European Journal of Clinical Nutrition (2011) 65, 546–552 & 2011 Macmillan Publishers Limited All rights reserved 0954-3007/11 www.nature.com/ejcn ORIGINAL ARTICLE Effect of cooking loss in the assessment of vitamin intake for epidemiological data in Japan M Kobayashi1,2, HY Adachi2, J Ishihara2,3 and S Tsugane2 for the JPHC FFQ Validation Study Group 1Department of Food Science, Faculty of Home Economics, Otsuma Women’s University, Tokyo, Japan; 2Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan and 3Department of Nutrition, Junior College of Tokyo University of Agriculture, Tokyo, Japan Background/Objectives: The effect of cooking loss on vitamin intake is an important consideration in dietary and epidemiological studies in Japanese. However, because few published food values have considered cooking effect, allowing for cooking loss in the assessment of vitamin intake in Japan has been difficult. Subjects/Methods: Seven-day dietary records and a fasting blood sample were collected from 102 men and 113 women in August of 1994 or 1995. Vitamin intake were estimated using two food databases, one composed of raw food only and the second of cooked food. Estimates were compared with blood levels. Results: Water-soluble vitamin intake using a food database including cooked food was lower than intakes estimated using a database composed of raw food only, except for pantothenic acid and vitamin B12 intake. In particular, vitamin B1 intake was 18.9% lower in men and 16.8% lower in women. However, when subjects were classified into the same and adjacent categories by joint classification by quintiles, appreciable change in ranking of a subject was not observed. Furthermore, the relationship between vitamin intake and biomarker did not improve when intake was calculated using a food database including cooked food. Conclusion: Although the effect of cooking loss on absolute values is not negligible, this might not significantly impact the ranking of subject intake estimations of vitamin intake in epidemiological studies. European Journal of Clinical Nutrition (2011) 65, 546–552; doi:10.1038/ejcn.2011.10; published online 23 February 2011 Keywords: cooking loss; vitamin intake assessment; food composition database; epidemiology Introduction Cooking procedures in Japan are diverse and often complicated. Vitamin-rich vegetables are commonly boiled, Dietary evaluation methods have an important role in stewed or stir-fried. The Japan Public Health Center- epidemiological study of the relationship between dietary based (JPHC) Prospective study, for example, a large-scale habits and the risk of lifestyle-related diseases. Evaluation of population-based prospective study, reported that the most dietary assessment requires the evaluation of factors, which frequent method for cooking vegetables among 22 528 men may impact that assessment. One of the most important and 25 310 women was stir-frying (39.4% in men, 38.4% in factors is the effect of different cooking procedures women), followed by boiling or stewing (35.5% in men, on nutrient changes in food: because the vitamin and 29.0% in women) (Tsugane et al., 2001). The effect of mineral content values of foods are influenced by cooking cooking loss on vitamin intake in Japanese is considerable. procedures, accurate evaluation of nutrient intake is The revised and enlarged fifth edition of the standard hampered when the nutrient content values of raw food tables of food composition in Japan (FCT5) (The Council of are used. Science and Technology Agency Ministry of Education, 2005) added the composition of cooked foods. However, only 247 foods were included, hampering the consideration Correspondence: Dr M Kobayashi, Department of Food Science, Faculty of of cooking loss in the assessment of vitamin intake in Home Economics, Otsuma Women’s University, 12, Sanban-cho, chiyoda-ku, Japan. In response, a more detailed food composition Tokyo 102-8357, Japan. table was recently developed with a wider range of foods E-mail: [email protected] Received 19 March 2011; accepted 9 January 2011; published online 23 for which cooking loss should be considered (Wakiyama February 2011 et al., 2009). Effect of cooking loss on vitamin intake M Kobayashi et al 547 Here, we used this updated food database to calculate and a second, which included cooked food also (FDB_cook). vitamin intake and evaluate the effect of cooking procedures Calculations for the former were done using values for raw in comparison with intake calculated using the raw food- foods in FCT5, and for the latter using values for foods, only data in FCT5. In addition, we also compared estimated including cooked foods, in a recently developed food vitamin intake with biological indicators, such