Case Control Study
Copyright ©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Apr 14, 2017; 23(14): 2527-2538
Published online Apr 14, 2017. doi: 10.3748/wjg.v23.i14.2527
Colors of vegetables and fruits and the risks of colorectal cancer
Jeeyoo Lee, Aesun Shin, Jae Hwan Oh, Jeongseon Kim
Jeeyoo Lee, Aesun Shin, Department of Preventive Medicine, Seoul National University College of Medicine, Seoul 03080, South Korea
Jae Hwan Oh, Center for Colorectal Cancer, National Cancer Center, Goyang-si 10408, South Korea
Jeongseon Kim, Molecular Epidemiology Branch, Division of Cancer Epidemiology and Prevention, Research Institute, National Cancer Center, Goyang-si 10408, South Korea
Author contributions: Shin A and Kim J contributed equally to this manuscript, and considered to be the co-corresponding authors; Lee J performed the statistical analysis and drafted the manuscript; Shin A and Kim J advised the statistical analysis and helped to draft the manuscript; Shin A, Oh JH and Kim J conceived of the study and reviewed, guided, and edited the manuscript; all authors approved the final manuscript.
Supported by the National Research Foundation of Korea, No. 2010-0010276 and No. 2013R1A1A2A10008260; and the National Cancer Center, Korea, No. 0910220 and No. 1210141.
Institutional review board statement: The study protocol was approved by the Institutional Review Board of the National Cancer Center (IRB No. NCCNCS-10-350 and NCC2015-0202).
Informed consent statement: All patients gave informed consent.
Conflict-of-interest statement: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Data sharing statement: Technical appendix, statistical code, and dataset available from the corresponding author at shinaesun@snu.ac.kr and jskim@ncc.re.kr.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Jeongseon Kim, PhD, Molecular Epidemiology Branch, Division of Cancer Epidemiology and Prevention, Research Institute, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang-si 10408, South Korea. jskim@ncc.re.kr
Telephone: +82-31-9202570 Fax: +82-31-9202579
Received: November 17, 2016
Peer-review started: November 18, 2016
First decision: January 10, 2017
Revised: February 20, 2017
Accepted: March 20, 2017
Article in press: March 20, 2017
Published online: April 14, 2017

Abstract
AIM

To investigate the relationship between the colors of vegetables and fruits and the risk of colorectal cancer in Korea.

METHODS

A case-control study was conducted with 923 colorectal cancer patients and 1846 controls recruited from the National Cancer Center in Korea. We classified vegetables and fruits into four groups according to the color of their edible parts (e.g., green, orange/yellow, red/purple and white). Vegetable and fruit intake level was classified by sex-specific tertile of the control group. Logistic regression models were used for estimating the odds ratios (OR) and their 95% confidence intervals (CI).

RESULTS

High total intake of vegetables and fruits was strongly associated with a reduced risk of colorectal cancer in women (OR = 0.32, 95%CI: 0.21-0.48 for highest vs lowest tertile) and a similar inverse association was observed for men (OR = 0.60, 95%CI: 0.45-0.79). In the analysis of color groups, adjusted ORs (95%CI) comparing the highest to the lowest of the vegetables and fruits intake were 0.49 (0.36-0.65) for green, and 0.47 (0.35-0.63) for white vegetables and fruits in men. An inverse association was also found in women for green, red/purple and white vegetables and fruits. However, in men, orange/yellow vegetables and fruits (citrus fruits, carrot, pumpkin, peach, persimmon, ginger) intake was linked to an increased risk of colorectal cancer (OR = 1.61, 95%CI: 1.22-2.12).

CONCLUSION

Vegetables and fruits intake from various color groups may protect against colorectal cancer.

Key Words: Vegetable and fruits, Colorectal cancer, Korea

Core tip: Although many studies have focused on the associations between vegetable and fruit intake and health, few studies have classified vegetables and fruits by their colors, which reflect their unique contents of phytochemicals and micronutrients. In the current study, most color groups of vegetables and fruits showed protective benefits against colorectal cancer regardless of the anatomical subsites.



INTRODUCTION

Vegetables and fruits contain nutrients such as vitamins, minerals, folate, dietary fiber, plant sterols, carotenoids and various phytochemicals[1,2] . These nutrients may reduce mortality and prevent chronic diseases, including various cancers, cardiovascular diseases and even mental illnesses, through their antitumor activity as well as their anti-obesity, antioxidant and anti-inflammatory agents[1,3-7].

According to the latest research on the prevention of colorectal cancer from the Continuous update project of the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR), which was published in 2011, non-starchy vegetables and fruits have been evaluated as a “limited-suggestive” preventive factor[8]. A recent meta-analysis of 15 cohort studies of vegetable and fruit intake and the risk of colorectal cancer found that there was a small (8%) reduction and a nonlinear inverse association between colorectal cancer risk and the intake of vegetables and fruits[9]. The relationship between cruciferous vegetables, citrus fruits, brassica vegetables, leafy vegetables, root vegetables and total vegetables and fruits consumption were not consistent[10-15].

Phytochemicals from vegetables and fruits contain many colorful and dark pigments, such as flavonoid and polyphenols, and may be distinguished (in terms of their various physiological effects and actions) by their specific colors. A previous study suggested classifying vegetables and fruits according to their nutritional phytochemicals when providing guidelines for the public[16]. Pennington and Fish have classified 9 color groupings of vegetable and fruit subgroups based on a consideration their unique nutritional values, features and potential correlations[17,18].

There have been studies of vegetable and fruit classification, by color, for stroke[19], coronary heart disease[20], and colorectal cancer[15]. Our present case-control study, therefore, explored the association between vegetables and fruits color groups and colorectal cancer risk in the Korean population.

MATERIALS AND METHODS
Study subjects

The colorectal cancer cases were recruited from the Center for Colorectal Cancer of the National Cancer Center in Korea between August 2010 and August 2013. Among 1427 eligible patients, 1070 agreed to participate in the study. Colorectal cancer cases with incomplete semi-quantitative food frequency questionnaire (SQFFQ) data (145 cases) and those with implausible energy intakes below 500 Kcal/d or above 4000 Kcal/d (2 cases) were excluded. Controls were persons who received health screenings provided by the National Health Insurance Corporation between October 2007 and December 2014 at the same institute. Among 14201 potential control participants, individuals with incomplete SQFFQ (n = 5044) and with implausible energy intakes (n = 120) were excluded. Patients and eligible controls were matched in a 1:2 ratio according to their sex and 5 year age groups. Ultimately, there were 923 cases and 1846 controls whose data were used in the final analysis. All the participants provided written informed consent, and this study’s protocol was approved by the Institutional review board of the National Cancer Center (IRB No. NCCNCS-10-350 and No. NCC 2015-0202).

Data collection

A trained dietitian performed questionnaire surveys through face-to-face interviews. Information on general characteristics, family history of cancer, alcohol consumption, cigarette smoking, and exercise habits was obtained using a structured questionnaires. Dietary information was assessed using the semi-quantitative food frequency questionnaire (SQFFQ) developed by the Korea Centers for Disease Control and Prevention[21]. The SQFFQ was designed to measure typical food intake habits during the course of one year. The reliability and validity of this questionnaire have been previously reported[21]. Subjects were queried by a trained dietitian on their usual intake amount of 106 food items during the last 12 mo before the interview. Daily vegetable and fruit intake and calorie intake were calculated using the Nutritional Analysis Program for Professionals ver. 4.0 (CAN-Pro 4.0 the Korean Nutrition Society, 2012, Seoul, Korea). Vegetables and fruits were classified into 4 color groups according to Pennington and Fish’s[17,18] categories (e.g., green, orange/yellow, red/purple and white) (Table 1). On the basis of outcomes form the Food Balance Wheels (Ministry of Health and Welfare, Dietary Reference Intakes for Koreans, 2015), potatoes and sweet potatoes, which have high starch content, were not included as vegetables. Additionally, we did not include kimchi, pickled vegetables and jam as vegetables and fruits, because of their high salt and sugar content. And the fruit juice beverages were included in the analysis. We have performed an analysis according to the anatomical location of the origin of cancer: proximal colon (cecum, ascending colon, hepatic flexure, transverse colon, splenic flexure); distal colon (descending colon, sigmoid-descending colon junction, sigmoid colon); and rectum (rectosigmoid colon, rectum).

