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Lecture 5 page 1 2 3 4 5 6 7 8

Obesity
Causation, Endocrinology and Physiology,
Body Composition Analysis and Weight Reduction Diets

Obesity is the most prevalent nutritional problem in the United States today and is a major factor in the pathogenesis of hypertension, diabetes mellitus, hypercholesterolemia, heart disease, and such common forms of cancer as breast cancer, prostate cancer, uterine cancer and colon cancer. According to the 1998 National Heart Lung and Blood Institute guidelines for diagnosing overweight and obesity, one of every two Americans is overweight or obese. In some ethnic groups, one of every two women is obese, while in the general population one of three adults is obese. One of every three women is on a diet at any time, and the American public spends billions of dollars on fad diets and unproven remedies for weight reduction and nutritional health each year.

Why has obesity been a blind spot for American medicine until recent years? Our medical schools are based on allopathy, the use of drugs and surgery to treat disease. Prevention and nutrition have only recently been introduced into the curriculum of a minority of American medical schools, but form the basis of medical education in much of the rest of the world. Asian medicine, which was not influenced as much by the English system of the Royal College of Barbers and Surgeons, includes nutrition, food herbs, and herbal medicines as an integral part of health maintenance and treatment. Most American physicians today ignore the problem of obesity. They will treat patients for high blood pressure, high cholesterol or diabetes with drugs, without addressing the underlying nutritional etiology of these diseases. When asked why this is so, they respond with the following :

    • I donít have the time
    • Nothing works anyway
    • I am paid to see my patients for diseases
    • I donít know much about obesity
    • Even if they lose weight, they will regain the weight

On January 1, 1998, The New England Journal of Medicine, a widely quoted and respected journal ran an editorial entitled, " Weight Loss: An Ill-Fated New Yearís Resolution" in which they asserted that weight loss was not achievable, the treatments were more risky than the disease itself, and even if you lost weight you wouldnít live longer. In fact, subsequent studies have shown that the morbidities associated with getting old occur over a shorter period of time in health conscious individuals, saving money for the health care system while improving quality of life for the elderly.

In fact, the pharmaceutical industry has developed its own diets and promulgated diets through organizations such as the American Heart Association, the American Cancer Society, and the American Diabetes Association that fail to deal with the nutrition-related chronic diseases related to obesity. In dealing with individuals with obesity, the dietary guidelines promulgated for populations must be individually tailored to meet the needs of the person dealing with the problem. The California Cuisine Pyramid was designed by the UCLA Center for Human Nutrition to move ahead from the late 1980ís pyramids to one designed for chronic disease prevention. The rationale for this pyramid will be developed later in the course.

After finishing this section of the course you should:

1) Understand the definition and causes of obesity.

2) Understand the impact of excess fat on endocrine/metabolic processes
impacting major chronic diseases in the U.S.

  • Heart disease and hyperlipidemia
  • Hypertension
  • Diabetes mellitus
  • Common forms of cancer including breast, prostate,
    colon, ovarian and uterine cancer

Obesity is defined as excess body fat. Increased body weight does not always equate to increased body fat. For example, a professional football player could weigh 260 pounds and be six feet tall with no excess fat, just increased lean body mass.

One can assess body fat in several ways:

Body weight for height can be used in average people

Rule of thumb:

Females 5 ft. tall = 100 lb.

add 5 lb. per inch over 5 ft.
e.g. 5 ft. 4 in. = 120 lb.

Males 5 ft. tall = 106 lb.

add 6 lb. per inch over 5 ft.
e.g. 5 ft. 10 in. = 166 lb.

Life insurance tables can also be used to assess ideal weight based on minimum mortality. The most famous tables are the Metropolitan Life Insurance Tables of 1959 and 1983. These relate mortality from all causes to body weight at the time of life insurance medical examination. By this classification degrees of obesity are:

> 120 % IBW = obesity
> 130 % IBW = significant obesity
> 200 % IBW = morbid obesity

Prevalence of obesity from the USDA National Health and Nutrition Examination Survey (NHANES) by these standards is as follows:

Obese ( > 120% IBW)

25-30 % in males 30 to 70
40-45 % in females 40 to 70

Severely Obese ( >150% IBW)

4.9% in males 21 to 74
7.2% in females 21 to 74

Body Mass Index is used to estimate excess fat

Body Mass Index = Wt.(in kg.) / Ht.2(in meters2)

< 20 = malnutrition
20 - 25 = normal
25 - 30 = overweight
30 - 40 = obese
> 40 = severe or morbid obesity

Overall morbidity and mortality increases exponentially at a calculated BMI of greater than 30. At any given BMI women have a greater percent body fat than men, so other methods are also needed to assess body fat clinically.

