New research shows that a low-calorie diet slows the progress of
prostate cancer in animals. Tumor progression was inhibited
irrespective of how the calories were reduced; ie, by cutting fat or
carbohydrates or by changing the overall diet. The research suggested
further that the way in which the lower-calorie diet slowed tumor
growth in rats and mice also helped retard the development of new
blood vessels in the tumor.
This study clearly demonstrated in two different animal models
that energy intake influences the growth of prostate tumors,
said Steven Clinton, md, phd, director of cancer prevention and
control at the Ohio State University Comprehensive Cancer
CenterArthur G. James Cancer Hospital and Solove Research
Institute. Our findings provide further evidence that prostate-cancer
development might be influenced by lifestyle. They also suggest that
maintaining a proper energy balancean appropriate weight for
heightmay inhibit the progression of prostate cancer. In
addition, these results will help clinical investigators design other
studies to explore the relationship between diet and prostate cancer
Three Sets of Experiments
The study, which appeared in a recent issue of the Journal of the
National Cancer Institute, involved three sets of experimentstwo
using rats and one using mice.
In the first set of experiments, malignant cells from a form of rat
prostate cancer were transplanted into four groups of cancer-free
rats. Each group of rats was then assigned a specific diet. One group
was allowed to eat as much as desired. A second group, made up of
castrated rats, was also allowed to eat freely. The third and fourth
groups were fed diets containing 20% and 40% fewer calories,
respectively, than the groups following unrestricted diets. The
researchers used castrated rats because depriving prostate tumors of
androgens is one of the most effective ways of slowing tumor growth.
Clinton was investigating how diet would affect tumor growth compared
to the standard method of androgen deprivation.
The second experiment also involved groups of castrated and
noncastrated rats that were allowed to eat at will, plus three other
groups fed 30% fewer calories. The groups differed in the source of
caloric restriction. One group
had fewer calories from fat, another had fewer calories from
carbohydrates, and a third had fewer calories in the overall diet.
After 16 weeks, the researchers removed the tumors and weighed and
measured them. They examined tumor structure, rates of cell
proliferation and cell death, and the number of blood vessels within
each tumor. They also measured the activity of the gene for vascular
endothelial growth factor (VEGF).
In the third set of experiments, the researchers transplanted human
prostate tumor cells into mice lacking an immune system (ie, severe
combined immunodeficient [SCID] mice). This approach allowed them to
determine whether human prostate cancer cells might also be sensitive
to dietary intervention. Four groups of mice were used. One group was
allowed to eat at will, while the other three were fed diets
containing 30% fewer calories. As in the preceding rat experiment,
one group was fed a totally restricted diet, while the second and
third groups were fed diets restricted in fat and carbohydrates.
Fewer Calories Equals Smaller Tumors
All experiments ran for 16 weeks. Noncastrated rats from the first
experiment had tumor diameters averaging 2.2 cm. Castrated rats, on
the other hand, had tumor diameters averaging only about one-fourth
that size. Animals fed 40% fewer calories had tumors averaging about
60% of the size of tumors in castrated rats, while those fed 20%
fewer calories had tumors that were three-quarters of the size of
tumors in castrated animals.
The second rat experiment demonstrated that the type of caloric
restriction whether overall, or from fat or
carbohydratehad no significant influence on tumor size. All
slowed tumor growth to a similar degree.
The mouse experiment using transplanted human prostate tumor cells
also showed that a diet lower in calories slowed prostate tumor
growth, regardless of how the calories were cut.
It may be that a high-fat diet has little influence on prostate
cancer if men exercise, consume a diet of modest calories, and
maintain a lean body mass and an appropriate weight for their
height, said Dr. Clinton.
Angiogenesis Also Reduced
The study also suggested that both castration and a low-calorie diet
reduced angiogenesis in prostate tumors, as well as the production by
tumors cells of growth factors that promote angiogenesis.
We now need to conduct nutritional studies in men with early
prostate cancer to learn if dietary changes can alter the course of
their disease, and if so, whether it is related in some way to tumor
angiogenesis, said Dr. Clinton.