Untangling the Causes of Increasing Obesity in Youth

According to the Centers for Disease Control and Prevention, the rate of childhood obesity has tripled in a single generation of youth--up to around 17 percent of all children and adolescents today. Obese kids are more likely to have a host of medical problems--such as an increased risk of insulin resistance and type 2 diabetes and higher blood pressure--as well as social and psychological problems, such as discrimination and poor self-esteem.

While the consequences of childhood obesity are fairly well understood, the causes of it are harder to unravel. Environmental factors contribute, but there is the obvious question of which is the most significant contributing factor to the development of obesity: "calories in" (the growing consumption of less healthy foods) or "calories out" (the growth of a more sedentary lifestyle with an absence of physical activity)?

A Growing Consensus on "Calories In"

An earlier Child Policy newsletter summarized RAND research on these environmental factors. While it stressed the thinness of the data, it did highlight some suggestive trends in terms of calories in--an increase in snacking toward foods high in calories and soda consumption with a decrease in the availability of affordable fruits and vegetables--and calories out--no increases in the amount of physical activity in school. The newsletter also noted that low-income groups and ethnic and racial minorities are more affected by the obesity epidemic than the general population, pointing to the potential effects that certain types of neighborhoods can have.

In the five years since the previous newsletter on this topic, RAND researchers have continued to study the problem from these different perspectives, and a new RAND research brief summarizes such obesity research as a whole. At this point, the growing consensus among researchers is that "calories in" seems to be the bigger factor.

Not Getting One's Fruits and Veggies

Previous RAND research has showed that limited access to stores that sell fresh fruits and vegetables affects obesity. But even if families have access, how do the prices of those fruits and vegetables affect childhood obesity? To examine this question, RAND researchers used data from the Early Childhood Longitudinal Study-Kindergarten Class (or ECLS-K), a survey of children from more than 1,000 schools nationwide who started school in the 1998--1999 academic year.

They merged the ECLS-K data with metropolitan-level data on food prices from the Council for Community and Economic Research (C2ER) and looked at the impact in terms of changes to children's body mass index (BMI). They found an increase in BMI in both boys and girls over a period of five years--an increase that is far greater than that listed on growth charts published by the Centers for Disease Control and Prevention. The researchers also found a consistent, long-term neighborhood effect, in that areas with higher real fruit and vegetable prices experienced greater increases in BMI. The study also found evidence of growing disparities, with higher BMI gains among black and Hispanic children.

Another study, also using the ECLS-K merged with food price data from C2ER, examined whether regional price differences for different types of food are associated with consumption patterns among fifth-grade students. That study showed that price variation does exist across metropolitan areas and that lower real prices for vegetables and fruits predict significantly higher consumption of them. Similar price effects were not found for fast food or soft drink consumption.

What If We Tax Soft Drinks?

The growing consumption of soda and other sugar- and artificially sweetened beverages is linked to growing obesity in kids. Once again using ECLS-K data--this time matched with state sales taxes on soda and individual-level data on children--RAND researchers examined whether small taxes are likely to change consumption and weight gain.

The study found that existing taxes on soda (typically not much higher than 4 percent in grocery stores) do not substantially affect overall levels of soda consumption or obesity rates. To have a measurable effect on consumption, taxes would need to be tied to consumption, and they would need to be larger than the existing state variation in sales taxes. But subgroups of at-risk children--those who are already overweight, come from low-income families, or are African American--may be more sensitive than others to soda taxes, especially when soda is available at school. A greater impact of these small taxes could come from dedicating the revenues they generate to other obesity prevention efforts rather than through their direct effect on consumption.

INTERVIEW

Increasingly, We Are What We Eat Ashlesha Datar is a senior economist at RAND who studies the role of families, schools, and other contextual factors in determining the health and educational outcomes of young children. She has conducted extensive research on both the causes and consequences of childhood obesity, examining, in particular, how environments in schools (e.g., access to junk food, physical education instruction) and neighborhoods (e.g., proximity to fast-food restaurants, food prices) influence childhood obesity. She is studying the factors explaining the emergence of socioeconomic disparities in childhood obesity. Datar has received several grants from federal agencies and private foundations, including the National Institutes of Health, the U.S. Department of Agriculture, and the Robert Wood Johnson Foundation. Her research has been published in prominent health, education, and policy journals. She received her Ph.D. in policy analysis from the Pardee RAND Graduate School. Much of the research from RAND and others is pointing toward the foods we don't eat as an important driver of obesity in kids. That's true. America's kids don't eat enough fruits and vegetables. Consumption is way below recommended U.S. dietary guidelines. That's part of the motivation behind why the government replaced the "Food Pyramid" with "My Plate." They are recommending that half of a person's meal plate should consist of fruits and vegetables. Why is it so hard to increase fruit and vegetable consumption? It's hard primarily because of affordability and access issues. Fresh fruits and vegetables cost much more relative to energy-dense foods, such as hamburgers. Such affordability issues strike hardest among low-income and minority populations, who are also more directly affected by access issues, often living in "food deserts" that lack access to fresh fruits and vegetables. So, how can we get kids to fill up their plates with fruits and vegetables? Economists think decreases in the price of healthy foods (e.g., subsidizing fruits and veggies) and increases in the price of unhealthy foods (e.g., taxing soda) would encourage individuals to eat higher-quality and more nutritious foods. Similarly, increasing access to healthy foods would effectively lower the costs of obtaining these foods and would encourage healthy eating, while decreasing access to unhealthy foods would raise the costs of obtaining these foods and also encourage health eating. What does the research say? As we saw above, new research suggests that lowering the prices of fruits and vegetables can significantly increase the amount of fresh, healthy foods kids eat. But taxing soda does not seem to influence how much teens drink it. We need more research to fully understand how children's food intake patterns respond to economic (dis)incentives. Insights from behavioral economics suggest that individuals may not respond symmetrically to discounts for healthy foods versus taxes on unhealthy foods. Also, the relationship between food prices and consumption choices is more complex in children, because they are generally not the ones making food purchase decisions. So where can we intervene to increase kids' consumption of healthy foods? Schools offer a unique opportunity. Children spend most of their waking hours in school, where they consume most of their daily calories; also, they are more likely to make food and beverage consumption decisions independent of their parents there. How would this work? There is a national trend toward increasing access to healthy foods in school cafeterias and other school food venues. At the same time, stricter regulations are reducing access to unhealthy foods in schools. Such efforts may increase consumption of healthy foods and decrease consumption of unhealthy foods, but we must also support these efforts with strategies that encourage healthy consumption away from school.

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