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School of Public Affairs, Baruch College, City University of New York, New York, NY 10010
3 To whom correspondence should be addressed. E-mail: diane_gibson{at}baruch.cuny.edu.
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ABSTRACT |
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 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • overweight • obesity • food stamps • girls • women
Previous research using longitudinal data has found a positive and significant relationship between Food Stamp Program (FSP)4 participation and overweight in young girls and obesity in low-income women (1,2). This study used longitudinal data on young girls and their mothers from the National Longitudinal Survey of Youth 1979 (NLSY79) to examine whether these relationships occurred simultaneously for members of the same family. This question is of interest given the adverse health consequences of overweight and obesity in children and adults and the fact that households with children make up the majority of households participating in the FSP (3).
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SUBJECTS AND METHODS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Two samples were created from the NLSY79 mother-child data. The first included young daughters, and the second included their mothers. The samples included observations from the 1986 through the 2000 waves of the survey, although data from earlier survey years were used to create income history variables. An observation on a girl was included in the daughter sample in each survey year she was between the ages of 4.5 and 11.5 y and there was current information on her weight and height, mother's weight, family FSP participation, and income. This age range was selected because Gibson (1) found that long-term FSP participation was positively and significantly related to overweight in girls in this age range. The data on daughters were arranged as a panel so that there were multiple observations per daughter, and the unit of analysis was a daughter-year. The final daughter sample contained 8099 observations on 3594 daughters from 2520 families. The mean age of the daughter-year observations in the sample was 7.8 y with a standard deviation of 2.0 y.
An observation on a woman was included in the mother sample in each survey year where she had one or more daughters in the daughter sample. The resulting panel contained multiple observations per mother, and the unit of analysis was a mother-year. The final mother sample contained 6760 observations on 2520 mothers. The mean age of the mother-year observations in the sample was 32.4 y with a standard deviation of 4.3 y.
Conceptual framework. Conceptual models of the weight of individuals that have been used to motivate empirical analyses of the relationship between FSP participation and weight have assumed that an individual's weight is influenced by current and past FSP participation as well as other current and past individual, family, and environment characteristics. These characteristics are assumed to affect the individual's weight directly or indirectly through their influence on health behaviors related to weight or food insecurity (1,2).
For each survey year the weight status of daughters and mothers was categorized using a set of binary outcomes. The outcomes that were considered with the daughter data were daughter overweight, daughter overweight and mother not obese ("daughter-only overweight"), and daughter overweight and mother obese ("daughter-mother overweight"). This set of outcomes will be referred to as the "daughter weight status" outcomes. The outcomes that were considered with the mother data were mother obese, mother obese and no daughters in the daughter sample overweight ("mother-only obese"), and mother obese and at least one daughter in the daughter sample overweight ("mother-daughters obese"). This set of outcomes will be referred to as the "mother weight status" outcomes. The empirical models of weight status followed the conceptual models and controlled for current and past individual, family, and environment characteristics (more details are available elsewhere [1,2]) and did not control for food insecurity. However, the exclusion of food insecurity will be factored into the interpretation of the relationship between FSP participation and the weight status outcomes.
With these models the association between long-term FSP participation and the probability a daughter is overweight (the "overall" association) can be broken into the sum of 2 components, 1 accounting for the association between long-term FSP participation and daughter-only overweight and the other accounting for the association between long-term FSP participation and daughter-mother overweight (the "simultaneous" association). The fraction of the overall association accounted for by the simultaneous association provides an estimate of how much of the relationship between FSP participation and weight can be considered a family as opposed to an individual-only phenomenon. The association between long-term FSP participation and maternal obesity can be broken down in a similar fashion.
Dependent variables. A daughter's weight and height in a survey year were combined to calculate her body mass index (BMI, kg/m2) in that survey year. A daughter was categorized as overweight in a survey year if her BMI was greater than or equal to the 95th percentile of sex- and age-in-months-specific BMIs from the Centers for Disease Control in 2000 (4). Daughter weight and height were mother-reported or measured with a scale and tape measure.
A mother's self-reported weight in a survey year was combined with her self-reported height information from 1985 (the most recent maternal height information available) to calculate her BMI in that survey year. A mother was categorized as obese in a survey year if her BMI was greater than or equal to 30 kg/m2 (5).
Independent variables. All of the empirical models of weight status included long-term FSP participation. This variable measured the percentage of time a family participated in the FSP over the previous 5 calendar years preceding the survey year (hereafter referred to as the "previous 5 years"). The models also included a measure of long-term family resources other than long-term FSP participation. FSP eligibility income was defined as total family income excluding FSP benefits in the calendar year preceding the survey year. The FSP eligibility income-to-needs ratio for a survey year was calculated by dividing the FS eligibility income of a family by the poverty threshold appropriate for the family's size (6). Long-term family resources other than long-term FSP participation was approximated with the mean of the family's FS eligibility income-to-needs ratios over the previous 5 years.
The models of daughter weight status included daughter fixed effects, and the models of mother weight status included mother fixed effects (see Cawley [7] for a detailed discussion of fixed effects models). Other control variables in the models of weight status were the number of children in the family, mother's marital status, mother's employment status, mother's highest grade completed, mother's pregnancy status, region and urbanicity of residence, an indicator for mother-reported daughter weight or height, and indicators for survey year. The models of daughter weight status also included daughter's age in months squared and mother's age in years squared. The models of mother weight status included mother's age in years squared, an indicator variable for a daughter <8 y old, and an indicator variable for a daughter at least 8 y old.