Table 1 Classification of vegetables and fruits according to type and color group1.
Color groupVegetables and fruits typeVegetables and fruits item
Green (23.2%)2Dark green leafy vegetables (27.1%)3Water dropwort, mugwort, crown daisy, spinach, perilla leaf, chicory, kale, pumpkin leaf, leak beet
Lettuces (10.6%)Lettuce
Other green fruits and vegetables (62.3%)Melon, zucchini, green cucumber, green pepper, cabbages, broccoli, celery
Orange/yellow (17.5%)Citrus fruits (57.5%)Citrus fruits juices, orange, mandarin orange, kumquat
Other orange/yellow fruits and vegetables (42.5%)Carrot, pumpkin, peach, persimmon, ginger
Red/purple (19.0%)Berries (38.3%)Strawberry , grape
Other red fruits and vegetables (61.7%)Watermelon, tomato, red cabbage, red pepper, plum
White (40.3%)Allium family bulbs (15.1%)Garlic, leek, onion
Hard fruits (41.8%)Apple, pear
Cauliflower (13.4%)Asian radish
Other white fruits and vegetables (29.7%)Oriental melon, mushroom, banana, deodeok, burdock, lotus root, balloon flower root
Statistical analysis

Chi-square tests were used to compare the distribution of general characteristics and health related behavior factors among cases and controls. Intake levels of vegetables and fruits were categorized into sex-specific tertiles according to the distribution among control groups. The potential confounding variable considered were age, education, alcohol consumption, regular exercise, body mass index (BMI), fiber intake, red meat consumption, processed meat consumption, and energy intake, all of which were selected based on the literature[9,13,22-24]. After considering multi-collinearity, we finally adjusted age, education level, alcohol consumption, BMI, regular exercise, red meat consumption, processed meat consumption, and total energy intake by residual methods. Nutrient intakes were adjusted for total individual energy intakes using the residual method[25]. Binary and polytomous logistic regression models were used to assess the ORs and their 95%CIs for the association between the colors of the vegetables and fruits consumed and the risk of colorectal cancer. All statistical analyses were performed using SAS software (version 9.4; SAS Institute Inc. Cary, NC, United States).

RESULTS

The characteristics of the study subjects are presented in Table 2. Male colorectal cancer patients showed differences compared to controls in marital status, education level, household income, obesity, smoking status, alcohol consumption and regular exercise. The female subjects showed a similar pattern, but the cancer patients had a higher percentage of obese individuals and current smokers.

Table 2 General characteristics of the study subjects n (%).
VariableMale (n = 1875)
P value1Female (n = 894)
P value1
CaseControlCaseControl
(n = 625)(n = 1250)(n = 298)(n = 596)
Age group (yr)0.9970.994
-49128 (20.5)258 (20.6)82 (27.5)166 (27.9)
50-59227 (36.3)453 (36.2)111 (37.3)221 (37.1)
60+270 (43.2)539 (43.1)105 (35.2)209 (35.1)
Missing0 (0.0)0 (0.0)0 (0.0)0 (0.0)
Marital status< 0.001< 0.001
Married557 (89.1)1162 (93.0)216 (73.0)493 (83.4)
Single66 (10.6)72 (5.8)80 (27.0)98 (16.6)
Missing2 (0.3)16 (1.3)2 (0.7)5 (0.8)
Education level< 0.001< 0.001
Under middle school183 (29.3)175 (14.0)138 (46.3)106 (18.1)
High school266 (42.6)329 (26.3)103 (34.6)258 (44.0)
College or more176 (28.2)712 (57.0)57 (19.1)223 (38.0)
Missing0 (0.0)34 (2.7)0 (0.0)9 (1.5)
Income (10000won/mo)< 0.001< 0.001
< 200222 (35.5)254 (20.3)99 (33.2)134 (25.0)
200-400253 (40.5)534 (42.7)134 (45.0)218 (40.7)
> 400150 (24.0)363 (29.0)65 (21.8)184 (34.3)
Missing0 (0.0)99 (7.9)0 (0.0)60 (10.1)
Body mass index (kg/m2)< 0.0010.270
< 25432 (69.1)734 (58.7)207 (69.5)435 (73.0)
≥ 25192 (30.7)516 (41.3)91 (30.5)161 (27.0)
Missing1 (0.2)0 (0.0)0 (0.0)0 (0.0)
Smoking status0.076< 0.001
Non-smoker145 (23.2)245 (19.6)264 (88.6)571 (95.8)
Ex-smoker303 (48.5)671 (53.7)15 (5.0)16 (2.7)
Current smoker177 (28.3)334 (26.7)19 (6.4)9 (1.5)
Missing0 (0.0)0 (0.0)0 (0.0)0 (0.0)
Alcohol consumption< 0.0010.186
Non-drinker107 (17.1)199 (15.9)172 (57.7)362 (60.7)
Ex-drinker103 (16.5)136 (10.9)26 (8.7)33 (5.5)
Current drinker415 (66.4)915 (73.2)100 (33.6)201 (33.7)
Missing0 (0.0)0 (0.0)0 (0.0)0 (0.0)
Regular exercise< 0.001< 0.001
No387 (61.9)490 (39.2)225 (75.5)262 (44.0)
Yes238 (38.1)715 (57.2)73 (24.5)333 (56.0)
Missing0 (0.0)45 (3.6)0 (0.0)1 (0.2)
Family history of cancer0.0020.141
No392 (62.7)686 (54.9)171 (57.4)311 (52.2)
Yes233 (37.3)560 (44.8)127 (42.6)285 (47.8)
Missing0 (0.0)4 (0.3)0 (0.0)0 (0.0)
Family history of colorectal cancer< 0.0010.926
No560 (89.6)1188 (95.0)277 (93.0)555 (93.1)
Yes65 (10.4)58 (4.6)21 (7.1)41 (6.9)
Missing0 (0.0)4 (0.3)0 (0.0)0 (0.0)

Table 3 presents consumption of vegetables and fruits for the cases and controls, separated by sex. Total energy intake was higher among controls in both sexes; thus, the energy adjusted average intake levels of vegetables and fruits were compared. Among cancer cases, consumption of total vegetables and fruits, vegetables, fruits, color group vegetables and fruits and even red meat was lower than controls.

