Zinc-Specific Food Frequency Questionnaire

Abstract

Purpose: A new dietary zinc assessment tool (ZAT) was evaluated to determine its usefulness in estimating zinc intakes among college students.

Methods: A food frequency questionnaire specifically designed for calculating average zinc intakes was administered to university students who had also completed three-day food records. Zinc intakes from die two instruments were compared.

Results: Among 171 participants (38 male, 133 female) aged 20.2 �1.6 years (mean � standard deviation), the two dietary assessment methods were positively correlated (r=0.33, p<0.001). The ZAT correctly identified 76% of the women who were obtaining less than the National Academy of Sciences Recommended Dietary Allowance for zinc (8 mg/ day for females, 1 1 mg/ day for males) .

Conclusions: This convenient tool may assist in the identification of problematic dietary patterns at an early stage. Further design modifications and expanded studies are warranted.

(Can J Diet Prac Res 2007;68:150-152)

(DOI: 10.3148/68.3.2007.150)

R�sum�

Objectif. Un nouvel outil d'estimation du zinc alimentaire (ZAT) a �t� �valu� pour d�terminer son utilit� pour estimer les apports en zinc chez des �tudiants d'universit�.

M�thodes. Un questionnaire de fr�quence de consommation alimentaire pr�cis�ment con�u pour calculer les apports moyens en zinc a �t� administr� � des �tudiants d'universit� qui ont aussi rempli des relev�s alimentaires de trois jours. On a compar� les apports en zinc obtenus avec les deux outils.

R�sultats. Chez les 171 participants (38 hommes, 133 femmes) �g�s de 20,2 �1,6 ans (moyenne � �cart-type), les deux m�thodes �taient en corr�lation positive (r=0,33; p<0,001). Le ZAT a d�cel� correctement que 76 % des femmes avaient des apports en zinc inf�rieurs aux apports recommand�s par la National Academy of Sciences (8 mg/jour pour les femmes, 11 mg/jour pour les hommes).

Conclusions. Cet outil commode peut aider � d�celer � un stade pr�coce des profils alimentaires inad�quats. Des modifications � l'outil et d'autres �tudes seraient justifi�es.

(Rev can prat rech di�t�t 2007;68:150-152)

(DOI: 10.3148/68.3.2007.150)

INTRODUCTION

Zinc is required for key enzymatic, structural, and regulatory activities in human physiology (1). Unlike testing for iron, however, testing for marginal zinc deficiency is difficult, if not impossible: serum indicators usually fall only in cases of severe deficiency, after die tightly sequestered zinc pools start to decline (2). Pregnant and non-pregnant women, children, adolescents, vegetarians, and the elderly are at particular risk for zinc deficiency (1,3,4).

Zinc has recendy been associated with leptin expression and secretion (5), and thereby is potentially involved in appetite regulation. Increasingly, zinc intake is being identified as an important factor in the cause and/ or treatment of certain disordered eating patterns (6,7). Bakan and colleagues (8) have reported that approximately 50% of anorexia patients are vegetarians; they recommend that vegetarians be routinely assessed for zinc status.

The richest food sources of zinc are animal muscles, particularly beef, and oysters. Whole (but not refined) cereal grains and legumes contain substantial amounts of zinc. Whenever breakfast cereals are enriched, manufacturers are required to add 3.5 mg of zinc per 100 g (9). Because zinc bioavailability is reduced by phytic acid, zinc intakes of 50% above the Recommended Dietary Allowance (RDA) have been suggested for people consuming mainly plantbased diets (1).

A quick, reliable meuhod is needed to establish zinc intakes and estimate zinc status. The current study was designed to develop, administer, and examine the effectiveness of a semi-quantitative food frequency questionnaire (FFQJ for evaluating zinc intake in university students.

METHODS

The West Chester University Committee for die Protection of Human Subjects approved the study. The zinc-specific FFQ was developed by assembling a list of medium- (1 g per serving) to high-zinc items, as well as basic staples containing a modest amount of zinc (e.g., peanut butter and pizza), which college students commonly consume. Past three-day diet records from introductory nutrition students were examined for any frequently consumed items. Items were then grouped into eight different food categories: grains, beans, fish, dairy products, nuts/seeds, poultry/eggs, meat, and miscellaneous. Within each group, those with similar zinc content were listed together, with their zinc amounts averaged in the final calculation.

The final two-page zinc assessment tool (ZAT) consisted of 33 main items (and additional subcategories for fish/shellfish and breakfast cereals) (Table 1). The five possible choices of consumption frequency "over the past month" were "two to three times a day," "once a day," "two to three times a week," "once a week," or "once or twice a month." "Less than once a month" (i.e., rarely or never) was signified by leaving the item blank, as explained in the directions. A computer program was designed for quick conversion of the ZAT information to average monthly zinc totals.