Statistical analysis. The sample of daughters was used to examine differences in the unweighted prevalence of the daughter weight status outcomes among FSP participation categories (using Pearson chi-squared tests and P < 0.05) and to estimate ordinary least squares (OLS) models for each of the daughter weight status outcomes (models 1–3). The sample of mothers was used to examine differences in the unweighted prevalence of the mother weight status outcomes among FSP participation categories (using Pearson chi-squared tests and P < 0.05) and to estimate OLS models for each of the mother weight status outcomes (models 4–6). Statistical analyses were completed with STATA (8).
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RESULTS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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DISCUSSION |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Previous research on food insecurity and weight has also found a positive relationship between mild food insecurity and overweight in women (11–13) and a negative or not significant relationship between food insecurity and overweight in children in a similar age range as the girls in the daughter sample (14,15). Given this previous research, if food insecurity alone were responsible for the relationships between long-term FSP participation and the weight status of daughters and mothers, long-term FSP participation would be expected to be positively related to weight outcomes involving maternal obesity but not daughter overweight. Because long-term FSP participation was not significantly related to mother-only obesity but was positively and significantly related to both daughter-mother overweight and mother-daughters obesity, this suggests that long-term FSP participation was not solely a proxy for food insecurity. However, the possibility still remains that the omission of food insecurity influenced the estimates of the relationships between long-term FSP participation and weight status and that the estimates of the relationship between long-term FSP participation and weight status were biased as a result of reverse causality or selection bias.
Any potential mechanism for the relationship between FSP participation and the weight of daughters and mothers will have to simultaneously influence daughter overweight and maternal obesity. Beyond genetic similarities, explanations for the positive correlation in weight between daughters and mothers include the positive correlation within families in nutrient intakes as well as activity levels (16,17). Previous research has not explored the relationship between FSP participation and activity levels, and estimates of the relationship between FSP participation and nutrient intakes have not been consistent across studies (18). Additional research is needed that considers how the family food or activity environment changes with FSP participation.
The policy implications of these results depend primarily on the currently unknown mechanism for the relationship between FSP participation and the weight of daughters and mothers. However, regardless of the mechanism, the results in this paper provide further support for the use of the FSP as a vehicle for nutrition and health education programs that encourage healthy eating and weight reduction (1,2). The results further suggest that these programs should consider taking a family focus.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 This research was supported by a grant from the PSC-CUNY Research Awards Program.
4 Abbreviations used: BMI, body mass index; FSP, Food Stamp Program; NLSY79, National Longitudinal Survey of Youth 1979; OLS, ordinary least squares.
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LITERATURE CITED |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Gibson D. Long-term food stamp program participation is differentially related to overweight in young girls and boys. J Nutr. 2004;134:372–9.
2. Gibson D. Food stamp program participation is positively related to obesity in low income women. J Nutr. 2003;133:2225–31.
3. U.S. Department of Agriculture, Food and Nutrition Service. Characteristics of food stamp households: fiscal year 2002, 2003. http://www.fns.usda.gov/oane/menu/Published/fsp/FILES/Participation/2002characteristics.pdf (accessed September, 2004).
4. Centers for Disease Control and Prevention, National Center for Health Statistics. CDC growth charts: United States. Advance data number 314, Atlanta: CDC, 2000.
5. U.S. National Institutes of Health, National Heart, Lung and Blood Institute. Clinical guidelines on the identification, evaluation and treatment of overweight and obesity in adults. Washington, D.C.: National Institutes of Health, National Heart, Lung and Blood Institute, 1998.
6. U.S. Department of Health and Human Services. Summary historical figures and Federal Register references for the HHS poverty guidelines since 1982, 2002. http://www.aspe.hhs.gov/poverty/figures-fed-reg.htm (accessed December 12, 2002).
7. Cawley J. The impact of obesity on wages. J Hum Resour. 2004;39:451–75.
8. StataCorp. STATA version 8.0. College Station, TX: Stata Corporation.
9. Frongillo E. Understanding obesity and program participation in the context of poverty and food insecurity. J Nutr. 2003;133:2117–8.
10. Gundersen C, Oliveira V. The food stamp program and food insufficiency. Am J Agric Econ. 2001;83:875–87.
11. Townsend M, Peterson J, Love B, Achterberg C, Murphy S. Food insecurity is positively related to overweight in women. J Nutr. 2001;131:1738–45.
12. Frongillo E, Jr., Olson C, Rauschenbach B, Kendall A. Nutritional consequences of food insecurity in a rural New York State county. Discussion Paper no. 1120–97. Madison, WI: Institute for Research on Poverty, University of Wisconsin, 1997.
13. Sarlio-Lahteenkorva S, Lahelma E. Food insecurity is associated with past and present economic disadvantage and body mass index. J Nutr. 2001;131:2880–4.
14. Jones S, Jahns L, Laraia B, Haughton B. Lower risk of overweight in school-aged food insecure girls who participate in food assistance. Arch Pediatr Adolesc Med. 2003;157:780–4.
15. Bhattacharya J, Currie J, Haider S. Food insecurity or poverty? Measuring need-related dietary adequacy. NBER working paper 9003. Cambridge, MA: National Bureau of Economic Research, 2002.
16. Birch L, Davison K. Family environmental factors influencing the developing behavioral controls of food intake and childhood overweight. Pediatr Clin North Am. 2001;48:893–907.[Medline]
17. Fogelholm M, Nuutinen O, Pasanen M, Myöhänen E, Säätelä T. Parent–child relationship of physical activity patterns and obesity. Int J Obes. 1999;23:1262–8.[Medline]
18. Currie J. U.S. Food and Nutrition Programs. Working Paper. Los Angeles: Department of Economics, University of California at Los Angeles, 2000.
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