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Body Mass Index as Health Index

Body Mass Index also known as BMI, is a rough Health Index to determine how healthy a person is. It is a heuristic proxy for human body fat based on an individual's weight and height. It is defined as the individual's body weight divided by the square of his or her height. BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her height.

WHO regard a BMI of less than 18.5 as an indicator for underweight due to malnutrition (an eating disorder, or other health problems), while a BMI greater than 25 is considered overweight and above 30 is considered obese. These ranges of BMI values are valid only as general statistical indicator. This is not an absolute or a sole indicator of good health.

BMI varies from country to country. The WHO health guidelines recommend lowering the normal/overweight threshold for South East Asian body types to around BMI 23, instead of BMI 25 for Americans. Further revisions are to emerge from clinical studies of different body types. For an average Normal Indian the upper limit of BMI is placed at 24 instead of 25 for  an average American.

Care for Children: BMI is used differently for children. It is calculated the same way as for adults, but then compared to typical values for other children of the same age and sex. Instead of BMI, the "BMI Percentile" is used which allows comparison with children of the same sex and age. Consult your doctor if the child's BMI value varies widely from the normal so as to determine his "BMI Percentile".

BMI shouldn't be calculated for Pregnant Women and Nursing Mothers.

Known as Waist–Hip Ratio or Waist-to-Hip Ratio (WHR) is the ratio of the circumference of the waist to that of the hips i.e. While physicians use it as also one of the indices for ascertaining the distribution of fat in ones body, some psychologists suggest that the waist-hip ratio (WHR) is a significant measure of female attractiveness.

A WHR of 0.7 for women and 0.9 for men have been shown to correlate strongly with general health and fertility. Women within the 0.7 range have optimal levels of estrogen and are less susceptible to major diseases such as diabetes, cardiovascular disorders and ovarian cancers (tenuous). Men with WHRs around 0.9, similarly, have been shown to be more healthy and fertile with less prostate cancer and testicular cancer.

Women with a 0.7 WHR are usually rated as more attractive by men and thus WHR is known as a Beauty Index also. 

Measurement of waist hip ratio:

Measurement of waist hip ratio: In a lean person (left in picture), the waist can be measured at its narrowest point, while for a person with convex waist (right in picture), it may be measured at about one inch above the navel. The hip is measured at its widest point at left (in picture), and at the great trochanters at right (in picture), although the object cheats a bit by not having his legs close together.

Click here for more details on WHR from wikipedia