Abstract
Dietary fiber and phytonutrients can protect against colorectal cancer, yet their consumption is low in the US. Avocados are a potential source of these beneficial nutrients. Therefore, this study aimed to examine the relationship between avocados/guacamole consumption and colorectal cancer risk in the Multiethnic Cohort Study. We assessed avocados/guacamole consumption by using a food frequency questionnaire. We classified participants into three consumer groups: <1 serving/month, 1–3 servings/month, and ≥1 serving/week with one serving defined as ½ avocado or ½ cup. Colorectal cancer cases were ascertained through the Surveillance, Epidemiology and End Results Program cancer registries. Cox proportional hazards models of colorectal cancer were used to calculate hazard ratios and 95% confidence intervals across avocados/guacamole intake groups in each sex overall and by anatomic subsite (i.e., right colon, left colon, rectum) and race and ethnicity. Of 192,651 eligible participants, 62.8% reported consuming <1 serving/month avocados/guacamole, 26.7% reported 1–3 servings/month, and 10.5% reported ≥1 serving/week. When adjusted for relevant covariates, there was no significant association with incident colorectal cancer overall, for subsites, or within racial and ethnic subgroups (all p for trend≥0.06). In this large prospective cohort study, we did not find that consumption of avocados/guacamole was associated with colorectal cancer risk.
Keywords: Cancer, Colorectal Cancer, Avocado, Multiethnic Cohort, Prospective Cohort Study
Introduction
Colorectal cancer is the third leading cause of death from cancer globally (1). It costs approximately $14.1 billion in medical expenses annually, the second highest among all cancers in the United States (2). Fortunately, it is one of the most preventable cancers, with a number of established modifiable risk factors, including screening and diet (1).
Avocados contain numerous nutrients, such as phytonutrients, dietary fiber, and monounsaturated fatty acids, which can be protective against colorectal cancer (3). The bioactive phytonutrients in avocados include glutathione, carotenoids, and phenols, which have been shown to have anticarcinogenic properties (4). In addition, dietary fiber has been studied for its protective role against colorectal cancer because it shortens transit time in the bowel, which can decrease the effect of carcinogens (5). Avocados are an excellent source of dietary fiber, providing 4.6 grams in half of an avocado (3). Lastly, a case-control study conducted in Iran reported that oleic acid intake was inversely associated with colorectal cancer (6). There are 6.7 grams of monounsaturated fatty acid (MUFA) in one half of a medium size avocado, and oleic acid is the predominant MUFA (7). Although the exact mechanism is still being examined, some studies suggest that oleic acid can hinder cell proliferation in different tumor cell lines (8).
Despite these promising findings, studies examining the direct association between avocados and colorectal cancer risk are limited. Only one recent study has examined this relationship and found that those who reported consuming more than one weekly serving (vs. less than one serving per month) of avocados had a lower risk of colorectal cancer in the Health Professionals Follow-Up Study (HPFS) (9). Therefore, it is important to replicate and further explore this association using a larger, more ethnically diverse cohort. This study aimed to investigate the relationship between avocados/guacamole consumption and colorectal cancer risk using the Multiethnic Cohort (MEC) Study.
MATERIALS AND METHODS
Study Population
The MEC is a prospective cohort study with the aim of examining the association between diet and cancer in the United States (10). In 1993–1996, 215,251 women and men, between 45–75 years old, were recruited from California (primarily Los Angeles County) and Hawaii with the following racial and ethnic distribution: Japanese American (26.4%), White (22.9%), Latino (22.0%), African American (16.3%), Native Hawaiian (6.5%), and other ancestry (5.8%) (10).
At baseline (1993–1996), participants completed a self-administered, comprehensive questionnaire that included demographics, usual diet, lifestyle and health-related information, and consent to participate in the study. Institutional review boards at the University of Hawaii and the University of Southern California reviewed and approved the MEC study.
