1. In this prospective cohort study, greater consumption of healthful plant-based foods was associated with lower risk of aggressive forms of prostate cancer.

2. Furthermore, a higher healthful plant-based diet index was associated with decreased risk of total, lethal, and fatal prostate cancer in men younger than 65 years old, but not in older men.

Evidence Rating Level: 2 (Good)

Prostate cancer is the most common cancer type, and the second leading cause of cancer death, among men in the United States. Previous animal studies have shown that a diet containing more plant protein compared to animal protein slowed tumor growth in prostate cancer. However, the relationship between plant-based protein consumption and prostate cancer in human populations is unclear. This study investigated the association between plant-based diets and prostate cancer risk.

This prospective cohort study included 47,239 male health professionals who were part of the Health Professionals Follow-Up study (1986-2014). Men were excluded from the study if they had a history of cancer, consumed <800 or >4200 calories per day, or had more than 70 items missing on the reported food frequency questionnaire (FFQ). Data regarding lifestyle, medical history, and disease outcomes were collected every 2 years. Dietary information was collected every 4 years with a validated FFQ and was used to calculate overall plant-based diet index, healthful plant-based diet index, and unhealthful plant-based diet index. Self-reported cancer diagnosis and clinical features were confirmed through medical records or state tumor registries. The primary outcome was prostate cancer incidence and severity of disease.

The results of the study demonstrated an overall significant association between higher plant-based diet index and lower risk of fatal prostate cancer, but not total prostate cancer or localized disease. When patients were stratified by age, results showed that higher healthful plant-based diet index was associated with lower risk of total, lethal, and fatal prostate cancer in men younger than 65 years old, but not in older men. However, this study was limited by its use of diet indices developed for diabetes and cardiovascular disease which may misclassify certain foods as healthy or unhealthy contrary to epidemiological studies specific to prostate cancer. Nonetheless, these results suggested a potential benefit of plant-based food as an environmental risk reduction strategy for prostate cancer.

Click to read the study in The American Journal of Clinical Nutrition

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