doi: 10.1377/hlthff.2009.0666 HEALTH AFFAIRS 29, NO. 3 (2010): 398 404 2010 Project HOPE The People-to-People Helth Foundtion, Inc. By Crmen Pierns nd Brry M. Popkin Trends In Sncking Among U.S. Children Crmen Pierns is predoctorl student t the Crolin Popultion Center, University of North Crolin t Chpel Hill. Brry M. Popkin (popkin@ unc.edu) is professor of nutrition t the Crolin Popultion Center nd director of the Interdisciplinry Center for Obesity, University of North Crolin. ABSTRACT Ntionlly representtive surveys of food intke in U.S. children show lrge increses in sncking between the 1989 91 to 1994 98 nd 1994 98 to 2003 06 periods. Childhood sncking trends re moving towrd three sncks per dy, nd more thn 27 percent of children s dily clories re coming from sncks. The lrgest increses hve been in slty sncks nd cndy. Desserts nd sweetened beverges remin the mjor sources of clories from sncks. There hs been little systemtic exmintion of recent eting ptterns nd longer-term trends, including those for childhood sncking. The rise of childhood obesity coincides with reported increse in dily sncking nd decline in the consumption of three principl mels. Popultion-bsed studies show incresed food consumption relted to the sncking hbit. 1,2 More frequent sncking hs been positively ssocited with body weight in children. 1 Other epidemiologicl nd intervention studies in children nd dolescents hve linked more even distribution of food consumed throughout the dy with lower body mss index (BMI). 1,3,4 Most cross-sectionl studies, fter djusting for body weight, hve found tht obese children do not et more thn len children. 5 Sncks re redily vilble to ll children nd dolescents in severl environments, 6 nd energy-dense sncks hve been linked with decresed stiting (feeling of fullness) effect 7,8 Greter intke of slty sncks nd sweetened cloric beverges nd incresed portion sizes of sncks hve been observed s potentil contributors to dily food consumption. 9,10 Consequently, these my ply n importnt role in childhood obesity. This study is focused on more recent dynmics of sncking in ll of its dimensions. In this study, current sncking ptterns nd key foods consumed during childhood were exmined long with long-term trends in sncking behvior cross four ntionlly representtive surveys of food intke in U.S. children over the pst three decdes. Among our most importnt findings is n increse in the number of sncking events in the pst decde. The lrgest increses in sncking events hve been in slty snck nd cndy consumption; however, desserts nd sweetened beverges remin the mjor sources of clories from sncks. Study Dt And Methods SURVEY DESIGN AND SAMPLE We selected 31,337 children nd dolescents, ges 2 18, from four ntionlly representtive surveys of food intke in the U.S. popultion: 12,231 respondents from the 1977 1978 Ntionwide Food Consumption Survey (NFCS77); 3,148 from the 1989 1991 Continuing Survey of Food Intke by Individuls (CSFII89); 8,621 from the 1994 1996, 1998 Continuing Survey of Food Intke by Individuls (CSFII98); nd 7,337 from the joint U.S. Deprtment of Agriculture (USDA) Ntionl Helth nd Nutrition Exmintion Surveys (NHANES03 06). More detils re presented elsewhere. 11 13 It is importnt to note tht the methodology used in NHANES is bsed on erlier CSFII methodologies. This is the first set of surveys tht fully integrted the USDA nd NHANES dietry dt 398 HEALTH AFFAIRS MARCH 2010 29:3