Dietary assessment
A food frequency questionnaire (FFQ) assessed consumptions of more than 180 food items including a single question for avocados/guacamole. A more detailed description of the MEC FFQ has been published elsewhere (10). In brief, participants were asked on average last year how often (e.g., never or hardly ever, once a month, 2–3 times a month, once a week, 2–3 times a week, 4–6 times a week, once a day, or 2 or more times a day) they had consumed a list of food items (e.g., avocados/guacamole) and the usual serving size (e.g., 2 slices or 2 tablespoons, ¼ avocado or ¼ cup, ½ avocado or ½ cup or more). A second FFQ was collected between 2003–2008.
Participants were categorized into three avocados/guacamole consumer groups: <1 serving/month, 1–3 serving/month, and ≥1 serving/week with one serving defined as ½ avocado or ½ cup, consistent with the avocados consumer groups in Ericsson et al.’s study for comparison (9).
Colorectal Cancer
Incident diagnoses of colorectal cancer were captured through the California and Hawaii state cancer registries which are part of the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute. Cases in this study were limited to invasive adenocarcinoma of the large bowel using International Classification of Diseases for Oncology, 3rd Edition [ICD-O-3] codes C18.0-C18.9, C19.9, and C20.9: for anatomic subsites, C18.0-C18.5 for right colon, C18.6-C18.7 for left colon, and C19.9 and C20.9 for rectum. There were 5,522 colorectal cancer cases identified during an average of 19 years of follow-up through December 31, 2017.
Covariates
The following relevant covariates were derived from the baseline questionnaire: age, race/ethnicity, family history of colorectal cancer, history of colorectal polyp, history of diabetes, body mass index, cigarette smoking, multivitamin use, nonsteroidal anti-inflammatory drug use, physical activity, menopausal hormone therapy use (women only), alcohol consumption, total energy intake, and the Healthy Eating Index-2015 (HEI-2015).
The HEI-2015 quantified adherence to the 2015–2020 Dietary Guidelines for Americans, consisting of 13 components: total fruits, whole fruits, total vegetables, greens and beans, whole grains, dairy, total protein foods, seafood and plant proteins, fatty acids, refined grains, sodium, added sugars, and saturated fats (11). Six components were scored from 0 to 5, and seven were scored from 0 to 10, with a total score ranging from 0 to 100 (11).
Statistical Analyses
We performed descriptive statistics to summarize baseline characteristics among the three avocado consumption groups by sex. We calculated hazard ratios (HRs) and associated 95% confidence intervals (CI) for colorectal cancer risk for women and men separately, overall and by anatomic subsite (i.e., right colon, left colon, rectum) across avocados/guacamole consumer groups using Cox proportional hazards models with age as the time metric. Observation starts at cohort entry and ends at colorectal cancer diagnosis, death or closure date of 12/31/2017. The reference group was <1 serving/month. Trend variables were assigned the sex- and race/ethnicity-specific medians for the avocados/guacamole consumption groups.
We constructed two multivariate-adjusted Cox models. Model 1 adjusted for age at cohort entry (continuous) as a covariate and race/ethnicity (African American, Japanese American, Latino, Native Hawaiian, or White) as a strata variable. Model 2 further adjusted for family history of colorectal cancer (yes or no), history of colorectal polyp (yes or no), history of diabetes (yes or no), body mass index (<25 kg/m2, 25‒29.9 kg/m2, or ≥30 kg/m2), pack-years of cigarette smoking, multivitamin use (yes or no), nonsteroidal anti-inflammatory drug use (yes or no), physical activity (hours spent in moderate and vigorous activity per day, continuous), women only: menopausal hormone therapy use (never, former, or current), alcohol consumption (grams per day, continuous), total energy intake (log transformed kcal per day, continuous), and HEI-2015 (continuous). We also considered dietary fiber and processed/red meat intakes as covariates but did not include them in the final models because adjusting for these variables did not alter the results. The proportional hazards assumption was examined with Schoenfeld residuals and found to be met. We stratified the analysis by race/ethnicity (model 2). Wald statistics for cross-product terms of trend variables and subgroup membership (sex and race/ethnicity) was used to test for heterogeneity between subgroups.
