To the Editor: The article by Popkin et al. (Sept. 5, 1996,issue)1 on dietary trends presents a potentially misleadingpicture of fruit and vegetable intake in the United States.The implied serving sizes (grams of dietary intake in Table4 of the article divided by numbers of servings in Table 3)range from 33.7 to 56.9 g (1.2 to 2.0 oz), lower than weightscorresponding to recommended serving sizes (2 to 6 oz). In addition,the reported numbers of servings in Table 3 (4.3 to 4.8 forwhites and 3.9 to 5.4 for blacks) generally exceed and run counterto those previously reported for the same survey (4.4 for whitesand 3.9 for blacks).2 These differences are not easily explainedby the information provided. For national estimates to be valid,sample weights should be used to adjust for nonresponse andfor the different rates of selection.3 It appears that suchweights were used in only one table. Furthermore, it appearsthat the authors did not use specialized software that adjustsfor the clustered nature of the sample in the calculation ofstandard errors.3 Therefore, the standard errors reported maybe too small and result in tests of significance indicatingreal differences when, in fact, the differences might be dueto sampling variation. Finally, the use of a single 24-hourdietary recall to represent the distribution of intake is problematic.Because persons with extreme intakes on the recall day wouldreceive higher or lower scores than their usual intake wouldmerit, the proportions of both persons meeting the recommendationsand those with very poor diets are likely to be overestimatedin Table 2.
The measurement of fruit and vegetable intake is critical formonitoring dietary trends. The numbers of servings given inthe article may represent an overstatement of both actual consumptionand the proportion of the general population with good diets.
Blossom H. Patterson, M.A. Susan M. Krebs-Smith, Ph.D. Amy F.Subar, Ph.D. National Cancer Institute Bethesda, MD 20892-7354
References
Popkin BM, Siega-Riz AM, Haines PS. A comparison of dietary trends among racial and socioeconomic groups in the United States. N Engl J Med 1996;335:716-720. [Free Full Text]
Krebs-Smith SM, Cook A, Subar AF, Cleveland L, Friday J. US adults' fruit and vegetable intakes, 1989 to 1991: a revised baseline for the Healthy People 2000 objective. Am J Public Health 1995;85:1623-1629. [Free Full Text]
Interagency Board for Nutrition Monitoring and Related Research. Nutrition monitoring in the United States: chartbook I: selected findings from the National Nutrition Monitoring and Related Research Program. Washington, D.C.: Government Printing Office, 1993.
The authors reply:
To the Editor: While preparing our response to Patterson andcolleagues, we identified an error in the program that createdthe Diet Quality Index used in our paper. The calculation ofthe overall Diet Quality Index scores was affected by this error,as were the estimates of the numbers of servings of fruits andvegetables and grains and legumes.
The corrected fruit, vegetable, and grain estimates and DietQuality Index scores substantially change our conclusions. Weconcluded that "in 1965, there were large differences amonggroups in dietary quality, with whites of high socioeconomicstatus eating the least healthful diet, as measured by the index,and blacks of low socioeconomic status the most healthful. Bythe 1989–1991 survey, the diets of all groups had improvedand were relatively similar." The corrected results (Table 1)indicate that in 1965 the diets of whites of all socioeconomicgroups and blacks of low socioeconomic status were similar.In 1989–1991, the differences among racial and socioeconomicgroups remained small, except for blacks of high socioeconomicstatus, who had the highest-quality diets.
Table 1. Mean Diet Quality Index Scores and the Distribution of Individual Scores of <4 or >10, According to Socioeconomic Status and Race for Each Survey.
The primary outcome was the score (range, 0 to 16) on the DietQuality Index, a composite of eight food-and-nutrient–basedrecommendations from the National Academy of Sciences. A scoreof 4 or less was considered to indicate a relatively more healthfuldiet, and a value of 10 or more a relatively less healthfuldiet. Our corrected results indicate that in 1965, 2.7 percentof whites of low socioeconomic status, 4.2 percent of blacksof low socioeconomic status, and 2.9 percent of whites of highsocioeconomic status had mean scores of 4 or less. We incorrectlyreported these percentages as 9.3 percent, 16.4 percent, and4.7 percent, respectively. For the 1989–1991 survey, thecorrect percentages are 7.4 for whites of low socioeconomicstatus, 6.0 for blacks of low socioeconomic status, 10.7 forwhites of high socioeconomic status, and 15.5 percent for blacksof high socioeconomic status. We incorrectly reported thesepercentages as 19.9 percent, 23.5 percent, 20.0 percent, and2.7 percent, respectively.