Table 3 Intake of vegetables and fruits between cases and controls.
Total energy adjusted intake (g/d), mean ± SDMale (n = 1875)
Female (n = 894)
Case (n = 625)Control (n = 1250)Case (n = 298)Control (n = 596)
Total energy intake (kcal/d)2127.7 ± 509.11731.6 ± 545.81814.4 ± 523.51604.6 ± 577.4
Total vegetables and fruits279.4 ± 155.7350.2 ± 236.7343.1 ± 192.8470.7 ± 383.4
Total vegetables148.5 ± 77.3186.7 ± 126.2155.8 ± 85.4205.3 ± 138.2
Total fruits125.0 ± 115.3174.5 ± 197.8185.9 ± 152.1271.7 ± 230.0
Green vegetables and fruits64.8 ± 38.086.2 ± 69.672.7 ± 52.1105.5 ± 84.5
Orange/yellow vegetables and fruits49.4 ± 45.454.2 ± 66.875.4 ± 71.295.2 ± 97.7
Orange/yellow vegetable10.1 ± 12.19.3 ± 17.013.0 ± 16.311.7 ± 23.1
Orange/yellow fruits37.7 ± 46.257.0 ± 109.165.0 ± 84.794.7 ± 117.0
White vegetables and fruits105.9 ± 65.4149.8 ± 120.4128.8 ± 100.3186.2 ± 135.0
Red/purple vegetables and fruits55.2 ± 65.966.1 ± 88.866.0 ± 62.689.1 ± 89.8
Red meat56.0 ± 36.264.4 ± 41.940.9 ± 26.943.7 ± 28.7
Processed meat0.5 ± 1.83.5 ± 25.11.9 ± 13.81.7 ± 6.1

Table 4 shows the ORs and the 95%CIs for the colors of the vegetables and fruits consumed and the risks of colorectal cancer. After adjustments for the confounding variables, we found that higher intake of total vegetables and fruits (OR = 0.60, 95%CI: 0.45-0.79, highest vs lowest tertiles); vegetables (OR = 0.48, 95%CI: 0.36-0.64); green vegetables and fruits (OR = 0.49, 95%CI: 0.36-0.65); and white vegetables and fruits (OR = 0.47, 95%CI: 0.35-0.63) reduced the risks of colorectal cancer for men. However, for orange/yellow vegetables and fruits, a significant association with the risks of colorectal cancer was found (OR = 1.61, 95%CI: 1.22-2.12). In women, all categories of vegetables and fruits intake showed decreased risk of colorectal cancer (OR = 0.32, 95%CI: 0.21-0.48 for total vegetables and fruits; OR = 0.37, 95%CI: 0.24-0.57 for vegetables; OR = 0.41, 95%CI: 0.27-0.63 for fruits; OR = 0.25, 95%CI: 0.16-0.40 for green vegetables and fruits; OR = 0.66, 95%CI: 0.44-0.99 for red/purple vegetables and fruits; OR = 0.34, 95%CI: 0.22-0.52 for white vegetables and fruits).

Table 4 Odds ratios and 95% confidence intervals for colorectal cancer risk in relation to intake of vegetables and fruits.
Total energy adjusted vegetables and fruits intakeMale (n = 1875)
Female (n = 894)
Total (n = 2769)
ControlsAge-adjustedMultivariateControlsAge-adjustedMultivariateControlsAge-adjustedMultivariate
/cases (n)OR (95%CI)OR1 (95%CI)/cases (n)OR (95%CI)OR1 (95%CI)/cases (n)OR (95%CI)OR1 (95%CI)
Total vegetables and fruits (g/d)
T1 (< 224.2)417/2751.001.00T1 (< 317.7)199/1661.001.00616/4411.001.00
T2 (224.2-< 380.0)416/2300.83 (0.67-1.04)0.94 (0.74-1.21)T2 (317.7- < 534.8)199/910.55 (0.39-0.75)0.60 (0.42-0.85)615//3210.72 (0.60-0.87)0.81 (0.67-0.99)
T3 (≥ 380.0)417/1200.43 (0.34-0.56)0.60 (0.45-0.79)T3 (≥ 534.8)198/410.25 (0.17-0.37)0.32 (0.21-0.48)615/1610.36 (0.29-0.45)0.50 (0.40-0.63)
P for trend2< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001
Total vegetables (g/d)
T1 (< 123.0)416/2561.001.00T1 (< 135.9)198/1431.001.00614/3991.001.00
T2 (123.0-< 203.6)418/2701.05 (0.84-1.30)1.19 (0.93-1.52)T2 (135.9- < 219.1)200/1100.76 (0.55-1.04)0.89 (0.62-1.26)618/3800.94 (0.79-1.13)1.05 (0.86-1.28)
T3 (≥ 203.6)416/990.38 (0.29-0.50)0.48 (0.36-0.64)T3 (≥ 219.1)198/450.31 (0.21-0.46)0.37 (0.24-0.57)614/1140.36 (0.29-0.45)0.43 (0.34-0.55)
P for trend< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001
Total fruits (g/d)
T1 (< 68.3)416/2241.001.00T1 (< 135.0)198/1291.001.00614/3531.001.00
T2 (68.3-< 178.1)418/2651.18 (0.94-1.47)1.36 (1.06-1.74)T2 (135.0- < 307.1)199/1240.96 (0.70-1.31)1.03 (0.73-1.46)617/3891.09 (0.91-1.31)1.21 (1.00-1.48)
T3 (≥ 178.1)416/1360.61 (0.47-0.78)0.77 (0.58-1.02)T3 (≥ 307.1)199/450.35 (0.23-0.51)0.41 (0.27-0.63)615/1810.51 (0.41-0.63)0.67 (0.53-0.84)
P for trend< 0.0010.017< 0.001< 0.001< 0.001< 0.001
Green vegetables and fruits (g/d)
T1 (< 48.8)417/2381.001.00T1 (< 61.0)199/1511.001.00616/3891.001.00
T2 (48.8-< 93.6)417/2801.17 (0.94-1.46)1.21 (0.94-1.54)T2 (61.0-< 114.2)198/1150.76 (0.56-1.04)0.89 (0.63-1.27)615/3951.01 (0.84-1.21)1.06 (0.87-1.30)
T3 (≥ 93.6)416/1070.45 (0.34-0.58)0.49 (0.36-0.65)T3 (≥ 114.2)199/320.21 (0.14-0.32)0.25 (0.16-0.40)615/1390.35 (0.28-0.44)0.39 (0.31-0.50)
P for trend< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001
Red/purple vegetables and fruits (g/d)
T1 (< 22.1)416/1911.001.00T1 (< 39.5)199/1121.001.00615/3031.001.00
T2 (22.1- < 62.2)417/2661.39 (1.10-1.75)1.63 (1.26-2.11)T2 (39.5-< 98.5)199/1211.08 (0.78-1.49)1.21 (0.84-1.73)616/3871.27 (1.06-1.54)1.46 (1.19-1.79)
T3 (≥ 62.2)417/1680.88 (0.68-1.12)1.10 (0.83-1.44)T3 (≥ 98.5)198/650.58 (0.41-0.84)0.66 (0.44-0.99)615/2330.77 (0.63-0.94)0.96 (0.77-1.20)
P for trend0.0420.7060.0020.027< 0.0010.033
Orange /yellow vegetables and fruits (g/d)
T1 (< 21.1)416/1621.001.00T1 (< 40.7)199/891.001.00615/2511.001.00
T2 (21.1- < 54.0)417/2641.63 (1.28-2.07)1.91 (1.47-2.49)T2 (40.7- < 100.6)198/1401.58 (1.14-2.20)1.77 (1.23-2.56)615/4041.61 (1.33-1.95)1.78 (1.45-2.20)
T3 (≥ 54.0)417/1991.23 (0.96-1.58)1.61 (1.22-2.12)T3 (≥ 100.6)199/690.77 (0.53-1.12)0.85 (0.56-1.27)616/2681.07 (0.87-1.31)1.33 (1.06-1.66)
P for trend0.6180.0210.0510.1630.2860.576
Orange /yellow fruits (g/d)
T1 (< 15.9)416/2301.001.00T1 (< 32.5)199/1051.001.00615/3351.001.00
T2 (15.9- < 47.9)417/2301.00 (0.79-1.25)1.17 (0.91-1.51)T2 (32.5- < 90.6)198/1301.24 (0.90-1.72)1.43 (1.00-2.06)616/3601.07 (0.89-1.29)1.20 (0.98-1.47)
T3 (≥ 47.9)417/1650.72 (0.56-0.91)0.98 (0.75-1.28)T3 (≥ 90.6)199/630.60 (0.42-0.87)0.64 (0.43-0.97)615/2280.68 (0.56-0.83)0.85 (0.69-1.06)
P for trend0.0030.0030.0020.002< 0.001< 0.001
Orange /yellow vegetable (g/d)
T1 (< 2.7)416/1441.001.00T1 (< 3.2)198/771.001.00614/2211.001.00
T2 (2.7- < 7.7)417/1881.30 (1.01-1.68)1.47 (1.11-1.95)T2 (3.2- < 9.1)200/690.89 (0.61-1.30)1.14 (0.75-1.73)617/2571.16 (0.94-1.43)1.30 (1.04-1.64)
T3 (≥ 7.7)417/2932.09 (1.63-2.67)2.41 (1.83-3.16)T3 (≥ 9.1)198/1522.01 (1.43-2.83)2.28 (1.55-3.34)615/4452.06 (1.69-2.51)2.19 (1.77-2.73)
P for trend< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001
White vegetables and fruits (g/d)
T1 (< 87.9)416/30111T1 (< 109.9)199/15611615/45711
T2 (87.9- < 153.9)418/2190.72 (0.57-0.90)0.84 (0.66-1.08)T2 (109.9- < 198.0)199/990.63 (0.46-0.87)0.78 (0.55-1.11)617/3180.69 (0.58-0.83)0.8 (0.66-0.98)
T3 (≥ 153.9)416/1050.34 (0.27-0.45)0.47 (0.35-0.63)T3 (≥ 198.0)198/430.28 (0.19-0.41)0.34 (0.22-0.52)614/1480.32 (0.26-0.40)0.43 (0.34-0.55)
P for trend< 0.001< 0.001< 0.001< 0.001< 0.001< 0.001