 

Other Methods of Estimating Body Fat

1. Underwater weighing
Since fat floats in water, by comparing body weight on land and underwater, one can calculate percent body fat. Since air also floats, a correction must be made for lung volume, and subjects are encouraged to exhale as they put their heads underwater. This method is especially useful for athletes, but not sick patients. It has a precision of about 2 % .

2. Total body potassium
In this method the natural decay of potassium 40 to potassium 39 is used to estimate total body potassium which is largely intracellular. This can be used to calculate lean body mass which when subtracted from total body weight will yield body fat mass. A research facility for this exists at UCLA, but this measurement is not widely available for clinical use.

3. Bioelectrical Impedance
This is the most useful method clinically. A portable device with paste electrodes similar to those used with an EKG are attached to the right hand and foot. With the patient supine, the total body electrical impedance or resistance is measured. The accuracy of this method is 4 to 7 %. Since water conducts electricity while fat is an insulator, the machine measures body water and calculates body fat. This machine cannot be used in patients with edema and will be affected by shifts in water balance for any reason.

Percent Body Fat
Percent body fat can be estimated as the body fat mass divided by total body weight. If lean body mass or fat free mass is determined, this number is subtracted from total body weight to give the fat mass.

Normal body fat

15 to 20 % for men
22 to 28 % for women

These are averages and will be lower for athletes.

 

Abnormal Fat Distribution
Upper body subcutaneous fat is a marker for intra-abdominal fat in men and women. When men become obese, they primarily accumulate upper body fat. Witness the gas station attendant who pays an embarrassing price for buckling his pants lower to maintain the same waist size. Women can accumulate upper and lower body fat, and tend to have lower body fat before the menopause and upper body fat after the menopause.

Fat depots can be measured with skinfold calipers.

Male Fat Depots: Upper Chest, Upper Abdomen
Female Fat Depots: Triceps, Lower Abdomen, Thighs

Waist to Hip Ratio measures the ratio of upper to lower body fat. 0.85 to 1.0 is the normal ratio.

Male or Android Fat Cells
Upper body fat cells release more fatty acids in response to a standard hormonal stimulus and increased numbers of upper body fat cells correlate in population studies with an increased incidence of diabetes mellitus, hypertension, and hypercholesterolemia. Women with upper body fat have increased circulating levels of free male hormones compared to women with lower body fat.

Female or Gynoid Fat
Lower body fat cells are more resistant to lipolytic stimuli. These fat cells are stimulated during pregnancy and may contribute significantly to post-pregnancy weight gain. They tend to atrophy following the menopause, but intracellular receptors for female hormones have not been identified and their growth and development is not well understood.

Body Composition
The Body Mass Index = Wt (kg) / Ht2 (m2) gives a general idea of the degree of obesity or excess fat in populations. In an individual there may be a difference between estimated percent body fat and the measured body fat by bioelectrical impedance or other methods. "in special groups, such as old people and very muscular athletes, Quetelet's Index will give an inaccurate indication of obesity, but these are not groups in whom obesity is an important clinical problem, and in any case, methods such as density, water, and potassium are also liable to give wrong estimates of fatness in such people. "J.S. Garrow and Joan Webster." Quetelet's Index (W/H2) as a Measure of Fatness" Int. J. Obesity 9:147-153, 1985.

Garrow and Webster found that the regression of fat4/ H2 on weight/ H2 was 0.955 for women and 0.943 for men. Prediction equations were developed based on these findings. Fat in kg can be calculated from weight and height as follows:

For Women: Fat (kg) = (0.713 W/H2- 9.74)H2

For Men: Fat(kg) = (0.715 W/H2 - 12.1)H2

These authors found that the errors were approximately 4.2 kg and 5.8 kg of fat for men and women respectively. This error is of similar magnitude to that found with the densitometry, total body water by dilution, and total body potassium counting. However, it was recognized in the original publication that this formula was not suitable for athletes or the elderly where there would be significant variations in lean body mass.

 

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Lecture 1
:Introduction to Nutrition in Western Civilization
Lecture 2:
Dietary Macronutrients, Body Fat, and Blood Lipids
Lecture 3:
Digestion and Absorption of Macronutrients
Lecture 4:
Basic Principles of Nutrient Metabolism
Lecture 5:
Obesity
Lecture 6:
Fuel Utilization During Exercise
  Lecture 7:Biochemistry of Oxidant Stress in Health and Disease Antioxidants
Lecture 8:Nutrition for the 21st Century

 

 

 

 

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