collection systems. 14 The USDA Food Composition tbles nd methods of coding nd probing were used. DIETARY RECORDS Dietry intke in the NFCS nd in the CSFII89 ws collected over three consecutive dys using single interviewer-dministered twenty-four-hour recll. The CSFII98 consisted of interviewer-dministered twentyfour-hour reclls on two nonconsecutive dys (three to ten dys prt). NHANES03 06 ws bsed on two nonconsecutive dys of twentyfour-hour dietry recll dt (the dy-one interview ws conducted by trined dietry interviewers in the Mobile Exmintion Center, nd the dy two interview ws conducted by telephone three to ten dys fter the first interview). For children younger thn ge twelve, informtion ws obtined from the child s cregiver. For comprbility, only the first two dys of dietry intke from ech survey re included. SNACK CONSUMPTION Sncks nd mels were self-defined in ech survey, s ws the time when ech eting occsion begn; they re comprble with second publiction on dults. 15 We combined snck events consumed in fifteen-minute period s single sncking occsion. Subjects who hd sncks on ny dy were deemed snckers. Contributions to dily intke in subjects who sncked on both dys were verged. A lrge number of people reported consuming snck food t mel (for exmple, chips with lunch). We chnged these reports of sncking to mel if food consumed during mel ws defined s snck food. In the NFCS77, the CSFII89 91, nd the CSFII94 98, we found eting occsions defined s other or no nswer. If child ws not reported to hve hd three mels, those missing occsions were recoded s mels ccording to the eting time. The remining missing eting occsions were considered s sncks. We estblished three principl mels, if possible, nd then we studied the sncking behvior outside them, in ll yers surveyed. Our pproch represents conservtive definition of sncking. FOOD GROUPING SYSTEM The University of North Crolin Chpel Hill pproch begins with USDA food groupings nd breks them down into more detiled food groupings in systemtic method. 16 We hve linked ll foods from ech of the USDA surveys together so tht comprble food compositions, Ltin binomil nmes, nd nutrient compositions re used for ech food, becuse mjor chnges in numbering nd mesurement qulity hve occurred over time. The food grouping system hs been described elsewhere. 17 The mount of energy provided by ech food group for ll individuls ws clculted nd then divided by the totl energy from sncking. Food groupings contributing the most to sncking clories re reported. Consumption of wter s beverge ws collected differently cross the surveys. Plin wter ws dded s food item in 2003, ccounting for up to 5 percent of ll reported foods in 2003 06 versus 0 percent in ll the other previous surveys. To ensure comprbility, wter s food item ws deleted in ll yers. STATISTICAL ANALYSIS Individuls were strtified by ge: ges 2 6, ges 7 12, nd ges 13 18. Differences testing, by student s t-test (which llows the use of smll number of mesurements to estimte wht my be true of the whole popultion), used STATA, version 10, type of dt nlysis nd sttisticl softwre, to weight the results nd control stndrd errors for smple design effects. We used survey commnds to ccount for survey design, weighting, nd clustering. A p (probbility) vlue of 0.01 ws set for sttisticl significnce. (A p vlue of less thn 0.05 is considered sttisticlly significnt tht is, not likely to be due to chnce lone.) Study Results CHARACTERISTICS OF SNACKERS The percentges of children consuming sncks by sociodemogrphic chrcteristics were lwys higher thn 97 percent for ech ctegory in 2003 06. We identified mles, non-hispnic whites, with high household income level (greter thn 350 percent of the federl poverty level) nd eduction (high school diplom or higher) s the ctegories with slightly higher percentges of snckers (unreported results). DYNAMIC CHANGES IN SNACKING BEHAVIOR Dily sncking mong children hs incresed mrkedly over the periods studied (Exhibit 1). The prevlence of snckers mong ll children (ges 2 18) incresed from 74 percent in 1977 78 to 98 percent in 2003 06. Mjor increses were observed from 1989 to 1994 nd from 1994 to 2006.We found smll differences in percentges of sncking mong the ge groups for ech survey. INCREASES