Moreover, we conducted a sensitivity analysis by using the average intake of avocados/guacamole based on the baseline and 10-year follow up FFQs among respondents to both surveys. Covariates were from the 10-year follow-up survey and outcome was incident colorectal cancer occurring after the 10-year follow-up.
Statistical analyses were performed using SAS 9.4 (SAS Institute, Inc.) and P value <0.05 (two-tailed) was considered the level of significance.
Protocol Submission and checklist
We adhered to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist to ensure reporting quality.
Data Availability Statement
The data generated in this study will be made available upon request, pending application to and approval by the Multiethnic Cohort Research Committee (https://www.uhcancercenter.org/for-researchers/mec-data-sharing).
RESULTS
Of the 215,251 MEC participants, 22,600 were excluded because they were not one of the main five racial and ethnic groups (n=12,206), had colorectal cancer prior to baseline (n=2,224), or reported implausible diets (n=8,170). As a result, 192,651 were in this analysis. For the fully adjusted model (Model 2), participants with missing data on covariates (n=19,224) were further excluded, resulting in 173,427 participants.
As shown in Table 1, 62.8% reported consuming <1 serving/month avocados/guacamole, 26.7% reported 1–3 servings/month, and 10.5% reported ≥1 serving/week. More than half (55%) of the participants were women. The mean ages at cohort entry were similar across the three intake groups. Among the highest intake group, most participants were Latino (men: 49.5%; women: 40.8%), followed by White (22.3%; 23.3%), Japanese American (15.1%; 17.9%), African American (8.8%, 12.1%), and Native Hawaiian (4.3%; 5.9%). Compared to the lowest group, the highest intake group had slightly lower percentages of participants with family history of colorectal cancer, history of intestinal polyps, and history of diabetes, and slightly higher percentages of individuals with overweight. The highest (vs. lowest) avocados/guacamole intake group also had a higher HEI-2015, processed/red meat intake, dietary fiber intake, alcohol intake, energy intake, multivitamin use, and physical activity.
Table 1.
Baseline characteristics of participants by avocado/guacamole intake
| Men (n= 86,741) |
Women (n= 105,910) |
||||||
|---|---|---|---|---|---|---|---|
| <1/month | 1–3/month | ≥1/week | <1/month | 1–3/month | ≥1/week | ||
|
| |||||||
| No. of participants | 53670 | 23548 | 9523 | 67233 | 27903 | 10774 | |
| Age at cohort entry (years), mean ± SD | 60.1 ± 8.9 | 60.3 ± 8.7 | 60.5 ± 8.6 | 59.8 ± 8.9 | 59.5 ± 8.7 | 60.0 ± 8.6 | |
| Ethnicity, n (%) | |||||||
| African American | 8824 (16.4) | 2292 (9.7) | 838 (8.8) | 15765 (23.4) | 3743 (13.4) | 1303 (12.1) | |
