Cancer-patient and animal studies add to growing list of research reports pinning increased risk of prostate and colon cancer on America’s fatty acid imbalance
by Craig Weatherby
Recent weeks have added more fuel to fight to redress America’s unhealthful imbalance in intake of omega-6 fatty acids (too much) omega-3 fatty acids (too little).
Today’s issue of Vital Choices contains a related report on new evidence of the role this imbalance plays in promoting diabetes and heart disease, by promoting the cluster of factors called Metabolic Syndrome (See “Omega-6/Omega-3 Imbalance Pushing Heart/Diabetes Perils”).
A new evidence review from Boston’s Dana-Farber Cancer Institute – home of the famed, Red Sox-sponsored Jimmy Fund for childrens' cancers – adds damning evidence against the "standard American diet", defined as being low in greens, fruit, and fish, but high in red meats, sugars, and omega-6 fatty acids.
And a new animal study from Wake Forest University lends support to the hypothesis that changing the omega-3 to omega-6 ratio typical of the standard American diet might reduce the risk of common cancers.
Together, they strengthen the case for a fat-shift in America's kitchens, deli counters, supermarkets, and restaurants.
Dana-Farber report: standard American reduces colon-cancer survival rates
We already have ample evidence that the standard American diet increases the risk of colon cancer.
But earlier this month, researchers at the Dana-Farber Cancer Institute reported that the standard American diet seems to increase the risk that colon cancer patients will die from the disease or suffer a recurrence (Meyerhardt JA et al 2007).
The unhealthful standard American diet is grossly imbalanced in favor of pro-inflammatory, generally cancer-fueling omega-6 fats – see "Sources of omega-6s, below – and low in anti-inflammatory omega-3 fats from fish and leafy greens (Simopoulos AP 1999).
Sources of omega-6s
Most of the excess dietary omega-6 fatty acids in Americans’ diets come from common vegetable oils – corn, soy, canola, sunflower, safflower, and cottonseed – which predominate in home cooking and in packaged and restaurant foods.
(Soy and canola oils are the major sources of omega-3s in the diets of most Americans, but these oils are much higher in omega-6s, so they are far from ideal sources.)
This is why researchers recommend using oils low in omega-6s, such as olive oil, macadamia nut oil, and “hi-oleic” versions of safflower or sunflower oil.
Americans also get lots of omega-6 fat from factory-farmed cattle, pigs, and poultry, which are fed grain-heavy diets high in omega-6s and low in omega-3s. (Farmed salmon are also quite high in omega-6s, while wild salmon have much lower levels.)
They analyzed the diets reported by 1,009 colon cancer patients treated with surgery and chemotherapy, in whom the disease had spread to the lymph nodes but not to distant sites, such as the liver or lungs – defined as stage III colon cancer – between April of 1999 and May of 2001.
The cancer patients whose diets followed the typical American pattern most closely were about three times as likely to die or have their cancers recur as patients who strayed further from the American norm.
The researchers identified two major dietary patterns: the “Western” or “standard American” diet, characterized by high intakes of red and processed meats, sweets, refined grains, and desserts, and the “Prudent” diet, defined as one high in fruits, vegetables, and poultry and fish in place of red meat.
They followed the cancer patients for about five years, during which 324 experienced recurrences of their colon cancer and 223 died as a result: 28 patients with no evidence of cancer recurrence died.
Compared with patients who strayed furthest from it, the patients who followed the standard American diet most closely were nearly 3.5 times more likely to suffer a recurrence of their colon cancer and/or die.
In contrast, they found no relationship between following the Prudent diet pattern and increased risk of suffering a recurrence of colon cancer or dying.
The Dana-Farber team noted that further research is needed to pinpoint which components of the two diets were the most harmful and beneficial.
Given the large body of evidence from epidemiological, animal, and laboratory (human cell) studies concerning its cancer-fueling effects, we would predict that the high omega-6/omega-3 intake ratio that characterizes the standard American diet will be found to play a major role.
Prostate risk in mice cut by omega-3s and raised by omega-6s
In March of 2006, we reported the results of two studies in human prostate cancer cells, which showed that omega-3s retard, and omega-6s fuel their growth (see “Omega-3s Slow, Omega-6s Speed Prostate Cancer Growth”).
And last August, scientists from UCLA reported similarly encouraging cell-study results.
The UCLA team’s findings showed that raising the omega-3 to omega-6 ratio higher than the one typical of the standard American diet reduced prostate cancer tumor growth rates and lowered levels of prostate specific antigen (PSA). High PSA levels are associated with the possible presence of prostate cancer (Kobayashi N et al 2006).
The Wake Forest University team made these cogent comments in the report of their new mouse study (Berquin IM et al 2007):
- “Current Western diets have omega-6/omega-3 ratios of approximately 30 to 1, although they can be as high as 50 to 1.
- “Some evidence suggests that cyclooxygenase [COX] inhibitors, which block the metabolism of omega-6s, are beneficial in prevention of colon and prostate cancer. However, the cardiovascular toxicity of cyclooxygenase-2 [COX-2] inhibitors [e.g., Vioxx and Celebrex] has jeopardized the clinical utility of these drugs.”