IN SNACKING HABITS OVER TIME Significnt chnges in sncking behvior were observed for ll children from 1977 78 to 2003 06 (round 1.11 more sncks per dy). Children ges 2 6 ccounted for the highest number of sncks per dy nd the lrgest increment from 1977 to 2006 (pproximtely 1.41 events more). The ltest increment in number of sncks per dy hs been linked with smll decline in clories per sncking event; however, the incresed energy per snck from 1977 to 2006 ws still significnt. Grms consumed per snck event incresed significntly from 1977 to 2003 in ll ge groups MARCH 2010 29:3 HEALTH AFFAIRS 399
EXHIBIT 1 Percentge Of U.S. Children Consuming Sncks Over A Two-Dy Period, Selected Yers 1977 2006 Percent SOURCE Content bsed on uthors ssessments. NOTE Percentge of children consuming sncks on dy 1 of interview, dy 2 of interview, or both. (round 50 grms more per snck). The chnges in grms consumed per snck from 1994 to 2003 were not significnt except for children ges 13 18 (round 76 grms more). Regrding the totl energy intke coming from sncks, we observed tht ll children consumed pproximtely 168 more clories dy from sncking from 1977 to 2006 (Appendix Exhibit 1). 18 From 1977 78 to 2003 05, the percentge of sncking clories incresed to 27 percent in ll children (Exhibit 2). Regrding dily energy intke, children incresed their cloric intke by 113 clories per dy from 1977 to 2006. The lrgest increse ws found mong children ges 2 6, who consumed 182 clories more per dy. TRENDS IN ENERGY DENSITY AND FOOD SOURCES Within ech ge group, sncking energy density mintined its trends over the periods covered (Exhibit 3). For children ges 7 12 nd 13 18, the energy density of beverges from sncks nd mels showed significnt decresed trend over the periods studied. Importnt shifts in the mjor sncking sources from 1977 to 2006 re shown in Exhibit 4. Although consumption of desserts decresed in 2003 06, they remined the min contributors to sncking clories in 2006. The second min source of sncking energy ws slty sncks, which experienced the lrgest increse in the pst three decdes. Consumption of cndy nd fruit drinks lso incresed over the periods covered. We observed n importnt shift from higher intke of fresh fruit in 1977 to more frequent consumption of fruit juice in 2006. Consumption of sweetened beverges showed little chnge over this period but ws found to be the third-highest contributor to sncking energy in 2006. Discussion This study hs documented importnt increses in sncking behvior cross ll child ge groups during the pst three decdes. Children in the United Sttes, especilly the young, re consuming lmost three sncks per dy, nd sncking ccounted for up to 27 percent of children s dily cloric intke in 2006. Our results showed mjor rises in sncking prevlence nd cloric intke from 1989 91 to 1994 98 nd gin from 1994 98 to 2003 06. Importnt shifts towrd consuming more slty sncks nd cndy hve been reported, lthough sweetened beverges nd desserts remined the mjor sncking sources. Previous studies in children nd young dults found tht the contribution of sncking to the totl energy intke ccounted for up to 25 percent nd 23 percent, respectively, in 1996. 19,20 400 HEALTH AFFAIRS MARCH 2010 29:3
EXHIBIT 2 Contribution Of Sncking To Totl Dily Energy Intke, By Yer And Age Group, Selected Yers 1977 2006 b Energy from sncks Energy from mels b, b b Kiloclories per dy SOURCE Content bsed on uthors ssessments. NOTES Red brs represent the percentge of energy from sncks. Stndrd errors for the totl kiloclories for sncking re found in Appendix Exhibit 1, s in Note 18 in text. Significnt differences in sncking kiloclories from the previous yer (student s t-test;p < 0:01). b Significnt differences in sncking kiloclories between 1977 78 nd 2003 06 (student s t-test;p < 0:01). These studies lso reported n incresed trend in the totl clories coming from sncks nd in the totl number of sncking occsions. Our results re consistent with trends from previous reserch, except for the importnt jump in sncking behvior in this decde. ENERGY DENSITY Some importnt key issues relted to the energy intke showed interesting trends over the yers studied. First, the energy density of sncks ws constnt over the yers studied. Other findings in young dults reported n incresing trend until 1996. 