In this study we found that adherence to the USDA Dietary Guidelines for Americans, as measured by the Healthy Eating Index, appeared to have limited value in preventing ovarian cancer. Overall, our study provided little support for a role of diet on ovarian cancer risk, which is consistent with current evidence linking nutritional factors and ovarian cancer prevention [5
The HEI was revised in 2005 to increase emphasis on the quality of an individual’s diet rather than quantity. Hence, components such as whole grains, whole fruit, and dark green and orange vegetables were added to the revised version of the index. Due to small numbers in the “poor” and “good” categories, we used tertile cutpoints for the HEI score instead of conventional thresholds. However, this is not unique to our study as several other studies that have investigated the association between HEI-2005 and cancer risk have also used quintiles and quartiles for the HEI in place of standard thresholds [18
]. Pre-specified cutoffs are also not emphasized in the development of the HEI-2005 [23
]. Nonetheless, it is possible that we were unable to detect an association between the HEI and ovarian cancer risk because there was not enough range in the HEI values in this population. The HEI has been utilized in the past to estimate colorectal cancer risk [19
], breast cancer risk [18
] endometrial cancer risk [17
], major chronic disease risk [21
], and food avoidance due to oral health problems [33
]. However, the HEI’s potential to successfully predict these health conditions has not always been consistent. For instance, similar to our study, studies that evaluated major chronic disease (including cancer) risk in men and women [21
] and endometrial cancer risk [17
] reported limited evidence for adherence to dietary guidelines in predicting disease risk. There was one study that investigated adherence to the dietary guidelines for Americans and incident ovarian cancers using data from the Iowa Women’s Health Study [40
]. In contrast to the HEI, their index included body mass index and physical activity. They reported increased ovarian cancer risk associated with higher dietary guidelines scores (meaning better compliance with the recommendations). However, when they evaluated their dietary guidelines index after excluding physical activity and BMI, the relationship disappeared and results were similar to ours.
In our study, when each of the 12 food components (total fruit, whole fruit, total vegetables, dark green and orange vegetables, total grain, whole grain, milk, meat and beans, oils, saturated fat, sodium, and total calories from solid fat, alcoholic beverages, and added sugar) making up the HEI was individually analyzed, no major associations emerged. Our findings are consistent with other studies [5
] and with the conclusion of the 2007 WCRF/AIRC Report [10
], which found the evidence linking diet and ovarian cancer to be limited.
Certain limitations of this study should be noted. Some institutional barriers precluded the concurrent recruitment and data collection in the ovarian case group and the controls in the EDGE Study, as initially planned. However, we conducted a secular trend analysis for cases and controls to assess possible changes in dietary intake over time. There was no significant difference in age adjusted mean values for the HEI score, total vegetable, total fruit, or percentage of saturated fat intake between two time periods for either cases or controls.
As in any case-control study, the issue of recall bias cannot be ignored especially for a disease such as ovarian cancer. Ovarian cancer is typically diagnosed in advanced stages, and cases tend to be very sick when they are diagnosed, which could impair their ability to recall their dietary intake prior to diagnosis. However, consistency of our findings with current literature on the topic provides some reassurance. Another concern is the low response rates. Participation rates around 50% in population-based studies are not unusual today, particularly among controls [41
]. To evaluate possible selection bias, we compared the characteristics of women consenting to participate in the study to all women diagnosed with epithelial ovarian cancer using New Jersey State Cancer Registry data in the same counties during a similar time period [42
]. Race and ethnic distribution was similar, while the cases consenting tended to be slightly younger with a median age of 56 years at diagnosis, compared to a median age of 61 years at diagnosis for the total population of cases. The distribution by histology, stage, and grade was generally similar. For controls, we do not have information on those who could not be reached or did not participate; however the distribution of the main risk factors in cases and controls is similar to that reported in other studies. This provides some reassurance that any potential selection bias may be minimal.
In conclusion, we did not observe any evidence that following the Dietary Guidelines for Americans helps in reducing ovarian cancer risk. However, this has not been evaluated in large cohort studies, which may provide more definite evidence regarding their possible role on ovarian cancer prevention.