fixes, but through long-term lifestyle changes, which include not only adjusting nutritional intake, but also making time for regular physical activity.
Body Fat Ranges
To describe obesity, first think of fat in general. Fat is a substance the body either ingests or manufactures which is stored in adipose cells located under the skin, around organs, and between the muscles. It acts as an energy supply, vitamin and hormone transport facilitator, and insulator. Fat is a problem when there is too much of it because bioenergetic mechanisms become inefficient. Those with excess fat are efficient at storing, but not using it.
The following tables list standard body fat percent ranges. Influences on "normal" body composition include: ethnic background; gender; and hormone levels (birth control pills can increase body fat).
Standard Body Fat Ranges
| Low Body Fat | Optimal Range | Moderately High | High Body Fat | Dangerously High | |
|---|---|---|---|---|---|
| WOMEN | < 15% | 15-25% | 26-30% | 31-35% | > 35% |
| MEN | < 10% | 10-20% | 21-25% | 26-30% | > 30% |
Body Fat Norms Based on Ethnic Background (Bailey, 1991):
| Women | Men | |
|---|---|---|
| African | 19% | 12% |
| Asian | 25% | 18% |
| European | 22% | 15% |
Actual body fat percentages for "average" Americans (Bailey, 1991):
| < 30yr old | > 30yr old | |
|---|---|---|
| WOMEN | 24.8% | 31.2% |
| MEN | 20% | 25% |
Body Mass Index
If you can't invest in any of the paraphernalia necessary to measure your body fat, there is still the good old-fashioned weight for height measurement. The Body Mass Index (BMI) is a variation of this ratio. To calculate your BMI, divide your mass in kilograms by your height in meters squared:
BMI = kg/m2
Compare the result to the following figures:
| BMI | Classification |
|---|---|
| < 25 | Desirable Range |
| < 30 | Grade 1 Obesity |
| < 41 | Grade 2 Obesity |
| 41 or higher | Grade 3 Obesity |
Although many Americans show concern for weight and health, habits are learned early. The technologies that make life convenient contribute to the problem. People drive even short distancesinstead of walk or, and ride elevators and escalators instead of taking stairs. Kids play video games instead of playground games. Instead of walking through store aisles, people shop by poking pointing devices named after rodents. Fat-laden, over-processed, fast and packaged foods are chosen over whole, healthful foods. These things add up over time.
Obesity Theories
Obesity happens when there is a positive caloric balance over an extended time. There are many theories on how people become obese. The following paragraphs discuss some of these theories.
The setpoint theory is based on the idea that the body strives to maintain a set state. Most dieters, after reaching their goals and resuming normal habits, crept back to their previous, or even higher weight. To a certain degree, a setpoint exists, however it fluctuates, and this setpoint has more to do with the body's nutritional needs rather than a general desired level of weight or body composition. When one diets without exercising, lean body mass is lost and metabolic rate decreases -- the body needs less calories to survive (lower setpoint). After dieting, caloric needs remain low. When normal dietary patterns are resumed, weight is gained.
The fat gene theory was originally based on the fact that many fat parents also had fat kids -- obesity ran in the family, which led to research into a "fat gene." There have actually been a few fat genes discovered, including the leptin receptor gene, and the melanocortin 4 receptor(MC4R). However, the defects in these genes seem to be activated by lifestyle and there are inconsistencies as to which genes may be activated. For many, obesity may be familial because children often pick up habits from their parents, regardless of whether a mutated gene was activated or not.
At different stages (infancy, puberty, pregnancy, high weight gain), the number of adipose cells where fat is stored may increase. Adipose cell hypertrophy theory assumes adipose cells somehow want to be filled, so when one has more adipose cells, one tends to be fatter, however, there is no proof that adipose cells need to be filled. Recent research on this theory has centered around leptin, a hormone released by the adipocytes, which regulates energy homeostasis, satiety, and neuroendocrine response, although there is no concrete proof that leptin has a major role in regulating either glucose or fat metabolism. (Mick et al, 1998).
