BMI or Body Mass Index is a mathematical formula that relates weight to height. It is a better indicator of body fat than weight alone. Body Mass Index = weight (kilograms) over height (meters square). The risk of health problems is generally lower when the BMI is within the acceptable range of 19 to 25. The Body Mass Index applies to adults 20 years or older but is not considered reliable for pregnant women, the frail elderly, children and body builders (because muscle weighs more than fat).

The commonly used weight tables were developed based on weights associated with the lowest mortality rates among insured populations of adults. Weight tables may not be applicable to some populations, such as the lower socioeconomic or some ethnic groups.

The disadvantage of using the Body Mass Index is the difficulty in interpreting BMI units to actual weight (in pounds ) that must be lost. For practical purposes, one BMI unit is the equivalent of 4 to 8 pounds.

Obesity is defined here as a BMI above 30. The World Cancer Research Fund and the American Institute for Cancer Research (WCRF/AICR) panel believes that diets high in calories increase the risk of obesity. This risk is even greater for populations typically sedentary.

There is convincing evidence that obesity (a BMI above 30) increases the risk of cancer of the endometrium (lining of the uterus). There is evidence for the probable increased risk of cancer of the breast in postmenopausal women and cancer of the kidney. And obesity possibly increases the risk of cancer of the colon.

Overweight (a BMI between 25 and 30), not obesity, increases the risk of cancer in general. Smoking as a way to control weight is not worth the risk. Smoking causes and contributes to cancers of the mouth, pharynx, nasopharynx, larynx (voice box), esophagus, lung, pancreas, colon, rectum, cervix, kidney and bladder.

See Recommendation 2 "How to" for calculating your BMI

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Prepared 1998 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.