The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 6 No.
5 • November-December 2003
Lycopene May Not Provide All the Benefits of Tomatoes in Preventing Prostate Cancer
A new study shows that when foods contain a number of potentially beneficial compounds, studies based on just one of them may give you a false picture of that food’s health-promoting qualities. This study compared the effects of tomato powder, lycopene, and caloric restriction in preventing the development of prostate cancer in rats fed N-methyl-N-nitrosourea and testosterone to induce that cancer.
194 rats treated with the carcinogen and testosterone were divided into groups receiving whole tomato powder (containing 13 mg lycopene/kg of diet), lycopene beadlets (161 mg lycopene/kg of diet*) or control beadlets. The rats in each group were then subdivided randomly into groups receiving ad libitum feeding or 20% dietary restriction. The results showed that the risk of death with prostate cancer was lower for rats fed the tomato powder than for the rats fed control beadlets and the rats fed the lycopene beadlets (even though the lycopene-fed rats had greater plasma concentrations of total lycopene than the rats fed the tomato powder). The mortality from prostate cancer was similar between the control and lycopene-beadlet-fed rats.
Not surprisingly, 79% of the ad libitum-fed rats died with prostate cancer, while only 65% of the restricted-fed rats did so.
As mentioned in the paper, tomatoes contain many compounds besides lycopene that may have been involved in the tomato-powder protection, including all-trans-beta-carotene, 9-cis-beta-carotene, polyphenolic compounds such as quercetin, other phenolics, vitamin C, and folate, to name a few. The authors do not rule out that lycopene may have been a contributor to the total effects of tomato powder, but they note that since 82% of lycopene intake is obtained by American men from just one source, tomatoes, epidemiological studies cannot differentiate which of the many substances in tomato are responsible for its protection against prostate cancer.
The editorial that commented on this paper also notes that Americans consume an average of 91 pounds of tomatoes per capita per year, second only to potatoes among all fruits and vegetables. In other words, the fact that men with elevated plasma lycopene levels or who consumed more tomato products and therefore had higher lycopene intake have been shown to have a lower prostate cancer risk is undoubtedly (at this point) due to their higher consumption of tomatoes rather than of lycopene supplements.
Another paper that had results consistent with the above was an epidemiological study of the effects of dietary lycopene, consumption of tomato products, and cardiovascular disease in women. The study group was 39,876 middle-aged and older women initially free of CVD and cancer. While dietary lycopene was not found to be strongly associated with the risk of CVD, there was a possible inverse association between CVD and consumption of higher levels of tomato products (at least 2 servings/week each of tomato sauce and of pizza).
Other work, such as the effect of lycopene on prostate cancer cells in culture or the chemical properties of lycopene, suggests that lycopene itself may have protective effects. Only more research can sort this out. In the meantime, we are both† continuing to take our lycopene supplements as well as consuming tomatoes and tomato products.
- Boileau et al. Prostate carcinogenesis in N-methyl-N- nitrosourea (NMU)-testosterone-treated rats fed tomato powder, lycopene, or energy-restricted diets. J Natl Cancer Inst 95(21):1578-86 (2003).
- Gann, Khachik. Tomatoes or lycopene versus prostate cancer: is evolution anti-reductionist? J Natl Cancer Inst 95(21):1563-65 (2003).
- Gann et al. Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis. Cancer Res 59:1225-30 (1999).
- Giovannucci et al. A prospective study of tomato products, lycopene, and prostate cancer risk. J Natl Cancer Inst 94(5):391-8 (2002).
- Kim et al. Effect of lycopene on prostate LNCaP cancer cells in culture. J Med Food 5(4):181-7. (Lycopene significantly decreased the growth of cells in a dose-dependent manner.)
- Di Mascio et al. Lycopene as singlet oxygen quencher. Arch Biochem Biophys 274(2):532-8 (1989).
- Sesso et al. Dietary lycopene, tomato-based food products, and cardiovascular disease in women. J Nutr 133:2336-41 (2003).