Higher diet quality associated with reduced risk of prostate cancer grade reclassification

A new study reveals that men with prostate cancer undergoing active surveillance may significantly reduce their risk of disease progression by adhering to a healthy diet, highlighting the impact of nutrition on cancer outcomes.

Study: Diet Quality, Dietary Inflammatory Potential, and Risk of Prostate Cancer Grade Reclassification. Image Credit: PeopleImages.com – Yuri A/Shutterstock.com

A recent article in JAMA Oncology examined whether the risk of prostate cancer grade reclassification was affected by dietary quality and inflammation.

Early prostate cancer is typically managed by active surveillance. Such patients often try to reduce their risk of progression by adopting a healthier diet despite the lack of evidence for this outcome.

For instance, the Men’s Eating and Living (MEAL) randomized clinical trial (RCT) failed to demonstrate a reduced risk of disease progression after increasing vegetable intake.

The current study sought to understand how chronic inflammation promoted by dietary factors was associated with prostate cancer progression.

About the study

The study included 886 mostly White men with grade group (GG) 1 prostate cancer diagnosed between January 2005 and February 2017. All were under active surveillance. The median age was 66 years.

At the beginning of the surveillance program, the participants provided data on their dietary habits using a food frequency questionnaire. The median follow-up period was 6.5 years.

The food data was analyzed based on the Healthy Eating Index 1999-2000 (HEI) and the energy-adjusted HEI (E-HEI). This allowed researchers to classify the participants for adherence to the Dietary Guidelines for Americans.

The dietary inflammatory index (DII) and energy-adjusted DII (E-DII) are measures of dietary inflammatory potential. These indices were calculated from the self-reported nutritional data. As expected, they were inversely proportional to the HEI and E-HEI scores.

These indices were then analyzed for association with prostate cancer grade reclassification from GG1 to GG2 or higher grades during the period of active surveillance. The results were adjusted to compensate for established prognostic factors related to active surveillance and for smoking history at baseline.

Reclassification and dietary quality

After a median follow-up of 6.5 years, 187/886 men, or 21%, were reclassified to grade GG2 or higher. Of these, 55, or 6%, were reclassified to GG3 or higher, termed extreme grade reclassification.

At three years, five years, and ten years, the proportion of men who were grade-reclassified was 7%, 15%, and 33%, respectively. For those reclassified to GG3 or higher, the proportion was 2%, 4%, and 10%, respectively.

The scientists sought associations between prostate cancer grade reclassification and a healthy diet at baseline. The risk of grade reclassification fell by 15% and 14% for each standard deviation increase in baseline HEI and E-HEI scores, respectively. For extreme grade reclassification, the risk fell by 28% and 27% per standard deviation increase in HEI and E-HEI scores, respectively, at baseline.

Baseline DII and E-DII failed to show associations with grade reclassification despite their inverse association with HEI and E-HEI scores.

Importance of these associations

This is the first study to report such an association. The larger cohort size and prospective design, as well as the longer period of surveillance, lend validity to the observations.

Previous smaller studies that reported outcomes in patients with GG1 grade disease and a few with GG2 did not find significant inverse associations between diet quality in terms of these scores and grade reclassification during follow-up.

This study also demonstrates, for the first time, that dietary inflammation is not linked to grade reclassification risk. This is despite the suggested link between a higher diet quality and lower dietary inflammation.

In contrast, many studies have shown that men with a higher DII and E-DII have a higher risk of developing prostate cancer.

These results may not be generalizable since most patients were White, had a higher frequency of surveillance biopsies than in other studies, and had markers of a generally healthier lifestyle. Alternatively, they may have under-reported their energy intake.

Conclusions

Men with early prostate cancer may have a lower risk of grade reclassification, especially to higher grades that require active treatment, if they follow healthy dietary guidelines.

This suggests that interventions to improve dietary quality have the potential to prevent the progression of early prostate cancer, keeping it below the threshold for treatment.

Further work in more diverse groups is required to validate and confirm these findings. Meanwhile, this study may help to promote adherence to healthy diets among patients on active surveillance who are already eager to execute lifestyle changes that might prevent disease progression.