20 Additionl components of the incresed energy intke from sncking re the grms nd clories consumed per snck event. 21 We found incresed portion sizes of sncks in terms of grms; however, becuse of the incresed intke of cloric beverges, there ws smll decrese in clories per snck from 1994 98 to 2003 06, consistent with erlier studies. 22 However, without further reserch, it is uncler whether this most recent period represents shift towrd lower portion sizes, or just the combintion of more smller sncks nd more cloric beverges overll. Furthermore, there is miniml evidence on the helth effects of these sncking chnges. 23,24 This study found meningful increse in the intke of energy-dense slty sncks nd cndy s sources of sncking energy. Also, children re consuming more beverges, such s fruit drinks, sport drinks, nd fruit juice, while decresing fruit s sncking source. Desserts remined the mjor sncking source, consistent with previous work. 20 However, the smller, less representtive Boglus Hert Study found decresing grms consumed from fruit juices nd fruit, desserts, nd cndy from 1973 to 1994 in tenyer-olds. 25 INCONSISTENT DEFINITIONS These results my differ becuse snck nd mel definitions hve not been clerly estblished. In our study, we defined sncks s eting occsions outside mels. Foods defined s snck foods but consumed with mel were recoded s mels.we lso combined ll snck food consumed within fifteen minutes s one sncking event. A smll proportion of food with missing designtions of eting occsions were ssigned first to mels, nd the remining were considered s sncks (there ws smll effect of shift in prevlence of less thn tenth of deciml plce). This conservtive definition llowed us to define three principl mels MARCH 2010 29:3 HEALTH AFFAIRS 401
EXHIBIT 3 Trends In Energy Density Of Mels And Sncking Occsions In U.S. Children Ages 2 18, Selected Yers 1977 2006 Energy density (kcl/grm) Age group/eting occsion 1977 78 1989 91 1994 96 2003 06 Ages 2 6 Totl sncking 1.34 1.59 b 1.34 c 1.28 c Totl mels 1.15 1.15 1.15 1.17 Sncking food 2.76 2.86 2.55 b,c 2.54 b,c Mel food 1.91 1.90 1.90 1.96 Sncking beverges 0.48 0.47 0.48 0.47 Mel beverges 0.49 0.48 0.48 0.49 Ages 7 12 Totl sncking 1.42 1.56 1.48 1.42 Totl mels 1.21 1.22 1.20 1.25 b,d Sncking food 2.78 2.68 2.78 2.79 Mel food 1.93 1.99 2.02 b 2.09 b,c,d Sncking beverges 0.47 0.42 b 0.43 b 0.42 b Mel beverges 0.50 0.48 b 0.46 b 0.45 b,c Ages 13 18 Totl sncking 1.28 1.30 1.23 1.32 Totl mels 1.20 1.20 1.18 1.21 Sncking food 2.84 3.00 2.87 2.96 Mel food 1.96 2.07 b 2.05 b 2.16 b,c,d Sncking beverges 0.43 0.40 b 0.40 b 0.40 b Mel beverges 0.46 0.42 b 0.41 b 0.40 b Ages 2 18 Totl sncking 1.34 1.49 b 1.35 c 1.34 c Totl mels 1.19 1.19 1.18 1.21 b,d Sncking food 2.80 2.83 2.73 2.78 Mel food 1.94 1.99 b 1.99 b 2.08 b,c,d Sncking beverges 0.46 0.43 b 0.44 b 0.43 b Mel beverges 0.48 0.46 b 0.45 b 0.44 b,c,d SOURCE Content bsed on uthors ssessments. Totl sncking nd totl mels combine food plus beverges. b Significntly different from 1977 78 (student s t-test,p < 0:01). c Significntly different from 1989 91 (student s t-test,p < 0:01). d Significntly different from 1994 96 (student s t-test,p < 0:01). nd then study sncking outside of mels for ll yers surveyed. Different reserchers hve defined sncks ccording to the nme identified by the respondent, time of dy, or type of food. Sncking foods hve even been counted s single eting occsions within unique time intervl. 