Food Stamps and Obesity: Ironic Twist or Complex
Puzzle?
Michele
Ver Ploeg
Lisa
Mancino
Biing-Hwan Lin
USDA and Getty Images
With its roots in the Great Depression
and expansion during the 1970s after the Government’s
declared war on poverty, the Food Stamp Program
was designed to provide a nutritional safety net
for low-income households while boosting demand
for domestic agricultural products. Today it is
the Nation’s largest food assistance program,
providing monthly benefits to about 24 million people
at a cost of $27 billion in 2004. The program plays
a vital role in stabilizing the incomes of the poor
and in promoting food consumption. However, as the
major nutrition problems facing the U.S. population
have shifted from too little intake to overconsumption
and obesity, some have questioned whether food stamps
encourage participants to eat too much.
Because food stamps are designed to serve as a first-line
defense against hunger, it would be ironic if food
stamps were connected to America’s obesity
problem. Though such a connection appeared to exist
in the late 1980s and early 1990s, it does not appear
to hold today. National health and nutrition data
from 1988-94 show that adults who received food
stamps had a greater Body Mass Index (BMI) than
adults who were similarly poor but did not participate
(eligible nonparticipants), by an amount that is
unlikely due to chance, that is, the difference
is statistically “significant” (see
“Weighty Matters”).
Weight differences were especially striking for
women; 42 percent of women who participated in food
stamps were obese, compared with 30 percent of eligible
nonparticipating women and 22 percent of women with
incomes above the eligibility limit.
According to data from 1999-2002, however, differences
among these three groups of women have largely disappeared.
For women, increases in BMI and obesity have accelerated
more rapidly among those who did not receive food
stamps than among those who did. For men, the connection
between weight status, receipt of food stamps, and
income has also weakened over time.
Furthermore, these data suggest that the relationship
between program participation and weight is neither
uniform across sex, race, and ethnicity, nor consistent
over time. Weight status is a result of eating and
physical activity behaviors that interplay with
individual and household economic, social, cultural,
and genetic factors. Identifying how food stamp
participation fits into this complex mix of behaviors
and individual and household characteristics requires
rich data and careful statistical modeling.
Weighty
Matters
Body Mass Index (BMI) is calculated as an
individual’s weight in kilograms divided
by the square of his or her height in meters.
For adults, numerical thresholds of BMI
distinguish healthy weight from underweight,
overweight, and obesity. For children and
adolescents, sex-specific BMI-for-age thresholds
using the 2000 Centers for Disease Control
and Prevention growth charts distinguish
healthy weight from underweight, at-risk
of overweight, and overweight.
-
Underweight = BMI below
18.5
-
Healthy weight = BMI
at or above 18.5 but below 25
-
Overweight = BMI at
or above 25 but below 30
-
Obese = BMI at or above
30
-
Underweight = Below
the 5th percentile of BMI-for-age
-
Healthy weight = At
or above the 5th percentile but below
the 85th percentile of BMI-for-age
-
At-risk of overweight
= At or above the 85th percentile but
below the 95th percentile of BMI-for-age
-
Overweight = At or
above the 95th percentile of BMI-for-age
|
Why Might Food Stamps Cause Weight
Gain?
The Food Stamp Program was designed
to alleviate hunger by distributing coupons or,
currently, Electronic Benefit Transfer cards, that
can be used at grocery stores to purchase almost
any kind of food. (Benefits cannot be used to purchase
alcohol or tobacco, foods eaten in the store or
hot foods prepared at the store, nonfood items,
or vitamins and medicine.) The program was designed
to boost food consumption and energy intake. It
is an entitlement program available to all households
(subject to certain work and immigration status
requirements). Eligibility and benefits are based
on household size, household assets, and gross and
net income (gross monthly income cannot exceed 130
percent of the Federal poverty guidelines). The
average food stamp benefit in 2004 was $86 per person
and $200 per household each month.