- “Epidemiological studies suggest that consumption of fish or fish oil reduces prostate cancer incidence. One of the largest prospective studies, involving 6,272 men with 30 years of follow-up, indicated that fatty fish consumption was associated with decreased risk of prostate cancer. Serum [blood] levels of omega-3s were reported to be significantly lower in patients with benign prostate hyperplasia and prostate cancer, and omega-6 levels were higher in patients with prostate cancer compared with age-matched controls.”
- “Reducing the intake of omega-6s and increasing the proportion of dietary omega-3 is an attractive [alternative] approach [to reducing prostate and colon cancer risk].”
For the new research, the from Wake Forest University team used mice engineered to lack the Pten gene.
This gene suppresses growth of prostate and other tumors by enabling an immune response known as apoptosis, which causes nascent cancer cells to commit "suicide". Absence of the Pten gene results in spontaneous development of prostate and other cancers.
About 65 percent of men with metastatic prostate cancers lack the Pten gene.
The mice were randomly assigned to eat one of three diets with differing omega-6 to omega-3 ratios (all three provided 30 percent of calories from fat):
- One part omega-6 to one part omega-3 (“high omega-3”)
- 20 parts omega-6 to one part omega-3 (“low omega-3”)
- 40 parts omega-6 to one part omega-3 (“high omega-6”)
The standard America diet typically provides from 20 parts to 40 parts omega-6 fatty acids to one part omega-3s… ratios that match the undesirable “low omega-3” and “high omega-6” diets given two of the three mouse groups.
Mice with the tumor suppressor gene did not develop tumors and had a 100 percent survival rate, regardless of diet.
But among mice with the gene defect, the fatty acid ratio was critical, with higher ratios of omega-3s to omega-6s improving survival:
- 60 percent of the high omega-3 diet group survived.
- 10 percent of the low omega-3 diet group survived.
- None of the high omega-6 diet group survived.
This stark outcome suggests that with regard to human prostate cancer, presence of the inherited tumor-suppressor gene may overcome the effect of an imbalanced fatty acid intake.
But very few of us know whether we have the protective gene. And if one lacks that tumor-suppressor gene, making one susceptible to prostate cancer, it seems that diet could be vital to prevention.
So it seems foolish not to pursue an omega--3-rich diet, given the the omega-6 overload in most cooking oils, meats, and packaged/prepared foods, and the many benefits associated with consuming omega-3s and omega-6s in roughly equal ratios.
And as the Wake Forest team said wither regard to prostate cancer, “…prostate cancer is usually diagnosed in men age 60 or older, and cancer cells proliferate slowly. Therefore, dietary and/or chemoprevention are of particular importance for the management of prostate cancer. Our data imply a beneficial effect of omega-3s on delaying the onset of human prostate” (Berquin IM et al 2007).
We’ll keep our eye on ongoing research and report it as it appears. In the meantime, cut back on omega-6 sources and keep eating fish… especially oily fish!
- Berquin IM, Min Y, Wu R, Wu J, Perry D, Cline JM, Thomas MJ, Thornburg T, Kulik G, Smith A, Edwards IJ, D'Agostino R, Zhang H, Wu H, Kang JX, Chen YQ. Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids. J Clin Invest. 2007 Jul;117(7):1866-75.
- Meyerhardt JA, Niedzwiecki D, Hollis D, Saltz LB, Hu FB, Mayer RJ, Nelson H, Whittom R, Hantel A, Thomas J, Fuchs CS. Association of dietary patterns with cancer recurrence and survival in patients with stage III colon cancer. JAMA. 2007 Aug 15;298(7):754-64.
- Kobayashi N, Barnard RJ, Henning SM, Elashoff D, Reddy ST, Cohen P, Leung P, Hong-Gonzalez J, Freedland SJ, Said J, Gui D, Seeram NP, Popoviciu LM, Bagga D, Heber D, Glaspy JA, Aronson WJ. Effect of altering dietary omega-6/omega-3 fatty acid ratios on prostate cancer membrane composition, cyclooxygenase-2, and prostaglandin E2. Clin Cancer Res. 2006 Aug 1;12(15):4662-70.
- Simopoulos AP. 1999. Essential fatty acids in health and chronic disease. Am. J Clin Nutr 70(3 Suppl.):560S–569S.
- Weber PC. 1989. Are we what we eat? Fatty acids in nutrition and in cell membranes: cell functions and disorders induced by dietary conditions. In Fish, fats and your health. Proceedings of the International Conference on Fish Lipids and Their Influence on Human Health. August 9–11. Svanoy, Norway. Svanoy Foundation. 9–18.
- Dana-Farber Cancer Institute. Western diet linked to increased risk of colon cancer recurrence. Accessed online August 26, 2007 at http://www.dana-farber.org/abo/news/press/2007/western-diet-linked-to-increased-risk-of-colon-cancer-recurrence.html