In the analysis of orange/yellow vegetables and fruits separately, orange/yellow fruits intake reduced the risks of colorectal cancer in women (OR = 0.64, 95%CI: 0.43-0.97). We found that higher intake of orange/yellow vegetables elevated the risks of colorectal cancer in both sexes (OR = 2.41, 95%CI: 1.83-3.16 for men; OR = 2.28, 95%CI: 1.55-3.34 for women). In the subsite analysis (Table 5), similar associations by subsite were observed for both men and women.

Table 5 Odds ratios and 95% confidence intervals for colorectal cancer subsites in relation to intake of vegetables and fruits.
Control
Proximal colon
No.Distal colon
No.Rectum
No.No.Age-adjusted OR (95%CI)Multivariate OR1 (95%CI)Age-adjusted OR (95%CI)Multivariate OR1 (95%CI)Age-adjusted OR (95%CI)Multivariate OR1 (95%CI)
Men
Total vegetables and fruits (g/d)
T1 (< 224.2)417461.001.00761.001.001451.001.00
T2 (224.2- < 380.0)416450.97 (0.63-1.49)1.08 (0.68-1.69)730.95 (0.67-1.35)1.10 (0.76-1.58)1070.74 (0.55-0.98)0.82 (0.61-1.12)
T3 (≥ 380.0)417220.47 (0.28-0.80)0.63 (0.36-1.09)290.38 (0.24-0.59)0.50 (0.32-0.80)680.47 (0.34-0.64)0.67 (0.47-0.94)
P for trend20.0040.086< 0.0010.003< 0.0010.018
Total vegetables (g/d)
T1 (< 123.0)416401.001.00661.001.001421.001.00
T2 (123.0-< 203.6)418461.13 (0.72-1.77)1.26 (0.79-2.01)881.32 (0.93-1.87)1.50 (1.04-2.16)1300.91 (0.69-1.20)1.05 (0.77-1.41)
T3 (≥ 203.6)416270.67 (0.40-1.11)0.80 (0.47-1.37)240.36 (0.22-0.59)0.44 (0.27-0.74)480.34 (0.24-0.48)0.43 (0.29-0.63)
P for trend0.0890.34< 0.0010.002< 0.001< 0.001
Total fruits (g/d)
T1 (< 68.3)416371.001.00691.001.001131.001.00
T2 (68.3- < 178.1)418521.38 (0.89-2.16)1.59 (1.01-2.52)761.09 (0.76-1.55)1.26 (0.88-1.83)1291.14 (0.85-1.52)1.30 (0.96-1.78)
T3 (≥ 178.1)416240.64 (0.38-1.09)0.83 (0.47-1.44)330.47 (0.31-0.74)0.59 (0.38-0.94)780.69 (0.50-0.95)0.90 (0.63-1.27)
P for trend0.0350.269< 0.0010.010.0080.318
Green vegetables and fruits (g/d)
T1 (< 48.8)417391.001.00641.001.001291.001.00
T2 (48.8- < 93.6)417491.24 (0.80-1.94)1.26 (0.79-1.99)871.35 (0.95-1.92)1.43 (0.99-2.07)1361.05 (0.80-1.39)1.08 (0.79-1.46)
T3 (≥ 93.6)416250.63 (0.38-1.07)0.67 (0.39-1.16)270.42 (0.26-0.67)0.46 (0.28-0.74)550.43 (0.30-0.60)0.47 (0.32-0.68)
P for trend0.0480.092< 0.001< 0.001< 0.001< 0.001
Red/purple vegetables and fruits (g/d)
T1 (< 22.1)416341.001.00601.001.00911.001.00
T2 (22.1- < 62.2)417481.40 (0.88-2.22)1.63 (1.01-2.04)731.21 (0.84-1.75)1.39 (0.95-2.04)1381.52 (1.13-2.04)1.84 (1.33-2.53)
T3 (≥ 62.2)417310.90 (0.55-1.50)1.12 (0.66-1.88)450.75 (0.50-1.13)0.92 (0.60-1.41)911.00 (0.72-1.38)1.28 (0.90-1.81)
P for trend0.3710.8950.0670.3790.3550.666
Orange/yellow vegetables and fruits (g/d)
T1 (< 21.1)416281.001.00471.001.00861.001.00
T2 (21.1- < 54.0)418431.52 (0.93-2.50)1.80 (1.08-3.01)731.55 (1.05-2.29)1.86 (1.24-2.80)1381.61 (1.19-2.18)1.86 (1.34-2.59)
T3 (≥ 54.0)416421.49 (0.90-2.45)1.94 (1.16-3.27)581.23 (0.82-1.85)1.60 (1.04-2.46)961.12 (0.81-1.55)1.47 (1.04-2.09)
P for trend0.2170.030.6830.1210.8370.178
Orange /yellow fruits (g/d)
T1 (< 15.9)416381.001.00691.001.001201.001.00
T2 (15.9-< 47.9)417461.20 (0.77-1.89)1.43 (0.90-2.27)610.88 (0.61-1.27)1.04 (0.71-1.52)1150.96 (0.72-1.28)1.11 (0.82-1.52)
T3 (≥ 47.9)417290.76 (0.46-1.25)1.04 (0.62-1.75)480.69 (0.47-1.02)0.92 (0.61-1.38)850.71 (0.52-0.96)0.97 (0.69-1.36)
P for trend0.1550.8490.0650.6250.020.724
Orange /yellow vegetable (g/d)
T1 (< 2.7)416311.001.00381.001.00701.001.00
T2 (2.7-< 7.7)417270.87 (0.51-1.48)1.01 (0.59-1.75)551.44 (0.93-2.23)1.68 (1.07-2.63)1011.44 (1.03-2.01)1.64 (1.15-2.34)
T3 (≥ 7.7)417551.79 (1.12-2.86)2.15 (1.32-3.51)852.28 (1.51-3.44)2.72 (1.77-4.18)1492.19 (1.59-3.02)2.51 (1.77-3.54)
P for trend0.003< 0.001< 0.001< 0.001< 0.001< 0.001
White vegetables and fruits (g/d)
T1 (< 87.9)416511.001.00871.001.001561.001.00
T2 (87.9- < 153.9)418460.88 (0.58-1.35)1.04 (0.67-1.61)680.77 (0.54-1.09)0.89 (0.62-1.28)1000.63 (0.48-0.84)0.76 (0.55-1.03)
T3 (≥ 153.9)416160.31 (0.17-0.55)0.40 (0.22-0.73)230.26 (0.16-0.42)0.34 (0.21-0.56)640.41 (0.29-0.56)0.58 (0.41-0.83)
P for trend< 0.0010.003< 0.001< 0.001< 0.0010.002
Women
Total vegetables and fruits (g/d)
T1 (< 317.7)199291.001.00641.001.00701.001.00
T2 (317.7-< 534.8)199190.65 (0.35-1.20)0.66 (0.35-1.25)280.44 (0.27-0.71)0.47 (0.28-0.79)410.58 (0.38-0.90)0.65 (0.41-1.03)
T3 (≥ 534.8)19850.17 (0.07-0.45)0.22 (0.08-0.58)210.33 (0.19-0.56)0.41 (0.23-0.71)130.19 (0.10-0.35)0.25 (0.13-0.47)
P for trend< 0.0010.002< 0.0010.001< 0.001< 0.001
Total vegetables (g/d)
T1 (< 135.9)198261.001.00511.001.00611.001.00
