==== Front JAMA Netw Open JAMA Netw Open JAMA Network Open 2574-3805 American Medical Association 36961468 10.1001/jamanetworkopen.2023.4680 zld230029 Research Research Letter Online Only Oncology Association of Dietary Fiber Intake With Gastrointestinal Tract Cancer Among Korean Adults Association of Dietary Fiber Intake With Gastrointestinal Tract Cancer in Korea Association of Dietary Fiber Intake With Gastrointestinal Tract Cancer in Korea Jun Shinyoung PhD 1 Lee Jeonghee MS 1 Kim Jeongseon PhD 2 1 Department of Cancer Biomedical Science, National Cancer Center Graduate School of Cancer Science and Policy, Goyang-si, Republic of Korea 2 Department of Cancer, AI & Digital Health, National Cancer Center Graduate School of Cancer Science and Policy, Goyang-si, Republic of Korea Article Information Accepted for Publication: February 8, 2023. Published: March 24, 2023. doi:10.1001/jamanetworkopen.2023.4680 Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2023 Jun S et al. JAMA Network Open. Corresponding Author: Jeongseon Kim, PhD, Department of Cancer, AI & Digital Health, National Cancer Center Graduate School of Cancer Science and Policy, 323 Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do 10408, Republic of Korea (jskim@ncc.re.kr). Author Contributions: Drs Jun and Kim had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: Jun. Acquisition, analysis, or interpretation of data: All authors. Drafting of the manuscript: Jun. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: Jun, Lee. Obtained funding: Jun, Kim. Administrative, technical, or material support: Kim. Supervision: Kim. Conflict of Interest Disclosures: Dr. Jun reported receiving grant funding from the National Research Foundation of Korea during the conduct of study. Dr. Kim reported receiving grant funding from the National Research Foundation of Korea during the conduct of study. No other disclosures were reported. Funding/Support: This work was supported by grant 2021R1A6A3A01087058 from the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education. Role of the Funder/Sponsor: The sponsor had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. Data Sharing Statement: See Supplement 2. 24 3 2023 3 2023 24 3 2023 6 3 e2346804 10 2022 8 2 2023 Copyright 2023 Jun S et al. JAMA Network Open. https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the CC-BY License. jamanetwopen-e234680.pdf This cohort study assesses the association between dietary fiber intake and incident gastrointestinal tract cancer among Korean adults. ==== Body pmcIntroduction Epidemiological studies have suggested a beneficial effect of dietary fiber on gastrointestinal tract cancers (GICs).1,2 In particular, the World Cancer Research Fund–American Institute for Cancer Research has recognized and promoted dietary fiber as a protective factor against colorectal cancer.3 However, most prospective studies on dietary fiber and GICs have been conducted in North America and Europe.1,3 Little is known about the association of dietary fiber with incident GIC among Koreans, although food sources of fiber and their health effects may differ across cultures and locations. The burden of GICs (ie, cancers of the esophagus, stomach, liver, pancreas, gallbladder, colon, rectum, and anus) in Korea is substantial, accounting for 36% of all cancer cases.4 Therefore, we assessed the association between dietary fiber intake and incident GIC among Korean adults. Methods The Cancer Screenee Cohort recruited participants attending check-ups at the National Cancer Center Korea (NCC).5 We linked data from the Korea Central Cancer Registry and the NCC electronic medical records to identify GIC cases diagnosed from January 1, 1988, through December 31, 2019. Of 11 086 adults 20 years and older who enrolled between October 16, 2007, and December 31, 2018, we excluded 1840 who developed any cancer