The percentage of respondents with less healthful diets (scoresof 10 or more) increased substantially in all groups after wecorrected our findings (Table 1). Nonetheless, overall dietaryquality still improved in all groups, from a mean index scoreof 8.3 in 1965 to 7.5 in 1989–1991. We incorrectly reportedthese scores as 7.4 and 6.4, respectively.
Corrected values for the number of servings of fruits and vegetablesand grains and legumes are given in Table 2. We previously stated:"The consumption of fruits and vegetables varied little overtime, except for an increase among blacks of medium and highsocioeconomic status." Our corrected results indicate that theconsumption of fruits and vegetables decreased among whitesof middle and high socioeconomic status, decreased slightlyamong blacks of low and middle socioeconomic status, and increasedamong blacks of high socioeconomic status.
Table 2. Intake of Dietary Components According to Socioeconomic Status and Race for Each Survey.
These errors do not affect the results of other studies thatused the Diet Quality Index.1,2 The previous work done usingthe 1987 U.S. Department of Agriculture survey is correct. Inapplying the original Diet Quality Index program from 1987 tothe 1965, 1977–1978, and 1989–1991 Department ofAgriculture survey data, a line of coding was overlooked thatassigned subjects with no intake of fruits, vegetables, grains,or legumes values of zero. Data for such respondents were mistakenlycoded as missing, which caused the errors in our calculationsof the mean numbers of servings for these foods, as well asthe Diet Quality Index scores. The error had less effect onthe results for grains and legumes, since most people consumedsome of these foods daily. Other components of the Diet QualityIndex were not affected by this error.
Barry M. Popkin, Ph.D. Anna Maria Siega-Riz, Ph.D. Pamela S.Haines, Ph.D. University of North Carolina Chapel Hill, NC 27514
References
Patterson RE, Haines PS, Popkin BM. Diet Quality Index: capturing a multidimensional behavior. J Am Diet Assoc 1994;94:57-64. [CrossRef][Medline]
Patterson RE, Haines PS, Popkin BM. Health lifestyle patterns of U.S. adults. Prev Med 1994;23:453-460. [CrossRef][Medline]
To the Editor: The revised analyses and conclusions of Popkinet al. warrant a follow-up on my editorial about the implicationsof their analysis of U.S. dietary trends.1 The error in theiroriginal estimate of fruit and vegetable intakes apparentlydistorted the understanding of dietary trends between 1965 and1989–1991 in two ways. The new finding that is most troublingfrom a public health perspective is that the proportion of thepopulation meeting the guidelines for healthful diets, whichwas less than 25 percent in the original report, was overestimated,because those with the worst diets (in terms of fruit and vegetableintake on the survey day) had been inadvertently excluded. Inthe revised calculations, even though the situation did improvesomewhat over time, the percentages with favorable dietary patternscores were extremely low in all three periods. For example,in the 1989–1991 survey, only 1 in 10 high-income whitesmet the recommended dietary pattern on the day recalled.
Popkin et al. incorrectly reported that as compared with middle-or high-income groups, the least-advantaged populations (peoplewith low incomes and black people) had significantly betterdietary patterns initially and showed relatively less improvementover time. The revised data suggest similar, slightly upwardtrends across all groups in the percentage with favorable dietary-patternscores. This result is more encouraging than the prior indicationthat things were worsening for the poor relative to the richor for blacks relative to whites, but it is surely no causefor celebration. Now all groups are reported to be worse offthan was previously thought. Most important, the desirable pattern— one in which the most disadvantaged would be gainingground faster — has yet to be achieved.
Shiriki Kumanyika, Ph.D., M.P.H. University of Illinois at Chicago Chicago,IL 60612-7256
References
Kumanyika S. Improving our diet -- still a long way to go. N Engl J Med 1996;335:738-740. [Free Full Text]
Strolla, L. O., Gans, K. M., Risica, P. M.
(2006). Using qualitative and quantitative formative research to develop tailored nutrition intervention materials for a diverse low-income audience. Health Educ Res
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Dixon, L. B., Cronin, F. J., Krebs-Smith, S. M.
(2001). Let the Pyramid Guide Your Food Choices: Capturing the Total Diet Concept. J. Nutr.
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Ames, B. N.
(1999). Cancer prevention and diet: Help from single nucleotide polymorphisms. Proc. Natl. Acad. Sci. USA
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Levine, M., Rumsey, S. C., Daruwala, R., Park, J. B., Wang, Y.
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