AICR e.Newsletter
August 2006
Diet and Cancer News

Fishing for Cancer Protection

It takes a lot of evidence to show that some food or food component prevents disease.  There are five or six categories of studies used to investigate diets.  The experts look for consistent results within each category and confirmation among the categories.
 
In regard to fish and cancer, we’re only halfway there.  Many studies suggest populations that eat more fish have less cancer.  The Inuit Indians, who consume an extraordinary amount of fatty fish, have less cancer than other populations. Similarly, the Japanese, for whom fish is a staple, have less breast and prostate cancer than people living on a typical western diet.

The results of such population studies sent researchers to the laboratory to see exactly what it is in fish that reduces cancer risk. Research conducted in test tubes or with laboratory animals showed that the omega-3 fatty acids, so plentiful in cold-water fish, impede the development of cancer in several ways.

Once paired with certain enzymes, omega-3 fatty acids break down into molecules that reduce the production of compounds that promote cancer.  They also promote apoptosis (cancer cell suicide) and impede the growth of the blood vessels tumors need to survive.

Omega-3s also thwart the cancer-promoting activity of omega-6 fatty acids.  These fatty acids have almost identical structures and pair with the same enzymes. When omega-6s do so, they break down into molecules that promote inflammation, stimulate cells to multiply and suppress apoptosis. By competing for those same enzymes, omega-3s limit the effect of omega-6s and reduce the likelihood of cancer developing.

All of this molecular activity has been demonstrated in the laboratory. But the experts want to see evidence that these same processes occur in the human body.  To test this, researchers conduct observational studies (such as cohort studies) and intervention studies (such as clinical trials). They follow or manage the dietary intake of fish among a large number of individuals and relate that to their cancer incidence.

Human Studies Hit a Reef
 
At this stage the confusion sets in.  During the last two years, three articles that systematically review cohort studies and clinical trials have been published. They all describe the evidence as conflicting and inconclusive. The clinical trials show no effect of omega-3s on cancer.  Some cohorts did find an association between fish consumption and lower risk for breast, colon, lung and prostate cancer.  But as many or more failed to find that association, and even a few studies showed increased risk.

 It is not clear if these studies failed to find the expected association because it doesn’t exist or because their designs were flawed.  It is notoriously difficult to conduct such studies in regard to diet.  They require well-designed questionnaires and accurate self-reporting, both of which are hard to come by.  It remains to be seen if improvements in the way these studies are conducted will lead to more positive results.

Meanwhile, where does that leave us?  Although the experts are not yet convinced, a sizeable body of evidence suggests that omega-3 fatty acids may reduce cancer risk.  Even more evidence suggests that fish consumption reduces risk of heart disease, Alzheimer’s disease and arthritis.  So for most people (there are some exceptions) it would be wise to eat several servings of fish a week while waiting to see the outcome of the research on fish and cancer.  Be sure to include the cold-water fish with the highest yield of omega-3 fatty acids.  They are herring, salmon, sardines, mackerel, rainbow trout, bluefish, seabass, albacore tuna and bluefin tuna.

Perhaps the best reason to eat these and other fish on a regular basis is that they are good sources of protein without the heavy dose of saturated fat and calories that usually come with it.  AICR recommends that people concerned with reducing cancer risk and managing their weight cover 2/3 (or more) of their plate with vegetables, fruit, whole grains and beans and 1/3 (or less) animal protein.  One of the best possible choices for that “1/3 or less” is fish.

Learn how to cook fish with this easy AICR recipe.

For more fish recipes visit our Recipe Corner online.