T2 (135.9-< 219.1)200220.83 (0.45-1.51)1.02 (0.53-1.95)410.80 (0.50-1.26)0.97 (0.59-1.57)450.73 (0.47-1.12)0.82 (0.52-1.31)
T3 (≥ 219.1)19850.19 (0.07-0.50)0.22 (0.08-0.61)210.41 (0.29-0.71)0.50 (0.28-0.89)180.29 (0.17-0.51)0.36 (0.20-0.65)
P for trend< 0.0010.0030.0010.018< 0.001< 0.001
Total fruits (g/d)
T1 (< 135.0)198211.001.00461.001.00591.001.00
T2 (135.0-< 307.1)199271.29 (0.70-2.35)1.37 (0.73-2.58)461.00 (0.63-1.57)1.05 (0.65-1.69)480.81 (0.53-1.25)0.88 (0.56-1.38)
T3 (≥ 307.1)19950.24 (0.09-0.64)0.27 (0.10-0.76)210.45 (0.26-0.79)0.52 (0.29-0.93)170.29 (0.16-0.51)0.35 (0.19-0.64)
P for trend0.0030.0020.0040.006< 0.001< 0.001
Green vegetables and fruits (g/d)
T1 (< 61.0)199261.001.00601.001.00601.001.00
T2 (61.0- < 114.2)198230.87 (0.48-1.59)1.03 (0.55-1.93)390.65 (0.42-1.02)0.78 (0.49-1.26)510.85 (0.56-1.29)0.98 (0.62-1.54)
T3 (≥ 114.2)19940.15 (0.05-0.43)0.18 (0.06-0.54)140.23 (0.12-0.43)0.28 (0.15-0.53)130.21 (0.11-0.40)0.26 (0.14-0.50)
P for trend< 0.0010.002< 0.001< 0.001< 0.001< 0.001
Red/purple vegetables and fruits (g/d)
T1 (< 39.5)199201.001.00411.001.00471.001.00
T2 (39.5- < 98.5)199261.30 (0.70-2.41)1.54 (0.81-2.95)441.07 (0.67-1.71)1.19 (0.72-1.95)491.04 (0.67-1.63)1.18 (0.73-1.89)
T3 (≥ 98.5)19870.35 (0.15-0.85)0.43 (0.17-1.06)280.69 (0.41-1.15)0.75 (0.43-1.30)280.60 (0.36-1.00)0.71 (0.41-1.21)
P for trend0.0130.0520.1180.2320.0350.157
Orange/yellow vegetables and fruits (g/d)
T1 (< 40.7)199161.001.00331.001.00401.001.00
T2 (40.7- < 100.6)198221.38 (0.70-2.71)1.58 (0.78-3.20)501.52 (0.94-2.47)1.72 (1.03-2.87)621.56 (1.00-2.43)1.74 (1.08-2.80)
T3 (≥ 100.6)199150.93 (0.45-1.93)1.05 (0.49-2.24)300.91 (0.53-1.55)0.98 (0.56-1.72)220.55 (0.32-0.96)0.61 (0.34-1.09)
P for trend0.6740.8910.4610.6340.0130.041
Orange/yellow fruits (g/d)
T1 (< 32.5)199181.001.00381.001.00481.001.00
T2 (32.5- < 90.6)199221.22 (0.63-2.34)1.44 (0.72-2.85)471.24 (0.77-1.98)1.43 (0.87-2.35)561.17 (0.76-1.80)1.35 (0.85-2.15)
T3 (≥ 90.6)198130.72 (0.35-1.52)0.79 (0.37-1.70)280.74 (0.44-1.25)0.77 (0.44-1.35)200.42 (0.24-0.73)0.44 (0.25-0.80)
P for trend0.2810.370.150.198< 0.0010.002
Orange/yellow vegetable (g/d)
T1 (< 3.2)198131.001.00271.001.00341.001.00
T2 (3.2- < 9.1)200110.84 (0.37-1.91)1.17 (0.49-2.75)281.03 (0.59-1.81)1.35 (0.75-2.46)280.82 (0.48-1.40)1.04 (0.59-1.84)
T3 (≥ 9.1)198292.21 (1.11-4.40)2.87 (1.36-6.03)582.20 (1.33-3.64)2.54 (1.48-4.36)621.85 (1.16-2.95)2.05 (1.24-3.40)
P for trend0.0050.002< 0.001< 0.0010.0010.002
White vegetables and fruits (g/d)
T1 (< 109.9)199311.001.00601.001.00611.001.00
T2 (109.9- < 198.0)199150.49 (0.25-0.93)0.59 (0.30-1.16)360.60 (0.38-0.95)0.75 (0.46-1.22)450.74 (0.48-1.14)0.93 (0.59-1.48)
T3 (≥ 198.0)19870.22 (0.10-0.50)0.25 (0.10-0.59)170.28 (0.16-0.50)0.35 (0.19-0.63)180.30 (0.17-0.52)0.37 (0.21-0.67)
P for trend0.0010.002< 0.0010.001< 0.001< 0.001
DISCUSSION

In this case control study, we investigated the relationship between vegetables and fruits groups categorized by color and the risks of colorectal cancer. The investigation revealed that the green vegetables and fruits and white vegetables and fruits color groups and total vegetables and fruits intake were strongly related to a reduced risk of colorectal cancer in men and women. In addition, it was shown that in women, the total amount of fruit consumed, as well as consumption of the red/purple color groups, attenuated colorectal cancer risk. However, no significant association was found for the red/purple color groups in men. Surprisingly, a high intake from the orange/yellow vegetables and fruits color group was associated with a higher risk of colorectal cancer in men.

The protective effect of total vegetables and fruits intake as related to colorectal cancer risk was consistent with previous case-control studies[12,26-28] and meta-analysis[9]. However, recent cohort studies[13,14,23,29], and a recent case- control study[12], do not comply with our results.

In the present study, green vegetables and fruits intake was shown to be inversely associated with the risk of CRC in both sexes. Green vegetables and fruits are thought to decrease the risk of CRC through their high folate, fiber, lutein, sulforaphane and indole level, which induce apoptosis in cancer cells and inhibit cell damage and the growth of cancer cells[30,31]. The Netherlands Cohort Study[10], as well as a case-control study for Guangzhou (in men)[15] and the NIH-AARP study[11] reported the beneficial effects of green vegetables and fruits. However, other cohort studies and case control studies have produced null findings[12,13,32,33].