| Japanese American | 18490 (34.5) | 5459 (23.2) | 1439 (15.1) | 19932 (29.6) | 6716 (24.1) | 1925 (17.9) | |
| Latino | 8429 (15.7) | 8602 (36.5) | 4717 (49.5) | 10827 (16.1) | 8214 (29.4) | 4393 (40.8) | |
| Native Hawaiian | 4055 (7.6) | 1512 (6.4) | 407 (4.3) | 5086 (7.6) | 2043 (7.3) | 641 (5.9) | |
| White | 13872 (25.8) | 5683 (24.1) | 2122 (22.3) | 15623 (23.2) | 7187 (25.8) | 2512 (23.3) | |
| Family history of colorectal cancer, n (%) | 4032 (7.5) | 1615 (6.9) | 600 (6.3) | 5917 (8.8) | 2328 (8.3) | 801 (7.4) | |
| History of intestinal polyps, n (%) | 3903 (7.3) | 1497 (6.4) | 510 (5.4) | 2954 (4.4) | 1234 (4.4) | 400 (3.7) | |
| History of diabetes, n (%) | 6868 (12.8) | 2876 (12.2) | 1116 (11.7) | 7926 (11.8) | 2783 (10.0) | 1060 (9.8) | |
| Body mass index, n (%) | |||||||
| <25 kg/m2 | 19778 (36.9) | 7825 (33.2) | 3350 (35.2) | 30338 (45.1) | 12604 (45.2) | 4852 (45.0) | |
| 25‒29.9 kg/m2 | 24543 (45.7) | 11315 (48.1) | 4516 (47.4) | 20851 (31.0) | 8892 (31.9) | 3526 (32.7) | |
| ≥30 kg/m2 | 8931 (16.6) | 4250 (18.0) | 1600 (16.8) | 14683 (21.8) | 6008 (21.5) | 2227 (20.7) | |
| Smoking status, n (%) | |||||||
| Never | 15865 (29.6) | 6949 (29.5) | 2896 (30.4) | 36612 (54.5) | 15181 (54.4) | 6153 (57.1) | |
| Former | 27655 (51.5) | 12007 (51.0) | 4816 (50.6) | 19989 (29.7) | 8107 (29.1) | 2978 (27.6) | |
| Current | 9600 (17.9) | 4324 (18.4) | 1653 (17.4) | 9460 (14.1) | 4097 (14.7) | 1316 (12.2) | |
| Pack-years among ever smokers, mean ± SD | 21.5 ± 16.7 | 19.7 ± 16.6 | 18.0 ± 16.0 | 15.6 ± 14.4 | 15.5 ± 14.5 | 14.1 ± 14.4 | |
| Multivitamin use, n (%) | 24704 (46.0) | 11171 (47.4) | 4679 (49.1) | 35005 (52.1) | 14821 (53.1) | 5878 (54.6) | |
| NSAID use, n (%) | 26592 (49.5) | 12063 (51.2) | 4792 (50.3) | 34748 (51.7) | 14948 (53.6) | 5895 (54.7) | |
| Physical activity (h/day), mean ± SD | 1.26 ± 1.43 | 1.39 ± 1.57 | 1.50 ± 1.71 | 1.05 ± 1.21 | 1.13 ± 1.29 | 1.19 ± 1.40 | |
| MHT use, n (%) | |||||||
| Never | - | - | - | 34778 (51.7) | 14249 (51.1) | 5730 (53.2) | |
| Past | - | - | - | 11636 (17.3) | 4988 (17.9) | 1938 (18.0) | |
| Current | - | - | - | 18718 (27.8) | 7836 (28.1) | 2715 (25.2) | |
| Alcohol intake (g/day), mean ± SD | 13.7 ± 31.9 | 15.9 ± 33.5 | 17.0 ± 35.4 | 3.8 ± 14.4 | 5.1 ± 15.8 | 4.8 ± 14.9 | |
| Total energy intake (kcal/day), mean ± SD | 2215 ± 989 | 2582 ± 1130 | 3213 ± 1436 | 1810 ± 859 | 2128 ± 960 | 2651 ± 1241 | |
| Dietary fiber intake (g/day), mean ± SD | 23.0 ± 13.4 | 28.5 ± 15.3 | 40.9 ± 21.6 | 22.8 ± 13.6 | 27.0 ± 14.9 | 38.1 ± 20.4 | |
| Processed/red meat intake (g/day), mean ± SD | 68.2 ± 54.0 | 83.3 ± 62.2 | 98.0 ± 79.5 | 46.5 ± 41.3 | 57.7 ± 46.7 | 66.1 ± 60.7 | |
| Healthy Eating Index-2015, mean ± SD | 64.9 ± 10.8 | 65.7 ± 9.6 | 68.0 ± 9.0 | 68.7 ± 10.8 | 68.6 ± 9.9 | 70.7 ± 9.2 | |
Abbreviations: MHT, menopausal hormone therapy; NSAID, nonsteroidal anti-inflammatory drug.
