Photo: Mariana Stern, Ph.D., of the Keck School of Medicine of USC / by Jon Nalick
New research from the University of Southern California (USC
) and Cancer Prevention Institute of
has found that eating salmon and other dark, fatty fish may decrease
the risk of developing prostate cancer, while consuming flounder and
other white, lean fish may increase the risk.
It depends on how the fish is cooked.
Previous studies have emphasized the health benefits of dark fish —
rich in omega-3 fatty acids — linking their consumption to the
prevention of various diseases.
“One would expect eating dark and oily fish would be beneficial in
preventing prostate cancer, but that protective effect seems lost if
fish are cooked with high-temperature methods, in particular
pan-frying. Similarly, diets high in lean, white fish seem to mostly
increase risk when the fish is pan-fried, and appear to offer no
protective benefit when cooked using other methods,” said Mariana Stern,
, associate professor of preventive medicine at the Keck School of Medicine of USC
Stern led the analysis, “Fish
intake, cooking practices, and risk of prostate cancer: results from a
multi-ethnic case-control study,” which appears online in the
journal Cancer Causes & Control
It is the first study to show that fish type and its method of cooking
may be relevant in terms of protecting against or increasing the risk
for prostate cancer, Stern added.
In the United States, more than 240,000 men are diagnosed annually with
prostate cancer and about 33,720 die from the disease, according to the
National Cancer Institute. Only lung cancer kills more American men.
According to the Prostate Cancer Foundation, there are no proven
strategies for preventing the disease, but changes in diet and
lifestyle appear to have reduced the risk of disease progression.
The researchers analyzed data from nearly 3,000 men who participated in
the California Collaborative Prostate Cancer Study in the Los Angeles
and San Francisco Bay areas. Sue A. Ingles,
, associate professor of preventive medicine at the Keck
School of Medicine of USC and Esther
M. John, Ph.D.
of the CPIC headed that collaborative project. Study participants
completed a comprehensive survey that included questions about the
amount and types of fish they consumed on a weekly basis and how the
fish was cooked. More than 60 percent of the men were diagnosed with
advanced prostate cancer.
The analyses found that diets high in dark fish like salmon, mackerel
and sardines reduced the risk of prostate cancer if the fish were
cooked at low temperatures, like baking or boiling. This suggested
protective effect disappeared when the fish was cooked at high
temperatures, such as broiling, grilling or pan-frying.
Surprisingly, men who ate two or more servings per week of white fish
cooked using high-temperature methods were twice as likely to develop
advanced prostate cancer than men who never ate any fish. The study
found no association between cancer and diets high in white fish cooked
using low-temperature methods.
The study also noted that high intake of deep-fried fish, such as fish
sticks and fish sandwiches, was linked to an increased risk of prostate
cancer among Hispanic men, but not among non-Hispanic whites or
African-Americans, who reported the highest intake of fried fish than
any other ethnic group studied.
The researchers do not know what causes the disparities they observed
between dark and white fish, but they propose two hypotheses. One,
carcinogens may form while cooking fish at high temperatures, harm from
which may be negated by the omega-3 fatty acids in dark fish.
Alternatively, given that white fish absorbs more oil than dark fish
when pan-fried, this cooking method could alter the ratio of good fats
to bad ones.
“It’s too early to make any dietary recommendations but, given the few
known risk factors for prostate cancer, the results of this study
emphasize that diet may be a relevant modifiable factor for prostate
cancer risk,” Stern said.
Co-authors include Amit D. Joshi, who received his Ph.D. in molecular
epidemiology from the Department of Preventive Medicine at the Keck
School of Medicine; Ingles of USC; CPIC’s John and Jocelyn Koo, also of
the CPIC. They received financial support from the California Cancer
Research Program, the National Cancer Institute, the National Institute
of Environmental Health Sciences and the Prostate Cancer Foundation.