Eating more vegetables does not reduce low-grade prostate cancer progression risk
medwireNews: A behavioral intervention to increase vegetable consumption does not reduce the risk for disease progression over 2 years in men with early-stage prostate cancer undergoing active surveillance, phase 3 study data show.
J Kellogg Parsons (UC San Diego Moores Comprehensive Cancer Center, La Jolla, California, USA) and co-investigators say their findings “fail to support prevailing assertions in evidence-based clinical guidelines and the popular media that diets high in micronutrient-enriched vegetables improve cancer-specific outcomes among prostate cancer survivors.”
The multicenter Men’s Eating and Living (MEAL) Study included 443 men aged 50 to 80 years with early-stage prostate cancer (grade group 1 for those under 70 years of age, grade group ≤2 for older participants, stage cT2a or less, prostate-specific antigen [PSA] <10 ng/mL) who were randomly assigned to complete a diet-focused behavioral intervention (n=226) or a control intervention (n=217).
Men in the intervention group received regular telephone-based counseling that used motivational interviewing techniques to promote the consumption of at least seven servings of fruit or vegetable per day including at least two servings of both cruciferous vegetables and tomatoes. The control group did not receive counseling calls but were given printed information from the Prostate Cancer Foundation encouraging the consumption of a vegetable-rich diet.
At 12 months, participants in the intervention group reported significant increases compared with controls in daily total vegetable intake (mean change, 2.43 vs 0.45 servings), cruciferous vegetable intake (mean change, 43.10 vs 6.44 g/day), and total carotenoids (mean change, 13,839.31 vs 2030.79 μg/day), which persisted at 24 months.
The researchers describe the magnitude of theses dietary changes, as “substantial,” adding that the intervention had “a clinically meaningful effect.”
In spite of this, there was no significant difference between the groups in the time to prostate cancer progression, and no difference in estimated 24-month progression-free survival rates at 43.5% and 41.4% in the intervention and control groups, respectively.
Over the 2-year follow-up period, 124 participants in the intervention group and 121 in the control group experienced disease progression, which was defined as a PSA level of 10 ng/mL or greater, a PSA doubling time of less than 3 years, or upgrading (increased tumor volume or grade) on follow-up prostate biopsy.
Writing in JAMA, Parsons and co-authors note that “enthusiasm for diet-based cancer interventions remains high, driven by assumptions of causality made from epidemiological data.”
However, they point out that these studies are limited by “small effect sizes and substantial confounding.”
Therefore, the “overdependence of prostate cancer nutrition guidelines on observational studies with uncertain clinical validity suggests a need to shift nutritional research toward definitive [randomized controlled trials],” they add.
Parsons et al conclude that their findings “do not support use of [the MEAL] intervention to decrease prostate cancer progression in this population, although the study may have been underpowered to identify a clinically important difference.”
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