1 serving = ½ avocado or ½ cup
Table 2 presents the results from the two multivariate-adjusted Cox models. Both models showed no significant associations between avocados/guacamole consumption and colorectal cancer risk overall and by anatomic subsite. Results remained similar when stratified by race/ethnicity (Table 3) and when using the average of baseline and 10-year follow-up intakes of avocados/guacamole (Table 4).
Table 2.
Association between avocado/guacamole intake and colorectal cancer risk in the Multiethnic Cohort, 1993–2017
| Men (n=86,741) |
Women (n = 105,910) |
P for heterogeneityd | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Cases | HR (95% CI)a | Casesb | HR (95% CI)c | Cases | HR (95% CI)a | Casesb | HR (95% CI)c | ||
|
| |||||||||
| Colorectum | |||||||||
| <1/month | 1741 | 1.00 (ref.) | 1609 | 1.00 (ref.) | 1745 | 1.00 (ref.) | 1523 | 1.00 (ref.) | |
| 1–3/month | 765 | 1.03 (0.94–1.12) | 709 | 1.03 (0.94–1.13) | 700 | 1.02 (0.93–1.12) | 629 | 1.06 (0.96–1.16) | |
| ≥1/week | 296 | 1.02 (0.90–1.16) | 264 | 1.03 (0.90–1.19) | 275 | 1.05 (0.92–1.19) | 242 | 1.15 (0.99–1.32) | |
| P for trend | 0.888 | 0.7566 | 0.4798 | 0.0801 | 0.7997 | ||||
| Right colon | |||||||||
| <1/month | 746 | 1.00 (ref.) | 684 | 1.00 (ref.) | 951 | 1.00 (ref.) | 810 | 1.00 (ref.) | |
| 1–3/month | 325 | 1.01 (0.88–1.15) | 298 | 1.00 (0.86–1.15) | 368 | 0.99 (0.87–1.12) | 333 | 1.05 (0.92–1.20) | |
| ≥1/week | 116 | 0.90 (0.73–1.10) | 101 | 0.87 (0.70–1.09) | 148 | 1.03 (0.86–1.23) | 127 | 1.12 (0.92–1.36) | |
| P for trend | 0.4537 | 0.4155 | 0.9648 | 0.3121 | 0.5440 | ||||
| Left colon | |||||||||
| <1/month | 484 | 1.00 (ref.) | 450 | 1.00 (ref.) | 447 | 1.00 (ref.) | 395 | 1.00 (ref.) | |
| 1–3/month | 217 | 1.08 (0.92–1.27) | 200 | 1.09 (0.92–1.29) | 171 | 0.98 (0.82–1.17) | 152 | 1.02 (0.84–1.23) | |
| ≥1/week | 88 | 1.14 (0.90–1.44) | 80 | 1.23 (0.95–1.59) | 62 | 0.95 (0.72–1.24) | 58 | 1.15 (0.86–1.53) | |
| P for trend | 0.3839 | 0.2197 | 0.4764 | 0.5505 | 0.4166 | ||||
| Rectum | |||||||||
| <1/month | 457 | 1.00 (ref.) | 425 | 1.00 (ref.) | 290 | 1.00 (ref.) | 267 | 1.00 (ref.) | |
| 1–3/month | 203 | 1.04 (0.88–1.23) | 192 | 1.06 (0.89–1.27) | 138 | 1.20 (0.97–1.47) | 123 | 1.14 (0.92–1.42) | |
| ≥1/week | 86 | 1.14 (0.90–1.44) | 77 | 1.16 (0.89–1.51) | 54 | 1.23 (0.91–1.65) | 46 | 1.19 (0.86–1.66) | |
| P for trend | 0.4375 | 0.3922 | 0.0464 | 0.1872 | 0.8549 | ||||
1 serving = ½ avocado or ½ cup
Adjusted for age at cohort entry and race/ethnicity.