Evidence suggests that the program
has successfully increased food expenditures. Not
only does the program increase food expenditures
beyond what households would spend without the program,
households spend more on food than they would if
the same amount of benefit was given as cash. Estimates
show that a dollar in food stamps increases expenditures
on food by $0.17 to $0.47 while a dollar of cash
increases expenditures on food by about $0.11. (A
dollar of food stamps does not lead to a dollar
in additional spending on food because the food
stamp benefit allows cash previously spent on food
to be spent on nonfood goods such as rent or child
care.) This boost in food expenditures has been
blamed for increasing food consumption such that
program participants are more prone to obesity.
Increased resources for food spending could be used
to purchase more expensive foods that were previously
out of reach. If participants purchase higher priced
but more healthful foods, food stamps could have
a positive effect on weight. But if participants
purchase higher priced, less healthful foods or
simply greater quantities of the same foods, then
food stamps could lead to weight gain. Studies on
food stamps’ effect on eating behaviors and
nutrient intake are not conclusive. Food stamps
do increase the availability of food energy, protein,
and some micronutrients (vitamin A and iron, for
example). Further, those who receive food stamps
consumed more meat, added sugars, and total fats,
but did not consume more fruits, vegetables, grains,
and dairy products.
Does the monthly food stamp cycle, in which benefits
are issued once a month, contribute to sporadic
consumption of food? In the first few weeks after
benefits are issued, food may be abundant for a
household, and much less so near the end of the
month. A household’s eating patterns may mirror
the cyclic availability of food. Food deprivation
has been linked with binge eating when food later
becomes plentiful. Further, binge eating has been
linked to weight gain over time. If many food stamp
recipients tend toward this behavior, the monthly
cycle of food stamps may contribute to weight gain
independent of the amount and form of the benefit.
Weight Gain Was Not Consistent
Across Subgroups
If food stamps by themselves cause
systematic weight gain, then we expect food stamp
participants to be heavier than eligible nonparticipants.
Simple prevalence estimates of weight status using
1988-94 data from the National Health and Nutrition
Examination Survey (NHANES) indicate that not all
age, gender, and racial/ethnic groups showed a positive
association between food stamps and weight.
Differences between food stamp participants and
eligible nonparticipants were greatest among women,
but these differences were concentrated among non-Hispanic
White women. (Women account for about two-thirds
of adult food stamp recipients.) Among this subgroup,
those who received food stamps in 1988-94 had greater
BMI and were more likely to be obese than eligible
nonparticipants. The same was true for Mexican-American
women. These associations were not, however, present
for non-Hispanic Black women. (The 1988-94 NHANES
oversampled Mexican Americans, but not other Hispanic
Americans. The sample size does not support separate
estimates representative of all Hispanic Americans,
only Mexican Americans.)
Men who receive food stamps tended to be lighter
than their eligible nonparticipant and higher income
counterparts. For both non-Hispanic Black and White
men in 1988-94, those who participated in food stamps
were less likely to be overweight than eligible
nonparticipants and higher income men of the same
ethnicity. On the other hand, Mexican-American men
who received food stamps were more likely to be
obese and had higher average BMI than eligible nonparticipating
Mexican-American men.
The relationships between food stamp receipt and
weight status for children were not as strong as
they were for adults. Estimates from 1988-94 for
children age 5-19 and for each sex and racial/ethnic
group showed no differences between food stamp participants
and eligible nonparticipants in terms of average
BMI and the probabilities of being at-risk of overweight
or overweight. The one exception, which contradicts
the notion that food stamps cause children to be
overweight, is for non-Hispanic Black boys, who
were less likely to be overweight than
eligible nonparticipating Black boys.
Thus, simple prevalence estimates showed that not
all gender, age, and racial/ethnic subgroups demonstrated
a positive association between food stamps and weight.
In fact, differences in weight status between adult
food stamp recipients and nonparticipants were primarily
driven by differences among non-Hispanic White women
alone.
