Body Mass Index
Body mass index, or BMI, is a calculation of total body fat based on height and weight. It is used to determine whether a patient is underweight, at a healthy weight or overweight. A high BMI can alert both doctor and patient to potential health risks associated with obesity, such as type 2 diabetes, hypertension, breathing difficulties, severe sleep apnea or certain cancers. A low BMI can help to diagnose various illnesses which lead to or are precipitated by malnutrition, such as anemia, eating disorders or other types of cancer.
A BMI is calculated, using the following factors:
Another indicator of weight risk factors is waist circumference which indicates how much abdominal fat a patient has and can help in patient weight and health risk assessment. The following guidelines are used to determine categories of body mass index:
- Underweight: less than 18.5 BMI
- Normal weight: 18.5-24.9 BMI
- Overweight: 25-29.9 BMI
- Obese: 30 or greater BMI
BMI calculations do not take into account factors such as muscle mass and pregnancy, so a very muscular man or a pregnant woman may be misdiagnosed as overweight using this index. In a similar way, an elderly person with very little muscle mass may be misdiagnosed as underweight.
Patients whose BMIs are 30 or higher face an increased risk of weight-related health problems. The risk is even higher for men with a waist circumference of more than 40 inches, or 102 cm, and women with a waist circumference of more than 35 inches, or 88 cm. Categories of risk are designated as follows:
- BMI of 30-34.9 - High Risk
- BMI of 35-39.9 - Very High Risk
- BMI of 40 or more - Extremely High Risk
Other factors may combine with high BMI to increase health risks. These factors include:
- High LDL cholesterol or low HDL cholesterol
- High blood glucose
- High triglycerides
- Family history of premature heart disease
- Physical inactivity
Decreasing BMI by a relatively small amount through weight loss can significantly decrease risk to patients. Losing 15 to 20 percent of body weight results in measurable health gains, particularly when combined with an increase in physical activity, giving up smoking or controlling cholesterol limits.