as serum database. This database is a compensated database, which carotenoid and plasma vitamin C, B6,B12 and folate considers cooking loss, and has been described in detail concentrations. elsewhere (Wakiyama et al., 2009). In brief, the cooking methods considered were boiling, grilling, deep- and stir- frying, steaming, kippering, or pickling. The quantity of Subjects and methods cooking loss for each food was calculated as follows: = Subjects NC ac ¼ðNC bc fct5 NC ac fct5ÞÂNC bc Subjects were a subsample of participants in the JPHC where study, an ongoing cohort study of 140 420 participants in 11 NC_ac: nutrient composition of the target food after prefectural public health center areas investigating cancer, cooking. cardiovascular disease and other lifestyle-related diseases NC_ac_fct5: nutrient composition of a related food (Watanabe et al., 2001). A total of 247 volunteers were after cooking as described in FCT5. recruited from the Ninohe, Yokote, Saku and Chubu NC_bc: nutrient composition of the target food in (previously named Ishikawa) public health center areas for a its raw state as described in FCT5. validation study of a food frequency questionnaire (Tsubono NC_bc_fct5: nutrient composition of a related food et al., 1996). For the present report, we analyzed the data of as described in FCT5. 215 subjects (102 men and 113 women) who provided complete 7-day dietary records (DRs). Of these 215 subjects, For example, pork ham (grilled) ¼ (pork loin (grilled)/pork 191 (90 men and 101 women) provided a blood sample. loin (raw))  pork ham (raw). Where necessary, substitute foods with similar botanical or zoological relevance were used. For foods having no Data collection reference in the FCT5, we used a food composition table of The data was collected as part of the validation study of the the United States Department of Agriculture and performed food frequency questionnaire used to assess dietary intake of a similar calculation as when using FCT5. Weight changes of the main cohort. Details of the study design and data foods after cooking were calculated using the table of weight collection have been described elsewhere (Tsugane et al., change rate in the FCT5 (The Council of Science and 2003). In brief, subjects completed DRs for 7 consecutive Technology Agency Ministry of Education, 2005). Nutrient days in August 1994 (Ninohe, Yokote and Saku) or August intakes were then calculated using weight change rate and 1995 (Chubu). Local dietitians instructed the subjects to nutrient composition values after cooking. weigh all foods and beverages with the scales and measuring utensils provided, and to record the results in a specially designed booklet. The subjects were instructed to use Statistical analysis standardized portion sizes for some foods that were difficult Vitamin intakes (retinol, a-carotene, b-carotene, lycopene, to weigh (semi-weighed DRs). The subjects described each vitamin D, vitamin E, vitamin K, vitamin B1, vitamin B2, food, method of cooking preparation and names of dishes in niacin, vitamin B6, vitamin B12, folate, pantothenic acid and detail. The DRs were reviewed in a standardized manner, and vitamin C) were calculated using these two databases for all foods described in a DR were coded as raw food by local each subject. Nutrient losses were estimated by subtracting dietitians. the values calculated with FDB_cook from those calculated Peripheral blood was collected just after the summer with FDB_raw, and the differences were tested by the paired session. Plasma and serum samples were stored in separate t-test. tubes at À80 1C until analysis. Serum carotenoid concentra- Estimated intakes of vitamin C, a-carotene, b-carotene, tions were measured for men and women, while plasma lycopene, vitamin B6, vitamin B12 and folate were adjusted vitamin B6,B12 and folate were measured for men only. for total energy intake using the residual model (Willett and Measurement of blood levels of carotene, ascorbic acid, Stampfer, 1986), and the subjects were classified into the folate, vitamin B6 and vitamin B12 were as described same and adjacent categories by joint classification by previously (Iso et al., 2003; Kobayashi et al., 2003). quintiles. Spearman’s rank correlation coefficient was used to assess the associations between vitamin intakes estimated from FDB_cook and FDB_raw. Calculation of nutrient intake Further, vitamin intakes estimated from FDB_cook We created two databases, one to calculate nutrient intake and FDB_raw were compared with their serum/plasma con- using a food database composed of raw food only (FDB_raw), centrations using Spearman’s rank correlation coefficient. European Journal of Clinical Nutrition Effect of cooking loss on vitamin