This study suggested that high white vegetables and fruits intake has protective effects on colorectal cancer risk. White vegetables and fruits contains various phytochemicals and nutrients, such as the polysaccharides of apples, theglucans of mushroom, saponins of root and bulb vegetables, and the quercetin of onions and apples, which play important roles in antioxidant activity, reduction of DNA damage, and anticancer activity[34]. However, epidemiological studies of white vegetables and fruits intake are still contradictory. In the case of apples, with the exception of one study[33], most research has shown a beneficial significant association[12,35] or no association between apple intake and colorectal cancer risk. Several recent meta-analyses have been published[36-39] on bulbs in the allium family, and the results of these papers show that garlic consumption is not associated with colorectal cancer.

Studies that classify vegetables and fruits by color are rare regardless of the disease. One case-control study was conducted in China[15]. In a case-control study from Switzerland, citrus fruit, a main component of the orange/yellow vegetables and fruits category, was found to be significantly inversely associated with colorectal cancer risk[40]. However, most studies show no significant associations with orange/yellow vegetables and fruits consumption[10,12,13,29,32,33]. In two case control studies conducted in China and Hawaii, it was found that high orange/yellow vegetables and fruits intake reduces colorectal cancer risk[15,41]. Orange/yellow vegetables and fruits are known to be rich in carotene, which can function as provitamin A[42]. Vitamin A may have a positive effect by controlling the growth and metastasis of cancer cells and may act as an antioxidant in reducing cancer[43]. However, our study found that high orange/yellow vegetable and fruit intake was significantly associated with increased risk of colorectal cancer for men. The Nurse’ Health Study and Health Professionals Follow-Up Study conducted in the United States suggested that citrus consumption can contribute to the development of melanoma[44]. Citrus is rich in psoralens and furocoumarins, which raise melanoma risk through photocarcinogens. However, negative health effects of psoralens and furocoumarins on colorectal cancer have not been found in epidemiologic studies. Therefore, we cannot explain the association and possible mechanism for the increased risk of colorectal cancer.

This study shows that high orange/yellow vegetables intake elevates the risk of colorectal cancer. Orange/yellow vegetables include carrot, pumpkin, and ginger. In a case control study from Western Australia[12] and Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial study[45] reported the protective effects of dark yellow vegetables (carrot, pumpkin) for colorectal cancer risk. Gingerol and supplementation with ginger root extract inhibit colorectal carcinoma progress in vivo and humans[46,47]. However, safrole, ingredients that generated when ginger rotted, and group 2B carcinogen classified by the IARC[48], is known to induce cancer in rodents[49,50]. Also, the remaining chemical additives (fertilizer, preservatives, pesticide) after washing are likely to cause cancer. We have no definite explanation that orange/yellow vegetables intake increase the risk of developing colorectal cancer. More research is needed to verify this observation.

Our results showed a sex difference. Although the underlying mechanism for the sex difference of our study between sexes is not clearly known, few possibilities can be considered from various aspects. Previous studies have suggested that estrogen exposure[51] and the use of oral contraception[52] prevented the development of colorectal cancer. Also, taking hormonal replacement therapy (HRT) in postmenopausal women showed reduced colorectal cancer risks in Women’s Health Initiative (WHI) study[53] and a meta-analysis[54]. Another reason is that women tend to prefer vegetables and fruits than men. Because usually women are responsible in buying and cooking foods in Korean culture, they tend to have more information about beneficial health effects of vegetable/fruits and consume more of them[55]. Other factors such as prevalence of diabetes, physical activity, education and income levels, and lifestyle differences between sexes may influence the relationship between vegetables and fruits intake and colorectal cancer risk.

Korean diet has a unique synchronic serving method/style of which all dishes are served at one time on a table. On the other hand, Western or Chinese diet is diachronic (course meal), serving dishes at different points of time[56]. A Typical and common Korean table is set with bap (steamed rice), kuk or chigae (broth, stew), banchan (side dishes) and kimchi[57]. Bap is the main Korean dish that gives a major source of energy. Kuk or chigae, which are different than the Western soups[58] are eaten with bap. Usually, banchan (side dishes) are composed of more than three kinds of foods such as namul, legumes, fish, meat, and kimchi, and are seasoned with jang, sesame or perilla seed/oil, vinegar, and herbs. Korean diet is usually well-balanced and nutritious. Based on these features, the health benefits of the Korean diet are reported in many cases of diseases[59,60]. Currently, peoples believe that colorful vegetables and fruits are the most nutritious and indicate that the distinction between the color of vegetables and fruits is a powerful factor in food selection[61]. The information presented in this study could be used to advise members of the general Korean public who are interested in the phytochemicals of vegetables and fruits. However, it is difficult to generalize to the population of many countries in the world. Because each country has its own traditional recipe and the unique vegetables and fruits that are naturally grown in each climate and topography.

The present study has several limitations. First, because the design of our study relied on hospital-based case-control groups, and the control group was recruited from participants in the health check-up program of the National Health Insurance Corporation, the results of our study may not be representative of the source population of the cases[62]. The control group could have had healthy behaviors and habits compared to the patients. Second, recall bias is an inherent weakness in case-control study design. Case and control groups tend to have differences in recall. Colorectal cancer patients are likely to overestimate or underestimate their poor eating habits compared to the control group[25]; therefore, there is the possibility of exaggerating of the association. To reduce this problem, we tried to survey the case group as soon as their cancer was diagnosed or just before surgery. Third, we did not evaluate the manufacturing method (cooked, raw, or frozen) or extra ingredients (seasoning, dressing, etc.). The majority of study suggested that the inverse relationship for cancer may be stronger for raw vegetables, in which destruction of nutrients is minimized compared to cooked vegetables. But, compared to other cancers, colorectal cancer showed similar results between raw vegetables and cooked vegetables[63]. Lastly, we could not further consider the molecular characteristics such as microsatellite Instability or CpG island methylator phenotype of colorectal cancer patients, which could be related with differential risk.

In conclusion, our results suggest that total vegetables and fruits intake by color was inversely related to colorectal cancer risk. However, the orange/yellow vegetables and fruits color group showed an elevated risk for colorectal cancer. Further studies are necessary to confirm the relationship between vegetable and fruit intake by color and colorectal cancer risk.

COMMENTS
Background

The colors of vegetable and fruit reflect their contents of unique phytochemicals and micronutrients. In this case-control study, the authors investigated the relationship between the colors of vegetable and fruit and the risk of colorectal cancer.

Research frontiers

The authors conducted a case-control study to investigate the association between the vegetable and fruit color group and colorectal cancer risk in the Korea population.

Innovations and breakthroughs

Methods that classify vegetables and fruits by color are rare in most studies of disease including colorectal cancer. Vegetables and fruits that are consumed by Koreans were classified according to the criteria.

Applications

Results of this study may be used to advise the general Koreans who are interested in prevention of colorectal cancer.

Terminology

The color of vegetables and fruits reflect the contents of unique phytochemicals and micronutrients. Vegetables and fruits intake in various color groups may protect against colorectal cancer.

Peer-review

Presented manuscript depicts interesting way of seeing of diet-factors impact to colorectal cancer genesis. Discrimination of vegetables and fruits according to only their colour and hypothetical natural consent is substantially difficult in light of reliable statistical analysis. However, there are consistent preventive data of cruciferous vegetables, garlic or fiber-rich plants. The meaning of achieved results should be very careful. Available vegetables and fruits include diversified values of chemical additives, various preservatives and chemical fertilizers as well. Vast used, e.g., to citrus preservation, fungicides such as enilkonasol and also tiabendasol have documented pro-cancerous action. Because of that, estimation of influence of dietary plants to cancer is especially difficult in the age of chemically modified plants.

