Food Stamps and Obesity: What We Know and What It
Means
Food stamp benefits do
not increase obesity for most program participants,
but there is a potential link for some subgroups.
Michele
Ver Ploeg
Katherine
Ralston
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Food Stamp Program participation does
not increase the likelihood of being
overweight or obese for men
or children. |
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Women
are the only group for which multiple
studies show a potential link between
food stamp participation and body weight.
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Devising
policy changes for household members
who may be at risk of gaining weight,
without harming those who are not but
still need food assistance, is a difficult
challenge.
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This
article is drawn from . . . |
Food
Stamps and Obesity: What Do We Know?
by Michele Ver Ploeg and Katherine Ralston,
EIB-34, USDA, Economic Research Service, March
2008.
|
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may also be interested in . . . |
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An Economic Perspective by Joanne
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Ephraim Leibtag, Biing-Hwan Lin, Lisa Mancino,
Mark Nord, Mark Prell, David Smallwood, Jayachandran
Variyam, and Michele Ver Ploeg, EIB-29, USDA,
Economic Research Service, September 2007.
“Food
Stamps and Obesity: Ironic Twist or Complex
Puzzle?” by Michele Ver Ploeg, Lisa
Mancino, and Biing-Hwan Lin, in Amber
Waves, Vol. 4, No. 1, USDA, Economic
Research Service, February 2006.
The
ERS Briefing Room on the Food Stamp Program
The
ERS Briefing Room on Diet and Health
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Critics of the Food Stamp Program
point to higher rates of obesity among some low-income
populations and question whether the program might
have been too successful in boosting food consumption.
They assert that giving assistance in the form of
benefits redeemable for food, instead of cash, has
led participants to spend more on food and eat more
than they would have otherwise. Others wonder if
the monthly issuance of food stamp benefits is linked
to boom-and-bust cycles of consumption that could
lead to weight gain over the long term.
A recent ERS report explores whether
there is any evidence of a causal link between food
stamp participation and obesity. ERS reviewed and
synthesized the growing and sometimes conflicting
research on the issue. Researchers placed greater
weight on studies that used statistical methods
to control for the fact that people choose to participate
in the program and those who participate are likely
to be different from those who do not in ways that
researchers cannot always observe. These differences
could be related to body weight.
The weight of evidence from these
studies indicates that for most program participants,
food stamp benefits do not increase either Body
Mass Index (BMI—a measure of weight adjusted
for height) or the likelihood of being obese. A
review of the research indicates that food stamp
benefits do not increase the likelihood of being
overweight or obese for men or children. For nonelderly
adult women, who account for 28 percent of all food
stamp participants, multiple studies show a potential
link between food stamp receipt and an increase
in obesity and BMI, although this effect appears
to be small—about 3 pounds for a woman 5’4”
to 5’6” tall. Some studies found that
long-term participation in the program appears to
heighten the impact on obesity.
It is not clear why participation
in the Food Stamp Program may increase the probability
of obesity for women but not for men or children.
Research about the causes underlying these results
is not conclusive. Differences in energy requirements,
activity levels, and eating patterns could be possible
explanations. Because the Food Stamp Program is
administered as a household-level program, devising
program changes that are appropriately targeted
to household members who may be at risk of gaining
weight, without harming those who are not and need
the nutritional assistance, is a challenge. Policy
changes that help program participants improve their
overall diets or help them “smooth”
their food consumption over periods of high and
low income may be more effective. For example, issuing
food stamp benefits on a biweekly, or even weekly
basis, may help food stamp participants obtain and
consume food on a more even basis.
Too Much Money for Food or Too Infrequently
Issued?
The Food Stamp Program is an entitlement
program available to all U.S. households that meet
the eligibility requirements pertaining to income,
assets, work, and immigration status. Program benefits
can be used to purchase almost any food sold by
participating food retailers, except for food prepared
in the store, hot foods, and alcohol and tobacco.
The average monthly benefit level in 2007 was $96
per person and $215 per household, which translates
roughly to $3.20 per person per day or $7.16 per
household per day to spend on food. Most program
participants spend some of their own money on food
in addition to their monthly food stamp allotment.
There are two leading explanations
for how food stamp benefits could contribute to
weight gain that may lead to obesity. The first
argues that restricting food stamp benefits to food
purchases results in participants spending more
money on food and, thus, consuming more food than
they otherwise would if they did not participate
in the program. Although food stamp benefits may
have the intended effect of reducing undernourishment
or underweight for at least some participants, this
explanation implies that the benefits may also be
pushing a portion of participants into overweight
or obesity. If true, then one solution is to deliver
food stamp benefits as cash. Cash benefits have
been found to induce smaller increases in food spending
than benefits that can be spent only on food.