26 28 Although there is no current consensus bout definitions, our pproch my be more linked to the wy we understnd the metbolic consequences of foods eten together t one short period occsion. DAYS OF SNACKING SURVEYED Dys of intke surveyed my lso be influencing disprities between studies. To be consistent, we used two dys of intke to crete comprble mesurements over time. This llowed us to hve closer pproximtion of usul intke. Further, we found tht the third dy of sncking dt for the two erlier studies ws different from the other dys nd probbly represented underestimtes of sncking. The NFCS78 nd CSFII89 reported tht only 4 percent of subjects hd sncks on dy three, nd this lst dy is suspected to be gretly underreported. 19 OTHER LIMITATIONS Other limittions inherent in this study re relted to the use of different surveys. Chnges in surveys from the 1980s to the 1990s hve been importnt, lthough subsequent chnges in the number of psses nd probes hve been much smller. As with ll USDA surveys, the NHANES03 06 methodology is the sme s tht of the CSFII developed by the USDA, since the surveys were merged with the USDA tking the led on the diet component. 14 This ws the reson for dding the second dy of dietry record for NHANES beginning in 2003. Unfortuntely, no bridging study between the 1980s nd 1990s nor between the 1990 nd 2003 2006 survey methods exists, s ws undertken erlier by the USDA. 29 The University of North Crolin Chpel Hill food grouping system developed by this tem ws used to link different foods coded nd collected in the first survey with the foods consumed in the lst peri- 402 HEALTH AFFAIRS MARCH 2010 29:3
EXHIBIT 4 Proportion Of Sncking Clories From Food Groupings In U.S. Children Ages 2 18, Selected Yers 1977 2006 Fruit drinks Sports drinks Fruit juice Fresh fruit High-ft milk Low-ft milk High-ft diry Low-ft diry High ft Low ft High ft Low ft Cndy Nuts nd seeds Redy-to-et cerel Percent of dily energy from sncks SOURCE: Content bsed on uthors ssessments. NOTES The University of North Crolin Chpel Hill food grouping system ws used to select the min food groupings. Desserts include ckes, cookies, pies, brs, ice crem, nd geltin desserts. Slty sncks include crckers, chips, popcorn, nd pretzels. High-ft desserts nd slty sncks were defined s those with more thn 5 grms of ft per 100 grms of food. ods, ensuring consistently high-qulity estimtes of nutrient vlues over time. 16 CONCLUSION Our findings suggest tht children ges 2 18 re experiencing importnt increses in sncking behvior nd re moving towrd consumption pttern of three mels plus three sncks per dy. This rises the question of whether the physiologicl bsis for eting is becoming dysregulted, s our children re moving towrd constnt eting. Finncil support for this pper ws provided by the Ntionl Institutes of Helth. NOTES 1 Nickls TA, Yng SJ, Brnowski T, Zkeri I, Berenson G. Eting ptterns nd obesity in children: the Boglus Hert Study. Am J Prev Med. 2003;25(1):9 16. 2 Nielsen SJ, Sieg-Riz AM, Popkin BM. Trends in energy intke in U.S. between 1977 nd 1996: similr shifts seen cross ge groups. Obes Res. 2002;10(5):370 8. 3 Nickls TA, Morles M, Linres A, Yng SJ, Brnowski T, De Moor C, et l. Children s mel ptterns hve chnged over 21-yer period: the Boglus Hert Study. J Am Diet Assoc. 2004;104(5):753 61. 4 Summerbell CD, Moody RC, Shnks J, Stock MJ, Geissler C. Reltionship between feeding pttern nd body mss index in 220 free-living people in four ge groups. Eur J Clin Nutr. 1996;50(8):513 9. 5 Rocndio AM, Ansotegui L, Arroyo M. Comprison of dietry intke mong overweight nd non-overweight schoolchildren. Int J Obes Relt Metb Disord. 2001;25(11): 1651 5. 6 Butler D, Person H. Dietry dvice: flsh in the pn? Nture. 2005;433 (7028):794 6. 