ArticleEuropean journal of nutrition2026
Accounting for culinary practices to improve FFQ-based vitamin C estimates in epidemiological studies: a cross-sectional analysis.
Article in European journal of nutrition, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
purposeConventional vitamin C intake estimations via food frequency questionnaires (FFQ) typically ignore cooking techniques, which can significantly alter nutrient content. This study evaluates the effect of incorporating a home cooking frequency questionnaire (HCFQ) alongside a FFQ to calculate vitamin C intake and its impact on adherence to dietary recommendations.
methodsWe conducted a cross-sectional analysis in the PREDIMAR study, a randomized trial that aims to evaluate the effect of a Mediterranean diet supplemented with extra virgin olive oil on atrial fibrillation recurrence after ablation. Vitamin C intake was estimated in two ways: derived from (1) raw food using a FFQ and the Spanish food composition tables, and (2) from raw and cooked food using a FFQ+HCFQ. Adherence to estimated average requirements and a recommended intake of 200 mg/day were used to assess nutritional adequacy. Paired t-Test compared vitamin C mean intakes derived from both methods, and paired McNemar tests assessed differences in adequacy rates.
resultsAmong 447 patients (25.1% female; mean age = 59.7 years (10.1)), mean vitamin C intake (SD) was significantly higher when derived solely from the FFQ (173.7 mg/day (71.2)) vs. FFQ+HCFQ (160.1 mg/day (68.8); p < 0.001). The largest decreases of vitamin C, when cooking techniques were considered, were observed in legumes (- 88.0%), tubers (- 62.7%), and vegetables (- 12.5%). The main source of between-person variability in vitamin C intake from vegetables and tubers was raw vegetables and boiled potatoes, respectively. Adequacy of vitamin C intake significantly dropped using FFQ+HCFQ (21.5%) vs. FFQ alone (30.4%, p < 0.001).
conclusionsIgnoring cooking methods may lead to overestimation by approximately 8% of both vitamin C intake and adequacy prevalence in epidemiologic research. Incorporating a cooking-frequency questionnaire yields more conservative and potentially accurate estimates, improving nutritional epidemiology precision.
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