Excluding participants with missing information on covariates.
Further adjusted for family history of colorectal cancer, history of intestinal polyps, history of diabetes, body mass index, pack-years of cigarette smoking, multivitamin use, non-steroidal anti-inflammatory drug use, physical activity, menopausal hormone therapy use for women only, alcohol intake, total energy intake, and HEI-2015 score.
Tests for heterogeneity between men and women were performed based on the fully adjusted models.
Table 3.
Association between avocado/guacamole intake and colorectal cancer risk by race and ethnicity in the Multiethnic Cohort, 1993–2017
| African American | Japanese American | Latino | Native Hawaiian | White | P for heterogeneity | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||||
| Cases | HR (95% CI)a | Cases | HR (95% CI)a | Cases | HR (95% CI)a | Cases | HR (95% CI)a | Cases | HR (95% CI)a | ||
|
| |||||||||||
| Men | |||||||||||
| <1/month | 275 | 1.00 (ref.) | 695 | 1.00 (ref.) | 202 | 1.00 (ref.) | 112 | 1.00 (ref.) | 325 | 1.00 (ref.) | |
| 1–3/month | 61 | 0.86 (0.65–1.14) | 215 | 0.99 (0.84–1.15) | 241 | 1.15 (0.95–1.39) | 46 | 1.08 (0.76–1.54) | 146 | 1.11 (0.91–1.35) | |
| ≥1/week | 20 | 0.78 (0.49–1.25) | 49 | 0.87 (0.65–1.17) | 127 | 1.18 (0.93–1.50) | 14 | 1.16 (0.65–2.09) | 54 | 1.15 (0.85–1.55) | |
| P for trend | 0.2784 | 0.3816 | 0.1631 | 0.5798 | 0.3102 | 0.2321 | |||||
| Women | |||||||||||
| <1/month | 402 | 1.00 (ref.) | 531 | 1.00 (ref.) | 192 | 1.00 (ref.) | 88 | 1.00 (ref.) | 310 | 1.00 (ref.) | |
| 1–3/month | 94 | 1.00 (0.79–1.25) | 183 | 0.99 (0.84–1.18) | 155 | 1.08 (0.87–1.34) | 49 | 1.25 (0.87–1.79) | 148 | 1.08 (0.89–1.32) | |
| ≥1/week | 35 | 1.14 (0.80–1.63) | 70 | 1.30 (1.00–1.68) | 67 | 0.99 (0.74–1.33) | 9 | 0.76 (0.37–1.55) | 61 | 1.27 (0.96–1.68) | |
| P for trend | 0.493 | 0.0633 | 0.9615 | 0.4319 | 0.0947 | 0.4025 | |||||
1 serving = ½ avocado or ½ cup
Adjusted for age at cohort entry, family history of colorectal cancer, history of intestinal polyps, history of diabetes, body mass index, pack-years of cigarette smoking, multivitamin use, non-steroidal anti-inflammatory drug use, physical activity, menopausal hormone therapy use for women only, alcohol intake, total energy intake, and HEI-2015 score.
Table 4.
