Obesity Definition and Measurement with the Help of Body Mass Index Chart -Healt

Source: Author: Dr. S.C. Mehta Published date: 2008-07-30  

Obesity is a growing and costly health problem in the developed world. Data from the National Health and Nutrition Examination Surveys (NHANES) show that approximately 33% of adults in USA are obese (BMI>30) and as many as 64% of US adults ¡Ý 20 years of age were overweight (defined as BMI>25 ). The increasing number of obese persons is a matter of great concern as numerous disorders are associated with excess body weight. The most important and common of these are hypertension, type 2 diabetes, hyperlipidemia, gallstones, ischemic heart disease, osteoarthritis, male hypogonadism, and psychosocial disability. Cancers of colon, rectum, and prostrate in men, ovarian, uterine, biliary tract, and breast cancer in women are also more prevalent in the obese.

Obesity Definition and Measurement

The survival of an animal species requires a continuous supply of energy for physiological functioning. As the supply of food is intermittent, this requirement is met by storing energy as triglycerides in the fat cells of adipose tissue depots. When needed, the stored energy is released as free fatty acids for use at other sites. The mechanism controlled by the so called thrifty genes, permits humans to survive starvation for as long as several months. However, an ample supply of calorie rich food and a sedentary life style increases adipose energy stores and causes-obesity.

Obesity may be defined as an excess of body fat or body weight that is 20% over the ideal. More precisely obesity can be measured by the unit: Body Mass Index (BMI). The BMI is body mass (kg) divided by the square of the height (meters). The BMI closely correlates with body fat. Healthy people have a BMI of 20-25, overweight has a BMI of 25-30, obese has a BMI of >30 and extreme obesity is BMI >40.

Factors other than body weight are also have substantial implications for morbidity, specifically excess fat around the waist and flank is more hazardous than the fat in the thighs and buttocks. The waist-to-hip ratio of >0.9 in women and >1.0 in men is considered a risk factor for diabetes, hypertension, stroke, and coronary artery disease.

Table 1. Body Mass Index Chart

To use this table (shown in the picture), find the appropriate height in the left hand column. Move across the row to a given weight. The number at the top of the column is BMI for that weight and height. A normal BMI is 18.5 -24.9. Overweight has BMI of 25-29.9. Class I obesity is 30-34.9;class II obesity is a BMI of 35-39.9 and extreme obesity is a BMI of >40.

Causes of Obesity

Obesity mainly results due to the disturbance in the complex regulatory system that control energy intake and expenditure. A number of genes affect the energy balance. Five genes affecting control of appetite have been identified in mice. Mutation in each gene result in obesity. Identification of ob gene mutation in genetically obese (ob/ob) mice gave a major breakthrough in the field. The product of ob gene is the peptide Leptin. High leptin levels decrease food intake and increase energy expenditure. Resistance to leptin is caused by defects in leptin synthesis and mutation in leptin receptors in the hypothalamus as seen in db/db mice also result in obesity. Numerous other candidate genes for human obesity has been identified.

Other factors such as chronic excess of nutrient intake and lack of physical activity contribute to obesity.

[back to top] [Print This Article] [Close]

Prev: Weight Loss Diets Fads - Why They Aren't For Everyone -Health Centre   Next: Alternative Remedies for Depression -Health Centre