BKR TeamGina Segovia-Siapco,1,2 Pramil Singh,3 Karen Jaceldo-Siegl,1,4 and Joan Sabaté 1,3,4
1Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA, USA
2Department of Public Health, School of Graduate Studies, Adventist International Institute of Advanced Studies, P O Box 038, Silang, Cavite 4118. Philippines
3Department of Biostatistics and Epidemiology, School of Public Health, Loma Linda University, Loma Linda, CA, USA
4The Adventist Health Study II, School of Public Health, Loma Linda University, Loma Linda, CA, USA
Modification of dietary habits is an important component in the prevention, management, and treatment of chronic diseases. In large scale community-based intervention trials, the use of more precise methods of dietary assessment such as dietary recalls, food records, or diet histories, can be particularly expensive. Thus, in this study, we developed a 171-item food frequency questionnaire (FFQ) to measure nutrient intake and validated it against six 24-dietary recalls which were collected during the dietary intervention trial. We intended to use this FFQ as a tool to measure dietary intake in future dietary intervention trials of similar nature. The study had two purposes: (1) to determine whether the FFQ we developed provided a valid measure of nutrient intake among the participants of the study, and (2) to examine whether the FFQ can measure the effect of the dietary intervention (in this case, walnut supplementation) in the intake of a specific nutrient that can be considered an excellent dietary intervention nutrient marker.
Eighty seven volunteers from Southern California (48 females and 39 males), aged 30-72 years old, joined the study. They were randomly assigned to either an intervention (walnut-supplemented) or a control diet. The prescribed 6-month dietary intervention was ≥ 28 grams of walnuts per day for the intervention or walnut-supplemented group and ≤ 2grams of walnuts per day for the control group. Participants provided at least six dietary recalls, all of which were unannounced and unscheduled, and had covered most days of the week. At the end of the six-month intervention, the FFQ was self-administered. Although the walnuts were provided free of charge, participants were not given any dietary advice except for the instruction that those in the walnut-supplemented diet were to eat their daily allotted walnuts while those in the control diet should refrain from eating walnuts.
Intake of 32 nutrients were measured from the FFQ and the 24-hr dietary recalls. Significant positive correlations that were corrected for measurement errors were found between the two measures for intake of total energy (r = 0.34), total carbohydrate (r = 0.42), vegetable protein (r = 0.43), total fat (r = 0.51), polyunsaturated fat (r = 0.77), total fiber (r = 0.60), linoleic acid (r = 0.78), and alpha linolenic acid (r = 0.79). Significant positive correlations were also found for vitamin C (r = 0.96), and certain minerals (ranging from 0.46 to 0.80 for calcium, phosphorus, magnesium, iron, and potassium). For some of the nutrients, we were unable to correct for measurements errors, but the correlations were also high (r > 0.40) for retinol, beta-carotene, folate, and alcohol. To determine if the FFQ can measure the effect of dietary intervention, we used a nutrient marker for walnut intake – alpha linolenic acid. Both diet recalls and FFQ showed a similar significant difference in alpha linolenic acid content between the walnut-supplemented and control diets.
Our findings suggest that the FFQ developed in this study demonstrated excellent relative validity compared with dietary recalls in the estimation of intake of some of the major nutrients in a dietary intervention trial. The FFQ also particularly provided a valid estimate of the intake of an important nutrient marker of walnut supplementation, alpha linolenic acid. Further work is needed to determine whether the FFQ can estimate nutrient intake in trials where the intervention diet is complex (such as a diet pattern) and the treatment effect represents a change in macronutrient intake (e.g., change in protein intake).
References:
[1] Gina Segovia-Siapco, Pramil Singh, Karen Jaceldo-Siegl and Joan Sabaté, “Validation of a food-frequency questionnaire for measurement of nutrient intake in a dietary intervention study,” Public Health Nutrition 10 (2007) 177-184.
[2] Sabaté J, Cordero-Macintyre Z, Siapco G, Torabian S, Haddad E. “Does regular walnut consumption lead to weight gain?,” Br J Nutr. 94 (2005) 859-864.
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Dr. Gina Segovia-Siapco is currently ranked as associate professor (of Nutrition) and serving as chair of the Department of Public Health in the School of Graduate Studies at Adventist International Institute of Advanced Studies. She graduated from Loma Linda University School of Public Health in 2004 and a member of the Delta Omega Honorary Society in Public Health. She can be reached by email at gssiapco [@] aiias.edu.