other than GIC, who were diagnosed with GIC within a year after enrollment, or who had implausible energy intake, or missing body mass index or physical activity information. The analysis was performed from August 1, 2022 to February 1, 2023. This cohort study was approved by the Institutional Review Board of the NCC and followed the STROBE–Nutritional Epidemiology reporting guideline. Written informed consent was obtained from all study participants. Habitual dietary intake was measured via a validated 106-item food frequency questionnaire.6 Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs for GIC or gastric cancer events comparing participants with dietary fiber intake at or above vs less than the median. Model 1 included age, sex, and total energy intake. Model 2 additionally included obesity, smoking, alcohol consumption, physical activity, comorbidity, and red and processed meat intake. A detailed description of the study design and methods can be found in the eMethods in Supplement 1. All analyses were conducted using SAS, version 9.4 (SAS Institute Inc). Two-sided P < .05 indicated statistical significance. Results Among 9246 participants, the mean (SD) age was 52.5 (8.2) years; 5901 (63.8%) were women and 3345 (36.2%) were men (Table 1). After a median follow-up of 7.8 (IQR, 1.0-12.2) years (70 605 person-years), 163 incident GIC cases were identified. Higher intake of total dietary fiber (ie, ≥ 17.8 g/d) was associated with lower GIC incidence in model 1 (HR, 0.61 [95% CI, 0.41-0.91]) and model 2 (HR, 0.63 [95% CI, 0.42-0.93]) (Table 2). An association of total dietary fiber intake and gastric cancer was also observed (model 2 HR, 0.42 [95% CI, 0.22-0.81]). Associations of dietary fiber intake from different food sources (ie, grains, vegetables, and fruits) with GIC risks were in the protective direction but not statistically significant. Table 1. Baseline Characteristics by Dietary Fiber Intake Among Participants of the Cancer Screenee Cohorta Characteristic All participants (N = 9246) Dietary fiber intake group P valueb Below median (n = 4623) At or above median (n = 4623) Follow-up, median (range), y 7.8 (1.0-12.2) 7.6 (1.0-12.2) 8.3 (1.0-12.2) NA Age, mean (SD), y 52.5 (8.2) 52.0 (8.2) 52.9 (8.1) <.001 Sex Men 3345 (36.2) 1670 (36.1) 1675 (36.2) .92 Women 5901 (63.8) 2953 (63.9) 2948 (63.8) BMI <25 6532 (70.6) 3330 (72.0) 3202 (69.3) .004 ≥25 2714 (29.4) 1293 (28.0) 1421 (30.7) Currently smoking 1338 (14.5) 680 (14.7) 658 (14.2) .52 Alcohol consumption None 3918 (42.4) 1923 (41.6) 1995 (43.2) .02 Moderate 4377 (47.3) 2251 (48.7) 2126 (46.0) Heavy 951 (10.3) 449 (9.7) 502 (10.9) Physical activity, MET-min/wk <600 2632 (28.5) 1480 (32.0) 1152 (24.9) <.001 ≥600 to <3000 4015 (43.4) 2038 (44.1) 1977 (42.8) ≥3000 2599 (28.1) 1105 (23.9) 1494 (32.3) Comorbidity (any history of diabetes, heart disease, and stroke) 767 (8.3) 383 (8.3) 384 (8.3) .97 Total energy intake, mean (SD), kcal/d 1651.2 (540.1) 1343.4 (351.9) 1979.0 (507.4) <.001 Dietary fiber intake, mean (SD), g/d Total fiber 19.7 (9.4) 12.8 (3.2) 26.5 (8.5) <.001 Fiber from grains 4.1 (1.9) 3.6 (1.4) 4.7 (2.1) <.001 Fiber from vegetables 8.6 (5.5) 5.1 (2.2) 12.0 (5.7) <.001 Fiber from fruits 2.7 (3.0) 1.5 (1.4) 3.9 (3.7) <.001 Red and processed meat intake, mean (SD), g/d 50.6 (46.6) 38.8 (32.6) 62.4 (54.7) <.001 Folate intake, mean (SD), μg/d 486.6 (237.7) 322.9 (92.9) 650.2 (225.5) <.001 Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); MET, metabolic equivalent of task; NA, not applicable. a Unless otherwise indicated, data are expressed as No. (%) of participants. Percentages have been rounded and may not total 100. b Differences by dietary fiber intake were tested using the χ2 test for categorical variables and the Wilcoxon rank sum test for continuous variables. Table 2. The Association Between Dietary Fiber Intake and Gastrointestinal Tract Cancer Among Participants of the Cancer Screenee Cohort Dietary fiber intakea Gastrointestinal tract cancer Gastric cancerb Model 1c Model 2d Model 1c Model 2d No. of cases/total No. of participants 163/9246 163/9246 62/9145 62/9145 Intake, HR (95% CI) Total fiber 0.61 (0.41-0.91) 0.63 (0.42-0.93) 0.41 (0.21-0.79) 0.42 (0.22-0.81) Fiber from grains 0.88 (0.61-1.28) 0.87 (0.60-1.27) 0.77 (0.42-1.39) 0.76 (0.42-1.38) Fiber from vegetables 0.76 (0.54-1.07) 0.75 (0.54-1.06) 0.76 (0.44-1.33) 0.75 (0.43-1.31) Fiber from fruits 0.74 (0.53-1.03) 0.78 (0.55-1.08) 0.76 (0. 