But even if receiving food stamp
benefits leads participants to spend more on food,
it does not mean that the additional spending results
in overconsumption and obesity. It is possible that
food stamp benefits allow people to choose a different
bundle of foods than they otherwise would. For example,
participants may shift spending toward relatively
more expensive foods that were previously out of
reach (e.g., fresh meats versus canned beans or
fresh fruit and vegetables instead of canned items).
Or, since food stamps can be redeemed for food only
in grocery stores, participation in the program
may shift a household’s food spending toward
foods prepared and consumed at home, as opposed
to food away from home. In either case, an increase
in food expenditures would not necessarily lead
to overconsumption of calories or a poorer diet.
The food stamp cycle explanation
argues that the practice of distributing food stamps
only once a month results in alternate periods of
under- and overconsumption, a pattern dubbed the
“food stamp cycle,” which may result
in weight gain. Households consume food every day
but purchase food less regularly—every few
days for some households, every few weeks for others.
It is possible that food stamp participants run
out of food (and benefits with which to purchase
more food) near the end of the month. As food becomes
scarce and food intake is restricted, a person may
lose weight. Then, when food is abundant, the individual
may overeat. This distorted pattern of consumption
with its periods of binge eating gradually can lead
to increased weight.
Teasing Out Cause and Effect
Two conditions can be associated
with each other, without one being the cause and
the other the effect. Food stamp benefits may be
associated with increases in body weight but may
not cause greater body weight if something else
is to blame. Determining cause and effect is difficult
because no experiments have been conducted comparing
the body weights of participants randomly assigned
to receive program benefits with those of others
assigned to a comparison program (or lack of a program).
Researchers must instead rely on nonexperimental
methods that try to determine what would have happened
if no one received food stamp benefits or if an
alternative program to food stamps was implemented.
Comparing body weights of food
stamp participants with those of eligible nonparticipants
is an obvious starting point, but this approach
may be problematic. Food Stamp Program participants
may have different characteristics than those who
are eligible for the program but choose not to participate.
Very poor individuals, for example, may be more
likely to participate than individuals who are less
poor but still eligible. A household with a strong
preference for food relative to other necessities
may be more likely to apply for food stamps than
an otherwise similar household. This strong preference
for food may also lead to weight gain that would
have occurred whether or not the household participated
in the program.
While most studies try to control
for as many differences between participants and
nonparticipants as possible, it is likely that important
differences are not observed. If these differences
are related to body weight, then the estimated effects
of food stamp participation could be biased. This
bias is called selection bias because individuals
self-select into the Food Stamp Program. Researchers
note that poverty is associated with higher risk
of obesity in some population subgroups (for example,
White women), but lower risk in others (among Black
and Hispanic men), suggesting that selection bias
can be positive or negative in the case of food
stamp participation and obesity. Accounting properly
for selection bias can reveal a higher or lower
risk of obesity than estimates that do not account
for such bias.
ERS researchers reviewed over
a dozen studies of the relationship between food
stamp participation and BMI and the likelihood of
obesity. Several of the earlier studies used cross-sectional
data (observations of many individuals for a single
point in time) and controlled for observed factors
that might be related to body weight, such as age,
race, sex, and education. While these studies are
useful for understanding broad trends and highlighting
possible relationships for further exploration,
they do not account for potential selection bias
and only observe individuals at a point in time,
so they are of limited use in drawing causal conclusions.
The ERS review focused primarily
on studies that attempt to control for selection
bias (often using longitudinal data with multiple
observations on the same individuals) and which
are better able to tease out cause and effect between
food stamp participation and weight. One can never
be sure that these methods are truly picking up
cause and effect, but the methods used in these
studies help researchers get closer to that goal.
Diverse Effects Reflect Diverse Participants
The Food Stamp Program serves
a diverse population. In 2006, children accounted
for almost half of all participants. Working-age
women made up 28 percent of the caseloads, working-age
men 13 percent, and the elderly age 60 and older
8 percent. Most of the food stamps issued go to
households containing a child, elderly adult, or
nonelderly disabled person (89 percent of all benefits).
Many of the households receiving food stamps are
single-adult households with children (34 percent).
The ERS review of the effects of food stamp participation
on body weight for this diverse group of participants
found that food stamp participation has a small
effect on obesity for adult women, but not for men
or school-age children. Only a few studies have
looked at children younger than 5 and the elderly,
and they did not control for selection bias, so
these subgroups are not discussed here.
Results for children ages 5-12
vary across sexes and differ in the direction of
the relationship between food stamp participation
and body weight. For young boys, studies found either
no relationship between food stamp participation
and BMI, or that food stamp participation is linked
to a lower probability of being overweight (BMI-for-age
greater than or equal to the 95th percentile).
For young girls, some studies
found no association between food stamp participation
and BMI. One study found that additional years of
food stamp participation were associated with greater
probability of being overweight. Another found a
negative relationship between food stamp participation
and being at-risk of overweight (BMI-for-age greater
than or equal to the 85th percentile).