Footnotes

Manuscript source: Invited manuscript

Specialty type: Gastroenterology and hepatology

Country of origin: South Korea

Peer-review report classification

Grade A (Excellent): 0

Grade B (Very good): B, B

Grade C (Good): C

Grade D (Fair): D

Grade E (Poor): 0

P- Reviewer: Bennett L, Bordonaro M, Chen WTL, Lewitowicz P S- Editor: Yu J L- Editor: A E- Editor: Wang CH

References
1.  Slavin JL, Lloyd B. Health benefits of fruits and vegetables. Adv Nutr. 2012;3:506-516.  [PubMed]  [DOI]
2.  Steinmetz KA, Potter JD. Vegetables, fruit, and cancer. II. Mechanisms. Cancer Causes Control. 1991;2:427-442.  [PubMed]  [DOI]
3.  Bellavia A, Larsson SC, Bottai M, Wolk A, Orsini N. Fruit and vegetable consumption and all-cause mortality: a dose-response analysis. Am J Clin Nutr. 2013;98:454-459.  [PubMed]  [DOI]
4.  Crowe FL. Fruit and vegetable consumption is associated with reduced all-cause and cardiovascular mortality. Evid Based Med. 2015;20:14.  [PubMed]  [DOI]
5.  Key TJ. Fruit and vegetables and cancer risk. Br J Cancer. 2011;104:6-11.  [PubMed]  [DOI]
6.  Liu X, Yan Y, Li F, Zhang D. Fruit and vegetable consumption and the risk of depression: A meta-analysis. Nutrition. 2016;32:296-302.  [PubMed]  [DOI]
7.  Wang X, Ouyang Y, Liu J, Zhu M, Zhao G, Bao W, Hu FB. Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies. BMJ. 2014;349:g4490.  [PubMed]  [DOI]
8.  Continuous Update Project Keeping the science current Colorectal Cancer 2011 Report. 2011;.  [PubMed]  [DOI]
9.  Aune D, Lau R, Chan DS, Vieira R, Greenwood DC, Kampman E, Norat T. Nonlinear reduction in risk for colorectal cancer by fruit and vegetable intake based on meta-analysis of prospective studies. Gastroenterology. 2011;141:106-118.  [PubMed]  [DOI]
10.  Voorrips LE, Goldbohm RA, van Poppel G, Sturmans F, Hermus RJ, van den Brandt PA. Vegetable and fruit consumption and risks of colon and rectal cancer in a prospective cohort study: The Netherlands Cohort Study on Diet and Cancer. Am J Epidemiol. 2000;152:1081-1092.  [PubMed]  [DOI]
11.  Park Y, Subar AF, Kipnis V, Thompson FE, Mouw T, Hollenbeck A, Leitzmann MF, Schatzkin A. Fruit and vegetable intakes and risk of colorectal cancer in the NIH-AARP diet and health study. Am J Epidemiol. 2007;166:170-180.  [PubMed]  [DOI]
12.  Annema N, Heyworth JS, McNaughton SA, Iacopetta B, Fritschi L. Fruit and vegetable consumption and the risk of proximal colon, distal colon, and rectal cancers in a case-control study in Western Australia. J Am Diet Assoc. 2011;111:1479-1490.  [PubMed]  [DOI]
13.  Vogtmann E, Xiang YB, Li HL, Levitan EB, Yang G, Waterbor JW, Gao J, Cai H, Xie L, Wu QJ. Fruit and vegetable intake and the risk of colorectal cancer: results from the Shanghai Men’s Health Study. Cancer Causes Control. 2013;24:1935-1945.  [PubMed]  [DOI]
14.  Leenders M, Siersema PD, Overvad K, Tjønneland A, Olsen A, Boutron-Ruault MC, Bastide N, Fagherazzi G, Katzke V, Kühn T. Subtypes of fruit and vegetables, variety in consumption and risk of colon and rectal cancer in the European Prospective Investigation into Cancer and Nutrition. Int J Cancer. 2015;137:2705-2714.  [PubMed]  [DOI]
15.  Luo WP, Fang YJ, Lu MS, Zhong X, Chen YM, Zhang CX. High consumption of vegetable and fruit colour groups is inversely associated with the risk of colorectal cancer: a case-control study. Br J Nutr. 2015;113:1129-1138.  [PubMed]  [DOI]
16.  Heber D, Bowerman S. Applying science to changing dietary patterns. J Nutr. 2001;131:3078S-3081S.  [PubMed]  [DOI]
17.  Pennington JA, Fisher RA. Classification of fruits and vegetables. J Food Compost Anal. 2009;22:S23-S31.  [PubMed]  [DOI]
18.  Pennington JA, Fisher RA. Food component profiles for fruit and vegetable subgroups. J Food Compost Anal. 2010;23:411-418.  [PubMed]  [DOI]
19.  Oude Griep LM, Verschuren WM, Kromhout D, Ocké MC, Geleijnse JM. Colors of fruit and vegetables and 10-year incidence of stroke. Stroke. 2011;42:3190-3195.  [PubMed]  [DOI]
20.  Oude Griep LM, Verschuren WM, Kromhout D, Ocké MC, Geleijnse JM. Colours of fruit and vegetables and 10-year incidence of CHD. Br J Nutr. 2011;106:1562-1569.  [PubMed]  [DOI]
21.  Ahn Y, Kwon E, Shim JE, Park MK, Joo Y, Kimm K, Park C, Kim DH. Validation and reproducibility of food frequency questionnaire for Korean genome epidemiologic study. Eur J Clin Nutr. 2007;61:1435-1441.  [PubMed]  [DOI]
22.  Shin A, Joo J, Bak J, Yang HR, Kim J, Park S, Nam BH. Site-specific risk factors for colorectal cancer in a Korean population. PLoS One. 2011;6:e23196.  [PubMed]  [DOI]
23.  Aoyama N, Kawado M, Yamada H, Hashimoto S, Suzuki K, Wakai K, Suzuki S, Watanabe Y, Tamakoshi A. Low intake of vegetables and fruits and risk of colorectal cancer: the Japan Collaborative Cohort Study. J Epidemiol. 2014;24:353-360.  [PubMed]  [DOI]
24.  Norat T, Aune D, Chan D, Romaguera D. Fruits and vegetables: updating the epidemiologic evidence for the WCRF/AICR lifestyle recommendations for cancer prevention. Cancer Treat Res. 2014;159:35-50.  [PubMed]  [DOI]
25.  Willett W. Nutritional epidemiology. 2012;.  [PubMed]  [DOI]
26.  Satia-Abouta J, Galanko JA, Martin CF, Ammerman A, Sandler RS. Food groups and colon cancer risk in African-Americans and Caucasians. Int J Cancer. 2004;109:728-736.  [PubMed]  [DOI]
27.  Terry P, Terry JB, Wolk A. Fruit and vegetable consumption in the prevention of cancer: an update. J Intern Med. 2001;250:280-290.  [PubMed]  [DOI]
28.  Franceschi S, Favero A, La Vecchia C, Negri E, Conti E, Montella M, Giacosa A, Nanni O, Decarli A. Food groups and risk of colorectal cancer in Italy. Int J Cancer. 1997;72:56-61.  [PubMed]  [DOI]
29.  Koushik A, Hunter DJ, Spiegelman D, Beeson WL, van den Brandt PA, Buring JE, Calle EE, Cho E, Fraser GE, Freudenheim JL. Fruits, vegetables, and colon cancer risk in a pooled analysis of 14 cohort studies. J Natl Cancer Inst. 2007;99:1471-1483.  [PubMed]  [DOI]
30.  Frydoonfar HR, McGrath DR, Spigelman AD. Sulforaphane inhibits growth of a colon cancer cell line. Colorectal Dis. 2004;6:28-31.  [PubMed]  [DOI]
