Body mass index, or BMI, is a form of measurement using your height and weight to assist in determining your risk for acquiring diseases related to obesity. A BMI of more than 30 may indicate that you have an unhealthy amount of body fat in relation to overall body mass, but does not specifically determine body fat percentage. This tool, used in conjunction with other measures of physical health, can assist in leading you on the track to long-term health. Factors including age, race and gender can have an effect on the reliability of BMI as a measurement defining obesity.
BMI Categories
According to the National Heart Lung and Blood Institute, BMI categories are underweight, less than 18.5; normal, from 18.5 to 24.9; overweight, 25 to 29.9; obese, 30 or more. Other factors may put you at risk for disease and should be considered, such as waist circumference, a history of cigarette smoking, an inactive lifestyle and heredity. The same BMI table is used for both men and women over the age of 20. For children from ages 2 to 19, a separate table is used that shows the results in relation to corresponding percentiles of other children in that age category. Normal is from the 5th to 85th percentile for this age group.
How Is BMI Determined?
BMI is calculated by dividing your weight in kilograms by your height in meters squared. Calculating measurements in metric units is the most common, but many BMI calculators allow you to input your height and weight measurements in pounds and inches as well. The resulting number is then converted, allowing for the BMI table to be universal.
BMI Reliability
The same BMI number for a man and a woman may result in slightly different conclusions. In general, women have a higher body fat percentage than men. As you age, muscle mass tends to decline and fat mass tends to increase. If you are an athlete or body builder, a higher-than-average BMI might be an indicator of increased muscle mass since muscle weighs more than fat.
Some studies have shown BMI to be falsely low, indicating that it may not adequately show whether or not you are are at risk for obesity related diseases. According to Mahburbur Rhaman, MD, and Abbey B. Berensen, MD, in the journal Obstetrics & Gynecology, "Current BMI cutoff values recommended by the NIH failed to identify nearly half of reproductive-aged women who met the criteria for obesity by percent body fat." Another finding was that white and Hispanic women had 2.9 percent more body fat for a given BMI than black women.
Risk Factors
BMI can be used as a guideline for determining the risk for obesity-related diseases. An increased BMI, a finding in the overweight or obese category, may be an indicator to determine if weight control is in order. Some of the most common diseases might be avoided if you take an active part in controlling your body size. According to the Centers for Disease Control, overweight individuals are at an increased risk for hypertension, high cholesterol, heart disease, stroke, respiratory dysfunction and certain types of cancer.
Decreasing BMI
According to the National Health and Nutrition Examination Survey, there has been a dramatic increase in BMI of U.S. women over the past 30 years. From 1980 to 1991, obesity in women went from 17 to 26 percent, with that number increasing to 34 percent by the year 2000. This study, using data from 1988 to 1994, also showed a disproportional percentage of obesity in women comparing white, at 23.1 percent; black, at 37.2 percent; and Hispanic, at 33.6 percent of women.
People can reduce their BMI by decreasing their body fat percentage in relation to overall weight. Diet modification and exercise are the primary means to achieve this result. Consult with a nutritionist or your doctor to find a plan that will allow you to meet your nutritional requirements while allowing you to safely decrease your BMI. Some ways to achieve this are by portion control, eating higher quality foods and learning to recognize the number of calories consumed daily in relation to calories expended. Decreasing fat while maintaining or increasing muscle mass is optimal for overall health.
This advice is for nutritional education only. The above information has neither been verified by the FDA nor reviewed by a medical doctor. Please consult your physician for any concerns with how this relates to your medical condition.
References
- National Heart Lung and Blood Institute: Calculate Your Body Mass Index
- Centers for Disease Control and Prevention: About BMI for Adults
- National Heart Lung and Blood Institute: Key Recommendations
- Obstetrics and Gynocology: Accuracy of Current Body Mass Index Obesity Classification for White, Black, and Hispanic Reproductive-Age Women
- National Health and Nutrition Examination Survey: Healthy Weight, Overweight, and Obesity Among U.S. Adults
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