These two studies used different methodologies,
which could account for the disparate results.
For adolescent children (ages
12-18), food stamp participation does not seem to
be related to BMI or the probability of being overweight.
None of the reviewed studies found a link between
program participation and body weight for teenage
boys or girls.
Only one reviewed study found
a significant link between food stamp participation
and BMI, overweight, or obesity status for men ages
19-59. That study found that food stamp participation
by men was positively related to BMI but not to
overweight or obesity. Previous studies comparing
average BMI for men across food stamp participation
and income levels found that for some racial and
ethnic groups, food stamp participants had lower
BMI than income-eligible nonparticipants and higher
income men. In view of that, it is possible that
either the positive effect of food stamps on BMI
was not large enough to shift more men into the
overweight (BMI greater than 25) and obese (BMI
greater than 30) categories, or the shift in BMI
was an improvement among underweight men.
Adult (ages 19-59) women are the
only food stamp participants for which multiple
studies show a link between food stamp participation
and overweight. Not all studies showed that participation
affects body weight. However, results from studies
that used different techniques to control for selection
bias indicate that food stamp participation may
increase the probability that a woman is obese.
The estimated 2- to 5-percentage-point change in
the probability of being obese translates into a
5- to 21-percent increase in obesity rates. Other
results show that food stamp participation is associated
with an estimated 0.5-point increase in BMI for
women, or about 3 pounds for a woman between 5’4”
and 5’6” tall.
Over Longer Participation,
Effects May Accumulate
The reviewed studies showed a
stronger connection between long-term food stamp
participation on body weight than short- or medium-term
participation. Two studies found that women who
received food stamp benefits for longer periods
of time (one study defined “long term”
as at least 2 consecutive years, the other as up
to 5 consecutive years) increased the probability
of being obese by 4.5 to 10 percentage points, which
translates into a 20- to 50-percent increase in
obesity rates.
Evidence is mixed with respect
to long-term food stamp participation and men’s
weight. One study found no relationship between
long-term participation (up to 5 consecutive years)
on BMI or the probability of obesity for men. A
second study found that participation for at least
2 consecutive years increased BMI and the probability
of obesity for men, but shorter and repeated participation
did not have these effects.
Most food stamp participants receive
benefits for less than a year—the median length
of food stamp participation is 6 to 8 months. Some
participants, however, cycle on and off food stamps
and others participate for longer periods. It is
possible that small but positive effects of current
food stamp participation on BMI may accumulate over
longer, or shorter but repeated, periods and result
in substantial total effects on BMI over time. Or,
if the causal mechanisms underlying weight gain
for women are related to periods of boom and bust
surrounding the monthly issuance of food stamp benefits,
then prolonged food stamp use could result in long-term
weight gain. Further research may be able to tell
a clearer story.
Implications for the Type
and Timing of Benefits
One hypothesis of how food stamp
participation causes weight gain is that benefit
amounts are too high, causing participants to spend
more money on food and, thus, consume more food
than they otherwise would. One of the reviewed studies
showed that the effect of food stamp participation
on obesity is larger for single women than for women
residing in households with more than one adult.
Other research found that food stamps have little
impact on the amount of money single women spend
on food (i.e., the benefit amount is at least as
big as what they otherwise would have spent on food).
In that case, “cashing out” food stamp
benefits to reduce overconsumption may not have
the intended effect on body weight. The group whose
weight is most affected by food stamp participation
would not change their food spending if the benefits
were shifted to cash.
Some studies measured participation
as a dichotomous yes-or-no condition, while others
looked at the amount of benefits the household received.
Studies that used the amount of benefits to measure
participation found a less consistent relationship
between food stamp benefit levels and obesity as
those that used the dichotomous measure. So, while
some studies suggest a relationship between food
stamp participation and obesity among women in particular,
the research does not clearly indicate that higher
benefit levels are associated with greater BMI and
obesity, or that lower benefits would lead to lower
BMI.
None of the studies reviewed explicitly
tested whether boom-and-bust food consumption patterns
associated with the benefit payment cycle contribute
to obesity. If further studies find a causal link
between the timing of benefits and disrupted patterns
of consumption, possible policy solutions could
include either increasing the frequency of benefit
payments (biweekly or weekly) or raising the benefit
amount, which could, paradoxically, help reduce
obesity by reducing hungry days at the end of the
benefit cycle.
The stronger relationship between
food stamp participation and body weight found for
women but not for men, the mixed relationships found
for young boys and young girls, and the lack of
any relationships found for adolescents make it
difficult to come up with appropriate changes to
the program to address obesity. Most food stamp
benefits go to households that contain a child,
elderly adult, or nonelderly disabled adult. Devising
program changes that are appropriately targeted
to household members who may be at risk of gaining
weight, without harming those who are not, will
be difficult. Nutrition education efforts and other
programs that help improve the overall diets of
all household members may be more effective.
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