In this large cohort of breast cancer survivors, post-diagnosis diets high in saturated and trans fat were associated with decreased all-cause survival. Though there were suggestive dietary associations for breast cancer survival, none were statistically significant.
Women who consumed the highest quartile of saturated fat (median of 13% kcal) had a 41% statistically significant higher risk of all-cause survival compared to women in the lowest quartile, who consumed a median of 7% calories from saturated fat (P-trend = 0.03). Doubling percentage of energy from trans fat was associated with a 78% statistically significantly greater risk of death (P-trend = 0.01).
A recent report from the Center for Disease Control and Prevention indicated that saturated fat intake as a percentage of energy intake decreased between 1971–2000 among US women from 13% to 11% (P
-trend = 0.01), but energy intake has increased over this period, suggesting similar exposure to absolute amounts of saturated fat over time [13
]. Average trans fat intake in the United States during the enrollment period for this study was approximately 2% to 3% of energy, which is greater than reported by participants of this study [14
]. Despite a large body of evidence that alcohol increases risk of breast cancer [15
], there was no association between alcohol intake and breast cancer survival. Others have recently reported either no association between alcohol intake and survival or an inverse relation between alcohol intake and survival, so this area warrants further study [16
Similar to our findings, qualitative reviews reported no consistent association between total fat consumption either pre- or post-diagnosis and breast cancer survival after energy adjustment [19
]. None of the studies reviewed by Rock and Demark-Wahnefried reported an association between total dietary fiber intake and breast cancer recurrence or overall survival; only three studies reported an inverse association between fruit and vegetable consumption and survival [21
Strengths of our study include the prospective design, its large sample size, and detailed information on diet obtained after the diagnosis of breast cancer. In addition, we were able to assess many potential confounding variables. The relation between saturated and trans fat intake and all-cause survival that we observed is consistent with observational and controlled-feeding studies of cardiovascular disease and other chronic diseases [22
]. This also supports the ability of our dietary assessment to detect moderate associations with survival.
When restricting attention to deaths related to cardiovascular disease (N = 123), there were suggestive (P-trend = 0.11) inverse associations between trans fat and survival, and positive associations between polyunsaturated fat (P-trend = 0.05) as well as alcohol (P-trend = 0.14) with survival, although these associations likely did not reach statistical significance, possibly because of the limited number of observed deaths.
Nonetheless, some limitations should be considered when interpreting these results. Though we used a validated self-reported measure of diet adapted from the Nurses’ Health Study (NHS), measurement error is a pervasive problem in dietary assessment [25
]. Because measurement error is likely non-differential with respect to outcome, this should lead to attenuation in risk estimates. We lacked information on the clinical status of breast cancer at the time of the CWLS questionnaire, but we excluded women who reported any recurrence of breast cancer at that time. Also, survival may depend upon hormone responsiveness [28
], but steroid receptor status was not available from state cancer registries for all CWLS participants.
The CWLS involved women that were previously enrolled in our sequential case-control studies of breast cancer, and thus women were not immediately followed from the initial diagnosis of their breast cancer. One practical limitation of the data is that our results may only be applicable to women who survive the first several years after breast cancer diagnosis. A potential concern is that the observed inverse associations with survival might reflect reverse causation if increased saturated and trans fat intakes are associated with worsening health and poor prognosis. The relatively short interval, however, between diagnosis and subsequent entry into the cohort for the majority of women minimizes the likelihood of bias caused by selective survival. Also, information was available on a number of surrogate measures including treatment interfering with diet, recent unintentional weight loss, general health status, and frequency of mammogram or physician breast or chest wall examination after diagnosis, and hazard ratios were essentially unchanged in analyses restricted to women in apparent good health at the time of CWLS entry and who had undergone screening since diagnosis. Taken together, these results suggest that reverse causation is unlikely to account for the inverse association of saturated and trans fat intake with overall survival in these data.
Finally, our study did not consider diet prior to breast cancer diagnosis, or the pre- to post-diagnosis change in dietary patterns. Our study, instead, was designed to inform how a woman’s post-diagnosis diet influences survival. This research provides little evidence for an association between dietary intake and breast cancer survival, but provides additional support for an adverse relationship between saturated and trans fat intake and overall survival following a breast cancer diagnosis.