7 Flood J, Roe L, Rolls B. The effect of incresed beverge portion size on energy intke t mel. J Am Diet Assoc. 2006;106(12):1984 90. 8 Rolls BJ, Roe LS, Meengs JS. Reductions in portion size nd energy density of foods re dditive nd led to sustined decreses in energy intke. Am J Clin Nutr. 2006;83 (1):11 7. 9 Tholin S, Lindroos A, Tynelius P, Akerstedt T, Stunkrd AJ, Bulik CM, et l. Prevlence of night eting in obese nd nonobese twins. Obesity (Silver Spring). 2009;17(5):1050 5. 10 Stunkrd AJ, Allison KC, O Rerdon JP. The night eting syndrome: progress report. Appetite. 2005;45 (2):182 6. 11 Rizek R. The 1977 78 Ntionwide MARCH 2010 29:3 HEALTH AFFAIRS 403
Food Consumption Survey. Fm Econ Rev. 1978;4:3 7. 12 U.S. Deprtment of Agriculture, Beltsville Humn Nutrition Reserch Center, Food Surveys Reserch Group. The Continuing Survey of Food Intkes by Individuls (CSFII) nd the Diet nd Helth Knowledge Survey (DHKS) 1989 91 (survey documenttion) [Internet]. Beltsville (MD): USDA; [cited 2010 Feb 10]. Avilble from: http://www.rs.usd.gov/services/docs.htm? docid=7797 13 U.S. Deprtment of Agriculture, Beltsville Humn Nutrition Reserch Center, Food Surveys Reserch Group. Wht we et in Americ, NHANES 2003 2004. Beltsville (MD): USDA; 2003. 14 Moshfegh AJ. The Ntionl Nutrition Monitoring nd Relted Reserch Progrm: progress nd ctivities. J Nutr. 1994;124(9 Suppl): 1843S 5S. 15 Pierns C, Popkin B. Sncking trends in U.S. dults between 1977 nd 2006. J Nutr. Forthcoming. 16 Popkin B, Hines P, Sieg-Riz A. Dietry ptterns nd trends in the United Sttes: the UNC-CH pproch. Appetite. 1999;32(1):8 14. 17 Duffey K, Gordon-Lrsen P, Jcobs D, Steffen L, Vn Horn L, Popkin BM. Differences in dietry ptterns ccount for differentil metbolic syndrome risk mong consumers of diet beverges: the CARDIA Study. Unpublished pper; 2008. 18 The Appendix Exhibits re vilble by clicking on the Appendix Exhibits link in the box to the right of the rticle online. 19 Jhns L, Sieg-Riz AM, Popkin BM. The incresing prevlence of sncking mong U.S. children from 1977 to 1996. J Peditr. 2001;138 (4):493 8. 20 Zizz C, Sieg-Riz AM, Popkin BM. Significnt increse in young dults sncking between 1977 1978 nd 1994 1996 represents cuse for concern! Prev Med. 2001;32 (4):303 10. 21 Schwrtz MB, Novk SA, Fiore SS. The impct of removing sncks of low nutritionl vlue from middle schools. Helth Educ Behv. 2009 Dec; 36(6):999 1011. 22 Smicikls-Wright H, Mitchell DC, Mickle SJ, Goldmn JD, Cook A. Foods commonly eten in the United Sttes, 1989 1991 nd 1994 1996: re portion sizes chnging? J Am Diet Assoc. 2003;103(1):41 7. 23 McGrw SA, Stone EJ, Osgnin SK, Elder JP, Perry CL, Johnson CC, et l. Design of process evlution within the Child nd Adolescent Tril for Crdiovsculr Helth (CATCH). Helth Educ Q. 1994;Suppl 2:S5 26. 24 Troino RP, Flegl KM. Overweight children nd dolescents: description, epidemiology, nd demogrphics. Peditr. 1998;101(3 Pt 2): 497 504. 25 Jgo R, Brnowski T, Wtson K, Brnowski JC, Nickls T, Zkeri IF. Reltionships between mternl nd child crdiovsculr risk fctors ethnic differences nd lck of influence of physicl ctivity. Arch Peditr Adoles Med. 2004;158 (12):1125 31. 26 Knt AK, Grubrd BI. Seculr trends in ptterns of self-reported food consumption of dult Americns: NHANES 1971 1975 to NHANES 1999 2002. Am J Clin Nutr. 2006;84(5):1215 23. 27 Howrth NC, Hung TT, Roberts SB, Lin BH, McCrory MA. Eting ptterns nd dietry composition in reltion to BMI in younger nd older dults. Int J Obes (Lond). 2007;31 (4):675 84. 28 Summerbell CD, Moody RC, Shnks J, Stock MJ, Geissler C. Sources of energy from mels versus sncks in 220 people in four ge groups. Eur J Clin Nutr. 1995;49(1):33 41. 29 Guenther PMBBP, Vizoli TL Jr. Seprting fct from rtifct in chnges in nutrient intke over time. J Am Diet Assoc. 1994;94:270 5. 404 HEALTH AFFAIRS MARCH 2010 29:3