For initial validation, the ZAT was administered to a group of 20 master's degree students to obtain feedback on its ease of use and readability. It was modified according to suggestions received. Reliability testing was not included in the current study.

Next, undergraduate university students enrolled in introductory nutrition courses were invited to participate in the study. Directions were given for keeping a three-day food record (for two "typical" weekdays and one weekend day) . When the nutrient analysis for the food records was completed (Diet Analysis Plus, version 6.1 for Windows, ESHA Research, Salem, OR, 2004), the 33-item ZAT was administered. Pearson correlations were used to examine the association between zinc intakes estimated with the ZAT and with three-day records (SYSTAT� 10 software program, SPSS Inc., Chicago, IL, 2000).

RESULTS

A total of 171 students (38 male, 133 female) participated in this pilot study (70% participation rate) and completed all records. The average age (� standard deviation) was 20.2 � 1.6 years.

Median zinc intake determined from three-day records was 8.0 mg (men, 1 1.8; women, 7.4); according to the ZAT, the median zinc intake was 11.1 mg (men, 14.6 mg; women, 10.2 mg). Forty-one percent of women and 34% of men had intakes below the Estimated Average Requirement (EAR) for zinc (EAR=9.4 mg for males and 6.8 mg for females) . Zinc intakes from the ZAT were associated with zinc intakes in the three-day records (r=0.33, p<0.001).

When the genders were examined separately, the association between zinc intakes from the three-day records and the ZAT remained statistically significant for the female students (r=0.30, p<0.001), but not for the male students (r=0.21, nonsignificant [NS]). Among the women whose intake was below the zinc RDA on the ZAT (n=44), 76% also had intakes below the RDA for zinc on their three-day records.

DISCUSSION

The 33-item ZAT permitted the identification of a majority of the women whose zinc intakes were below the RDA. The correlation coefficient, r=0.33, indicated a positive, although relatively weak, association between the two tools. In addition to the small sample size in this pilot study, other possible limitations of trying to correlate an FFQ with a three-day food record include the semiquantitative nature of the tool (requiring interpretation of the average portion sizes listed), exclusion of some popular food items on the short questionnaire, and the fact that only one set of three-day diet records was used for comparison.

For both genders, zinc values were consistently higher with die ZAT dian widi die diree-day diet records. Reducing the number of ZAT line items and providing a column for "less than once a month" may decrease the tendency to overestimate food intake.

Unexpectedly, approximately 33% of the male participants were found to have zinc intakes below the EAR. This could reflect a problem in the accurate recording of dietary data (e.g., portion size estimation or recall issues) . However, this finding may indicate that a subgroup of male university students is at risk for zinc inadequacy.

Shatenstein et al. (10) have reported a correlation coefficient of 0.48 (n=94) between the mean zinc intake from four nonconsecutive food records and that from a modified (73-item) version of the Block FFQ for adults living in Quebec. As in the current study, their results were stronger for the female participants. Other investigators have reported zinc correlations from 0.28 to 0.46 for women and 0.37 to 0.44 for men when zinc intakes were compared on multiple (nonconsecutive) food records and FFQs (106-food item Block FFQ, 126-item Willett FFQ and 124 food-item Diet History Questionnaire from the National Cancer Institute) (11).

Dietary zinc estimates from the Willett FFQ were not correlated with serum zinc (r=0.06, NS), and did not permit a ranking of subjects into appropriate quartiles of zinc intake (12). A tool focusing on zinc might more closely represent biochemical measures of zinc status.

RELEVANCE TO PRACTICE

University health professionals, as well as coaches and physical educators, could use diis tool to screen for inadequate zinc intake. Students could complete the ZAT during routine visits or training sessions, and students with very low zinc intakes could be referred to a dietitian for more comprehensive nutritional assessments. Relevant nutrition information could be provided to self-described vegetarians and those with unusual dietary regimens. If symptoms of disordered eating, including anorexia nervosa, were present, the person could be referred for further medical attention and possibly psychological counselling. In a classroom setting, the ZAT could illustrate FFQs and highlight common food sources of this essential micronutrient.

Future research could include an investigation of the ZAT's ability to predict biochemical indicators of zinc deficiency. An expanded validation study could involve a comparison of ZAT intakes with the average zinc intakes obtained from four diree-day records diroughout the month. Finally, testing the ZAT over a wider age range is warranted, as the generalizability of these pilot study results is limited to university students.

[Reference]

References

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[Author Affiliation]

JANET M. LACEY, DrPH, MS, MEd, RD, Program in Nutrition and Dietetics,

West Chester University of Pennsylvania, West Chester, PA