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What is BMI?

Body mass index, or BMI, is a number determined by calculating the amount of weight a person carries against his or her height. Invented nearly 200 hundred years ago by a Belgian scientist, BMI does not determine body fat percentage, but instead provides a general chart ranging from underweight to obese to help someone determine if they are at risk for suffering weight-related illnesses.

Using a BMI Calculator

A free BMI calculator is used to enter your height and weight, and the calculator immediately reports your BMI, which is involved in one of six categories:

  • A BMI less than 15 means you are severely underweight
  • A BMI between 15 and 18.5 means you are underweight
  • A BMI between 19 and 24.9 means you are in the optimal weight range
  • A BMI between 25 and 29.9 means you are overweight
  • A BMI between 30 and 40 means you are obese
  • A BMI over 40 means you are morbid obese
Please see BMI Categories for a more detailed description. In general, measuring waist size can also help determine whether you are overweight. The standard guideline used is this:
  • A waist circumference of less than 40 inches for men is considered healthy
  • A waist circumference of less than 35 inches for women is considered healthy

A BMI measurement can also be manually determined by dividing height in inches squared by body weight in pounds, and then multiplying that result by 705. For example, a woman who is 60 inches tall would square the number 60. She would than take 360 (60 squared) and divide that by her weight, which is 140 pounds. The resulting number of .39 is then multiplied by 705, which gives her a BMI of 27.4.

Statistics Regarding Obesity

If you have a BMI score above 25, this puts you at risk for developing diabetes, fertility issues and hypertension as well as many other weight-related diseases, such as:

  • Congestive heart failure
  • Gastroesophageal reflux disease (GERD)
  • Fatty liver disease
  • Gallstones (cholelithiasis)
  • Hernias
  • Colorectal cancer
  • Incontinence
  • Chronic kidney failure
  • Uterine and breast cancer
  • Gout (hyperuricemia)
  • Osteoporosis
  • Osteoarthritis
  • Depression
Other statistical information regarding overweight and obesity health issues provided by the Cleveland Clinic includes:
  • In the U.S., 68 percent of all adults are considered overweight or obese (BMI > 25)
  • Only about 1/3 of U.S. citizens are at a healthy weight
  • From 1962 to 2006, obesity rates increased from 14 percent to 35 percent among adults between 20 and 74 years old
  • A survey conducted between 2003 and 2006 found that nearly 13 percent of children age two and 11 were overweight. Almost 20 percent of teenagers were overweight as well
  • Obese individuals can expect to pay nearly 43 percent more for health costs than those who have BMIs of less than 29.

By using a BMI index to determine the severity of weight issues, individuals can begin to formulate a health weight loss diet plan incorporating regular exercise to reduce weight and eliminate the high risk of experiencing a debilitating disease caused by carrying excess fat.

Waist circumference can also indicate potential health risks. People whose fat distribution makes them "pear-shaped" have been found to be at risk for high blood pressure, diabetes and heart disease. Those whose fat distribution causes them to appear "apple-shaped" are more at risk for developing these medical problems

Dangers of Being Underweight

Being underweight by more than 10 or 15 pounds is not considered healthy either. A BMI of less than 17 means that person may be at risk for developing health problems associated with insufficient fat amounts, such as:
  • Anemia (low red cell count causing extreme fatigue and weakness)
  • Compromised immune system unable to fight over infection and diseases
  • Osteoporosis
  • Hair loss due to lack of protein in the diet
  • Heart failure exacerbated by anemia
  • Possible problems with anorexia/bulimia

The human body needs healthy fat provided by nuts, oils and some vegetables because it provides many essential vitamins and nutrients necessary to produce hormones and blood cells. In addition, the body extracts its energy from fat resources in the form of calories and carbohydrates. Having no fat reserves means no energy supply for the body or the brain, which contain neurons and axons that need quite a bit of energy-rich fat to function properly.

Problems with the BMI

Several issues arise when relying on BMI to provide a picture of someone's overall body condition. For example, the BMI index does not ask for gender, age or ethnicity specifics, which researchers have found to play a vital role in determining what a healthy weight should be for someone who is female, 50 years old and Asian.

Lean body mass is not taken into consideration when calculating BMI. Because fat is fluffy and lightweight, muscle mass weighs more than fat. With weight trainers and athletes who possess large amounts of lean body mass (muscles), BMI readings may not represent an accurate indication of health in regards to weight/height ratio. A bodybuilder who is 69 inches tall but weights over 200 pounds because of muscles mass will cause his BMI reading to show that he is overweight, which is not the case.

For individuals who do have an above average amount of lean muscle mass constituting their body, a more accurate measurement of body fat can be done using a sort of caliper that measures skin folds at certain areas of the body, namely the waist and underneath the upper arms.

While the body mass index is not meant to be used as a definitive assessment of health, it is a good screening tool to use which quickly provides indications of weight issues as well as being able to facilitate large-scale research studies involving statistical data and trends involving obesity.

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