Association between avocado/guacamole intake and colorectal cancer risk among respondents to 10-year follow-up survey in the Multiethnic Cohort, 2003–2017*
| Men (n=37,672) | Women (n = 47,400) | P for heterogeneityd | |||||||
|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||
| Cases | HR (95% CI)a | Casesb | HR (95% CI)c | Cases | HR (95% CI)a | Casesb | HR (95% CI)c | ||
|
| |||||||||
| <1/month | 417 | 1.00 (ref.) | 364 | 1.00 (ref.) | 429 | 1.00 (ref.) | 354 | 1.00 (ref.) | |
| 1–3/month | 177 | 1.02 (0.85–1.22) | 137 | 0.93 (0.76–1.15) | 171 | 0.83 (0.69–0.99) | 144 | 0.85 (0.70–1.04) | |
| ≥1/week | 59 | 0.95 (0.72–1.26) | 45 | 0.91 (0.66–1.26) | 65 | 0.87 (0.67–1.13) | 52 | 0.86 (0.63–1.16) | |
| P for trend | 0.705 | 0.5064 | 0.2101 | 0.2643 | 0.8932 | ||||
1 serving = ½ avocado or ½ cup
Average intake of baseline and 10-year follow-up. Cases occurred since 10-year follow-up.
Adjusted for age at 10-year follow-up and race/ethnicity.
Excluding participants with missing information on covariates.
Further adjusted for family history of colorectal cancer, history of intestinal polyps, history of diabetes, body mass index, pack-years of cigarette smoking, multivitamin use, non-steroidal anti-inflammatory drug use, physical activity, menopausal hormone therapy use for women only, alcohol intake, total energy intake, and HEI-2015 score (covariables from the 10-year follow-up survey).
Tests for heterogeneity between men and women were performed based on the fully adjusted models.
DISCUSSION
In this large and diverse prospective cohort study, we did not find that consumption of avocados/guacamole was associated with colorectal cancer risk.
Previous studies have suggested anticancer properties related to the high phytonutrient, dietary fiber, and monounsaturated fatty acid content of avocados (3). For example, in vitro studies have shown the anticarcinogenic properties of avocados against tumors of the lining cells of the colon and other organs (4). Observational epidemiological studies also have found an inverse relationship between fruits and vegetables (F&V), rich in many phytonutrients, and colorectal cancer risk. For example, Van Duijnhoven observed that when compared to those in the lowest F&V consumption group, individuals in the highest F&V consumption group had lower colorectal cancer risk (HR: 0.86; 95% CI: 0.75–1.00) (12). Similarly, Nomura et al. reported lower colorectal cancer risk in the highest F&V consumption group (HR: 0.74; 95% CI: 0.59–0.93) when compared to the lowest consumption group among men in MEC Study (13). Moreover, avocado is a great source of fiber with 4.6 grams in half of a fruit (3). Dietary fiber is protective against colorectal cancer as it can reduce bowel transit time, minimizing the negative effect of carcinogens (5). Similar to F&V, previous studies have generally found an inverse association between dietary fiber and colorectal cancer in various cohorts, such as MEC, PLCO Cancer Screening Trial, and EPIC (14–16). Lastly, researchers have found that MUFA may positively affect colorectal cancer by decreasing cell proliferation in different tumor cell lines (8). In a case-control study, Shekari et al. found that oleic acid intake was inversely associated with colorectal cancer (OR: 0.85; 95% CI: 0.80–0.90) (6). One half of a medium size avocado consists of 6.7 grams of MUFA, with oleic acid as the predominant MUFA (7).
Additionally, a recent study by Ericsson et al. observed a significant association between avocados and colorectal cancer in the HPFS but not in the Nurses’ Health Study (NHS) (9). It is important to note that we categorized our avocados/guacamole consumer groups similar to those of Ericsson et al.’s study (9) for a more direct comparison. In their study, they noted that compared to those who reported consuming less than one serving per month, individuals who reported consuming more than one weekly serving of avocados had a lower risk of colorectal cancer (HR 0.71; 95% CI 0.59–0.85) among 45,289 men in the HPFS but no association was found among 67,039 women in the NHS (9). Compared to Ericsson et al.’s study, our study had a greater percentage of participants in the highest consumer group among women (NHS (women): 5.2% vs. MEC women: 10.2%) but not among men (HPFS (men): 16.3% vs. MEC – men: 11%).
