Blog Post for: Marlene B. Schwartz, PhD
02/16/2007 | Marlene B. Schwartz, PhD
BMI Report Cards: My Opinion in a Sound Bite
The issue of schools measuring and reporting students’ BMI has been getting a lot of attention, and I’ve been asked several times if I think if “BMI report cards” are good or bad. My answer is that I have very mixed feelings about them. Mixed feelings are hard to express in a sound bite, but let me try to succinctly explain my two-part view of this strategy to address childhood obesity.
Part 1: I am completely in favor of tracking trends in BMI (as well as other obesity related health issues, such as asthma and type II diabetes) at the state, district, and even individual school level. We must keep a close eye on children's health in order to know if things are getting worse, better, or staying the same. The reason we need to know this at the school and district level is to help assess the impact of all of the wonderful, creative interventions that are taking place as part of the mandated 2006-2007 School Wellness Policies. While it's unlikely that there would be a significant change in obesity or diabetes rates after only one year, we must keep track or we'll miss the changes that may occur over time. This is the only way we'll be able to identify those factors that are contributing to those changes.
Part 2: The question about whether individual student BMI information should be sent home to parents is an entirely separate issue. The bigger question here is - what type of health related communication from the school to the family is most likely to result in positive behavior changes?
Wake-up call to parents? The hypothesized benefit of using BMI is that it will serve as a wake-up call to parents who are not aware that their child is at risk. I used to think that it was pretty unlikely that parents didn't realize their children are overweight, but I have been convinced by the research on this subject that in fact, many parents of overweight children don't realize it. This may be due to a variety of factors. Perhaps parents see their own children as more "normal" than they are in general, and weight is just one domain where this occurs. Perhaps the increase in childhood obesity overall has changed the norms we perceive, so it's easier for an overweight child to appear in the normal range. Certainly, there are also differences among ethnic groups in judgments of body shape and size, so a child that is overweight by the BMI standards seems perfectly fine to his or her family.
There is evidence that student BMI reporting to parents does increase parents' ability to correctly classify their children's weight status. In Arkansas, they've done a great job evaluating the numerous efforts that have been made to address childhood obesity in schools, and this is one finding that has been consistent. Amazingly, though, even though the numbers of accurate parental perception increased significantly, they were still surprisingly low - at baseline 40% of parents were able to correctly identify their child's weight status; after the intervention, it only went up to 53%. That means that 47% of parents are still unaware of their child's weight category.
Changing behavior at home. But does accurate perception by parents lead to changes in behavior at home? The research on this question is less convincing. In one study, parents were called on the phone after receiving the report and those who got the BMI information were more likely to say that they intended to change behavior (i.e., improve the healthfulness of meals and snacks at home, increase exercise). Similarly, in Arkansas, parents reported that they had, in fact, increased the frequency of family meals, improved recipes, and decreased the unhealthy snacks kept in the house. These are all good things - if they really happened. The biggest problem with this field of research in general is that people are very likely to say what they know is the right answer - and they may even truly intend to change their behavior - but there is a fairly weak relationship between knowledge, attitudes, and actual behavior change. I do not know of any studies that have looked at the self-reported changes at home and another outcome measure (such as child BMI or a separate assessment of children's diets).
Focus on behaviors, not body size. If it were up to me, I would move the emphasis away from BMI and toward assessments of children's behavior. Imagine this: a school is able to do a comprehensive assessment of the quality of a child's diet, eating habits, physical activity levels, and time spent in sedentary behaviors. While we were at it, we would also do a really good assessment of the child's body image and relationship with food. Then, the information sent home to parents would be much more specific and clear, concrete behavioral goals could be suggested. For example, a parent may get a letter that says:
Molly's BMI is in the 85% percentile for her age, which places her in the "at risk for overweight" range. She also reports eating one serving of fruit per day and 2 servings of vegetables per week. She reports having three dairy servings per day, and 3 servings a day of "snack / dessert" foods. She reports watching TV 3 hours a day.
Then, for each of these behaviors, there would be a graph that shows where Molly is compared to standard recommendations from the American Academy of Pediatrics or the Dietary Guidelines for Americans. This would be followed by some clear goals:
Based on this information, we suggest that you strive to incorporate three to four additional servings of fruits or vegetables into Molly's daily diet, and limit her intake of snack / dessert foods to one per day. We suggest limiting her TV time to 1 hour per day. Her dairy intake is right on target.
Then, the letter could include some suggested strategies on how to achieve each of these goals, as well as a resource person to consult with the family.
The nice thing about focusing on behavior is that it would provide relevant information to all children - not just the overweight ones. It is quite likely that there children whose BMI is in the normal range who are not eating very well.
So, anybody out there want to try this out? I would be delighted to try to help a school or district implement an assessment and feedback system such as this one and compare the impact with the BMI reporting strategies that are now underway in many states.