Today, Relationship Between Food
Stamps and Weight Weakening
Perhaps participation in the Food
Stamp Program does have deleterious effects for
some but not all, demographic groups. If this effect
were present for a subgroup, such as non-Hispanic
White women, then we would expect the association
between weight status and program participation
to be steady over time, especially since program
rules have not changed much since the 1970s. Instead,
the association between weight and food stamp participation
varies over time.
Overweight and obesity have been increasing in the
overall U.S. population. According to the Centers
for Disease Control and Prevention, 47 percent of
the U.S. adult population were overweight or obese
in 1976-80. By 1999-2002, over 65 percent were overweight
or obese. Further, rates of obesity doubled over
this period, from 15 percent to 31 percent. Are
these increases worse for food stamp participants
or do their trends simply mimic those of the U.S.
population at large?
Among women, food stamp participants are not getting
relatively heavier over time. Rather, BMI has grown
more among eligible nonparticipants—and even
among women with higher incomes—than for food
stamp recipients. This is especially true for non-Hispanic
White women. In 1976-80 and 1988-94, White women
who participated in food stamps had greater BMI
and were more likely to be overweight and obese
than eligible nonparticipants and those with higher
incomes. By 1999-2002, these differences had largely
disappeared; the only exception was that White women
in the moderate/high income group were still less
likely to be obese than food stamp recipients. The
closing of the BMI gap is due to changes in weight
status by nonparticipating women—the average
BMI of food stamp recipients remained steady. For
non-Hispanic Black women and Mexican-American women,
the trends are not as striking, but the general
picture is the same.
Over all three racial and ethnic groups, the probability
of a woman’s being overweight grew the least
for food stamp recipients over the study years.
For non-Hispanic Black and White women, the likelihood
of overweight grew the most for those with low/moderate
income. For Mexican-American women, the probability
of overweight grew the most for eligible nonparticipants
and moderate/high-income women.
Trends for men are almost the exact
opposite of those for women. Data from previous
years showed that food stamp recipients were less
likely to be overweight than eligible nonparticipants
and higher income men. However, the most recent
data show that differences in overweight status
have almost entirely disappeared.
Patterns in children’s weight status vary
over time and by gender, race, and ethnicity. For
girls age 5-19, there is little association between
weight status and program participation status.
Most differences that existed in previous years
are not present in more recent years. Similarly,
for non-Hispanic Black and White boys, few differences
in weight status among food stamp participation
and income groups were found in the most recent
data.
For Mexican-American boys, the story is different.
Data for 1999-2002 show Mexican-American boys who
participated in the Food Stamp Program have higher
average BMI than Mexican-American boys who are eligible
nonparticipants or in the highest income group.
Mexican-American boys who receive food stamps are
also more likely to be overweight than their nonparticipating
counterparts, regardless of income and eligibility
status.
Connection Uncertain
Overall, estimates from the latest
national data show a weakening relationship between
food stamp receipt and weight status. This reversal
is most noticeable among women, the group for which
differences between participants and nonparticipants
received the most attention and for whom previous
research has found the most consistent associations
between food stamps and weight. For women, multi-year
data show the opposite of what we would expect to
find if food stamps were behind increased obesity.
For men, it appears that food stamp participants
are catching up weightwise with nonparticipants.
Does this new evidence exonerate food stamps in
the obesity puzzle? Is there a potential problem
for men who receive food stamps? The reality is
that we do not know enough to conclude whether food
stamps are making low-income Americans fatter. Past
and current behaviors and characteristics affect
an individual’s weight at a given point in
time. Further, eligible individuals choose whether
or not to receive food stamps and those who choose
to participate may be different from those who do
not.
Disentangling how food stamp participation intersects
with these behaviors and characteristics and with
weight is difficult. Thus far, data and statistical
method limitations have prevented us from doing
so conclusively (see “What
Data Do We Need?”). Our results show that
food stamps do not systematically lead to weight
gain. Rather, links between food stamp participation
and weight status are consistent neither across
population subgroups nor over time. These findings
highlight the dangers of drawing causal conclusions
about food stamps and weight using data from a single
point in time.
