Fighting youth body fatness: The role of food prices
Michael Grossman, Erdal Tekin, Roy Wada, 28 September 2013
According to the
World Health Organization, childhood obesity is one of the most serious
public-health problems of the 21st century. The prevalence of obesity
among children has been on the rise globally over the last several
decades and is now an epidemic in the US.
- Since the mid-1970s, the proportion of children aged 12 to 19 who are obese has more than tripled from 5.0% to 18.1% in the US (Ogden et al. 2010).
These trends are extremely alarming.
- Childhood obesity has been associated with a host of chronic health problems, such as high blood pressure, hypertension, gallbladder disease, and Type 2 diabetes as early as adolescence (Serdula et al. 1993; Freedman et al. 1999; 2007; Hill, Catenacci, and Wyatt 2006).
Children who are
obese during early childhood are likely to be obese during adulthood.
This not only exacerbates the aforementioned health problems, but also
leads to negative long-term psychological and labour market outcomes
ranging from poor self-esteem and depression to discrimination and lower
wages (Daniels 2006; Mocan and Tekin 2011; Dietz 1998; Strauss 2000).
Why the extra weight?
There is a long list of explanations offered for the rapid rise in childhood obesity and overweightness. These include:
- Falling food prices.
- Increased demand for sugary drinks.
- Advertising of unhealthy foods targeted at children.
- Increased time spent in sedentary activities, such as watching TV or videos, using a computer, or playing computer games.
- Lack of vigorous physical activity.
- Increased food-portion sizes.
Just as there is no
single explanation for the obesity epidemic, there is no single or
simple solution. Most public interventions aimed at improving child and
adolescent health generally take the form of policies that limit access
and provide price incentives or disincentives.
The latest policy
proposals for reducing childhood obesity rates involve raising the
prices of unhealthy, nutrient-dense food items such as sugar-sweetened
beverages and fast-foods through taxations. Such policy proposals are
based on findings that selective applications of taxation and subsidies
are effective in shifting food consumption away from unhealthy food
towards healthier alternatives (Cawley 2010; Powell and Chaloupka 2009).
- In general, empirical studies that examined the effects of prices on obesity found stronger effects than studies that examined the effects of food taxes (Powell, Chriqui, and Chaloupka 2009; Fletcher, Frisvold, and Tefft 2010).1
- There is also reasonably consistent evidence demonstrating that fruit and vegetable prices, particularly of the non-starch variety, are associated with lower weight outcomes while fast-food prices are associated with higher weight outcomes for the adolescent population (Powell et al. 2013).
Moreover, these
effects tend to be larger for minorities, children in lower-income
families, and children whose mothers have less than a high school
education.
Problems with the BMI as an indicator of obesity
The existing
evidence almost exclusively comes from studies that rely solely on body
mass index (BMI) as the measure of obesity. This is not surprising since
BMI is easy to calculate and readily available from many social science
datasets, but its reliability for use in epidemiological studies has
come into question recently.
- It is argued that some of the weak or mixed results documented by studies using BMI may be due to its limited ability to correctly distinguish body fat from lean body mass (e.g., Yusuf et al. 2004, 2005; Romero-Corral et al. 2006, 2007).
Since it is body fat
(and not fat-free mass) that is responsible for the detrimental health
effects of obesity, several studies caution against a sole reliance on
BMI and point to a need for using direct measures of body composition in
obesity studies (e.g. Smalley et al. 1990; Romero-Corral et al. 2006).
Our contribution
In a recent paper,
we use clinically obtained body composition measures to conduct a
comprehensive and comparative analysis of the effects of various food
prices on body fatness among youths ages 12 through 18 and compare the
sensitivity of our findings to results using BMI (Grossman, Tekin, and
Wada 2013). Ours is the first study to consider clinically measured
levels of body composition to examine the effects of food prices on body
fatness among youths. It is important to assess the extent to which
alternative body fat measurements are reliable and precise in the
identification of the degree of obesity among youths in order to better
understand the risk factors associated with obesity and develop policies
to counter these risk factors.
The body composition
measure that we employ is percentage body fat (PBF). We derive our PBF
measure from three separate sources, two of which rely upon
bioelectrical impedance analysis (BIA) and one of which relies upon dual
energy x-ray absorptiometry (DXA). We also employ clinically measured
height and weight to estimate the effects of prices on BMI. We draw on
data from the restricted-use versions of National Health and Nutrition
Examination Survey (NHANES) to merge various county-level time-varying
price variables.
Results
Our findings suggest that:
- Increases in the real price of one calorie of food for home consumption and the real price of fast-food restaurant food result in significant reductions in the in PBF among youths.
- An increase in the real price of fruits and vegetables has negative consequences for these outcomes.
- Measures of PBF derived from BIA and DXA are no less sensitive and in some cases more sensitive to the food prices just mentioned than BMI, and serve an important role in demonstrating that rising food prices (except for those of fruits and vegetables) are associated with reductions in obesity rather than in body-size proportions alone.
Policy implications
These findings have
important implications for the optimal targeting of public policies
designed to reverse the epidemic of childhood obesity. In particular,
they have implications for how changes in agricultural, tax, and subsidy
policies might affect food and beverage consumption patterns.
- We show that selective taxes or subsidies may be able to accomplish part of this goal through changes in food prices.
We also document that uniform increases or decreases in the price of food have the expected impacts on body fatness.
- It should be kept in mind that taxes are blunt instruments that impose significant welfare costs on individuals who consume food in moderation.
There is also the
question as to whether parents may more easily and immediately affect
the choices made by their children than the government policies.
Some of our results
point to higher rates of time preference and lower expected future wage
rates among non-white parents and youths as explanations of why
minorities are more sensitive to fast-food prices and less sensitive to
fruits and vegetables prices than whites. These interpretations add to
the existing evidence on the wide range of benefits to early childhood
intervention programs emphasised by Heckman and colleagues (e.g., Conti
and Heckman 2012). We view our contribution as an important input into
the policy debate concerning the most effective ways to reverse the
upward trend in obesity.