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PROSTATE CANCER - MAYBE
TOMATO SAUCE DOES OFFER A BIT OF PROTECTION
(October 2004)
Healthful Life has maintained there is no diet that has been clearly shown
to promote prostate cancer and no dietary prescription that offers any
predictable reduction in risk. We may have to change that a bit - not
much, but a little bit.
There has been a lot of publicity given to the claim that tomatoes and
tomato products lower the risk of prostate cancer. Lycopene is found in
substantial amounts in tomatoes and has been said to be the active principle
responsible for protection. A very good experimental study of chemically-induced
prostate cancer in rats, published in the Journal of the National Cancer
Institute provides important information. The investigators examined the
effects of whole tomato powder, lycopene, and 20 percent caloric restriction
on prostate cancer deaths. In this model, most rats given a combination
of a chemical (a nitrosourea) plus testosterone develop prostate cancer
within one year. During a followup period of one and one-half years, 80
percent of the untreated rats died from prostate cancer as compared to
62 percent of those given the tomato powder in their diet, a 23 percent
statistically significant reduction. Those on a calorie-restricted diet
had a similar reduction in prostate cancer deaths. In contrast, lycopene
was not effective.
The tomato powder and calorie restriction acted independently, giving
the hope the two approaches could act additively.
The conclusion is that tomato powder offered modest protection, but it
was not due to the lycopene content of the tomatoes.
Commentary: The experimental rat studies need confirmation, but they are
very well conducted and the investigators make a strong argument that
the rat model of prostate cancer is a good one for understanding the problem
in men. Investigators from Harvard Medical School and the Harvard School
of Public Health have suggested that increased consumption of tomato-based
products may be prudent as a prostate cancer preventive. Their recommendation
is based on multiple diet questionnaires to a large group of health professionals
with about a 20-year followup period. In their studies, there was an 11
to 20 percent reduction in risk of prostate cancer with use of stewed
tomatoes and tomato sauce at least once a week and a reduction of risk
of 16 to 25 percent for two or more servings of tomato sauce a week.
The problem with the epidemiologic studies is that investigators have
assumed any benefit of tomato and tomato products (tomato sauce, tomato
juice, pizza, salsa, chili, ketchup) is due to the lycopene. Healthful
Life has pointed out that one-half the studies on tomatoes, tomato products,
and lycopene have been positive (tomatoes and tomato products reducing
risk of prostate cancer), one-half have shown no benefit. The Harvard
investigators seem to be one-half correct - although lycopene does not
seem to be responsible for any benefit, tomato products (particularly
tomato sauce) may offer some modest protection.
These are the issues with tomatoes and tomato products:
- The studies do not consistently show benefit for tomatoes themselves
or any tomato product, except tomato sauce which is made of tomato puree
and tomato paste and is cooked.
At present, we do not know whether raw tomatoes, pizza, salsa, or ketchup
offer any significant benefit. Tomato juice does not seem effective.
- Tomato sauce does seem to offer modest protection, but it does not appear
protective in those under age 65.
- Tomatoes have multiple potentially active substances (aside from lycopene),
including: phenols, vitamin C, folate, and a variety of carotenes. We
do not know which are the potentially effective constituents nor why cooking
seems to make the tomato products more effective; presumably, the cooking
makes the beneficial components more bioavailable, just as it does with
carrots.
to indicate the whole issue of tomato or tomato products as a preventive
for prostate cancer is unsettled. Certainly, at this point, there can
be no claim about tomato juice and the evidence on tomatoes themselves,
pizza, salsa, ketchup is not clear and we have inadequate information
on stewed tomatoes. Tomato sauce does appear encouraging even though the
effect is modest, but we need more epidemiologic studies to sort out whether
tomatoes or tomato products really do produce protection and, if so, how
much.
Meanwhile, the only tomato-related product that can be even tentatively
recommended is tomato sauce - at a dosage of two or more servings a week.
Even then, any benefit is modest. A couple of servings of tomato sauce
a week will not hurt; and it just might (or might not) offer some protection
against prostate cancer. Similarly, two or more servings of tomatoes a
week might reduce prostate cancer risk, but the evidence is a lot less
clear than with tomato sauce. As for lycopene supplements, unless we get
some new, strong, persuasive evidence - forget them. Of course, tomatoes
are part of a healthy diet that includes lots of vegetables and fruit.
Boileau, T., et al. Prostate carcinogenesis in n-methyl-n-nitrosourea
(NMU) - testosterone treated rats fed tomato powder, lycopene or energy
restricted diets. Journal of the National Cancer Institute. Vol 95 (November
5) Pgs 1578-1585. 2003.
Giovannucci, E., et al. A prospective study of tomato products, lycopene
and prostate cancer risk. Journal of the National Cancer Institute. Vol
94 (March 6) Pgs 391-398. 2002.
One member of our Scientific Advisory Board thinks that even a tentative
and cautious recommendation about tomato sauce is too strong. He views
the evidence as weak and prefers no recommendation.
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