CDC Features

CDC Features

Body Mass Index Measurement in Schools

There is not enough evidence to recommend for or against school-based body mass index measurement programs as an effective strategy for preventing or reducing childhood obesity. Decision makers need to consider the pros and cons. If implemented, these programs should be part of a comprehensive approach to address obesity.

As the United States continues to search for answers to the growing problem of obesity among children and adolescents, much attention has focused on Body Mass Index (BMI) measurement programs in schools. BMI is the ratio of weight to height squared. It is often used to assess weight status because it is relatively easy to measure and it correlates with body fat..

BMI = weight (kilograms)
{height (meters)}²

Assessing weight status in children and adolescents is a two step process, which involves calculating BMI and plotting the BMI on an age and sex-specific growth chart. This results in a BMI-for-age percentile. A child or adolescent's weight status is identified from his or her BMI-for-age percentile. This accounts for the growth changes that youth experience as they age and the differences in growth experienced by boys and girls. CDC offers a BMI calculator for children and adolescents that determines BMI-for-age percentiles: www.cdc.gov/healthyweight/assessing/bmi. For more information on BMI for children and adolescents, refer to CDC Division of Nutrition, Physical Activity, and Obesity.

Photo: A teacher with students BMI measurement programs in schools may be conducted for the purpose of surveillance, screening, or both. BMI surveillance programs assess the weight status of a specific population (e.g., students in an individual school, school district or state) to identify the percentage of students who are underweight, normal weight, overweight or obese. Surveillance data are typically anonymous and can be used for many purposes, including identifying population trends and monitoring the outcomes of interventions. BMI screening programs assess the weight status of individual students to identify those at risk for weight-related health programs, such as obesity, and provide parents with information to help them take appropriate action.

Some states have initiated BMI measurement programs in recent years. Arkansas, for example, implemented a statewide BMI screening and surveillance program in 2003. In California, students participate in physical fitness testing that assesses BMI along with other fitness-related variables.

Photo: A student Little is known about the outcomes of BMI measurement programs, including effects on weight-related knowledge, attitudes, and behaviors of students and their families. As a result, no consensus exists on using BMI screening programs for young people. The US Preventive Services Task Force concluded that insufficient evidence exists to recommend for or against BMI screening programs for youth in clinical settings as a means to prevent adverse health outcomes; however, an expert committee convened by the American Medical Association, in collaboration with the Health Resources and Services Administration and the Centers for Disease Control and Prevention, recommends that BMI should be calculated and plotted at least annually by the child’s medical provider. The Institute of Medicine recommends annual school-based screening, but school-based screening is not unanimously supported by other organizations.

Photo: A girl getting off of a school bus BMI screening meets some of the criteria established by the American Academy of Pediatrics (AAP) for determining whether school-based screening should be implemented for any pediatric health condition: obesity is an important and highly prevalent condition; BMI is an acceptable measure to assess weight status; and schools are a logical measurement site because they reach virtually all youth. However, BMI screening programs typically do not meet other AAP criteria: effective treatments for obesity are not available; research has not established the effectiveness and cost-effectiveness of BMI screening programs; and communities typically do not have resources in place to help at-risk individuals' access to treatment services. More evaluation is needed to determine whether BMI screening programs are a promising approach for addressing obesity among children and adolescents.

Photo: Book bag A number of concerns have been expressed about school-based BMI screening programs, including that they might stigmatize students and lead to harmful behaviors. Other concerns are that these programs might be ineffective, waste scarce health promotion resources, and distract attention from other school-based obesity prevention activities. More research is needed to assess the validity of these concerns. BMI surveillance programs are less controversial because they do not involve communication of sensitive information to parents and do not require individualized follow-up care for students identified to be at risk. Schools that initiate BMI measurement programs should have in place a safe and supportive environment for students of all body sizes and a comprehensive set of science-based strategies to promote physical activity and healthy eating. In addition, BMI screening programs should ensure that parents receive a clear and respectful explanation of the BMI results and appropriate follow-up actions, and that resources are available for safe and effective follow-up.

To reduce the risk of harming students, BMI measurement programs should adhere to the following safeguards:

Introduce the program to school staff and community members and obtain parental consent,
Train staff in administering the program (ideally, implementation will be led by a highly qualified staff member, such as a school nurse),
Establish safeguards to protect student privacy,
Obtain and use accurate equipment,
Accurately calculate and interpret the data,
Develop efficient data collection procedures,
Avoid using BMI results to evaluate student or teacher performance, and
Regularly evaluate the program and its intended outcomes and unintended consequences.

To date, there is not enough evidence to recommend for or against school-based BMI measurement programs as an effective strategy for preventing or reducing childhood obesity. Decision makers need to consider the pros and cons of such programs. Measuring student BMI in schools is just one approach to addressing obesity, and there is little research about the impact of this approach. If implemented, a BMI measurement program should be part of a comprehensive approach to address obesity, including physical activity and healthy eating policies and programs. The CDC has identified 10 key strategies that schools can use to prevent obesity by promoting physical activity and healthy eating.