31.  Nishikawa T, Tsuno NH, Okaji Y, Shuno Y, Sasaki K, Hongo K, Sunami E, Kitayama J, Takahashi K, Nagawa H. Inhibition of autophagy potentiates sulforaphane-induced apoptosis in human colon cancer cells. Ann Surg Oncol. 2010;17:592-602.  [PubMed]  [DOI]
32.  Nomura AM, Wilkens LR, Murphy SP, Hankin JH, Henderson BE, Pike MC, Kolonel LN. Association of vegetable, fruit, and grain intakes with colorectal cancer: the Multiethnic Cohort Study. Am J Clin Nutr. 2008;88:730-737.  [PubMed]  [DOI]
33.  Tayyem RF, Shehadah I, Abu-Mweis SS, Bawadi HA, Bani-Hani KE, Al-Jaberi T, Al-Nusairr M, Heath DD. Fruit and vegetable intake among Jordanians: results from a case-control study of colorectal cancer. Cancer Control. 2014;21:350-360.  [PubMed]  [DOI]
34.  Li YH, Niu YB, Sun Y, Zhang F, Liu CX, Fan L, Mei QB. Role of phytochemicals in colorectal cancer prevention. World J Gastroenterol. 2015;21:9262-9272.  [PubMed]  [DOI]
35.  Jedrychowski W, Maugeri U. An apple a day may hold colorectal cancer at bay: recent evidence from a case-control study. Rev Environ Health. 2009;24:59-74.  [PubMed]  [DOI]
36.  Hu JY, Hu YW, Zhou JJ, Zhang MW, Li D, Zheng S. Consumption of garlic and risk of colorectal cancer: an updated meta-analysis of prospective studies. World J Gastroenterol. 2014;20:15413-15422.  [PubMed]  [DOI]
37.  Turati F, Guercio V, Pelucchi C, La Vecchia C, Galeone C. Colorectal cancer and adenomatous polyps in relation to allium vegetables intake: a meta-analysis of observational studies. Mol Nutr Food Res. 2014;58:1907-1914.  [PubMed]  [DOI]
38.  Zhu B, Zou L, Qi L, Zhong R, Miao X. Allium vegetables and garlic supplements do not reduce risk of colorectal cancer, based on meta-analysis of prospective studies. Clin Gastroenterol Hepatol. 2014;12:1991-2001.e1-4; quiz e121.  [PubMed]  [DOI]
39.  Chiavarini M, Minelli L, Fabiani R. Garlic consumption and colorectal cancer risk in man: a systematic review and meta-analysis. Public Health Nutr. 2016;19:308-317.  [PubMed]  [DOI]
40.  Levi F, Pasche C, La Vecchia C, Lucchini F, Franceschi S. Food groups and colorectal cancer risk. Br J Cancer. 1999;79:1283-1287.  [PubMed]  [DOI]
41.  Le Marchand L, Hankin JH, Wilkens LR, Kolonel LN, Englyst HN, Lyu LC. Dietary fiber and colorectal cancer risk. Epidemiology. 1997;8:658-665.  [PubMed]  [DOI]
42.  Liu RH. Potential synergy of phytochemicals in cancer prevention: mechanism of action. J Nutr. 2004;134:3479S-3485S.  [PubMed]  [DOI]
43.  Reczek CR, Chandel NS. CANCER. Revisiting vitamin C and cancer. Science. 2015;350:1317-1318.  [PubMed]  [DOI]
44.  Wu S, Han J, Feskanich D, Cho E, Stampfer MJ, Willett WC, Qureshi AA. Citrus Consumption and Risk of Cutaneous Malignant Melanoma. J Clin Oncol. 2015;33:2500-2508.  [PubMed]  [DOI]
45.  Millen AE, Subar AF, Graubard BI, Peters U, Hayes RB, Weissfeld JL, Yokochi LA, Ziegler RG. Fruit and vegetable intake and prevalence of colorectal adenoma in a cancer screening trial. Am J Clin Nutr. 2007;86:1754-1764.  [PubMed]  [DOI]
46.  Zick SM, Turgeon DK, Ren J, Ruffin MT, Wright BD, Sen A, Djuric Z, Brenner DE. Pilot clinical study of the effects of ginger root extract on eicosanoids in colonic mucosa of subjects at increased risk for colorectal cancer. Mol Carcinog. 2015;54:908-915.  [PubMed]  [DOI]
47.  Bode ADZ. Ginger is an effective inhibitor of HCT116 human colorectal carcinoma in vivo. AMER ASSOC cancer research. USA: Philadelphia 2003; 1324S-1324S.  [PubMed]  [DOI]
48.  IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Overall Evaluations of Carcinogenicity: An Updating of IARC Monographs Volumes 1-42. Supplement 7. 1987;.  [PubMed]  [DOI]
49.  Leong TYM, Leong ASY. Epidemiology and carcinogenesis of hepatocellular carcinoma. Hpb. 2005;7:5-15.  [PubMed]  [DOI]
50.  Long EL, Nelson A, Fitzhugh O, Hansen W. Liver tumours produced in rats by feeding safrole. Arch Pathol. 1963;75:595-604.  [PubMed]  [DOI]
51.  Franceschi S, Gallus S, Talamini R, Tavani A, Negri E, La Vecchia C. Menopause and colorectal cancer. Br J Cancer. 2000;82:1860-1862.  [PubMed]  [DOI]
52.  Fernandez E, La Vecchia C, Balducci A, Chatenoud L, Franceschi S, Negri E. Oral contraceptives and colorectal cancer risk: a meta-analysis. Br J Cancer. 2001;84:722-727.  [PubMed]  [DOI]
53.  Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women’s Health Initiative randomized controlled trial. JAMA. 2002;288:321-333.  [PubMed]  [DOI]
54.  Grodstein F, Newcomb PA, Stampfer MJ. Postmenopausal hormone therapy and the risk of colorectal cancer: a review and meta-analysis. Am J Med. 1999;106:574-582.  [PubMed]  [DOI]
55.  Baker AH, Wardle J. Sex differences in fruit and vegetable intake in older adults. Appetite. 2003;40:269-275.  [PubMed]  [DOI]
56.  Lee DY, Lee EJ, Kim TH. Study on the semiotic characteristics for Korean food. J Korean Society Food Culture. 2013;28:135-144.  [PubMed]  [DOI]
57.  Kim SH, Kim MS, Lee MS, Park YS, Lee HJ, Kang S-a, Lee HS, Lee K-E, Yang HJ, Kim MJ. Korean diet: characteristics and historical background. J Ethnic Foods. 2016;3:26-31.  [PubMed]  [DOI]
58.  Kwon DY, Chung KR, Yang H-J, Jang D-J. Gochujang (Korean red pepper paste): a Korean ethnic sauce, its role and history. J Ethnic Foods. 2015;2:29-35.  [PubMed]  [DOI]
59.  Chae SW. Beneficial Effects of Korean Traditional Diet in Patients with Hypertension and Type 2 Diabetes. Food Indust Nutr. 2011;16:15-26.  [PubMed]  [DOI]
60.  Park Y, Lee J, Oh JH, Shin A, Kim J. Dietary patterns and colorectal cancer risk in a Korean population: A case-control study. Medicine (Baltimore). 2016;95:e3759.  [PubMed]  [DOI]
61.  Drewnowski A. From asparagus to zucchini: mapping cognitive space for vegetable names. J Am Coll Nutr. 1996;15:147-153.  [PubMed]  [DOI]
62.  Breslow NE, Day NE. Statistical methods in cancer research. Volume I - The analysis of case-control studies. IARC Sci Publ. 1980;5-338.  [PubMed]  [DOI]
63.  Link LB, Potter JD. Raw versus cooked vegetables and cancer risk. Cancer Epidemiol Biomarkers Prev. 2004;13:1422-1435.  [PubMed]  [DOI]