What
Data Do We Need?
Behaviors associated with
food consumption and weight gain are complex,
and it is difficult to identify direct links
between food stamps and excess weight. The
Food Stamp Program is an entitlement program,
where the law requires that benefits be
provided to everyone who is eligible and
takes the necessary steps to qualify. Thus,
randomized experiments, where “alike”
individuals are randomly assigned to the
experiment group (and receive food stamps)
and compared with individuals assigned to
a control group (who are denied food stamps),
are not legally feasible. As a result, researchers
must rely on existing survey data and statistical
methods to understand the effects of food
stamps on weight.
A basic problem in deciphering causal links
between program participation and outcomes
like weight is that eligible households
choose whether or not they participate.
Overall, in fiscal year 2004, 56 percent
of eligible persons participated in the
Food Stamp Program. Participation rates
vary by characteristics such as household
structure and gender. Those who choose to
participate may be different from those
who choose not to participate, and this
difference could also be related to weight
status. While demographic and other characteristics
can be used to help control for differences
between those who choose to participate
and those who do not, researchers often
cannot observe all these differences. For
example, strong preferences for food relative
to other goods is difficult to observe,
yet those people with such tastes may be
more likely to participate in the program
and more likely to be overweight. If such
positive “self-selection” is
not accounted for, estimates of the effect
of food stamps on weight will be overestimated
because these individuals may have gained
weight without the Food Stamp Program. Researchers
have used a variety of sophisticated statistical
procedures to counteract selection bias,
however, none of the techniques can guarantee
that selection bias has been eliminated.
We used multiple periods of data on similar
subgroups to see whether food stamp-weight
associations were consistent over time.
Implicit in examining such trend data is
that the composition of subgroups did not
change (especially with respect to their
propensities to become overweight or obese).
In reality, it is likely that changes in
economic conditions affected who is eligible
and who chose to receive food stamps. Changes
in other assistance programs for low-income
families, such as the 1996 changes to the
cash welfare program, also likely affected
who chose to participate. The number of
food stamp participants rose 47.4 percent
from 1988 to 1994, but then began to fall—so
much so that by 2000, the number of participants
was below the 1988 level. This span of time
included major changes in both economic
conditions and welfare policy. Because the
subgroups we compare do not consist of the
same people over time, we do not try to
draw causal conclusions about the effect
of food stamps on weight.
Collecting information on weight, program
participation, and other characteristics
for the same set of people over time could
help identify causal links. Ideally this
information would be collected before, during,
and after periods of food stamp participation.
It will also be important to collect data
over a number of years for each person to
see if long-term receipt of food stamps
has different impacts than short-term receipt,
and to observe long-term changes in weight.
Data that include multiple measures of the
specific amount and types of food eaten
and levels of physical activity for the
same set of people over time could also
be used to illuminate differences between
income and program participation groups.
|
Nutrition
and Health Characteristics of Low-Income Populations,
Volume 1, Food Stamp Participants and Nonparticipants,
by M.K. Fox and N. Cole, E-FAN-04014-1, USDA, Economic
Research Service, December 2004.
The Effect on Dietary
Quality of Participation in the Food Stamp and WIC
Programs, by P.E. Wilde, P.E. McNamara, and
C.K. Ranney, FANRR-9, USDA, Economic Research Service,
September 2000.
"Food Stamp Program Participation is Positively
Related to Obesity in Low Income Women,” by
D. Gibson, Journal of Nutrition, Vol. 133,
pp. 2225-2231, 2003.
"Dietary Effects of the Food Stamp Program,”
by B. Devaney and R. Moffitt, American Journal
of Agricultural Economics, Vol. 73, pp. 202-211,
February 1991.
The ERS Briefing
Room on the Food Stamp Program
The ERS Briefing
Room on Diet and Health
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