Obesity (Weight Loss) (cont.)

• Ethnicity. Ethnicity factors may influence the age of onset and the rapidity of weight gain. African-American women and Hispanic women tend to experience weight gain earlier in life than Caucasians and Asians, and age-adjusted obesity rates are higher in these groups. Non-Hispanic black men and Hispanic men have a higher obesity rate then non-Hispanic white men, but the difference in prevalence is significantly less than in women.
• Childhood weight. A person's weight during childhood, the teenage years, and early adulthood may also influence the development of adult obesity. For example,
  • being mildly overweight in the early 20s was linked to a substantial incidence of obesity by age 35;
  • being overweight during older childhood is highly predictive of adult obesity, especially if a parent is also obese;
  • being overweight during the teenage years is even a greater predictor of adult obesity.
• Hormones. Women tend to gain weight especially during certain events such as pregnancy, menopause, and in some cases, with the use of oral contraceptives. However, with the availability of the lower-dose estrogen pills, weight gain has not been as great a risk.

BMI is a calculated value and approximates the body's fat percentage. Actually measuring a person's body fat percentage is not easy and is often inaccurate if the methods are not monitored carefully. The following methods require special equipment, trained personnel, can be costly, and some are only available in certain research facilities.

• Underwater weighing (hydrostatic weighing): This method weighs a person underwater and then calculates lean body mass (muscle) and body fat. This method is one of the most accurate ones; however, it is generally done in special research facilities, and the equipment is costly.
• BOD POD: The BOD POD is a computerized, egg-shaped chamber. Using the same whole-body measurement principle as hydrostatic weighing, the BOD POD measures a subject's mass and volume, from which their whole-body density is determined. Using this data, body fat and lean muscle mass can then be calculated.
• DEXA: Dual-energy X-ray absorptiometry (DEXA) is used to measure bone density. It uses X-rays to determine not only the percentage of body fat but also where and how much fat is located in the body.

The following two methods are simple and straightforward:

• Skin calipers: This method measures the skinfold thickness of the layer of fat just under the skin in several parts of the body with calipers (a metal tool similar to forceps); the results are then used to calculate the percentage of body fat.
• Bioelectric impedance analysis (BIA): There are two methods of the BIA. One involves standing on a special scale with footpads. A harmless amount of electrical current is sent through the body, and then percentage of body fat is calculated. The other type of BIA involves electrodes that are typically placed on a wrist and an ankle and on the back of the right hand and on the top of the foot. The change in voltage between the electrodes is measured. The person's body fat percentage is then calculated from the results of the BIA. Early on, this method showed variable results. Newer equipment and methods of analysis seem to have improved this method.

Health clubs and weight-loss centers often use the skin caliper or bioelectric impedance analysis method; however, these can yield inaccurate results if an inexperienced person performs them or they are used on someone with significant obesity.

Source: MedicineNet.com
http://www.medicinenet.com/obesity_weight_loss/article.htm