In a few cases, an individual follows a prudent diet and exercises regularly and the pounds still increase. In these rare cases, hormonal levels can play a part in working against one's wishes. Many phenomena can influence hormonal levels and shifts. For starters, women naturally have more estrogen and less testosterone than men. Testosterone aids muscle hypertrophy, which in turn boosts metabolic rate, while estrogen encourages fat storage, so women are naturally more inclined to store more fat than men. Estrogen levels may also be artificially boosted by birth control pills -- these boosts can often be decreased with a change in prescription. Hormonal levels may also be influenced by physiological status. For example, hypothyroidism exists in a small percent of the population. In periods of high stress, the adrenal gland can become fatigued from constant stimulation. It becomes sluggish, and as a result, the sympathetic response also decreases.
In spite of efforts to pass the buck onto bad genes or hungry adipose cells, the number one cause of obesity is still lifestyle: sedentary activity level combined with poor diet. The typical American diet is high in calories, fat and high fructose corn syrup. Inactivity means that not only are these calories not used during activity, but also the body uses less calories in general since lean body mass is not maintained. The body atrophies -- gets rid of unneeded muscle tissue -- so caloric needs decrease while caloric intake remains constant. If lifestyle is a problem, think about possible underlying causes -- ignorance of healthy habits; reluctance to change habits because of perceived "laziness," or dislike of anything resembling exercise, absently snacking -- and use them to help formulate strategies.
Body Composition Protocols
The first step in losing fat is determining where you are now so you have some measure for comparison. Methods for determining body fat percentage include: hydrostatic weighing; skinfold calipry; electrical impedance; infrared measurement; Body Mass Index (weight-to-height ratio); and circumference measuring.
Hydrostatic weighing is the standard by which all other protocols are compared. Body weight is measured when completely submerged in water, with all air possible exhaled while holding as still as possible. The difference between under water and on-land weight are compared -- fat floats and lean sinks, so a leaner person is heavier in water. Because of the controlled lab atmosphere, hydrostatic weighing is highly accurate. This protocol is least accurate when the individual is unable to either exhale completely or hold still under water. When all air is exhaled, there is still a small volume of air in the lungs, which makes the individual lighter in water. This volume of air is estimated based on other lung volumes taken with a machine called a spirometer. However, if exhalation is incomplete, or if the subject moves a lot, it is difficult to obtain an accurate under-water weight.
In skinfold calipry, skin and underlying adipose tissues are "pinched" and measured. Measurements at several sites are summed and put into a calculation. Calipry protocols vary in the areas measured and number of areas measured. Skinfold calipry is most accurate when measurements are taken by a knowledgeable technician from many sites. Because people vary in where they tend to store fat, the test is least accurate when less sites are measured.
Electrical impedance measures resistance to electrical flow in the body. Because fat is an insulator, amount of fat in the body is proportional to resistance to electrical flow. Electrical impedance is one of the most commonly-utilized methods because prices on the machines are within reach of many consumers. Under ideal conditions, impedance is accurate within 3-5% depending on manufacturer. However, as it is often difficult to meet pre-test requirements, results may be less accurate. This test is influenced by anything altering electrical flow in the body, the most obvious factor being hydration level. Because of this, testing should take place after 12 hours of abstention from diuretics such as caffeine and alcohol and exercise, and at least 6 hours after eating and with no large intake of water.
Near-Infrared Interactance (NIR) and A-mode ultrasound are relatively new body composition protocols, and are reasonably accurate modes of body density measurement (Heyward, 1996; Williams et al, 1995; Yasukawa et al, 1995). The equipment for these protocols is cost- prohibitive, so they are most commonly used in lab settings as back-ups to hydrostatic weighing. Most research on these methods has been on white european populations, so there hasn't been enough cross-validation sampling on other ethnicities at this point (Heyward, 1996).
Body mass index compares weight to height. This is a less accurate form of determining obesity, however it is convenient in that it requires very little specialized equipment. Mortality rates seem to be directly proportional to BMI, however, BMI is less accurate with older people and those with high muscle mass. Someone with an acceptable BMI may be obese because he or she has less lean mass, and a very lean individual with a lot of muscle mass may have a high BMI. With age, lean mass tends to decrease, regardless of body weight.
With circumference measuring, a tape measure is used to measure the circumference of body limbs and torso. Circumference measuring is one of the least accurate forms of determining body composition, however it is a reasonable field test because it requires only a tape measure and can be done by anyone just about anywhere. Anyone who has ever noticed the relative tightness or looseness of a waistband has used a rough form of circumference measurement.
Intro | Facts
Cardio | Strength
Nutrition | Diet Industry
Resources
References