Weight Restrictions For Bmi

According to the National Heart, Lung, and Blood Institute at the National Institutes of Health, the body mass index (BMI) is a "measure of body fat based on height and weight." To calculate BMI, divide your weight in pounds by the square of your height in inches, and multiply by 703. You can compare your BMI to the national standards as very rough assessment of your health status.

Normal Weight

A normal BMI falls is from 18.5 to 24.9. The Centers for Disease Control and Prevention (CDC) predicts that adults within this BMI range to be at a normal weight status and at lower risk for chronic diseases that obesity may cause. Children and teenagers ages two to 19 years fall within this category if their BMI is between the fifth and 85th percentile for their age, according to BMI-for-age growth charts.

Underweight

The CDC classifies a BMI of less than 18.5 as underweight. This classification applies to men and women over the age of 20 years. For children and teenagers ages two to 19 years, a BMI less than the fifth percentile classifies as underweight. Being underweight with excessively low body fat has some health risks, with analysis from the CDC's National Health and Nutrition Examination Survey estimating that being underweight indirectly causes about 33,000 deaths per year in the United States.

Overweight and Obese

An adult BMI between 25.0 and 29.9 falls into the category of overweight, and a BMI of 30.0 or above is obese. For children and teenagers, an overweight BMI is between the 85th and 95th percentile of BMI-for-age, and obese is greater than the 95th percentile. According to the CDC, obesity is a risk factor for many chronic health conditions. These include hypertension, unfavorable blood cholesterol or triglyceride levels, Type 2 diabetes, sleep disorders, certain types of cancer, gallbladder disease, and osteoarthritis.

Considerations

There are some important factors to consider when interpreting BMI. It is only an estimate of body fat, and different components can affect its true relation to body fat. For example, men tend to have a higher percentage of muscle than women, and so a male with the same BMI as a female likely has a lower body fat percentage. Another example is with athletes in certain sports who may have BMIs that classify them as overweight or obese. In reality, they have very low amounts of body fat and high amounts of muscle.

Alternatives

BMI is one way to estimate body fat, but to get a more precise measurement, you can use other methods. For example, skinfold thickness measurements with calipers, underwater weighing, and dual x-ray absorptiometry (DXA) scans are all ways to measure body fat. In addition to total body fat or body fat percentage, the distribution of fat is important, which is why the National Heart, Lung, and Blood Institute publishes guidelines for weight circumference as a risk factor for health risks.