45-1.30) 0.82 (0.48-1.41) Abbreviation: HR, hazard ratio. a Intake is compared between participants at or above vs below the median. The median intake values for total dietary fiber was 17.8 g/d; for dietary fiber from grains, 3.9 g/d; for dietary fiber from vegetables, 7.5 g/d; and for dietary fiber from fruits, 1.7 g/d. b Participants who developed gastrointestinal tract cancer other than gastric cancer were excluded (n = 101) when the outcome was gastric cancer, the most common type of gastrointestinal tract cancer in Korea. c Included age, sex, and total energy intake. d Included obesity (body mass index [calculated as weight in kilograms divided by height in meters squared] <25 and ≥25), smoking (smoker and nonsmoker), alcohol consumption (heavy, moderate, and none), physical activity (<600, ≥600 to <3000, and ≥3000 metabolic equivalent of task–min/wk), comorbidity (any history of diabetes, heart disease, and stroke), and red and processed meat intake (≥38.1 vs <38.1 g/d [median]) in addition to covariates in the model 1. Discussion Among Korean adults, dietary fiber intake at or above the median was associated with reduced risk of GIC and gastric cancer, the most common GIC type in Korea.4 Our findings are generally aligned with previous findings from other geographical locations1 and support recommending higher dietary fiber intake for GIC prevention in Korea. Although the Cancer Screenee Cohort provides a rare opportunity to investigate the prospective association between diet and cancer among Koreans, the relatively small sample size and short follow-up precluded analyses of specific GIC types or the application of dietary fiber cutoffs other than the median. Larger studies are needed to validate the protective effect of dietary fiber on GIC or specific GIC types. Supplement 1. eMethods. Study Population, Design, and Analyses eReferences Click here for additional data file. Supplement 2. Data Sharing Statement Click here for additional data file. ==== Refs References 1 Veronese N, Solmi M, Caruso MG, . Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses. Am J Clin Nutr. 2018;107 (3 ):436-444. doi:10.1093/ajcn/nqx082 29566200 2 Capuano E. The behavior of dietary fiber in the gastrointestinal tract determines its physiological effect. Crit Rev Food Sci Nutr. 2017;57 (16 ):3543-3564. doi:10.1080/10408398.2016.1180501 27229126 3 World Health Research Fund/American Institute for Cancer Research. Diet, nutrition, physical activity and colorectal cancer: Continuous Update Project Expert Report. World Cancer Research Fund–American Institute for Cancer Research. Revised 2018. Accessed September 10, 2022. https://www.wcrf.org/wp-content/uploads/2021/02/Colorectal-cancer-report.pdf 4 Kang MJ, Won YJ, Lee JJ, ; Community of Population-Based Regional Cancer Registries. Cancer statistics in Korea: incidence, mortality, survival, and prevalence in 2019. Cancer Res Treat. 2022;54 (2 ):330-344. doi:10.4143/crt.2022.128 35313102 5 Kim J. Cancer screenee cohort study of the National Cancer Center in South Korea. Epidemiol Health. 2014;36 :e2014013. doi:10.4178/epih/e2014013 25119453 6 Ahn Y, Kwon E, Shim JE, . Validation and reproducibility of food frequency questionnaire for Korean genome epidemiologic study. Eur J Clin Nutr. 2007;61 (12 ):1435-1441. doi:10.1038/sj.ejcn.1602657 17299477