• Race. Racial 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. Hispanic men tend to develop obesity earlier than African American and Caucasian men.  
• Childhood weight. A person’s weight during childhood, teenage years, and early adulthood may also influence the development of adult obesity. For example:
       
  1. Being mildly overweight in the early 20’s was linked to a substantial incidence of obesity by age 35.      
  2. Being overweight during older childhood is highly predictive of adult obesity, especially if a parent is also obese.      
  3. Being overweight during 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 newer low dose estrogen pills, weight gain has not been as great a risk.

How is body fat measured?

Measuring a person’s body fat percentage is not easy, and 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 more 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.(1)  
• 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 calculated and the percentage of body fat is determined.  
• Bioelectric impedance analysis (BIA): Another seemingly simple method. 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. Change in voltage between electrodes is measured. The person’s body fat percentage is then calculated from the results of the BIA.

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