Despite these promising findings from previous studies and the underlying mechanisms to support this relationship, our study did not find a significant association between avocados/guacamole intake and colorectal cancer. There may be several reasons to explain these results. First, the MEC Study combined avocados and guacamole as one question in the FFQ. Therefore, this may have diluted the actual effect of avocados since guacamole contains a combination of ingredients besides avocados and the proportion of avocado used in guacamole may differ between recipes. Also, other ingredients (e.g., mayo or added oil) in guacamole may not protect against colorectal cancer, but we could not parse those effects. Second, the way in which different groups of people consume avocados could contribute to the inconsistent findings. For example, certain groups of individuals may eat avocado plain by itself, while others may consume it with other foods that are associated with higher colorectal cancer risk. These differences were likely captured by examining different ethnic groups, but we did not find any ethnic differences in the association. However, since we used FFQ in our study, we could not evaluate the foods commonly consumed with avocados. Thus, we cannot completely rule out the idea that those foods may differ even among individuals from the same ethnic group. Third, the amount of avocado consumed may not have reached the threshold to produce an effect in the MEC population. Flood et al. proposed this concept when discussing why F&V consumption was not associated with colorectal cancer risk in some studies (17). In our study, the means and medians of avocados/guacamole intakes in the three consumer groups were 0.03 and 0 (lowest consumer group), 0.38 and 0.29 (middle), and 2.12 and 1.24 (highest) serving/week, respectively. To put this into perspective, most clinical studies used one avocado per day (vs. a mean of one avocado per week in the highest consumer group) as an intervention to evaluate its effects on various outcomes (3). To examine higher intakes in the MEC, we compared those who consumed ≥1/2 serving or ≥1 serving/day vs. <1 serving/month of avocados/guacamole and did not find any significant association with colorectal cancer risk (Supplementary Table 1). However, the percentage of individuals daily consuming ≥1/2 or ≥1 serving was relatively small (1.4% and 0.5%, respectively).
Our study has several strengths. First, we used the MEC cohort, which included a large and diverse population in California and Hawaii. Second, this is a prospective cohort study, and colorectal cancer cases were identified through cancer registries of the SEER program with a virtually complete case ascertainment. Third, our fully adjusted model controlled for a large number of relevant covariates to better understand the association between avocados/guacamole consumption and colorectal cancer risk. Fourth, we used FFQ to assess avocados/guacamole intake, which is representative of typical intake than daily methods (18). However, our study includes several limitations. First, the baseline FFQ was collected between 1993 and 1996, so it may not represent current avocado consumption. Between 2011 and 2020, the annual consumption of avocado intake has risen from 5 to 9 pounds (i.e., 30 to 54 servings) per capita. Second, since the FFQ is self-reported, it may be prone to measurement error. Lastly, as mentioned above, avocados and guacamole were combined as one question in the FFQ. Thus, we could not account for the amounts of various ingredients used in guacamole, such as salt, mayo, added oil, and avocados, and separate those effects.
In conclusion, we did not find a significant association between avocados/guacamole and colorectal cancer risk in this large and diverse population. Future studies are warranted to further explore this association using other cohorts and a dietary assessment that captures avocado and guacamole intakes as individual food items, so we can better understand the discrepancy in findings among different studies.
Supplementary Material
Acknowledgments
Financial support, including the source and number of grants, for each author: partly supported by the National Cancer Institute (grant number U01 CA164973).
Footnotes
A conflict of interest disclosure statement; additional information is available at this link: Conflict of Interest Policy
FWC and NAF are employees of the Hass Avocado Board
CAH, LRW, LLM, and SYP declare no potential conflicts of interest.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The data generated in this study will be made available upon request, pending application to and approval by the Multiethnic Cohort Research Committee (https://www.uhcancercenter.org/for-researchers/mec-data-sharing).