Dr Gary Fraser is a Professor of Medicine and Epidemiology at Loma Linda University Health, and the former primary director of the Adventist Health Study; a prospective cohort study of 96,000 Seventh-day Adventist men and women in the US and Canada. His latest research, funded by World Cancer Research Fund (WCRF), is revealing a fascinating link between tomatoes and prostate cancer.
Prostate cancer is the second most common cancer worldwide. In the US, there were an estimated 165,000 new cases of prostate cancer and nearly 30,000 deaths in 2018. Since 1989, a research team at Loma Linda University Health has examined a number of dietary practices to see which offer promise in preventing chronic diseases such as heart disease and cancer. Earlier research in the Adventist Health Study and several other projects internationally suggest high lycopene intake is associated with reduced risk of prostate cancer. Tomato and tomato-based products are of particular interest as they are major sources of the carotenoid lycopene.
Seventh-day Adventists are well-known for encouraging their members to adopt healthy lifestyle practices. Loma Linda University Health is conducting what is widely recognised as the largest ongoing research of Adventists’ dietary choices and healthy living habits. To examine how tomato consumption may impact the development of prostate cancer, we looked for significant relationships between diet and prostate cancer in nearly 28,000 Adventist men in the US.
How our research was done
All Adventist Health Study participants agree to fill out self-administered food frequency questionnaires reporting the average number of times per week they ate approximately 200 different foods and beverages, and the serving sizes. After tracking the study’s male participants, all of whom were cancer-free when they enrolled in the project, we found that 1,226 of them had been diagnosed with prostate cancer, and 355 of those were aggressive cases.
As we focused on dietary lycopene levels, we found that men who consumed canned and cooked tomatoes five to six times a week had a 28 per cent decreased risk of prostate cancer compared with men who never consumed this food. The effect was still significant even after adjusting for potential confounders including ethnicity, education, obesity, exercise levels, alcohol consumption and others. Interestingly, we found no significant association between prostate cancer and consumption of raw tomatoes, tomato soup, tomato sauce and tomato-based vegetable juice.
While all tomatoes and tomato-based products contain lycopene, other studies have shown that lycopene is absorbed at different rates depending on the product consumed. Lycopene bioavailability is higher when tomatoes have been heated or cooked, and especially if cooked with oil. Processing tomatoes in this way contributes to the separation of the lycopene from the carrier proteins.
Our conclusion for cancer prevention
This research suggests that it is particularly cooked tomatoes that may play a significant role in reducing a man’s risk of developing prostate cancer. It may be their lycopene content that is the active principle. We will continue to look at tomato products and their potential to reduce prostate cancer risk. Still, men concerned about developing prostate cancer could consider adding cooked and canned tomatoes to their diet on a regular basis.